Scientific Programme

Clicking a presenter name allows you to find its presentation's title, abstract and slideshows/auxiliary material.

{[{programme.title}]}
{[{row.time}]}	{[{col.title}]}
	{[{col.content}]} {[{col.url_title}]}

{"title":"Day 1 - Monday, September 12","rows":[{"time":"08:30 - 09:00","separator":false,"expanded":false,"cols":[{"title":"Registration","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"09:00 - 09:30","separator":false,"expanded":false,"cols":[{"title":"Opening Session: FCG President Dr. Artur Santos Silva, FCT President Prof. Dr. Paulo Ferrão and FCT Board Member Prof. Dr. Ana Sanchez","bold":false,"expandable":false,"expanded":true,"content":""}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Plenary Talks (Chair: Vitor Cardoso)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Auditorium 3","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"09:30 - 10:30","separator":false,"expanded":false,"cols":[{"title":"Roberto Emparan","bold":false,"expandable":true,"expanded":false,"content":"Title: Black hole fusion made easy\n\nAbstract: The fusion of two black holes --- a signature phenomenon of General Relativity --- is usually regarded as a process so complex that nothing short of a supercomputer simulation can accurately capture it. In this talk I will explain how the event horizon of the merger can be found in an exact analytic way in the limit where one of the black holes is much smaller than the other. Remarkably, the ideas and techniques involved are elementary: the equivalence principle, null geodesics in the Schwarzschild solution, and the notion of event horizon itself. With these, one can study the detailed structure of the horizon, and find indications of universal critical behavior when the two black holes touch.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Monday/Emparan.pdf"}]},{"time":"10:30 - 10:40","separator":false,"expanded":false,"cols":[{"title":"Adam Day (IOP)","bold":false,"expandable":true,"expanded":false,"content":"Title: How to maximise the visibility of your research","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Monday/Day.pdf","url_title":"Presentation"}]},{"time":"10:40 - 11:00","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"11:00 - 12:00","separator":false,"expanded":false,"cols":[{"title":"Hans Ringström","bold":false,"expandable":true,"expanded":false,"content":"Title: Future stability results in cosmology \n\nAbstract: In the past ten years, a substantial number of future stability results of cosmological solutions to Einstein's equations have appeared. Most of them are concerned with solutions with a positive cosmological constant and they treat many different types of matter models. The first part of the talk will provide an overview of some of these results. In the second part, the restrictions on the topology imposed by the observation that what we see to the past seems close to a spatially flat FLRW model with a positive cosmological constant will be discussed. In the final part of the talk, we discuss the cosmic no-hair conjecture.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Monday/Ringstrom.pdf"}]},{"time":"12:00 - 13:00","separator":false,"expanded":false,"cols":[{"title":"Frans Pretorius","bold":false,"expandable":true,"expanded":false,"content":"Title: The Dynamical Strong-field Regime of General Relativity\n\nAbstract: In this talk I will discuss some of the consequences for our understanding of strong-field gravity that can be gleaned from the recent detection of gravitational waves by the LIGO/Virgo collaboration. The loudest event heard, GW150914, is consistent with the emission of gravitational waves from the late inspiral, merger and ringdown of two heavy stellar mass black holes. This has given us the first quantifiable pieces of evidence that the dynamics and properties of colliding black holes are governed by general relativity. At present certain exotic compact object alternatives to black holes within general relativity, such as boson stars or gravastars, cannot yet be ruled out due to lack of concrete predictions of the merger regime in such scenarios. However, I will argue that even if the progenitors of GW150914 where composed of such exotic matter, the gravitational wave data strongly suggests collision lead to the prompt formation of a Kerr black hole. I will further discuss constraints that this event, and the second binary black hole merger, GW151226, can place on alternative theories of gravity.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Monday/Pretorius.pdf"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Paralell Talks (Chairs: Ulrich Sperhake, Tomohiro Harada)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Auditorium 3","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"},{"title":"Room 2","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"14:30 - 14:45","separator":false,"expanded":false,"cols":[{"title":"David Hilditch","bold":false,"expandable":true,"expanded":false,"content":"Title: A First application of the Dual Foliation formalism\n\nAbstract: When solving general relativity numerically we must use a formulation of the field equations for which the resulting PDE problem is well-posed. Building such a good formulation usually requires making a coordinate choice. This leads to statements like `gauge freedom in general relativity is the choice of coordinates'. The latter two facts are bothersome, because one of the first lessons in relativity is that coordinates should, in some sense, not matter. In my talk I will explain the solution to my earlier confusion. I will then explain how the resulting formalism can be exploited for practical calculations.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Hilditch.zip"},{"title":"Jorge Zanelli","bold":false,"expandable":true,"expanded":false,"content":"Title: Quantum dress for a naked singularity\n\nAbstract: We compute the semiclassical backreaction on a naked singularity in (2+1)-dimensions.  In particular, we calculate the renormalized quantum stress-energy tensor for a conformally coupled scalar field on this singular spacetime and then obtain the backreacted metric via the semiclassical Einstein equations. We show that the quantum corrections dress the naked singularity with an event horizon, thus enforcing cosmic censorship. Some remarks can also be made on the rotating and extremal cases.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Zanelli.pdf"}]},{"time":"14:45 - 15:00","separator":false,"expanded":false,"cols":[{"title":"Alex Vano-Vinuales","bold":false,"expandable":true,"expanded":false,"content":"Title: Going beyond Bowen-York binary black hole initial data\n\nAbstract: The standard Bowen-York conformally flat ansatz simplifies the calculation of initial data for numerical simulations of binary black hole systems. However, it sets a limit on the largest achievable spin of the black holes and also includes extra unwanted spurious radiation, as Kerr black holes are not conformally flat. Within the conformal thin sandwich decomposition of the constraint equations, we use the puncture approach to set the free specifiable data to two non-conformally flat black holes and then solve the non-linear Hamiltonian constraint and the three linear components of the momentum constraint iteratively. Our goal is to obtain initial data for two boosted Kerr black holes, and so the first step presented here corresponds to solving for two boosted Schwarzschild black holes.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Vano-Vinuales.pdf"},{"title":"Cristián Martínez","bold":false,"expandable":true,"expanded":false,"content":"Title: A class of rotating hairy black holes in arbitrary dimensions\n\nAbstract: A class of rotating black hole solutions dressed with a scalar field saturating the Breitenlohner-Freedman bound is presented in arbitrary dimensions. The scalar field, which is regular on and outside the event horizon, is non-minimally coupled to gravity and a self-interaction potential is considered.  The spacetimes are asymptotically locally AdS and contain a single horizon. The thermodynamics is analyzed in the grand canonical ensemble. Due to the non-minimally coupling, the entropy does not follow the area. However, the first law is satisfied.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Martinez.pdf"}]},{"time":"15:00-15:15","separator":false,"expanded":false,"cols":[{"title":"Isabel Cordero-Carrión","bold":false,"expandable":true,"expanded":false,"content":"Title: Excision scheme for black hole numerical simulations\n\nAbstract: We will present recent developments of the excision technique in the case of the Fully Constrained Formalism. We will focus on spherically symmetric spacetimes representing the collapse of a neutron star to a black hole. We will present boundary conditions to be imposed at the excised surface, an arbitrary coordinate sphere inside the apparent horizon, in which a new parameter governs the final physical radius of the excised surface. We will show exponential convergence toward the stationary solution and stable long-term evolution of the newly formed black hole.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Cordero-Carrion.pdf"},{"title":"Masato Minamitsuji","bold":false,"expandable":true,"expanded":false,"content":"Title: Black hole solutions in the generalized Proca theory\n\nAbstract: We investigate the static and spherically-symmetric solutions in a class of the generalized Proca theory with the nonminimal coupling to the Einstein tensor. First, we show that the solutions in the scalar-tensor theory with the nonminimal derivative coupling to the Einstein tensor can be mapped to the generalized Proca theoy. We then show that when the field strength takes the nonzero value the static and spherically-symmetric solutions can be found only for the specific value of the nonminimal coupling constant. Finally, we investigate the slow-rotation corrections to the static and spherically-symmetric backgrounds.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Minamitsuji.pdf"}]},{"time":"15:15-15:30","separator":false,"expanded":false,"cols":[{"title":"Gonzalo Quiroga","bold":false,"expandable":true,"expanded":false,"content":"Title: MATE: A New CUDA-C Code for Tracing Orbits Around Compact Objects in General Relativity\n\nAbstract: A new general relativistic code for tracing orbits around compact objects is introduced. This code implements a Runge-Kutta-Fehlberg solver of fourth and fifth order, which leverages the advantage of the graphics processing units (GPUs) computing and the NVidia's Compute Unified Device Architecture (CUDA). We measure the execution time of MATE solving a large set of initial conditions, showing that using CUDA and GPUs several orders of magnitude are got over the standard multi-core CPU programming. Additionally, we study the numerical convergence by computing the precision quotient for a time-like test particle in the innermost stable circular orbit of the Schwarzschild space-time.","url_title":"Presentation","url":""},{"title":"Marcelo Salgado","bold":false,"expandable":true,"expanded":false,"content":"Title: Black holes in f(R) gravity: scalar-hair or absence thereof\n\nAbstract: We discuss the conditions under which BH's with trivial (i.e. constant) Ricci scalar exist in f(R) gravity and show that such BH's are identical to the corresponding BH's existing in GR except for a redefinition of the cosmological and the gravitational constants. We then focus on static and spherically symmetric spacetimes and provide the equations and regularity conditions required for the existence of spherically symmetric BH's. Using several specific f(R) models we provide analytical and numerical evidence for the absence of geometric scalar hair in asymptotically flat (AF) spacetimes. The analytical evidence\nconsists in the implementation of the no-hair theorem(s) that exist in the so called Einstein-Higgs system via a conformal transformation (i.e. using the Einstein frame representation). When the theorems do not apply or the use of the Einstein frame is ill-defined for some of the f(R) models, we solve the equations numerically in the original (Jordan) frame, and show that BH's solutions with non-trivial Ricci scalar in AF spacetimes seem to be absent, and the only ones that exist have exotic asymptotics.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Salgado.pdf"}]},{"time":"15:30-15:45","separator":false,"expanded":true,"cols":[{"title":"Nicolas Sanchis-Gual","bold":false,"expandable":true,"expanded":false,"content":"Title: Explosion and final state of the charged black hole bomb\n\nAbstract: A Reissner-Nordström black hole (BH) is superradiantly unstable against spherical perturbations of a charged scalar field, enclosed in a cavity, with frequency lower than a critical value. We use numerical relativity techniques to follow the development of this unstable system -- dubbed charged BH bomb -- into the non-linear regime, solving the full Einstein--Maxwell--Klein-Gordon equations, in spherical symmetry. I will show that: i) the process stops before all the charge is extracted from the BH; ii) the system settles down into a hairy BH: a charged horizon in equilibrium with a scalar field condensate, whose phase is oscillating at the (final) critical frequency. For low scalar field charge, q, the final state is approached smoothly and monotonically. For large q, however, the energy extraction overshoots and an explosive phenomenon, akin to a bosenova, pushes some energy back into the BH.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Sanchis-Gual.pdf","url_title":"Presentation"},{"title":"-","bold":false,"expandable":false,"expanded":false,"content":"Title: Metric-affine (non-singular) black holes sourced by anisotropic fluids in quadratic f(R) gravity\n\nAbstract: Working in a metric-affine (Palatini) framework, we obtain and analyze black hole solutions generated by anisotropic fluids with various equations of state. In particular, we study  the inner structure of the black holes and the geodesic completeness of these spacetimes in the context of quadratic f(R) gravity. We find that, depending on the matter model parameters, the standard point-like singularity can be replaced by a wormhole, which makes the spacetime non-singular. This throws further evidence on the fact that the metric-affine formulation in theories beyond General Relativity represents an encouraging approach to tackle the shortcomings posed by classical singularities.","url_title":"Presentation"}]},{"time":"15:45-16:00","separator":false,"expanded":false,"cols":[{"title":"Helvi Witek","bold":false,"expandable":true,"expanded":false,"content":"Title: Compact objects in Einstein-dilaton Gauss-Bonnet gravity\n\nAbstract: Although General Relativity (GR) has passed all tests so far with flying colors, the most recent of which being GW150914 and GW151226 in the strong-field, dynamical regime, a full theory combining GR with quantum field theory is still amiss.\nGuided by more fundamental candidate theories of quantum gravity, one possible extension of GR involves quadratic curvature corrections. In this talk I will focus on Einstein-dilaton Gauss-Bonnet gravity and, specifically, discuss properties of compact objects and black-hole formation processes in this theory.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Witek.zip"},{"title":"Marcello Ortaggio","bold":false,"expandable":true,"expanded":false,"content":"Title: On the uniqueness of the Myers-Perry spacetime as a type II(D) solution in six dimensions\n\nAbstract: We determine the full class of six-dimensional type II vacuum spacetimes with a \"non-degenerate\" aligned null direction, subject to a fall-off condition related to asymptotic flatness. The resulting spacetimes are shown to be equivalent to the Myers-Perry black hole metric or certain limits thereof.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Ortaggio.pdf"}]},{"time":"16:00-16:15","separator":false,"expanded":false,"cols":[{"title":"William Cook","bold":false,"expandable":true,"expanded":false,"content":"Title: Gravitational Wave Emission in Higher Dimensional Black Hole Collisions\n\nAbstract: Gravitational waves are a key diagnostic in the study of the properties of black holes (BHs). In four dimensional General Relativity the properties of gravitational waves emitted in BH-BH mergers have been extensively studied using numerical relativity, largely in astrophysical settings. Understanding higher dimensional BH-BH collisions is also an important goal for numerical relativity, firstly in order to observe the behavior of the theory in its most extreme, non-linear regime, and also due to its applications to areas of high energy physics. One such example is that of TeV gravity theories, in which it is proposed that high energy collisions in particle accelerators could cause black hole creation. In this work we present for the first time full non-linear simulations of head-on BH-BH collisions in up to 10 dimensions and present an analysis of the gravitational radiation emitted. We use a new method for analysis of the radiation, analogous to the well known Weyl scalar method based on the Newman-Penrose formalism in 4D. We find that as the number of dimensions is increased, the energy emitted in gravitational radiation is significantly suppressed. We also present a comparison of our numerical data with point particle calculations.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Cook.pdf"},{"title":"Umpei Miyamoto","bold":false,"expandable":true,"expanded":false,"content":"Title: Is wormhole formation prohibited by semi-classical effects?\n\nAbstract: It is desirable that wormhole formation is prohibited semi-classically from the viewpoint that a wormhole may be used to realize a closed time-like curve (a time machine), which leads to the violation of causality. In this work, we estimate the particle creation by the sudden removal of a both-sided Dirichlet wall in the middle of a 1D cavity, which mimics the dynamical merge of separated two spaces through a wormhole. The energy density and also total energy of created particles are found to diverge, suggesting that the back-reaction prohibits the merge of separated spaces and wormhole formation.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Miyamoto.pdf","url_title":"Presentation"}]},{"time":"16:15-16:30","separator":false,"expanded":false,"cols":[{"title":"Marius Oltean","bold":false,"expandable":true,"expanded":false,"content":"Title: Entropy theorems in classical mechanics, general relativity, and the gravitational two-body problem\n\nAbstract: In classical Hamiltonian theories, entropy may be understood either as a statistical property of canonical systems, or as a mechanical property, that is, as a monotonic function of the phase space along trajectories. In classical mechanics, there are theorems which have been proposed for proving the non-existence of entropy in the latter sense. We explicate, clarify and extend the proofs of these theorems to some standard matter (scalar and electromagnetic) field theories in curved spacetime, and then we show why these proofs fail in general relativity;\ndue to properties of the gravitational Hamiltonian and phase space measures, the second law of thermodynamics holds. As a concrete application, we focus on the consequences of these results for the gravitational two-body problem, and in particular, we prove the non-compactness of the phase space of perturbed Schwarzschild-Droste spacetimes. We thus identify the lack of recurring orbits in phase space as a distinct sign of dissipation and hence entropy production.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Oltean.pdf"},{"title":"Gonçalo Martins Quinta","bold":false,"expandable":true,"expanded":false,"content":"Title: Vacuum polarization near Lifshitz black holes\n\nAbstract: In this work we study quantum polarization effects in Lifshitz spacetimes for massive, non-minimally coupled scalar fields. To that aim, we adapt to the present situation an analysis previously developed for the case of asymptotically anti de Sitter black holes, where a mix of analytic and numerical computations are used to obtain an explicitly finite renormalized result. Some examples of numerical computations for particular values of the parameters are given. The interest of our work stems from the current application of the gauge/gravity duality to condensed matter theories, in particular gravity duals, i.e., Lifshitz spacetimes, of theories that exhibit anisotropic scaling, and from the further developments incorporating black hole solutions with Lifshitz asymptotics designed to understand finite temperature effects in the condensed matter systems.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Quinta.pdf"}]},{"time":"16:30-17:00","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"17:00-17:15","separator":false,"expanded":false,"cols":[{"title":"Jorge Rocha","bold":false,"expandable":true,"expanded":false,"content":"Title: Dynamics of confined double-shells systems, critical behavior and chaos\n\nAbstract: I will present a study of gravitational collapse in confined spaces employing the simplest possible two-body setting: a system composed of two thin shells in spherical symmetry. Confinement is introduced either by putting the system inside a totally reflecting spherical cavity or by formulating the problem in anti-de Sitter (AdS) spacetime. The two shells interact only through their gravitational attraction. The problem amounts to solving just two decoupled ODEs but it features highly non-trivial dynamics: depending on initial data, one observes prompt collapse, perpetual oscillations or black hole formation on arbitrarily long timescales. This confined double-shell system exhibits critical behavior reminiscent of the ``turbulent'' dynamics of massless scalar fields in AdS, as well as chaotic behavior. This extremely simple model heuristically supports the idea that the cascade of energies to shorter wavelength modes is the mechanism responsible for delayed collapse into black holes.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Quinta.pdf"},{"title":"Tomohiro Harada","bold":false,"expandable":true,"expanded":false,"content":"Title: Correspondence between sonic points of ideal photon gas accretion and photon spheres\n\nAbstract: In an accretion of fluid, its velocity may transit from subsonic to supersonic. The point at which such transition occurs is called sonic point and often mathematically special. We consider a steady-state and spherically symmetric accretion problem of ideal photon gas in general static spherically symmetric spacetime neglecting back reaction. Our main result is that the EOS of ideal photon gas leads to correspondence between its sonic point and the photon sphere of the spacetime in general situations. Despite of the dependence of the EOS on the dimension of spacetime, this correspondence holds for spacetimes of arbitrary dimensions.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Harada.pdf"}]},{"time":"17:15-17:30","separator":false,"expanded":false,"cols":[{"title":"Daniel Santos-Oliván","bold":false,"expandable":true,"expanded":false,"content":"Title: New Features of Gravitational Collapse in Anti-de Sitter Spacetimes\n\nAbstract: Gravitational collapse of a massless scalar field in spherically-symmetric Anti-de Sitter (AdS) spacetimes presents a new phenomenology with a series of critical points whose dynamics is discretely self-similar as in the asymptotically-flat case. Each critical point is the limit of a branch of scalar field configurations that have bounced off the AdS boundary a fixed number of times before forming an apparent horizon. We present a method that combines a Cauchy and a Characteristic evolution to focus on the interfaces between branches finding that there is a mass gap between these branches and subcritical configurations near the critical point form black holes with an apparent horizon mass that follows a power law with a new exponent that appears to be universal.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Santos-Olivan.zip"},{"title":"Filip Hejda","bold":false,"expandable":true,"expanded":false,"content":"Title: Generalised BSW effect including both charge and angular momentum: kinematic restrictions\n\nAbstract: In 2009 Bañados, Silk and West pointed out a possibility of having unbounded limit of centre-of-mass collision energy for test particles in the field of an extremal Kerr black hole, if one of them has fine-tuned parameters and the collision point is approaching the horizon. The possibility of this \"BSW effect\" attracted much attention: it was generalised to arbitrary (\"dirty\") rotating black holes and an analogy was found for collisions of charged particles in the field of non-rotating charged black holes. Our work considers, in a unified way, overlapping of these two mechanisms, which have been studied only separately so far. Exploring the enlarged parameter space, we find kinematic restrictions, which may prevent the fine-tuned particles from reaching the limiting collision point. These restrictions are first presented in a general form, which can be used with arbitrary black hole model, and then visualise them for the Kerr-Newman solution, relating previously known spec\n ial cases to the more general scheme.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Hejda.pdf"}]},{"time":"17:30-17:45","separator":false,"expanded":false,"cols":[{"title":"Miguel Zilhão","bold":false,"expandable":true,"expanded":false,"content":"Title: Holographic Heavy Ion Collisions in Non-Conformal Theories\n\nAbstract: Understanding the dynamics of out-of-equilibrium matter in strongly coupled systems is an important and challenging problem in theoretical physics. A particularly interesting example is the Quark-Gluon Plasma formed in relativistic colliders such as RHIC or the LHC, which motivates the study of the relaxation process in strongly coupled non-abelian field theories. We use holography to map the evolution of plasma in a non-conformal gauge theory to a gravitational system, namely to the collision of two gravitational shockwaves in Einstein-scalar field theory with an asymptotically Anti-de Sitter geometry, and study the effect of the non-conformality in the relaxation times of the resulting plasma.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Zilhao.zip"},{"title":"Guilherme Raposo","bold":false,"expandable":true,"expanded":false,"content":"Title: Love numbers of Black Holes\n\nAbstract: The relativistic theory of tidal deformations has been the focus of recent researches in astrophysics.  A general compact body will develop multipole moments when it is perturbed by an external tidal field. In Newtonian gravity the coefficients of proportionality between the two of them are known as tidal Love numbers. In recent years a relativistic theory for tidal Love numbers was developed with success. In this work, we review the main features of this theory and we focus specifically on the Love numbers of black holes. Previous results for the Love numbers of black holes in General Relativity are verified and we extend them for black hole solutions in modified gravity theories.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Raposo.pdf"}]},{"time":"17:45-18:00","separator":false,"expanded":false,"cols":[{"title":"Miguel Duarte","bold":false,"expandable":true,"expanded":false,"content":"Title: Asymptotically Anti-de Sitter Proca Stars\n\nAbstract: We show that complex massive spin-1 fields minimally coupled to Einstein's gravity with a negative cosmological constant, admit asymptotically anti-de Sitter self-gravitating solutions. We support our numerical results by finding analytical solutions in the test-field limit, where the Proca field equations can be solved in a fixed anti-de Sitter background. We show that these solutions share similar properties with their spin-0 counterparts, in particular, they are stable against spherically symmetric linear perturbations for a range of fundamental frequencies limited by their point of maximum mass. We finish with an overview of the behavior of Proca star solutions in 4+1 dimensions and argue that in more than 4 dimensions, a negative cosmological constant is necessary for the existence of stable solutions.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Duarte.pdf"},{"title":"Leonel Queimada","bold":false,"expandable":true,"expanded":false,"content":"Title: Cosmic Censorship and Gedanken Experiments\n\nAbstract: The cosmic censorship conjecture, firstly proposed by Penrose, asserts, in its weak form, that all singularities arising from gravitational collapse are hidden within black holes. Following the original idea by Wald, we study whether extremal black holes can be spun-up past extremality in two different setups:\n- Using point particles to destroy black holes which are parametrically small deviations away from the Kerr solution.\n- Using generic test fields to overspin/overcharge an extremal Kerr-Newman or Kerr-Newman-anti de Sitter black hole.\nIn both cases, the cosmic censorship is preserved. In this talk, I will try to clarify why this happens and place these results in the overall picture of gedanken experiments for cosmic censorship.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Monday/Queimada.pdf"}]}],"size":"20"}

{[{programme.title}]}
{[{row.time}]}	{[{col.title}]}
	{[{col.content}]} {[{col.url_title}]}

{"title":"Day 2 - Tuesday, September 13","rows":[{"time":"","separator":true,"expanded":false,"cols":[{"title":"Plenary Talks (Chair: Francisco Lobo)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Auditorium 3","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"09:00 - 10:00","separator":false,"expanded":false,"cols":[{"title":"Ruth Durrer","bold":false,"expandable":true,"expanded":false,"content":"Title: Testing General Relativity with the Large Scale Structure of the Universe\n\nAbstract: In my talk I shall explain how relativistic effects are relevant in the observations of the large scale structure of the Universe.\nThis renders the analysis of observations more challenging but it also allows us to measure not only the density field but also the velocity field and the metric from large scale structure observations. Im my talk I shall show how future observations, e.g. with ESA's Euclid satellite in preparation for launch in 2020, can be used not only to measure the large scale matter distribution but also to test General Relativity on cosmological scales.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Tuesday/Durrer.pdf"}]},{"time":"10:00 - 10:30","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"10:30 - 11:30","separator":false,"expanded":false,"cols":[{"title":"David F. Mota","bold":false,"expandable":true,"expanded":false,"content":"Title: Nonlinear Cosmological Probes of Screening Mechanisms in Modified Gravity\n\nAbstract: Extending General Relativity by adding extra degrees of freedom is a popular approach to explain the accelerated expansion of the universe and to build high energy completions of the theory of gravity. The presence of such new degrees of freedom is, however, tightly constrained from several observations and experiments that aim to test General Relativity in a wide range of scales and regimes. The viability of a given modified theory of gravity therefore strongly depends on the existence of a screening mechanism that suppresses the extra degrees of freedom in such scales and regimes. I describe how one can use nonlinear structure formation to probe extensions to General Relativity, and will present a set of astrophysical observables that could give smoking guns of screening mechanism.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Tuesday/Mota.pdf"}]},{"time":"11:30 - 12:30","separator":false,"expanded":false,"cols":[{"title":"Manuela Campanelli","bold":false,"expandable":true,"expanded":false,"content":"Title: Numerical Relativity Simulations of Binary Black Hole Mergers\n\nAbstract: Not long ago, the advanced LIGO observatories detected gravitational coming from the coalescence of binary black holes that occurred more than a billion of years ago. Numerical relativity simulations of binary black holes played a crucial role in the calculations of the expected gravitational wave signal that was just observed. I will review briefly the history of numerical relativity simulation efforts to model these systems, with an emphasis on the role that it currently plays in the new field of  gravitational wave astronomy. I will also present some exciting new results in the context of magnetohydrodynamical simulation indicating that supermassive binary black hole sources might be also detectable in the EM spectrum, in some not too distant future.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Tuesday/Campanelli.zip"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Parallel Talks (Chairs: Sante Carloni, Carlos Barceló)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Auditorium 3","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"},{"title":"Room 2","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"14:00 - 14:15","separator":false,"expanded":false,"cols":[{"title":"José Pedro Mimoso","bold":false,"expandable":true,"expanded":true,"content":"Title: Stabilization of the sign of the gravitational constant.\n\nAbstract: In Newton's law of gravitation, the gravitational constant, G, is assumed to be positive. This sign is a matter of choice, and it was Laplace that used the constant  for the first time in his \"Traité de Mécanique Céleste\". Extended gravity theories  with couplings between the space-time  geometry and the matter sector prescribe the variation of this fundamental quantity, which hence  ceases to be a constant.  Scalar-tensor  are the archetypal class of theories with such a feature.  It thus becomes, in principle, possible for G to change sign, trading attracting into repulsive gravity.  In the present  work,  we have investigated a cosmological mechanism that stabilizes the positiveness of the sign of G, even though it might exhibit transient periods in the negative region. We show that this cosmological feature relies on the role of a cosmological potential, which reproduces a positive cosmological constant  in the so-called Einstein frame. From this latter viewpoint it\n can be understood as another role of paramount importance of this remarkable constant.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Mimoso.pdf"},{"title":"Norichika Sago","bold":false,"expandable":true,"expanded":true,"content":"Title: Gravitational waves from a spinning particle in Kerr spacetime\n\nAbstract: We investigate the energy flux of gravitational waves from a spinning particle orbiting a Kerr black hole, by using the black hole perturbation approach. To evaluate the energy-momentum tensor of a spinning particle, we use the Papapetrou equations under the pole-dipole approximation. We calculate the perturbation analytically by solving the Teukolsky equation with the Mano-Suzuki-Takasugi method. In this work, as a first step, we consider a simple case in which a spinning particle moves along a circular orbit on the equatorial plane of the central black hole. We derive the post-Newtonian formula of the energy flux up to the linear order of the particle's spin.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Sago.pdf"}]},{"time":"14:15 - 14:30","separator":false,"expanded":false,"cols":[{"title":"Diego Saez-Gomez","bold":false,"expandable":true,"expanded":false,"content":"Title: Extending unimodular gravity\n\nAbstract: In this talk, we present some extensions of unimodular gravity, where actions beyond Hilbert-Einstein action are considered. From the classical point of view, the unimodular versions of such extensions are completely equivalent to their originals, but an effective cosmological constant arises naturally. Conformal transformations and cosmological solutions are analyzed within this framwework.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Saez-Gomez.pdf","url_title":"Presentation"},{"title":"Ryuichi Fujita","bold":false,"expandable":true,"expanded":false,"content":"Title: Gravitational waves from a particle orbiting a Kerr black hole in Brans-Dicke theory\n\nAbstract: We derive the energy fluxes from a particle in eccentric orbits around a Kerr black hole in massless Brans-Dicke theory by using the post-Newtonian approximation in the first-order black hole perturbation theory. We will investigate how the orbital eccentricity and scalar fluxes affect the orbital evolution of the particle in massless Brans-Dicke theory.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Fujita.pdf","url_title":"Presentation"}]},{"time":"14:30 - 14:45","separator":false,"expanded":false,"cols":[{"title":"Prado Martin-Moruno","bold":false,"expandable":true,"expanded":false,"content":"Title: Moving bimetric cosmologies\n\nAbstract: Cosmologies based on bimetric theories have been constructed within the frameworks of massive gravity or bigravity aiming to address the dark energy problem. These models assume that the two metrics are of the FLRW type with the same comoving frame. However, the decoupling of the second gravitational sector with respect to matter implies that the most generic situation is the one in which both metrics do not share a common rest frame. From the point of view of standard gravity, this amounts to the existence of a dark sector whose stress-energy tensor behaves as a perfect fluid which moves with respect to the ordinary matter and radiation. Possible observational implications of this scenario will be discussed.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Martin-Moruno.pdf"},{"title":"Georgios Lukes-Gerakopoulos","bold":false,"expandable":true,"expanded":false,"content":"Title: Gravitational waves from a spinning compact object in EMRI\n\nAbstract: The Mathisson-Papapetrou (MP) equations are describing the motion of a spinning particle in a curved spacetime. Thus, these equation can approximate the motion of a stellar compact object moving in the spacetime background of a supermassive Kerr black hole. For defining the wordline along which the MP equations evolve the body, we need a spin supplementary condition (SSC). There are various SSCs and each of them define a different worldline for a compact object. We will discuss the impact of the SSCs on the dynamics and on the gravitational wave production in the case of circular equatorial orbits.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Lukes-Gerakopoulos.pdf","url_title":"Presentation"}]},{"time":"14:45 - 15:00","separator":false,"expanded":false,"cols":[{"title":"Diego Rubiera-Garcia","bold":false,"expandable":true,"expanded":false,"content":"Title: Latest results on metric-affine theories\n\nAbstract: We discuss a number of results on metric-affine theories of gravity obtained during the last few years. These theories are defined by the removal of any a priori constraint between metric and affine structures, and arise within the macroscopic description of ordered structures with defects in solid state physics. As a result, they generically yield ghost-free and second-order equations of motion that reduce in vacuum to GR. In this talk we will introduce (some of) the phenomenology of (some of) these theories (f(R), quadratic, Born-Infeld gravity) regarding wormholes and their dynamical generation, (2+1) dimensional BTZ-like solutions, and scalar fields.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Rubiera-Garcia.pdf","url_title":"Presentation"},{"title":"Seth Hopper","bold":false,"expandable":true,"expanded":true,"content":"Title: Frequency domain techniques to analyzing unbound motion on Schwarzschild spacetime\n\nAbstract: Numerically solving for the field sourced by unbound motion on a black hole background presents challenges distinct from those of bound motion. While time domain codes are largely \"source agnostic\" and adapt quite naturally to unbound motion, frequency domain techniques must be adjusted significantly. In particular, while the source and field are both decomposed as Fourier series when considering bound geodesic motion, unbound motion requires a Fourier transform, with a dense spectrum. More significantly, the frequency domain source terms are not confined to a finite range, which can lead to substantial technical challenges. I will present new methods to overcome these difficulties and consider the benefits (and drawbacks) of using frequency domain techniques to compute the self force for unbound sources.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Hopper.zip","url_title":"Presentation"}]},{"time":"15:00 - 15:15","separator":false,"expanded":false,"cols":[{"title":"Ernesto Barrientos","bold":false,"expandable":true,"expanded":false,"content":"Title: A general relativistic approach with torsion to MOND\n\nAbstract: In this work we add a funtion of the torsion to the Hilbert-Einstein action. The explicit form of this function is  motivated by the general results obtained with the f(R) theories with torsion. From the resulting field equations we\nanalise the conditions under which it is possible to recover the MONDian acceleration in the weakest limit of this proposal. Then, from these ideas we make the link to the f(R,T) theories, where T is the trace of the energy-momentum and prove that similarly it is feasible to construct an entirely covariant action from which both, the Newtonian and MONDian terms are present. This is an encouraging step towards the construction of a relativistic theory of MOND.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Barrientos.pdf","url_title":"Presentation"},{"title":"Caio F. B. Macedo","bold":false,"expandable":true,"expanded":false,"content":"Title: Dark matter implications for black holes and gravitational waves\n\nAbstract: In viable models of minicharged dark matter, astrophysical black holes might be charged under a hidden U(1) symmetry and are formally described by the same Kerr-Newman solution of Einstein-Maxwell theory. These objects are unique probes of minicharged dark matter and dark photons. We show that the recent gravitational-wave detection of a binary black-hole coalescence by aLIGO provides various observational bounds on the black hole's charge, regardless of its nature. The pre-merger inspiral phase can be used to constrain the dipolar emission of (ordinary and dark) photons, whereas the detection of the quasinormal modes set an upper limit on the final black hole's charge. By using a toy model of a point charge plunging into a Reissner-Nordstrom black hole, we also show that in dynamical processes the (hidden) electromagnetic quasinormal modes of the final object are excited to considerable amplitude in the gravitational-wave spectrum only when the black hole is nearly extremal. The coalescence produces a burst of low-frequency dark photons which might provide a possible electromagnetic counterpart to black-hole mergers in these scenarios.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Macedo.pdf","url_title":"Presentation"}]},{"time":"15:15 - 15:30","separator":false,"expanded":false,"cols":[{"title":"Antonio Sanchez-Puente","bold":false,"expandable":true,"expanded":false,"content":"Title: Geodesic Completeness of n-Dimensional Wormholes in Palatini Theories\n\nAbstract: Charged black holes in gravity theories in the Palatini formalism present a wormhole structure instead of a central singularity. This wormhole is supported by a sourceless\nelectric flux and does not require exotic matter sources. In 3+1 dimensions, there are completely regular solutions for a specific relation of the charge and mass of the wormhole. If the charge and mass do not satisfy that relation, a divergence of curvature will appear at the wormhole throat. The study of the geometry in the divergent scenario reveals that geodesics are complete and can pass through the wormhole, and the geometry is non-singular. In my talk, I will review the case in n-Dimensions, give an overview of the mathematical derivation of these solutions, and study the geodesic completeness of the geometry.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Sanchez-Puente.pdf","url_title":"Presentation"},{"title":"Alejandro Torres-Forné","bold":false,"expandable":true,"expanded":false,"content":"Title: Denoising of gravitational wave signals via dictionary learning\n\nAbstract: Dictionary learning algorithms have been extensively developed in the last years. We have developed a machine learning algorithm based in dictionaries and we have applied successfully in the context of gravitational wave denoising. These dictionaries has been obtained from numerical relativity templates of binary black holes mergers (BBH) and from burst of magnetorotational core collapse. Our results show how these techniques can remove noise successfully in the case of a signal embedded in non-white Gaussian noise.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Torres-Forne.pdf","url_title":"Presentation"}]},{"time":"15:30 - 15:45","separator":false,"expanded":false,"cols":[{"title":"Ernesto F. Eiroa","bold":false,"expandable":true,"expanded":false,"content":"Title: Thin-shell wormholes in F(R) gravity\n\nAbstract: Different modifications of General Relativity have been proposed in order to understand the accelerated expansion of the Universe without invoking the presence of exotic fluids. Among them are the F(R) gravity theories, in which the Einstein-Hilbert Lagrangian is replaced by a function F(R) of the curvature scalar R. Within the framework of these theories, it is of interest the analysis of the behaviour of thin layers of matter by adopting the thin-shell formalism, which allows to match different solutions across a hypersurface. This formalism is characterized by the so called junction conditions, which have been extended from General Relativity to F(R) gravity in recent years. These conditions impose some requisites to the curvature scalar R, namely F(R) theories generally present a continuous R across the shell, with the exception of quadratic F(R) theories in which R can be discontinuous as in the General Relativity case. Here we review the main features of the thin-shell formalism in F(R) gravity and we apply it to the construction of traversable wormholes with a throat at the joining shell. We consider the particular case of  spherically symmetric configurations, for which we present a stability analysis under radial perturbations.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Eiroa.pdf","url_title":"Presentation"},{"title":"Dániel Barta","bold":false,"expandable":true,"expanded":false,"content":"Title: General-relativistic polytropic models for non-perfect fluid neutron star\n\nAbstract: Great number of equation of states inside very compact and massive objects like neutron stars have been investigated in recent years in order to develop realistic models. However, due to their complexity, non-adiabatic effects have been disregarded in most cases. We assume a two-component polytropic equation of state for the non-perfect fluid and investigate the possibility that non-adiabatic effects, such as viscosity or heat transfer significantly alter the internal structure of compact objects. For this reason, one has to solve numerically a system of differential equations describing the stellar structure, including the generalization of the Tolman–Oppenheimer–Volkoff equation. We obtained upper mass limit for such objects through mass-radius relation, and could correctly identify stable and non-stable models.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Barta.pdf","url_title":"Presentation"}]},{"time":"15:45 - 16:00","separator":false,"expanded":false,"cols":[{"title":"João Luís Rosa","bold":false,"expandable":true,"expanded":false,"content":"Title: Wormholes in generalized hybrid metric-Palatini gravity\n\nAbstract: In this work, we consider two groups of analytical solutions for asymptotically flat wormholes in the recently proposed hybrid metric-Palatini gravity theory. The conditions for the matter to satisfy the Null Energy Condition (NEC) are discussed and the solutions for the energy density, pressure and scalar fields are obtained.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Rosa.pdf","url_title":"Presentation"},{"title":"Andrew Coates","bold":false,"expandable":true,"expanded":false,"content":"Title: Gravitational Higgs Mechanism in Neutron Star Interiors\n\nAbstract: I will explain how nonminimally coupled scalar fields can lead to modification of the microphysics in the interiors of relativistic stars. As a concrete example, I will consider the generation of a non-zero photon mass in such high-density environments. This is achieved by means of a light gravitational scalar, and the scalarization phase transition in scalar-tensor theories of gravitation. I will present two distinct models, and phenomenological implications will be briefly discussed.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Coates.pdf","url_title":"Presentation"}]},{"time":"16:00 - 16:30","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"16:30 - 16:45","separator":false,"expanded":false,"cols":[{"title":"Peter Dunsby","bold":false,"expandable":true,"expanded":false,"content":"Title: Is cosmography a useful tool for testing cosmology?\n\nAbstract: Model-independent methods in cosmology has become an essential tool in order to deal with an increasing number of theoretical alternatives for explaining the late-time acceleration of the Universe. In principle, this provides a way of testing the Cosmological Concordance (or ?CDM) model under different assumptions and ruling out whole classes of competing theories. One such model-independent method is the so-called cosmographic approach, which relies only on the homogeneity and isotropy of the Universe on large scales. We show that this method suffers from many short-comings, providing biased results depending on the auxiliary variable used in the series expansion and is unable to rule out models or adequately reconstruct theories with higher-order derivatives in either the gravitational or matter sector. Consequently, in its present form, this method seems unable to provide reliable or useful results for cosmological applications.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Dunsby.pdf","url_title":"Presentation"},{"title":"Kota Ogasawara","bold":false,"expandable":true,"expanded":true,"content":"Title: Arbitrarily large energy extraction efficiency and escape probability in the super-Penrose process\n\nAbstract: We present an analytic approach to the arbitrary large energy extraction efficiency of super-Penrose process in the near-horizon of an extremal Kerr black hole.We study head-on collision of two subcritical particles and produced particle to escape to infinity with arbitrarily large energy.We show that the arbitrarily large energy extraction efficiency can be realize if escaping particle is near-critical and escaping probability can be 50% if we assume that the collision is isotropic distribution for the emission in the center-of-mass frame.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Ogasawara.pdf","url_title":"Presentation"}]},{"time":"16:45 - 17:00","separator":false,"expanded":false,"cols":[{"title":"Ismael Ayuso","bold":false,"expandable":true,"expanded":false,"content":"Title: On the stability and scalar perturbations growth in non-local extended gravity theories\n\nAbstract: We will discuss some of the main issues of gravitational actions in the context of extended theories of gravity for Lagrangians whose argument is the inverse of the d'Alembertian acting on the scalar curvature. Finally, we shall present the detailed procedure in order to extract the density contrast equation in the multi-potential local picture and the reliability of the standard quasi-static limit.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Ayuso.pdf","url_title":"Presentation"},{"title":"Sourabh Nampalliwar","bold":false,"expandable":true,"expanded":true,"content":"Title: Probing black holes with X-rays: A new code for calculating the transfer function\n\nAbstract: Accreting black holes are the most common systems where black holes are observed in our universe. Analysis of the radiation from such systems tells us about the accretion phenomena and the nature of black holes. The latter generally pertains to the mass and the spin, assuming a Kerr metric for the black hole. We would like to test the applicability of the Kerr metric to astrophysical black holes using X-ray data, e.g., Iron line, continuum fitting, etc. As a first step, in this talk I will present a new code for calculating the transfer function in an extended Kerr metric.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Nampalliwar.pdf","url_title":"Presentation"}]},{"time":"17:00 - 17:15","separator":false,"expanded":false,"cols":[{"title":"Alberto Rozas-Fernández","bold":false,"expandable":true,"expanded":false,"content":"Title: Observational constraints on a Unified Dark Matter scalar field model with fast transition\n\nAbstract: We study the observational viability of a Unified Dark Matter scalar field model with fast transition. For this purpose, we use a combination of geometric probes, some low redshift ones, and some high redshift ones (CMB related included). We find that the key parameters governing the transition can be well constrained and that the model fares well when compared to LCDM.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Rozas-Fernandez.pdf","url_title":"Presentation"},{"title":"Catarina Bastos","bold":false,"expandable":true,"expanded":false,"content":"Title: PT-symmetric self-gravitating dark-matter wave instability.\n\nAuthors: Catarina Bastos, Hugo Terças\n\nAbstract: In ﬂat spacetime, quantum ﬂuctuations in dark matter, as described as a Bose-Einstein conden-sate, are stable and display a relativistic Bogoliubov dispersion relation. In the weak gravitational ﬁeld limit, both relativistic and nonrelativistic models self-gravitating dark matter suggest the for-mation of structures as the result of a dynamical (Jeans) instability. Here, we show that in the presence of spontaneous symmetry breaking of the dark matter ﬁeld, the gravitational wave is damped for wave-lengths larger than the Jeans length. Such energy is converted to the Bogoliubov modes of the BEC that in their turn become unstable and grow, leading to the formation of struc-tures even in the absence of expansion. Remarkably, this compensated attenuation/ampliﬁcation mechanism is the signature of a discrete PT symmetry-breaking of the system at spacetime, quantum uctuations in dark matter, as described as a Bose-Einstein condensate, are stable and display a relativistic Bogoliubov dispersion relation. In the weak gravitational field limit, both relativistic and nonrelativistic models self-gravitating dark matter suggest the forpresence of spontaneous symmetry breaking of the dark matter field, the gravitational wave is damped for wave-lengths larger than the Jeans length. Such energy is converted to the Bogoliubov modes of the BEC that in their turn become unstable and grow, leading to the formation of structures even in the absence of expansion. Remarkably, this compensated attenuation/amplification mechanism is the signature of a discrete PT symmetry-breaking of the system.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Bastos.pdf","url_title":"Presentation"}]},{"time":"17:15 - 17:30","separator":false,"expanded":false,"cols":[{"title":"Teruaki Suyama","bold":false,"expandable":true,"expanded":false,"content":"Title: Primordial black hole scenario for the gravitational wave event GW150914\n\nAbstract: We point out that the gravitational wave event GW150914 observed by the LIGO detectors can be explained by the coalescence of primordial black holes (PBHs). It is found that the expected PBH merger rate would exceed the rate estimated by the LIGO scientific collaboration and Virgo collaboration if PBHs were the dominant component of dark matter, while it can be made compatible if PBHs constitute a fraction of dark matter. Intriguingly, the abundance of PBHs required to explain the suggested lower bound on the event rate, &gt;2 events/year/Gpc3, roughly coincides with the existing upper limit set by the non-detection of the CMB spectral distortion. This implies that the proposed PBH scenario may be tested in the not-too-distant future.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Suyama.pdf","url_title":"Presentation"},{"title":"Artur Alho","bold":false,"expandable":true,"expanded":false,"content":"Title: On dynamical systems approaches and methods in f(R) cosmology\n\nAbstract: We discuss dynamical systems approaches and methods applied to f(R)-cosmology. We argue that a complete description of the solution space of a model requires a global state space analysis that motivates globally covering state space adapted variables. This is shown explicitly by an illustrative example, f(R)=R+αR^2, α>0, for which we introduce new regular dynamical systems on global compactly extended state spaces for the Jordan and Einstein frames. As a result of applying dynamical systems methods such as blow-up of nilpotent fixed points, monotone functions, averaging, and center manifold analysis, we obtain pictures of the entire solution spaces in both the Jordan and the Einstein frames. This shows, e.g., that due to the domain of the conformal transformation between the Jordan and Einstein frames, not all the solutions in the Jordan frame are completely contained in the Einstein frame. (arXiv:1607.05715)","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Alho.pdf","url_title":"Presentation"}]},{"time":"17:30 - 17:45","separator":false,"expanded":false,"cols":[{"title":"Lara Sousa","bold":false,"expandable":true,"expanded":false,"content":"Title: Probing Cosmic Superstrings with Gravitational Waves\n\nAbstract: We compute the stochastic gravitational wave background generated by cosmic superstrings using a semi-analytical velocity-dependent model to describe their dynamics. We show that heavier string types may leave distinctive signatures on the stochastic gravitational wave background spectrum within the reach of present and upcoming gravitational wave detectors. We examine the physically motivated scenario in which the physical size of loops is determined by the gravitational backreaction scale and use NANOGRAV data to derive a conservative constraint of G?F&lt;3.2×10?9 on the tension of fundamental strings. We demonstrate that approximating the gravitational wave spectrum generated by cosmic superstring networks using the spectrum generated by ordinary cosmic strings with reduced intercommuting probability (which is often done in the literature) leads, in general, to weaker observational constraints on G?F. We show that the inclusion of heavier string types is required for a more accurate characterization of the region of the (gs,G?F) parameter space that may be probed using direct gravitational wave detectors. In particular, we consider the observational constraints that result from NANOGRAV data and show that heavier strings generate a secondary exclusion region of parameter space.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Sousa.pdf","url_title":"Presentation"},{"title":"Radu Slobodeanu","bold":false,"expandable":true,"expanded":false,"content":"Title: Recent progress on the shear-free conjecture\n\nAbstract: The talk will survey recent developments on the shear-free fluid conjecture in general relativity. Emphasis will be given to a complete proof for the case of a linear equation of state (including a non-zero cosmological constant), and two new results that hold for a general equation of state.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Slobodeanu.pdf","url_title":"Presentation"}]},{"time":"17:45 - 18:00","separator":false,"expanded":false,"cols":[{"title":"Tiago Barreiro","bold":false,"expandable":true,"expanded":false,"content":"Title: Screenings with three-form fields\n\nAbstract: We consider possible screening mechanisms for a three-form field conformally coupled to matter. Through spontaneous symmetry breaking the field can acquire a non-zero vev around high densities. We show how the three-form field profile around a massive body compares with a vector field and impose limits on the theory parameters from current observational bounds.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Barreiro.pdf","url_title":"Presentation"},{"title":"Antonio Dobado","bold":false,"expandable":true,"expanded":false,"content":"Title: Phase transitions induced by acceleration\n\nAbstract: In this work we consider the ontological status of the Unruh effect. Is it just a formal mathematical result?  Or the temperature detected by an accelerating observer can lead to real physical effects such as phase transitions?  In order to clarify this issue we use the Thermalization Theorem to explore the possibility of having a restoration of the symmetry in a system with spontaneous symmetry breaking of an internal continuous symmetry as seen by an accelerating observer in Minkowski space. We conclude that the Unruh effect is an ontic effec, giving rise, in the particular example considered here, to a phase transition (symmetry restoration) in the region close to the accelerating observer horizon.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Tuesday/Dobado.pdf","url_title":"Presentation"}]}],"size":"20"}

{[{programme.title}]}
{[{row.time}]}	{[{col.title}]}
	{[{col.content}]} {[{col.url_title}]}

{"title":"Day 3 - Wednesday, September 14","rows":[{"time":"","separator":true,"expanded":false,"cols":[{"title":"Plenary Talks (Chair: José P. S. Lemos)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Auditorium 3","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"09:00 - 10:00","separator":false,"expanded":false,"cols":[{"title":"Andrew King","bold":false,"expandable":true,"expanded":false,"content":"Title: Electromagnetic emission from mergers of black hole binaries, and what we might learn\n\nAbstract: As new gravitational wave detectors being to operate we will have more precise positions for black hole merger events. This will allow electromagnetic observations of the merger sites. I suggest that there may be delayed electromagnetic emission from black hole mergers. Detecting this emission would tell us a lot about the binary evolution producing the black hole binary, and also potentially about the black hole spins.","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Wednesday/King.pdf","url_title":"Presentation"}]},{"time":"10:00 - 10:30","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"10:30 - 11:30","separator":false,"expanded":false,"cols":[{"title":"Paulo Freire","bold":false,"expandable":true,"expanded":true,"content":"Title: Tests of general relativity with binary pulsars\n\nAbstract: In this talk, I will first introduce the basic concepts of pulsar timing. I will then introduce the historial tests of general relativity made in binary pulsars, in particular the discovery of gravitational waves in the 1980's using the first binary pulsar, PSR B1913+16, which led to the Nobel Prize in physics in 1993. I then emphasize the current best tests of gravity theories and the current timing projects, with an emphasis on the double pulsar, which provides an extremely precise test of the quadrupolar gravitational emission formula in GR, and the radiative tests using several new asymmetric pulsar - white dwarf binaries, which represent fundamental experiments on the nature of gravitational radiation and strongly constrain several classes of alternative theories of gravity.","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Wednesday/Freire.pdf","url_title":"Presentation"}]},{"time":"11:30 - 12:30","separator":false,"expanded":false,"cols":[{"title":"Patrick Sutton","bold":false,"expandable":true,"expanded":true,"content":"Title: Binary black hole mergers: Nature's most energetic events\n\nAbstract: LIGO's recent detection of gravitational waves from the binary black hole mergers GW150914 and GW151226 heralded the opening of the gravitational-wave sky. These mergers involved pairs of black holes with component masses from approximately ten to thirty times the mass of the sun. Each released a solar mass or more of energy in gravitational waves, making them the most energetic events ever witnessed, and offering insights into stellar evolution and tests of General Relativity in the dynamical strong-field regime. I will give a brief introduction to the LIGO detectors and discuss the properties of GW150914 and GW151226, and the prospects for further gravitational-wave detections in the coming years.","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Wednesday/Sutton.pdf","url_title":"Presentation"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Parallel Sessions (Chairs: Pedro Girão, Jorge Zanelli)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Auditorium 3","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"},{"title":"Room 2","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"14:00 - 14:15","separator":false,"expanded":false,"cols":[{"title":"Filipe Costa","bold":false,"expandable":true,"expanded":false,"content":"Title: Gravitomagnetism and the significance of the curvature scalar invariants\n\nAbstract: The curvature invariants have been subject of interest in recent years due to the ongoing debate concerning the notions of intrinsic/extrinsic frame-dragging, the use of the electromagnetic analogy in such classification, and the question of whether there is a fundamental difference between the gravitomagnetic field arising from the translational motion of the sources, detected via Lunar Laser Ranging and in the observations of binary pulsars, and the one produced by the rotation of the Earth, detected in the LAGEOS Satellites data and by the Gravity Probe-B mission. In this talk I shall discuss both the algebraic and physical meaning of the curvature invariants and their electromagnetic counterparts. The structure of the invariants in the astrophysical systems under scrutiny is physically interpreted, and its relationship with the gravitomagnetic effects dissected. Finally, a new classification for intrinsic/extrinsic gravitomagnetism is put forth.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Costa.pdf"},{"title":"Raül Vera","bold":false,"expandable":true,"expanded":false,"content":"Title: Double layers in quadratic theories of gravity\n\nAbstract: The junction conditions for the most general gravitational theory with a Lagrangian containing terms quadratic in the curvature are derived. Both the cases with a possible concentration of matter on the joining hypersurface, as well as the proper matching conditions where only finite jumps of the energy-momentum tensor are included. For the latter, we prove that the proper matching conditions are more demanding than in General Relativity. In the former case, we show that the shells/domain walls generically possess, in addition to the standard energy-momentum tensor, a double layer energy-momentum contribution which actually induces an external energy flux vector and an external scalar pressure/tension on the shell. We prove that all these contributions are necessary to make the entire energy-momentum tensor divergence-free, and we present the field equations satisfied by these energy-momentum quantities. The consequences of all these results are briefly analyzed.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Vera.pdf"}]},{"time":"14:15 - 14:30","separator":false,"expanded":false,"cols":[{"title":"Otakar Svitek","bold":false,"expandable":true,"expanded":false,"content":"Title: Properties of Robinson-Trautman solution with scalar hair\n\nAbstract: Explicit Robinson-Trautman solution with minimally coupled free scalar field was derived and analyzed recently. It was shown that this solution possesses curvature singularity which is initially naked but later the horizon envelopes it. However, this study concentrated on the general branch of the solution where all the free constants are nonzero. Interesting special cases arise when some of the parameters are set to zero. In most of these cases the scalar field is still present. One of the cases is a static solution which represents a parametric limit of Janis-Newman-Winicour scalar field spacetime. Additionally, we provide the calculation of Bondi mass which clarifies the interpretation of the general solution.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Svitek.pdf","url_title":"Presentation"},{"title":"Emma Jakobsson","bold":false,"expandable":true,"expanded":false,"content":"Title: Regularizing cones in 1+1 Minkowski\n\nAbstract: In this talk it is shown how cones in 2-dimensional flat spacetime can be made smooth by cutting away a region containing the conical singularity and replacing it with a piece of a spacetime of constant curvature. A similiar procedure of cutting and gluing can also be used to regularize pieces of Misner space.  The original motivation for this problem had to do with a paper on black to white hole transitions by Haggard and Rovelli, but the question has independent interest.\nThe cones are obtained by performing identifications using a boost, and we can produce several examples of cones depending on whether the flow of the boost in the region where the identification is performed is spacelike or timelike, and whether there is what we will call a conical \"deficit\" or \"excess\".?","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Jakobsson.pdf","url_title":"Presentation"}]},{"time":"14:30 - 14:45","separator":false,"expanded":false,"cols":[{"title":"Andrea Nerozzi","bold":false,"expandable":true,"expanded":false,"content":"Title: On spin coefficients in the Newman-Penrose formalism\n\nAbstract: Since its introduction the Newman-Penrose formalism has been widely used in analytical and numerical studies of Einstein's equations, like for example for the Teukolsky master equation, or as a powerful wave extraction tool in numerical relativity. Despite the many applications, the equations in the Newman-Penrose formalism appear complicated and somehow still obscure. In this talk I will approach the whole formalism with the goal of finding an invariant expression for the spin coefficients once a specific yet generally defined tetrad is chosen. I will show that it is possible to do so, and give a general recipe for the task, as well as an indication of the quantities and identities that are required. The proposed approach reduces dramatically the number of degrees of freedom in the NP formalism simplifying it considerably and represents a promising tool for the study of Einstein's equations.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Nerozzi.pdf","url_title":"Presentation"},{"title":"Ingemar Bengtsson","bold":false,"expandable":true,"expanded":false,"content":"Title: A Toy Penrose Inequality and its Proof\n\nAbstract: In Penrose's original formulation, a shell of null dust collapses into Minkowski space and a marginally trapped surface forms on it. The Penrose inequality (which assumes cosmic censorship) relates the area of this surface to the total mass of the shell. A reformulation turns the inequality into a statement about the area and the null expansions of a surface in Minkowski space, but a completely general proof has proved difficult. In our toy version the shell falls into a 2 + 1 dimensional anti-de Sitter space. An analogous inequality is proposed, and then proved in full generality.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Bengtsson.pdf","url_title":"Presentation"}]},{"time":"14:45 - 15:00","separator":false,"expanded":false,"cols":[{"title":"Norbert Van den Bergh","bold":false,"expandable":true,"expanded":false,"content":"Title: Goldberg-Sachs and the alignment condition for Einstein-Maxwell fields\n\nAbstract: A new characterisation is given of the Garcia-Plebanski and Plebanski-Hacyan metrics within the family of non-null aligned Einstein-Maxwell fields with a cosmological constant and of the Debever-Kamran-McLenaghan 'class D' metrics with non-vanishing cosmological constant within the general family of non-null Einstein-Maxwell fields.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/NvDB.pdf"},{"title":"José M M Senovilla","bold":false,"expandable":true,"expanded":false,"content":"Title: Shear-free surfaces and marginally trapped tubes\n\nAbstract: The concept of \"shear-free\" spacelike surface will be introduced. They arise as generalizations of surfaces orthogonal to a shear-free irrotational null vector field. Geometrically, they are surfaces umbilical along a normal direction. A simple, useful, way to characterize them will be given. Arguments supporting that they can be used to select a preferred marginally trapped tube (MTT) in dynamical black holes will be discussed.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Senovilla.pdf","url_title":"Presentation"}]},{"time":"15:00 - 15:15","separator":false,"expanded":false,"cols":[{"title":"Kentaro Tanabe","bold":false,"expandable":true,"expanded":false,"content":"Title: Charged rotating black holes at large D\n\nAbstract: We discuss the charged rotating black holes in the Einstein-Maxwell theory by using the large D expansion method, where D is a spacetime dimension. The charged rotating black hole solution is constructed as the solution of large D effective equations. We also give stability analysis of charged rotating black holes by performing perturbation analysis of the large D effective equations. As a result we find that the ultraspinning instability of charged rotating black holes in de Sitter describes the instability of de Sitter Reissner-Nordstrom black hole.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Tanabe.pdf","url_title":"Presentation"},{"title":"Nastassja Cipriani","bold":false,"expandable":true,"expanded":false,"content":"Title: Shear-free spacelike surfaces of transitivity of group of motions\n\nAbstract: In a recent work we characterized spacelike co-dimension two submanifolds that are shear-free along one normal direction. We use this characterization to study the surfaces of transitivity of group of motions.\nLet n+2 be the dimension of the spacetime and let S be one such transitivity (spacelike) surface with dimension n. We find that S is shear-free along a normal direction if and only if all scalar products of Killing vectors are functionally dependent. We present examples, and we also show how to generalize the result to conformal motions and other symmetries.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Cipriani.pdf","url_title":"Presentation"}]},{"time":"15:15 - 15:30","separator":false,"expanded":false,"cols":[{"title":"Ryotaku Suzuki","bold":false,"expandable":true,"expanded":false,"content":"Title: Large D Effective Theory\n\nAbstract: Recently, the large D effective theory method have been successful in the analysis of higher dimensional black holes in various setup. We will show that all the previous analysis, excluding a few non-decoupled analysis,  can be unified to an effective equation in the general setup within the decoupled regime. Some applications will be also shown.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Suzuki.pdf","url_title":"Presentation"},{"title":"José Luis Flores","bold":false,"expandable":true,"expanded":false,"content":"Title: Rigidity of geodesic completeness in gravitational wave spacetimes\n\nAbstract: We consider restrictions placed by geodesic completeness on spacetimes possessing a null parallel vector field, the so-called Brinkmann spacetimes. This class of spacetimes includes important idealized gravitational wave models in General Relativity, namely the plane-fronted waves with parallel rays, or pp-waves, which in turn have been intensely and fruitfully studied in the mathematical and physical literatures for over half a century. More concretely, we prove a restricted version of a conjectural analogue for Brinkmann spacetimes of a rigidity result obtained by M.T. Anderson for stationary spacetimes.  We also highlight its relation with a long-standing 1962 conjecture by Ehlers and Kundt.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Flores.pdf","url_title":"Presentation"}]},{"time":"15:30 - 15:45","separator":false,"expanded":false,"cols":[{"title":"Giovanni Acquaviva","bold":false,"expandable":true,"expanded":false,"content":"Title:  Thermodynamics of gravitational fields\n\nAbstract:  We explore the possibility of constructing a thermodynamic formulation of gravity following a purely geometrical approach.  The construction is based on the notion of energy-momentum provided by the \"square root\" of the Bel-Robinson tensor, whose components are interpreted in a fluid-like fashion as energy density, pressures and fluxes of the gravitational field.  We derive \"balance equations\" for such quantities and relate them to the behaviour of timelike congruences of the spacetime.  An important aspect to be investigated is the geometrical definition of gravitational temperature and its relation with usual results of horizon thermodynamics.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Acquaviva.pdf","url_title":"Presentation"},{"title":"Michal Pirog","bold":false,"expandable":true,"expanded":false,"content":"Title: Dragging and anti-dragging effects in rotating systems\n\nAbstract: I will consider weak perturbation with angular momentum of the Schwarzschild geometry. There is a strong numerical evidence that various types of dragging (anti-dragging) effects are positively correlated with the normalized angular momentum. I'm going to present the numerical result for many different numerical models which show the relation between abovementioned effects and such parameters of the system like total mass and asymptotic angular momentum.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Pirog.pdf","url_title":"Presentation"}]},{"time":"15:45 - 16:15","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"16:15 - 16:30","separator":false,"expanded":false,"cols":[{"title":"Carlos Barceló","bold":false,"expandable":true,"expanded":false,"content":"Title: Weyl's gravity revisited\n\nAbstract: In this talk I will revisit Weyl's unified theory of Electromagnetism and Gravity. I will highlight that at the mild cost of introducing an external volume element, one can construct a theory closely related to Einstein's gravity but sharing the conformal invariance of four-dimensional Electromagnetism in the absence of matter. The construction mixes ideas from Weyl-transverse gravity and Weyl's unified theory. I will argue that the former criticisms against Weyl's unified theory loose most of their power in the present reincarnation of the theory. I will also stress that the resulting theory is different enough from the Einstein-Maxwell theory so as to predict new observable effects.","url_title":"Presentation","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Barcelo.pdf"},{"title":"Kunihito Uzawa","bold":false,"expandable":true,"expanded":false,"content":"Title: Violation of cosmic censorship in dynamical p-brane systems\n\nAbstract: We discuss the cosmic censorship of dynamical p-brane systems in a D-dimensional background. This is the generalization of the analysis in the Einstein-Maxwell-dilaton theory. We present that a timelike curvature singularity generically appears from an asymptotic region in the time evolution of the p-brane solution. Since we can set regular and smooth initial data in a dynamical M5-brane system in 11-dimensional supergravity, this implies a violation of cosmic censorship.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Uzawa.pdf","url_title":"Presentation"}]},{"time":"16:30 - 16:45","separator":false,"expanded":false,"cols":[{"title":"Carlos Romero","bold":false,"expandable":true,"expanded":false,"content":"Title: Towards the completion of Weyl unified theory \n\nAbstract: In 1918, H. Weyl proposed a unified theory of gravity and electromagnetism based on a generalization of Riemannian geometry. In spite of its elegance and beauty, a serious objection was raised by Einstein, who argued that Weyl's theory was not suitable as a physical theory . According to Einstein, the theory led to the prediction of a \"second clock effect\", which is not observed by experiments. We briefly revisit this point and argue that a preliminary discussion on the very notion of proper time is needed in order to consider Einstein's critical point of view. We show that this notion may be fully provided by Perlick' conception of proper time.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Romero.pdf","url_title":"Presentation"},{"title":"Masashi Kimura","bold":false,"expandable":true,"expanded":false,"content":"Title: Mass Ladder Operators from Conformal Symmetry\n\nAbstract: We introduce a novel type of ladder operators, which map a scalar field with a mass into another scalar field with a different mass. It is shown that such operators are constructed from closed conformal Killing vector fields in an Einstein space/spacetime in arbitrary dimensions. As an example, we explicitly construct the ladder operators in AdS_2. It is also shown that in AdS_n, the ladder operators exist for any scalar field with the mass above the BF bound. Furthermore, we discuss a relation between Aretakis constants in AdS_2 and the ladder operators.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Kimura.pdf","url_title":"Presentation"}]},{"time":"16:45 - 17:00","separator":false,"expanded":false,"cols":[{"title":"Ondrej Hruška","bold":false,"expandable":true,"expanded":false,"content":"Title: Kundt Spacetimes in Quadratic Gravity\n\nAbstract: The Quadratic Gravity is an extension of Einstein's theory with additional terms in action that are quadratic combinations of the Riemann tensor and its contractions. These corrections are needed, for example, in perturbative quantum gravity. We consider the family of Kundt spacetimes, which is defined in a purely geometrical way by admitting a shear-free, twist-free and expansion-free null geodesic congruence. In particular, we focus on the Kundt solutions without gyratonic terms, and we investigate the constraints imposed by the Quadratic Gravity field equations. We investigate various special cases depending on the parameters in the theory, one of those cases being the Gauss-Bonnet gravity. The conditions for the metrics to be of various algebraic types are also studied.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Hruska.pdf","url_title":"Presentation"},{"title":"Hugo Ferreira","bold":false,"expandable":true,"expanded":false,"content":"Title: Anti-de Sitter, scalar fields and boundary conditions\n\nAbstract: Anti-de Sitter is not a globally hyperbolic spacetime. When studying a field theory on anti-de Sitter, one needs an appropriate choice of boundary conditions at the conformal boundary such that the classical field equation is well-posed. Moreover, at the level of the standard formulation of quantum field theory, the existence of a physical quantum state (a so-called Hadamard state) is only guaranteed on globally hyperbolic spacetimes.\nIn this talk, I consider a massive scalar field on anti-de Sitter and analyse all of the acceptable boundary conditions, including the commonly used Dirichlet boundary conditions as a particular example. I show that both the classical and quantum field theory is well-defined for these choices and, in particular, that there exists a physically relevant state, by proving for the first time that its two point function is of Hadamard form, for all choices of boundary conditions.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Ferreira.pdf","url_title":"Presentation"}]},{"time":"17:00 - 17:15","separator":false,"expanded":false,"cols":[{"title":"Tayebeh Tahamtan","bold":false,"expandable":true,"expanded":false,"content":"Title: Kundt spacetimes minimally coupled to scalar field\n\nAbstract: We derive an exact solutions belonging to Kundt class of spacetimes both with and without a cosmological constant that are minimally coupled to free massless scalar field. We show the algebraic type of these solutions and give interpretation of the results. Subsequently, we look for solutions additionally containing electromagnetic field satisfying nonlinear field equations.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Tahamtan.pdf","url_title":"Presentation"},{"title":"Paulo Luz","bold":false,"expandable":true,"expanded":false,"content":"Title: Raychaudhuri equation in space-times with torsion\n\nAbstract: The Raychaudhuri equation for a congruence of time-like and null curves in a N-dimensional space-time with the most general torsion is derived. Relating with the previous results in the literature it is concluded that many are wrong.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Luz.pdf","url_title":"Presentation"}]},{"time":"17:15 - 17:30","separator":false,"expanded":false,"cols":[{"title":"Anne Franzen","bold":false,"expandable":true,"expanded":false,"content":"Title: Stability properties of black hole interiors\n\nAbstract: Motivated by the Strong Cosmic Censorship Conjecture we are interested in stability/instability properties of Cauchy horizons on charged black hole interiors.\nAs a first proxy to the Einstein field equations we consider solutions of the scalar wave equation Box_g phi=0, without symmetry, on fixed black hole backgrounds (cM, g) containing a Cauchy horizon. In particular, we will compare asymptotically flat and asymptotically de Sitter solutions.\nPreviously established decay rates, so called Price's law tails, arising from sufficiently regular data on a two ended Cauchy hypersurface, serve as a starting point for the analysis.\nThe proof depends on energy estimates in the black hole interior which, in combination with commutation by angular momentum operators and application of Sobolev embedding, yield certain stability results at the Cauchy horizon.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Franzen.pdf","url_title":"Presentation"},{"title":"Rui André","bold":false,"expandable":true,"expanded":false,"content":"Title: Critical phenomena in Roberts-anti-de Sitter black holes\n\nAbstract: The Roberts massless scalar field solution has been used for studying critical phenomena in gravitational. Following its recent generalization to include a cosmological constant, we evaluate how it affects the power-law for the black hole mass near the critical solution in an anti-de Sitter background. The properties of the anti-de Sitter infinity allow for the reflection of a dispersing scalar wave. Interestingly, we find that, at each reflection, the scalar wave's properties may change and may eventually collapse to form a black hole.","url":"https://erep2016.tecnico.ulisboa.pt/Parallel/Wednesday/Andre.pdf","url_title":"Presentation"}]},{"time":"17:30 - 18:30","separator":true,"expanded":false,"cols":[{"title":"SPRG Meeting","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"},{"title":"SEGRE Meeting","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"20:00 - 00:00","separator":false,"expanded":false,"cols":[{"title":"Social Programme","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]}],"size":"20"}

{[{programme.title}]}
{[{row.time}]}	{[{col.title}]}
	{[{col.content}]} {[{col.url_title}]}

{"title":"Day 4 - Thursday, September 15","rows":[{"time":"","separator":true,"expanded":false,"cols":[{"title":"Plenary Sessions (Chair: José Natário)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Auditorium 3","bold":true,"expandable":false,"expanded":false,"content":"Expandable Content"}]},{"time":"09:00 - 10:00","separator":false,"expanded":false,"cols":[{"title":"Gonzalo Olmo","bold":false,"expandable":true,"expanded":false,"content":"Title: Black holes, wormholes, and singularities beyond Riemannian geometry.\n\nAbstract: The singular nature of black hole space-times in General Relativity has deep conceptual implications which call for a resolution. I will show that considering extensions of GR in a priori non-Riemannian backgrounds concepts such as geodesic incompleteness and curvature divergences become disentangled, providing a new perspective on the singularity problem. We will see that curvature divergences do not force geodesic incompleteness and that extended objects and waves can go through such regions without experiencing any dramatic effects. The discussion will be illustrated with several black hole solutions generated by electric fields and other sources.","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Thursday/Olmo.pdf","url_title":"Presentation"}]},{"time":"10:00 - 10:30","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]},{"time":"10:30 - 11:30","separator":false,"expanded":false,"cols":[{"title":"João Costa","bold":false,"expandable":true,"expanded":true,"content":"Title: On strong cosmic censorship in the presence of a positive cosmological constant.\n\nIn General Relativity, the defence of determinism leads to the Strong Cosmic Censorship Conjecture. In this talk, I will start by discussing the motivation for this conjecture and part of the subtleties concerning its formulation. I will then present some recent results that suggest its failure in the presence of a positive cosmological constant.","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Thursday/Costa.pdf","url_title":"Presentation"}]},{"time":"11:30 - 12:30","separator":false,"expanded":false,"cols":[{"title":"Gustav Holzegel","bold":false,"expandable":true,"expanded":true,"content":"Title: Linear Stability of the Schwarzschild Solution\n\nAbstract: I will discuss our recent proof (with M. Dafermos and I. Rodnianski) of the Linear Stability of the Schwarzschild Solution in General Relativity. The proof relies on progress in the study of linear wave equations on black hole backgrounds combined with some classical insights into the structure of the system of gravitational perturbations, which I will review. An important role is played by the pure gauge solutions of the system. Time permitting I will also discuss conservations laws for the system of gravitational perturbations on Schwarzschild and how to exploit them to control the dynamics.","url":"https://erep2016.tecnico.ulisboa.pt/Plenary/Thursday/Holzegel.pdf","url_title":"Presentation"}]},{"time":"12:30 - 12:35","separator":false,"expanded":false,"cols":[{"title":"Closing Remarks","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content"}]}],"size":"20"}