Program

XI Black Holes Workshop

Venue: Complexo Interdisicplinar, Instituto Superior Técnico

Conference dinner: Casa do Alentejo

Time length of the talks: 12 minutes + 3 minutes for questions

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{"title":"Day 1, Monday, December 17","rows":[{"time":"08:30 - 09:00","separator":false,"expanded":true,"cols":[{"title":"Registration and Opening Session","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"","separator":true,"expanded":true,"cols":[{"title":"Session 1 (Chair: Miguel Zilhão)","bold":true,"expandable":false,"expanded":false,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"09:00 - 09:15","separator":false,"expanded":true,"cols":[{"title":"Eric Gourgoulhon: Probing the vicinity of the galactic center black hole with LISA","bold":false,"expandable":true,"expanded":false,"content":"We shall discuss the gravitational wave emission and its detectability by LISA of various processes / materials on close orbits around the black hole Sgr A* at the center of our galaxy.","url":"","url_title":"Download"}]},{"time":"09:15 - 09:30","separator":false,"expanded":false,"cols":[{"title":"Juan Calderon Bustillo: Tracking black hole kicks using gravitational wave observations","bold":false,"expandable":true,"expanded":false,"content":"Binary black holes radiate anisotropic gravitational waves. This is the result of the anisotropic interaction of the different gravitational wave radiation modes. As a consequence, the final merged black hole inherits a characteristic velocity known as kick. In this work we show how the rich information encoded in the higher modes of the gravitational wave emission can be exploited to measure kicks of only 130km/s for signals with a signal-to-noise ratio of ~15 using current ground based detectors.","url":"","url_title":"Download"}]},{"time":"09:30 - 09:45","separator":false,"expanded":true,"cols":[{"title":"Nadja Magalhães: General relativity, galactic mass densities and their rotation curves","bold":false,"expandable":true,"expanded":false,"content":"The rotation curves of galaxies can be fit using general relativity and an amount of dark matter that is less than the necessary when other theories of gravitation are applied. In such approach, developed by Cooperstock and Tieu (CT model), a galaxy is modeled as low density baryonic dust in stationary, axially-symmetric rotation. It has been shown that non-linear gravitational effects play a significant role in the overall motion of matter. The fits can be used to determine mass densities as functions of galactocentric distances and heights, yielding galactic masses – a valuable information to investigate the presence of black holes in galactic cores. As a first approximation to their morphologies new information about the galaxies can be obtained from their mass-density functions. In this work the CT model is applied to the galaxy UGC 128, whose results are compared to others previously obtained for NGC 2403. These two galaxies are at identical positions on the Tully-Fisher relation, having almost identical luminosities as well as rotation velocities, being morphologically very similar. Nevertheless, they display large differences in surface brightness. Despite their almost identical rotational velocity profile, using the CT model it is found that their mass density profiles may be significantly different. In this work these results will be presented, highlighting their implications for the understanding of the nature of dark matter.","url":"","url_title":"Download"}]},{"time":"09:45 - 10:00","separator":false,"expanded":false,"cols":[{"title":"Jorge Rocha: Self-similarity in Einstein-Maxwell-dilaton theories and critical collapse","bold":false,"expandable":true,"expanded":true,"content":"Self-similar spacetimes emerge as intermediate attractors for gravitational collapses near the threshold of black hole formation, i.e., near criticality. In some cases, self-similarity is manifested as a continuous symmetry, occasionally allowing to derive analytic solutions. I will report on continuously self-similar solutions of 4D Einstein-Maxwell-dilaton theories. It is known that scale invariance of the metric generally does not imply the same property for gravitating matter fields. First I present general homothetic transformations of the dilaton and gauge fields consistent with scale invariance of the metric (but without assuming any further spacetime symmetries). I will then focus on spherically symmetric collapses and assess the impact of the electric field and its coupling to the dilaton on the phase space of solutions and, in particular, on Choptuik's critical exponent.","url":"","url_title":"Download"}]},{"time":"10:00 - 10:15","separator":false,"expanded":false,"cols":[{"title":"Rodrigo Vicente: Dynamical friction on a gaseous slab","bold":false,"expandable":true,"expanded":false,"content":"Dynamical friction, also known as gravitational drag force, was first studied by Subrahmanyan Chandrasekhar in 1943. When a massive object moves through a gaseous medium there will be a momentum (and, kinetic energy) transfer from the moving object to the surrounding medium, due to the gravitational interaction between them. Thus, in this process, the moving body will effectively feel a gravitational drag force. This phenomenon is of great importance for astrophysics (in particular, to understand the formation of planetary systems). However, as far as we know, all treatments of this phenomenon in the literature deal with a three-dimensional infinite gaseous medium. Here, we study the gravitational drag force that a massive object feels, when moving through a gaseous infinite slab. This should give us a more realistic setup to study the phenomenon of dynamical friction on disk-like gaseous mediums.","url":"","url_title":"Download"}]},{"time":"10:15 - 10:30","separator":false,"expanded":false,"cols":[{"title":"Richard Brito: The stochastic gravitational-wave background in the absence of horizons","bold":false,"expandable":true,"expanded":false,"content":"Gravitational-wave astronomy has the potential to explore one of the deepest and most puzzling aspects of Einstein’s theory: the existence of black holes. A plethora of ultracompact, horizonless objects have been proposed to arise in models inspired by quantum gravity. These objects may solve Hawking’s information-loss paradox and the singularity problem associated with black holes, while mimicking almost all of their classical properties. They are, however, generically unstable on relatively short timescales. Here, we show that this “ergoregion instability” leads to a strong stochastic background of gravitational waves, at a level detectable by current and future gravitational-wave detectors. The absence of such background in the first observation run of Advanced LIGO already imposes the most stringent limits to date on black-hole alternatives.","url":"","url_title":"Download"}]},{"time":"10:30 - 10:45","separator":false,"expanded":false,"cols":[{"title":"Ryuichi Fujita: Gravitational waves from eccentric orbits in Kerr spacetime","bold":false,"expandable":true,"expanded":false,"content":"Gravitational waves from a particle around a Kerr black hole are one of the main targets of LISA. Such extreme mass ratio inspirals (EMRIs) may have large orbital eccentricity, ~0.8, when they enter the sensitivity band of LISA and hence it is important to compute gravitational waveforms for the case of large orbital eccentricity in EMRIs. In this presentation, we will investigate gravitational waves for large orbital eccentricity in EMRIs by using post-Newtonian approximation in black hole perturbation theory. This may be the first time to compute gravitational waves from EMRIs without using small eccentricity approximation for the case of Kerr spacetime.","url":"","url_title":"Download"}]},{"time":"10:45 - 11:15","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Session 2 (Chair: Carlos Herdeiro)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"11:15 - 11:30","separator":false,"expanded":false,"cols":[{"title":"Ivica Smolić: Thermodynamics of black holes with nonlinear electromagnetic fields","bold":false,"expandable":true,"expanded":true,"content":"Classical Maxwell's electrodynamics is based on a system of linear differential equations. However, once the quantum effects are taken into account, the upgraded Maxwell's equations become a nonlinear system. Nonlinear electrodynamics has a long history, starting from early models of Born and Infeld and first QED corrections found by Euler and Heisenberg back in the 1930s. In this talk we shall discuss recent generalizations of the black hole thermodynamic relations (zeroth and first law, Smarr formula) in the presence of nonlinear electromagnetic fields. Most notably, we shall show that the generalized Smarr formula contains an additional term which is proportional to the integral of the trace of the electromagnetic energy-momentum tensor and can be written as a product of two conjugate variables.","url":"","url_title":"Download"}]},{"time":"11:30 - 11:45","separator":false,"expanded":false,"cols":[{"title":"Adrian del Rio: Quantum anomalies in curved spacetimes","bold":false,"expandable":true,"expanded":true,"content":"It is well known that not every symmetry of a classical field theory is a symmetry of the corresponding quantum version. When this occurs, one speaks of quantum anomalies. Their existence imply that some classical Noether charges are no longer conserved in the quantum theory, and their evolution is determined by the background geometry. In this talk I will introduce both chiral fermion and electric-magnetic duality anomalies in curved spacetimes, related to non-conservation of helicity, and discuss their consequences in astrophysics. In particular I will argue that a necessary condition for a spacetime to produce such asymmetry is the generation of gravitational radiation propagating to future null infinity with an excess of one particular polarization.","url":"","url_title":"Download"}]},{"time":"11:45 - 12:00","separator":false,"expanded":false,"cols":[{"title":"Kunihito Uzawa: Compact objects and the swampland","bold":false,"expandable":true,"expanded":false,"content":"Recently, two simple criteria were proposed to assess if vacua emerging from an effective scalar field theory are part of the string \"landscape\" or \"swampland\". However, there has been little attempt to examine the swampland criterion against explicit context of solitonic compact objects made up of scalar fields. In this presentation, we discuss the universal behavior that in the region wherein the boson stars are expected to be perturbatively stable, the compact objects may be part of the landscape. By contrast, in the region where they may be faithful black hole mimickers, in the sense they possess a light ring, the criteria fail (are obeyed) for static (rotating) ultracompact boson stars, which should thus be part of the swampland (landscape). We also consider hairy black holes interpolating between these boson stars and the Kerr solution and establish the part of the domain of existence where the swampland criteria are violated.","url":"","url_title":"Download"}]},{"time":"12:00 - 12:15","separator":false,"expanded":false,"cols":[{"title":"Rui André: Black holes in a box and thin shells: Thermodynamics and connections","bold":false,"expandable":true,"expanded":false,"content":"We discuss how York’s thermodynamic treatment of a black hole inside a box at fixed temperature is equivalent to the thermodynamics of a thin matter shell with the same size and temperature of the box. Other equivalences are also mentioned.","url":"","url_title":"Download"}]},{"time":"12:15 - 12:30","separator":false,"expanded":false,"cols":[{"title":"Gonçalo Quinta: Symmetry restoration of quantum fields around charged black holes","bold":false,"expandable":true,"expanded":false,"content":"We study the restoration of a spontaneously broken symmetry of an interacting quantum scalar field around a charged black hole in four dimensions. This is done by numerically solving the system of non-linear coupled equations describing the dynamics of the vacuum polarisation and the background field. We find that there is a bubble around the black hole inside which the field can only assume a value very close to zero, implying that symmetry is restored in regions close to the horizon.","url":"","url_title":"Download"}]},{"time":"12:30 - 12:45","separator":false,"expanded":false,"cols":[{"title":"Ricardo Ferreira: De-Sitter particle production and its connections to black hole evaporation","bold":false,"expandable":true,"expanded":true,"content":"During the accelerated expansion of the universe particles are produced at the Hubble horizon in a similar fashion to the Hawking radiation in the black hole case. These particles are then stretched by the expansion and become locally indistinguishable from a coordinate transformation. However, their cumulative production is known to cause a breakdown of perturbation theory on ultra large scales. In this talk I will present another perspective on such breakdown by exploring the effects on the local vacua of the asymptotic charges associated with these soft modes. In particular, I will show that the different vacua become orthogonal to each other when t_dS -> M_p^2/H^3, signaling the breakdown of the perturbative description on a time scale equivalent to the Page time in the black hole context.","url":"","url_title":"Download"}]},{"time":"12:45 - 13:00","separator":false,"expanded":false,"cols":[{"title":"Masashi Kimura: Stability analysis of black holes by the S-deformation method for coupled systems","bold":false,"expandable":true,"expanded":true,"content":"We propose a simple method to prove the linear mode stability of a black hole when the perturbed field equations take the form of a system of coupled Schrodinger equations. The linear mode stability of the spacetime is guaranteed by the existence of an appropriate S-deformation. Such an S-deformation is related to the Riccati transformation of a solution to the Schrodinger system with zero energy. We apply this formalism to some examples and numerically study their stability.","url":"","url_title":"Download"}]},{"time":"13:00 - 14:30","separator":true,"expanded":false,"cols":[{"title":"Lunch","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Session 3 (Chair: Masashi Kimura)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"14:30 - 14:45","separator":false,"expanded":false,"cols":[{"title":"Júlio Fabris: On the stability of naked singularities","bold":false,"expandable":true,"expanded":false,"content":"Naked singularities correspond to star-like solutions of the General Relativity equations where the singularity is not covered by an event horizon. In the simplest situations (Schwarzschild solution with negative mass, for example) naked singularities are unstable. We revise the results for the usual cases and extend the analysis of the stability to dilatonic solutions corresponding to naked singularity configurations.","url":"","url_title":"Download"}]},{"time":"14:45 - 15:00","separator":false,"expanded":false,"cols":[{"title":"Ángel Rincón: Black holes and running couplings: the planar anti-de Sitter case","bold":false,"expandable":true,"expanded":true,"content":"In this work, we investigate four-dimensional planar blackholes solutions in anti-de Sitter (AdS) spacetimes in light of the so-called scale-dependent scenario. To obtain this new family of solutions, the classical couplings of the theory, i.e., the gravitational coupling G_0 and the cosmological constant Lambda_0, are not taken to be fixed values anymore. In this sense, the set of classical parameters evolve to functions which change along the height z. The effective Einstein field equations are solved, and the results are analyzed and compared with the classical counterpart. Finally, the thermodynamic properties as the temperature and the entropy are investigated.","url":"","url_title":"Download"}]},{"time":"15:00 - 15:15","separator":false,"expanded":false,"cols":[{"title":"Kyriakos Destounis: Strong cosmic censorship in charged black hole spacetimes","bold":false,"expandable":true,"expanded":false,"content":"It was recently shown that Strong Cosmic Censorship may be violated in highly charged black-hole spacetimes living in a universe with a positive cosmological constant. Several follow-up works have since suggested that such result, while conceptually interesting, cannot be upheld in practice. We focus here on the claim that the presence of charged massive scalars suffices to save Strong Cosmic Censorship. To the contrary, we show that there still exists a finite region in parameter space where Strong Cosmic Censorship is expected to be violated.","url":"","url_title":"Download"}]},{"time":"15:15 - 15:30","separator":false,"expanded":false,"cols":[{"title":"Raimon Luna: Strong cosmic censorship: the nonlinear story","bold":false,"expandable":true,"expanded":false,"content":"A satisfactory formulation of the laws of physics entails that the future evolution of a physical system should be determined from appropriate initial conditions. The existence of Cauchy horizons in solutions of the Einstein field equations is therefore problematic, and expected to be an unstable artifact of General Relativity. This is asserted by the Strong Cosmic Censorship Conjecture, which was recently put into question by an analysis of the linearized equations in the exterior of charged black holes in an expanding universe. Here, we numerically evolve the nonlinear Einstein-Maxwell-scalar field equations with a positive cosmological constant, under spherical symmetry, and provide strong evidence that mass inflation indeed does not occur in the near extremal regime. This shows that nonlinear effects might not suffice to save the Strong Cosmic Censorship Conjecture.","url":"","url_title":"Download"}]},{"time":"15:30 - 15:45","separator":false,"expanded":false,"cols":[{"title":"José Luis Blazquez-Salcedo: Radial perturbations and stability of the scalarized Einstein-Gauss-Bonnet black holes","bold":false,"expandable":true,"expanded":true,"content":"In this talk we will discuss the stability of a new class of scalarized black holes found in scalar-tensor-Gauss-Bonnet theory, recently reported in arXiv:1711.01187, arXiv:1711.02080. The scalarization is induced by the curvature of the spacetime itself. We will analyze in detail the radial perturbations of the different branches of scalarized black holes, and we will discuss the effect of the particular coupling function. This talk is based on arXiv:1805.05755.","url":"","url_title":"Download"}]},{"time":"15:45 - 16:00","separator":false,"expanded":false,"cols":[{"title":"Pedro Cunha: Shadows and strong gravitational lensing","bold":false,"expandable":true,"expanded":false,"content":"For ultra compact objects, light rings and fundamental photon orbits (FPOs) play a pivotal role in the theoretical analysis of strong gravitational lensing effects, and of Black Hole (BH) shadows in particular. In this talk, specific models, namely Kerr BHs with bosonic hair, are considered to illustrate how FPOs can be useful in order to understand some non-trivial gravitational effects, hopefully providing some intuition and new insights for the underlying physics, which might be critical when testing the Kerr black hole hypothesis.","url":"","url_title":"Download"}]},{"time":"16:00 - 16:15","separator":false,"expanded":false,"cols":[{"title":"Taishi Ikeda: Electromagnetic emission from axionic clouds","bold":false,"expandable":true,"expanded":false,"content":"Although the existence of dark matter (DM) has been shown through various observations, nobody knows the identity of the DM. Axions were firstly introduced to solve the strong CP problem, and one of the possible candidate of DM.Due to the super-radiance instability, axion cloud is formed around Kerr BHs.Recently, it was suggested that once coupling to photons is considered, the laser of photons is emitted from the cloud through the coupling. In this talk, we solve numerically the Axion-Maxwell system, and confirm the existence of laser-like emission from clouds.","url":"","url_title":"Download"}]},{"time":"16:15 - 16:45","separator":true,"expanded":true,"cols":[{"title":"Coffee Break and Group Photograph","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"","separator":true,"expanded":true,"cols":[{"title":"Session 4 (Chair: Jorge Rocha)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"16:45 - 17:00","separator":false,"expanded":false,"cols":[{"title":"Henrique Oliveira: The affine-null formulation of the gravitational equations: spherical critical collapse","bold":false,"expandable":true,"expanded":false,"content":"A new evolution algorithm for the characteristic initial value problem based upon an affine parameter rather than the areal radial coordinate used in the Bondi-Sachs formulation is applied in the spherically symmetric case to the gravitational collapse of a massless scalar field. The advantages over the Bondi-Sachs version are discussed, with particular emphasis on the application to critical collapse. Unexpected quadratures lead to an evolution algorithm based upon two first order equations which can be integrated along the null rays. It is implemented as a global numerical evolution code based upon the Galerkin method. New results regarding the global properties of critical collapse are presented.","url":"","url_title":"Download"}]},{"time":"17:00 - 17:15","separator":false,"expanded":false,"cols":[{"title":"João Rosa: Towards observing superradiant scattering in pulsar-black hole binaries","bold":false,"expandable":true,"expanded":false,"content":"We analyze the scattering of gravitational waves emitted by a pulsar off a Kerr black hole companion, within the plane wave approximation. We compute the resulting phase shifts and amplification/absorption coefficients for different spheroidal multipoles and consider the possibility of measuring these with future gravitational wave detectors. In particular, we show that for circular polar orbits, which cover the full solid incidence angle, one may in principle determine the amplification factor at least for the lowest superradiant mode, thus paving the way to testing black hole superradiance in the near future.","url":"","url_title":"Download"}]},{"time":"17:15 - 17:30","separator":false,"expanded":false,"cols":[{"title":"Fabrizio Di Giovanni: Dynamical formation of Proca stars and quasi-stationary solitonic objects","bold":false,"expandable":true,"expanded":true,"content":"We perform fully nonlinear numerical simulations within the spherically symmetric Einstein-(complex)-Proca system. Starting with Proca field distributions that obey the Hamiltonian, momentum and Gaussian constraints, we show that the self-gravity of the system induces the formation of compact objects, which, for appropriate initial conditions, asymptotically approach stationary solitonlike solutions known as Proca stars. The excess energy of the system is dissipated by the mechanism of gravitational cooling in analogy to what occurs in the dynamical formation of scalar boson stars. We investigate the dependence of this process on the phase difference between the real and imaginary parts of the Proca field, as well as on their relative amplitudes. Within the timescales probed by our numerical simulations the process is qualitatively insensitive to either choice: the phase difference and the amplitude ratio are conserved during the evolution. Thus, whereas a truly stationary object is expected to be approached only in the particular case of equal amplitudes and opposite phases, quasistationary compact solitonic objects are, nevertheless, formed in the general case.","url":"","url_title":"Download"}]},{"time":"17:30 - 17:45","separator":false,"expanded":false,"cols":[{"title":"Nicolas Sanchis-Gual: Head-on collisions and orbital mergers of Proca stars","bold":false,"expandable":true,"expanded":true,"content":"Proca stars, aka vector boson stars, are self-gravitating Bose-Einstein condensates obtained as numerical stationary solutions of the Einstein-(complex)-Proca system. These solitonic objects can achieve a compactness comparable to that of black holes, thus yielding an example of a black hole mimicker, which, moreover, can be both stable and form dynamically from generic initial data by the mechanism of gravitational cooling. In this paper we further explore the dynamical properties of these solitonic objects by performing both head-on collisions and orbital mergers of equal mass Proca stars, using fully non-linear numerical evolutions.","url":"","url_title":"Download"}]},{"time":"17:45 - 18:00","separator":false,"expanded":false,"cols":[{"title":"Lorenzo Annulli: Scattering of scalar, electromagnetic, and gravitational waves from binary systems","bold":false,"expandable":true,"expanded":false,"content":"The direct detection of gravitational waves crowns decades of efforts in the modelling of sources and of increasing detectors’ sensitivity. Previously brushed-aside questions on environmental or other systematic effects in the generation and propagation of gravitational waves are now begging for a systematic treatment. Environmental effects, such as accretion disks, nearby stars, electric or magnetic fields, a cosmological constant or even dark matter, all can possible contribute to blur what is otherwise a clear picture of compact binaries. Along these lines, we studied the effect of an impinging gravitational wave on a gravitational-bound binary (arXiv:1809.05108 [gr-qc]). This process is the gravitational counterpart of the well-known electromagnetic scattering phenomena. Notably, the ratio between the gravitational scattered-wave amplitude and the incident wave can bring this into the realm of future gravitational-wave observatories.","url":"","url_title":"Download"}]},{"time":"18:00 - 18:15","separator":false,"expanded":false,"cols":[{"title":"Nicola Franchini: Strong-field gravity may hide new Physics","bold":false,"expandable":true,"expanded":false,"content":"Scalar-tensor theories naturally host a mechanism to evade weak-gravity constraints, the so-called spontaneous scalarization. It is a phase transition that can occur in ultra-dense environments such as neutron stars. The scalar field develops a non-trivial configuration once the star exceeds a compactness threshold. If the scalar exhibits some additional coupling to matter, it could give rise to significantly different micro-physics in these environments. In this presentation, I will show a toy model in which the photon is given a large mass when spontaneous scalarization occurs. These results demonstrate the possibility of having new physics confined in environments which are not fully explored.","url":"","url_title":"Download"}]},{"time":"18:15 - 18:30","separator":false,"expanded":false,"cols":[{"title":"Reinoud Slagter: On cosmic strings, infinite line-masses and conformal invariance","bold":false,"expandable":true,"expanded":false,"content":"We investigate the conformal invariant Lagrangian of the self-gravitating U(1) scalar-gauge field and find new features of the model on the time-dependent axially symmetric Bondi-Marder spacetime. By considering the conformal symmetry as exact at the level of the Lagrangian and broken in the vacuum, a consistent model is found with an exact solution of the vacuum Bondi-Marder spacetime $g_{\\mu\\nu}=\\omega^2 \\bar g_{\\mu\\nu}$, where $\\omega$ is the conformal factor and $\\bar g_{\\mu\\nu}$ the `un-physical` spacetime. One can then generate exact conformal equivalent (Ricci-flat) spacetimes from $g_{\\mu\\nu}$. If we try to match this vacuum solution onto the interior vortex solution of the coupled Einstein-scalar-gauge field, we need, besides the matching conditions, constraint equations in order to obtain a topological regular description of the small-scale behaviour of the model. Probably, one needs the five-dimensional warped counterpart model, where the 5D dilaton field act as a warp factor. Moreover, the tracelessness of the energy-momentum tensor could then be maintained by a contribution from the bulk. The model remains topological regular when one approaches smaller scales.","url":"","url_title":"Download"}]},{"time":"19:30 - 21:00","separator":true,"expanded":false,"cols":[{"title":"Conference Dinner","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"21:15 - 22:30","separator":true,"expanded":true,"cols":[{"title":"Session Commemorative (Chair: Júlio Fabris)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"21:00 - 21:15","separator":false,"expanded":true,"cols":[{"title":"José Lemos: The Black Hole 50 Years After:  Genesis of the Name","bold":false,"expandable":true,"expanded":true,"content":"Black holes are extreme spacetime deformations where even light is imprisoned. There is an extensive astrophysical evidence for the real and abundant existence of these prisons of matter and light in the Universe. Mathematically, black holes are described by solutions of the field equations of the theory of general relativity, the first of which was published in 1916 by Karl Schwarzschild. Another highly relevant solution, representing a rotating black hole, was found by Roy Kerr in 1963. It was only much after the publication of the Schwarzschild solution, however, that the term black hole was used to describe these objects. Who invented it? Conventional wisdom attributes the origin of the term to the prominent North American physicist John Wheeler who first used it in a general audience article published in 1968. This, however, is just one side of a story that begins two hundred years before in an Indian prison colloquially known as the Black Hole of Calcutta. Robert Dicke, also a distinguished physicist and colleague of Wheeler at Princeton University, aware of the prison's tragedy began, around 1960, to compare gravitationally completely collapsed stars to the black hole of Calcutta. The whole account thus suggests reconsidering who indeed coined the name black hole and commends acknowledging its definitive birth to a partnership between Dicke and Wheeler. See arXiv:1811.06587.","url":"","url_title":"Download"}]},{"time":"21:15 - 21:30","separator":false,"expanded":true,"cols":[{"title":"Port Wine Commemoration","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"21:30 - 21:45","separator":false,"expanded":true,"cols":[{"title":"Miguel Zilhão Trio: Miguel Zilhão - Bag Pipes, Inês Gonçalves - Bag Pipes and Percurssion, Jorge Dinis - Bag Pipes","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"21:45 - 22:30","separator":false,"expanded":false,"cols":[{"title":"Port Wine Commemoration continued","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]}],"size":"20"}

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{"title":"Day 2, Tuesday, December 18","rows":[{"time":"","separator":true,"expanded":true,"cols":[{"title":"Session 5 (Chair: José Natário)","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"09:00 - 09:15","separator":false,"expanded":false,"cols":[{"title":"Jerzy Lewandowski: The Petrov type D isolated horizons and the near horizon geometry equation","bold":false,"expandable":true,"expanded":false,"content":"The type D equation is imposed on geometric data induced on a horizon cross section: a metric tensor and a rotation 1-form potential. It is used to formulate a local version of the black hole uniqueness theorem, a local no-hair theorem. It excludes higher genus cross sections for a rotating horizon, it allows only spherical cross sections. On a bifurcation cross section the type D equation implies the axial symmetry without the rigidity theorem. Every axially symmetric solution of the type D equation corresponds to a section of the horizons contained either in a non-extremal Kerr / Kerr-de-Sitter / Kerr-anti-de-Sitter spacetime or in the near horizon limit of the extremal case. The equation is an integrability condition for the near horizon geometry equation. That relation is used to find all the solutions to the NHG equation on higher genus 2-surfaces.","url":"","url_title":"Download"}]},{"time":"09:15 - 09:30","separator":false,"expanded":false,"cols":[{"title":"Edgar Gasperin: The weak null condition and constraint damping in NR (or the good, the bad and the ugly in free-evolution schemes)","bold":false,"expandable":true,"expanded":false,"content":"All strategies for the treatment of future null-infinity in numerical relativity involve some form of regularisation of the field equations. In a recent proposal that relies on the dual foliation formalism this is achieved by the use of an asymptotically Minkowskian generalised harmonic tensor basis. For the scheme to work however, derivatives of certain coordinate light-speeds must decay fast enough. Presently, we generalise the method of asymptotic expansions for nonlinear wave equations to treat first order symmetric hyperbolic systems. We then use this heuristic tool to extract the expected rates of decay of the metric near null-infinity in a free-evolution setting. Additionally, it is shown, that, although under the expected asymptotics, the Bondi-mass seems to be unbounded, the diverging terms can be replaced using the Einstein field equations and the Bondi-mass loss formula is recovered within this framework. Moving to the main problem we show, within the asymptotic expansion, that by carefully modifying the non-principal part of the field equations by the addition of constraints, we are able to obtain optimal decay rates even when the constraints are violated. The light-speed condition can hence be satisfied, which paves the way for the explicit numerical treatment of future null-infinity.","url":"","url_title":"Download"}]},{"time":"09:30 - 09:45","separator":false,"expanded":false,"cols":[{"title":"Carlos Peón Nieto: Symmetries at Scri: The Kerr-de Sitter-like class","bold":false,"expandable":true,"expanded":false,"content":"Among all the features that characterize black holes, symmetries play an essential role to determine the rotational and stationary state of these spacetimes. Killing Initial Data (KID) equations provide a natural way to prescribe symmetries for spacetimes that admit a smooth Scri with conformal Killing vector fields. We study the Kerr-de Sitter-like class, which contains several families, including Kerr-de Sitter and other black hole families such as Schwarzschild-de Sitter.","url":"","url_title":"Download"}]},{"time":"09:45 - 10:00","separator":false,"expanded":false,"cols":[{"title":"Masato Nozawa: Uniqueness theorems of black holes based on divergence equations","bold":false,"expandable":true,"expanded":false,"content":"Equations of divergence type in static spacetimes play an important role in the proof of uniqueness theorems of black holes. We extend the divergence equation originally found by Robinson in four dimensional vacuum spacetimes into various directions. We find a three dimensional covariant tensor describing the deviation from spherical symmetry which is the crux for the construction of the desired divergence equation, allowing us to conclude the uniqueness of the Schwarzschild black hole without using Smarr’s integration mass formula. In Einstein-Maxwell(-dilaton) theory, we apply the maximal principle for a number of divergence equations to prove the uniqueness theorem of static black holes.","url":"","url_title":"Download"}]},{"time":"10:00 - 10:15","separator":false,"expanded":false,"cols":[{"title":"Ondřej Hruška: Interpreting Plebański–Demiański class of solutions","bold":false,"expandable":true,"expanded":false,"content":"The Plebański–Demiański metric is a general solution of Einstein’s equations of general relativity of algebraic type D with a cosmological constant and aligned non-null electromagnetic field. We study the so-called A and B-metrics, by the classification of Ehlers and Kundt, which are included in the Plebański–Demiański class. Together, they can describe objects moving both slower and faster than the speed of light. For example, the AI-metric is a generalization of the Schwarzschild black hole solution. On the other hand, the AII-metric together with the BI metric describe the gravitational field of a tachyon; hypothetical particle moving faster than light. Both such black holes and tachyons can be studied on the background with non-zero cosmological constant, i.e. de Sitter or anti-de Sitter spacetime.","url":"","url_title":"Download"}]},{"time":"10:15 - 10:30","separator":false,"expanded":false,"cols":[{"title":"João Oliveira: Two no-go theorems for scalar and electromagnetic solitons","bold":false,"expandable":true,"expanded":false,"content":"We present two no-go theorems for the existence of scalar and electromagnetic solitons in an Einstein-Maxwell-Klein-Gordon model with a non-minimal coupling between the electromagnetic and scalar fields. The first result for the electromagnetic field is obtained when considering a static background, while the second result is obtained when considering only the existence of the scalar field for the most general metric the matter field allows.","url":"","url_title":"Download"}]},{"time":"10:30 - 10:45","separator":false,"expanded":false,"cols":[{"title":"Eva Hackmann: Equilibrium configurations of charged fluids near black holes","bold":false,"expandable":true,"expanded":true,"content":"Active galactic nuclei, which are driven by accretion of matter onto a supermassive black hole, are among the most luminous energy sources in our universe. The accreting matter will in general form an accretion disk, which approaches the black hole on horizon scales. We will discuss equilibrium configurations of charged fluids around black holes in the presence of electromagnetic background fields. Assuming axial symmetry and stationarity, we present a general construction method and a specific example. The fluid configurations can serve as a simplified model for accretion disks with special emphasis on the interplay of electromagnetic and gravitational forces.","url":"","url_title":"Download"}]},{"time":"10:45 - 11:15","separator":true,"expanded":false,"cols":[{"title":"Coffee Break","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"","separator":true,"expanded":true,"cols":[{"title":"Session 6 (Chair: Vítor Cardoso)","bold":true,"expandable":false,"expanded":false,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"11:15 - 11:30","separator":false,"expanded":false,"cols":[{"title":"Jorge Delgado: Horizon geometry for Kerr black holes with synchronized hair","bold":false,"expandable":true,"expanded":false,"content":"We study the horizon geometry of Kerr black holes (BHs) with scalar synchronized hair, a family of solutions of the Einstein-Klein-Gordon system that continuously connects to vacuum Kerr BHs. We identify the region in parameter space wherein a global isometric embedding in Euclidean 3-space, E^3, is possible for the horizon geometry of the hairy BHs. For the Kerr case, such embedding is possible iff the horizon dimensionless spin j_H (which equals the total dimensionless spin, j), the sphericity s and the horizon linear velocity v_H are smaller than critical values, j^(S),s^(S),v_H^(S), respectively. For the hairy BHs, we find that j_H<j^(S) is a sufficient, but not necessary, condition for being embeddable; v_H<v_H^(S) is a necessary, but not sufficient, condition for being embeddable; whereas s<s^(S) is a necessary and sufficient condition for being embeddable in E^3. Thus, the latter quantity provides the most faithful diagnosis for the existence of an E^3 embedding with in the whole family of solutions. We also observe that sufficiently hairy BHs are always embeddable, even if j — which for hairy BHs (unlike Kerr BHs) differs from j_H — is larger than unity.","url":"","url_title":"Download"}]},{"time":"11:30 - 11:45","separator":false,"expanded":false,"cols":[{"title":"Adam Vrátný: Accelerating Taub-NUT black hole","bold":false,"expandable":true,"expanded":false,"content":"The talk will describe exact solution of Einstein's equations which represents an accelerating black hole with a NUT parameter. This solution was found by Chng, Mann and Stelea in 2006. We will present a new convenient form of this metric, and we will describe its algebraic, geometric and physical properties.","url":"","url_title":"Download"}]},{"time":"11:45 - 12:00","separator":false,"expanded":false,"cols":[{"title":"Edgardo Franzin: Sine-Gordon solitonic stars and black holes","bold":false,"expandable":true,"expanded":false,"content":"I present a method to generate static, spherically symmetric, solutions of minimally coupled Einstein-scalar gravity. The solutions can be fully parametrised by a single function, whose behaviour encodes all the information about the local and global behaviour of the spacetime. I give several explicit applications of the method including a horizonless, everywhere regular and positive-mass solution and a black hole sourced by a scalar field whose profile has the form of the sine-Gordon soliton.","url":"","url_title":"Download"}]},{"time":"12:00 - 12:15","separator":false,"expanded":false,"cols":[{"title":"Grigorios Panotopoulos: Minimal geometric deformation in a cloud of strings","bold":false,"expandable":true,"expanded":false,"content":"We find new exact analytical solutions in three-dimensional gravity applying the Minimal Geometric Deformation approach in a cloud of strings.","url":"","url_title":"Download"}]},{"time":"12:15 - 12:30","separator":false,"expanded":false,"cols":[{"title":"Diego Rubiera-Garcia: Non-singular black holes in Ricci-based theories of gravity","bold":false,"expandable":true,"expanded":false,"content":"We describe a family of exact spherically symmetric black hole solutions sourced by anisotropic fluids in different Ricci-based theories of gravity, built out of scalars constructed with the metric and the Ricci tensor, and formulated in metric-affine spaces. The non-singular character is established according to several criteria, most notably, that of geodesic completeness. We also discuss the extension of these results to the rotating case.","url":"","url_title":"Download"}]},{"time":"12:30 - 12:45","separator":false,"expanded":false,"cols":[{"title":"Davide Polini: Counting formulae for extremal black holes in the STU-model","bold":false,"expandable":true,"expanded":false,"content":"We present microstate counting formulae for extremal black holes in the N=2 STU-model.","url":"","url_title":"Download"}]},{"time":"12:45 - 13:00","separator":false,"expanded":false,"cols":[{"title":"Miguel Ferreira: Astrophysical signatures of scalar fields","bold":false,"expandable":true,"expanded":false,"content":"Scalar fields are a recurrent appearance in modern theoretical physics. Whether as a by-products of the low energy limit of string theory, as a model for dark energy or dark matter, scalar fields are at the center of a debate on several longstanding problems. In this work, we study the effects of the existence of scalar fields to the orbits of stars and to the light emitted by them. We explore two scenarios: one in which the scalar field develops quasi-stable profiles around supermassive BHs and another in which the scalar field collapses and forms stable, self-gravitating structures known as oscillatons. We find that orbits of stars are affected by the presence of these scalar field structures in such a way that orbital resonances may develop. We also show that the light emitted by stars embedded in these structures is redshifted with a time modulation which depends on the characteristics of the scalar field sourcing it. Both results are amenable to be used as astrophysical tests for the existence of a new scalar field in Nature.","url":"","url_title":"Download"}]},{"time":"13:00 - 14:30","separator":true,"expanded":false,"cols":[{"title":"Lunch","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"","separator":true,"expanded":true,"cols":[{"title":"Session 7 (Chair: José Sande Lemos)","bold":true,"expandable":false,"expanded":false,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"14:30 - 14:45","separator":false,"expanded":false,"cols":[{"title":"Oleg Zaslavskii: Super-Penrose process: new developments","bold":false,"expandable":true,"expanded":false,"content":"Let a body decay to two fragments or collision of two particles occur. If the energy of debris measured at infinity can be indefinitely large (in the test particle approximation), the corresponding process is called the super-Penrose (SPP) one. We consider two cases of SPP: 1) particle collision near the throat of a rotating wormhole. Then, SPP becomes possible if the lapse function is very small near the throat. Then, head-on collision leads to SPP. 2) decay of a particle in the flat space-time. This case is obtained as a limiting transition from the Denardo-Ruffini process when a black hole disappears. In doing so, the energy in the centre of mass can be finite.","url":"","url_title":"Download"}]},{"time":"14:45 - 15:00","separator":false,"expanded":false,"cols":[{"title":"Masato Minamitsuji: Scalarized black holes in the presence of the coupling to the Gauss-Bonnet gravity","bold":false,"expandable":true,"expanded":false,"content":"It is well-known that the coupling of the scalar field to the matter inside a relativistic star triggers a tachyonic instability, and spontaneously scalarizes the stars. Recently, it was noticed that in the presence of the coupling of the scalar-field to the Gauss-Bonnet gravity such a tachyonic instability can also take place in the higher curvature regions around a Schwarzschild black hole (BH) and scalarizes it. For the certain range of the parameters, new branches of BH solutions with nontrivial configurations of the scalar field appear, which are characterized by the different number of nodes. However, it was recently pointed out that the scalarized BHs in the original model with the quadratic order coupling are unstable against the radial perturbations. We will investigate the scalarized BHs in the presence of the quartic order coupling to the Gauss-Bonnet term, and clarify whether the higher order coupling modifies the properties of scalarized BHs and stability.","url":"","url_title":"Download"}]},{"time":"15:00 - 15:15","separator":false,"expanded":true,"cols":[{"title":"Juan Carlos Degollado: l-Boson stars","bold":false,"expandable":true,"expanded":false,"content":"Boson stars are compact, globally regular, configurations of self–gravitating boson fields possessing a large particle number and mass. In this talk I will present a fully nonlinear numerical solutions to the static, spherically symmetric Einstein-Klein-Gordon system for a collection of an arbitrary odd number N of complex scalar fields with an internal U(N) symmetry and no self-interactions, solutions that represent boson stars. These solutions are characterised, besides the mass of the field, by an angular momentum number.","url":"","url_title":"Download"}]},{"time":"15:15 - 15:30","separator":false,"expanded":false,"cols":[{"title":"Filip Hejda: Extraction of energy from axisymmetric extremal black holes with charged particle collisions","bold":false,"expandable":true,"expanded":false,"content":"Collisional Penrose process received a lot of attention due to the possibility of near-horizon collisions of test particles with arbitrarily high centre-of-mass energy. The original setup for extremal black holes described by Banados, Silk and West (BSW) was later refined by Schnittman. Although this led to significant revision of expected maximum efficiency of collisional Penrose process, strict unconditional upper bounds on the extracted energy and on the efficiency were found. However, for the electrostatic analogy of the BSW effect described for extremal Reissner-Nordström black hole by Zaslavskii, no such bounds were found. Therefore, it is of interest to study possible generalisations of this result for black holes closer to astrophysical situations. Our aim is to look at general extremal axisymmetric electrovacuum black holes. The overall setup for the generalised BSW effect in this background was described in our previous article [Phys. Rev. D 95, 084055 (2017)]. In the present work, we confirm that for charged particle collisions, there are no unconditional kinematic bounds on the extracted energy even for the extremal Kerr-Newman black holes with arbitrarily low charge. However, as the escaping particles can be produced only in specific kinematic regimes, it has to be checked carefully whether these are compatible with properties of the interactions responsible for the emission of the particles.","url":"","url_title":"Download"}]},{"time":"15:30 - 15:45","separator":false,"expanded":false,"cols":[{"title":"Paulo Luz: Influence of intrinsic spin in the formation of singularities","bold":false,"expandable":true,"expanded":true,"content":"The evolution of inhomogeneous space-times composed of uncharged fermions is studied for Szekeres metrics which have no Killing vectors, in general. Using the Einstein-Cartan theory to include the effects of (intrinsic) matter spin in General Relativity, the dynamics of a perfect fluid with nonnull spin degrees of freedom is considered. It is shown that, if the matter is composed by effective dust and certain constraints on the initial data are verified, a singularity will not form. Various special cases are discussed, such as Lemaître-Tolman-Bondi and Bianchi I space-times, where the results are further extended or shown explicitly to be verified.","url":"","url_title":"Download"}]},{"time":"15:45 - 16:00","separator":false,"expanded":false,"cols":[{"title":"Carlos Frajuca: An experiment to measure the speed of gravity","bold":false,"expandable":true,"expanded":false,"content":"The authors have experience with the SCHENBERG Gravitation Wave detector which is a resonant-mass developed by the Brazilian GRAVITON. Its spherical antenna weighs 1150 kg and it is monitored by six ultralow noise parametric transducers and is connected to the outer environment by a suspension system designed to attenuate local noise, both seismic and non-seismic, operating in a temperature of 4 K. With all the acknowledgment acquired the idea of making an experiment to measure the speed of gravity took form. Using monocrystalline sapphire with very high mechanical and electrical Q´s, ultralow phase noise microwave sources, Finite Element Modelling designed suspensions, parametric microwave transducers, excellent properties of noise filtering of the resonant-mass detectors and the development of high-speed rotation machines guided the authors to the design of the experiment. The experiment will measure oscillations caused by gravitational interaction with an amplitude of the order of 0.1 am (10-19 m).","url":"","url_title":"Download"}]},{"time":"16:00 - 16:15","separator":false,"expanded":false,"cols":[{"title":"Remo Garattini: Casimir wormholes","bold":false,"expandable":true,"expanded":false,"content":"After a brief description of what is a traversable wormhole we describe the connection between traversability and the Casimir effect. With the help of an equation of state we also discuss different form of solutions generated by the Casimir source. A connection with the Quantum Weak Energy Condition is also presented.","url":"","url_title":"Download"}]},{"time":"16:15 - 16:45","separator":true,"expanded":false,"cols":[{"title":"Cofee break","bold":true,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"","separator":true,"expanded":false,"cols":[{"title":"Session 8 (Chair:  Oleg Zaslavskii)","bold":true,"expandable":false,"expanded":false,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"16:45-17:00","separator":false,"expanded":false,"cols":[{"title":"Eugen Radu: Spontaneous scalarisation of charged black holes","bold":false,"expandable":true,"expanded":true,"content":"We argue that spontaneous scalarisation occurs also for electrovacuum Black Holes (BHs), when considered as solutions of a more general class of Einstein-Maxwell-scalar (EMs) models. The scalarised configurations bifurcate from the Reissner-Nordstrom BH 'trunk', forming an infinite (countable) number of branches, and possess a large freedom in their multipole structure. Unlike the case of electrovacuum, the EMs models admits static, asymptotically flat, regular on and outside the horizon BHs without spherical symmetry and even without any spatial isometries, which are thermodynamically preferred over the electrovacuum state.","url":"","url_title":"Download"}]},{"time":"17:00-17:15","separator":false,"expanded":false,"cols":[{"title":"Matteo Tuveri: Emergence of a dark force in corpuscolar gravity","bold":false,"expandable":true,"expanded":true,"content":"In this talk we propose an effective anisotropic fluid description for a generic infrared-modified theory of gravity. In our framework, the additional component of the acceleration, commonly attributed to dark matter, is explained as a radial pressure generated by the reaction of the dark energy fluid to the presence of baryonic matter. Using quite general assumptions, and a microscopic description of the fluid in terms of a Bose-Einstein condensate of gravitons, we find the static, spherically symmetric solution for the metric in terms of the Misner-Sharp mass function and the fluid pressure. At galactic scales, we correctly reproduce the leading MOND-like log(r) and subleading (1/r)log(r) terms in the weak-field expansion of the potential. Our description also predicts a tiny (of order 10^{-6} for a typical spiral galaxy) Machian modification of the Newtonian potential at galactic scales, which is controlled by the cosmological acceleration.","url":"","url_title":"Download"}]},{"time":"17:15-17:30","separator":false,"expanded":false,"cols":[{"title":"Leonel Queimada: Holographic complexity of charged black holes","bold":false,"expandable":true,"expanded":true,"content":"For the past few years there has been suggestions that the concept of “circuit complexity” should be included in the holographic dictionary. The two main proposals, complexity=volume (CV) and complexity=action (CA), are novel gravitational observables thought to be sensitive to properties of the black hole interior. Due to their properties, they appear to be good candidates to describe how complex the state of the CFT dual is. In this talk, I will overview and motivate these conjectures and comment on recent work regarding the holographic complexity of charged black holes. Namely, I will focus on a puzzling feature that arises for the CA proposal when considering the possible addition of a boundary term to the action which changes the boundary conditions imposed on the fields.","url":"","url_title":"Download"}]},{"time":"17:30-17:45","separator":false,"expanded":false,"cols":[{"title":"Watse Sybesma: Hyperbolic and spherical black holes with hyperscaling violation","bold":false,"expandable":true,"expanded":true,"content":"In this talk I present a family of charged, hyperscaling violating black hole solutions with hyperbolic and spherical horizons. In particular, I will focus on the phase structures of these black holes and discuss special properties of the hyperbolic solution.","url":"","url_title":"Download"}]},{"time":"17:45-18:00","separator":false,"expanded":true,"cols":[{"title":"Francisco Duque and Filipe Miguel: Motion in time-periodic backgrounds with applications to ultralight dark matter halos at galactic centers","bold":false,"expandable":true,"expanded":false,"content":"Historically, the motion of test particles has been used to test general relativity. In recent work (DOI: 10.1103/PhysRevD.98.024037), we showed how motion in spherically symmetric but time-dependent periodic backgrounds can lead to orbital resonances, even when dissipative effects are considered. These specific geometries arise in the context of a real minimally coupled massive scalar, usually used to describe dark matter. The field equations give rise to a class of compact objects known as scalar oscillations. Conversely, in the weak field limit of ultra-light dark matter, solutions of field equations are interpreted as a galactic halo. We applied our previous developments to both these systems. Remarkably, our results indicate that the motion of S-2 like stars may carry distinguishable observational imprints of ultra-light dark matter.","url":"","url_title":"Download"}]},{"time":"18:00-18:15","separator":false,"expanded":false,"cols":[{"title":"Fatemeh Mahdieh: Extra Symmetries at the de Sitter Horizon","bold":false,"expandable":true,"expanded":true,"content":"We Show that the near horizon geometry of a dynamical de Sitter spacetime possesses extra symmetries similar to those in asymptotically flat spacetimes. These extra symmetries enhance the SO(4,1) symmetry of de Sitter spacetime and can give rise to a non-conservation in the asymptotic charges. Ultimately the thermodynamics of this dynamical system is discussed and a definition for temperature and surface gravity can be presented.","url":"","url_title":"Download"}]},{"time":"18:15-18:30","separator":false,"expanded":false,"cols":[{"title":"Martin Lesourd: Causal structure of evaporating black hole spacetimes","bold":false,"expandable":true,"expanded":true,"content":"In 1974 Hawking argued that black holes could evaporate due to quantum field theory. This led to the suspicion that evaporating black hole spacetimes cause a failure in classical and semi-classical predictability. No theorem to this effect was formulated until Kodama's attempt in 1979. His theorem (which is a statement in Lorenzian geometry) regards the causal structure of such spacetimes, under one possible construal thereof. Wald (basing on an argument of Geroch) rewired and endorsed Kodama's theorem in a paper in 1984. We have recently observed an important lacuna in the argument of predictability loss based on the Kodama-Geroch-Wald theorem. In particular, a counterexample spacetime shows that their theorem does not imply the failure of global hyperbolicity. Thus, a spacetime could satisfy their theorem's conditions and still be predictable. We offer a rectification of this issue by formulating a new and more incisive theorem doing what the above was supposed to do. Namely, we prove that evaporating black hole spacetimes either fail to be causally continuous or causally simple; thus, we provide a mathematically rigorous justification for the suspicion that classical predictability fails in fully evaporating black hole spacetimes.","url":"","url_title":"Download"}]},{"time":"18:30-18:45","separator":true,"expanded":true,"cols":[{"title":"End of the XI Black Holes Workhop","bold":true,"expandable":false,"expanded":false,"content":"Expandable Content","url":"","url_title":"Download"}]},{"time":"18:45-19:30","separator":false,"expanded":false,"cols":[{"title":"General Assembly of the Portuguese Society of Relativity and Gravitation (SPRG)","bold":false,"expandable":false,"expanded":true,"content":"Expandable Content","url":"","url_title":"Download"}]}],"size":"20"}

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