Gravitational Waves, Black Holes and Fundamental Physics

Session

Coffee+Posters session

Jan 16, 2020, 3:00 PM

IFPU, Miramare campus, Trieste, Italy

49. A Bifocal Coordinate System in General Relativity

Mr Nikolaos Chatzarakis (Aristotle University of Thessaloniki)

Poster

Following the generalised form of non-stationary axisymmetric space-time (Chandrasekhar 1983), we assume a bifocale elliptic symmetry and attempt to show that this particular metric can be a solution to Einstein's field equations. We discuss the form of the metric and the curvature implied, as well as its possible physical meaning and applications.

9. A covariant simultaneous action for branes

Mr Giovany Cruz (CINVESTAV)

Poster

A covariant simultaneous action for branes in an arbitrary curved background spacetime is considered. The term `simultaneous' is imported from variational calculus and refers to the fact that extremization of the action produces at once both the ?first and second variation of a given geometrical action for the brane. The action depends on a pair of independent field variables, the brane...

58. A parametrized ringdown approach for black-hole spectroscopy of spinning black holes

Dr Andrea Maselli (Sapienza University of Rome)

Poster

Black-hole spectroscopy is arguably the most promising tool to test
gravity in extreme regimes and to probe the ultimate nature of black
holes with unparalleled precision. These tests are currently limited by
the lack of a ringdown parametrization that is both robust and accurate.
We develop an observable-based parametrization of the ringdown of
spinning black holes beyond general...

63. Beyond the Post-Newtonian expansion using Non-relativistic Gravity

Prof. Niels Obers (Nordita & Niels Bohr Institute)

Poster

I will discuss an action principle for non-relativistic gravity, as has recently been obtained from a covariant large speed of light expansion of Einstein's theory of gravity. This action reproduces Newtonian gravity as a special case, but goes beyond it by allowing for gravitational time dilation while retaining a non-relativistic causal structure. As a consequence, it can be shown that the...

21. Continuation of Schwarzschild exterior without a black hole in first order gravity

Prof. Sandipan Sengupta (IIT Kharagpur)

Poster

We present a smooth extension of the Schwarzschild exterior geometry, where the singular interior is superceded by a vacuum phase with vanishing metric determinant. Unlike the Kruskal-Szekeres continuation, this explicit solution to the first-order field equations in vacuum has no singularity in the curvature two-form fields, no horizon and no global time. The underlying non-analytic structure...

34. Dilatonic black holes and the weak gravity conjecture

Kunihito Uzawa (Kwansei Gakuin University)

Poster

We discuss the weak gravity conjecture (WGC) from black hole entropy in the Einstein-Maxwell-dilaton system or string theory. The WGC is strongly motivated by theorems forbidding global symmetries which arise in the vanishing-charge limit, and implies the fact that not only all non-BPS black holes but also extremal one without supersymmetry should be able to decay. It is shown that the large...

41. Duality of conformally and kinetically coupled scalar-tensor theories

Dmitry Gal'tsov (Moscow state University)

Poster

We show that the non-minimal conformally-coupled (CC) scalar-tensor theory and the Palatini theory with kinetic coupling of the scalar to the Ricci tensor (PKC) are the same. This is demonstrated by showing that both theories coincide in the Einstein frame. Using this duality as generating technique, we construct the PKC counterpart to the BBMB black hole of the CC theory. It turns out to be...

53. Formation and Abundance of Primordial Black Holes

Ilia Musco (University of Geneva)

Poster

Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of galaxies. If the perturbation is larger than a certain threshold, depending on the equation of state and on the...

62. Formation and evolution of the first Supermassive Black Hole Seeds

Ms Federica Sassano (Sapienza University of Rome)

Poster

In the last decade, many observations of bright quasars at $z > 5$, have revealed the existence of Supermassive Black Holes (SMBHs), giants of billion solar masses shining close to their Eddington limit. The mechanism of their
formation at these early epochs represents currently an open problem in galaxy evolution.
Several scenarios have been proposed to overcome this problem, such as the...

32. General Relativistic Study of the Structure of Highly Magnetized Neutron Stars

Dr Orlenys Troconis (International Centre for Theoretical Physics)

Poster

Neutron stars are one of the most compact and densest astrophysical objects known in nature, they result from the supernova explosion of a massive star. Many of the neutron stars have very strong magnetic fields, which lead to the emission of radio and X-ray radiation. This work is devoted to study the effects of strong magnetic fields in the structure of neutron stars, within the framework of...

29. Gravitational waves in Teleparallel theories of gravity

Viktor Gakis

Poster

The Teleparallel equivalent of General Relativity, where the connection is curvatureless, offers an alternative but equivalent way of describing gravity. In accordance to GR-based modified theories such as f(R) there are also torsion or non-metricity teleparallel modifications like f(T), where T the torsion scalar and f(Q), where Q is the non-metricity scalar both of them playing a role...

36. Gravity-induced quantum anomalies through gravitational wave polarization

Adrian del Rio

Poster

Axial-type anomalies predicted by quantum field theory in curved spacetime are determined by the Chern-Pontryagin invariant of the spacetime background. I will show that this geometric quantity is non-zero in spacetimes admitting gravitational radiation that propagates to future null infinity with an excess of one polarization mode over the other. I will further argue that typical scenarios...

73. GWxLSS: chasing the progenitors of merging binary black holes.

Giulio Scelfo

Poster

Cross-correlations between galaxy catalogs and gravitational wave maps can provide useful information regarding open questions in both cosmology and astrophysics. The detection of binary black hole mergers through gravitational waves by the LIGO-Virgo instrument sparked the discussion on whether they have astrophysical or primordial origin. According to a model whose popularity revived after...

14. Holographic Bound on Remnant Boundary Area of Black Hole Merger

Prof. Partha Sarathi Majumdar (School of Physical Sciences, Indian Association for the Cultivation of Science)

Poster

Using concomitantly the Generalized Second Law of black hole thermodynamics and the holographic Bekenstein entropy bound embellished by Loop Quantum Gravity corrections to quantum black hole entropy, we show that the boundary area of the remnant from the binary black hole merger in GW150914 is bounded from below. This lower bound is more general than the bound from application of Hawking's...

68. Kicking Q-balls and boson stars: stimulated emission of radiation by confined structures

Lorenzo Annulli (Instituto Superior Tècnico)

Poster

Scalar fields can give rise to confined structures, such as Q-balls or boson
tars, which can serve as interesting models for cold dark-matter. The existence and stability of objects in a given theory is relevant for a wide range of topics, from planetary science to a description of fundamental particles. Taking as starting point a theory describing a time-dependent scalar field, in this...

5. Moving black holes: energy extraction, absorption cross-section and the ring of fire

Mr Rodrigo Vicente (CENTRA - Instituto Superior Técnico)

Poster

We consider the interaction between a plane wave and a (counter-moving) black hole. We show that energy is transferred from the black hole to the wave, giving rise to a negative absorption cross-section. Moving black holes absorb radiation and deposit energy in external radiation. Due to this effect, a black hole hole of mass $M$ moving at relativistic speeds in a cold medium will appear...

55. New frontiers in cosmology using gravitational waves

Suvodip Mukherjee (IAP)

Poster

Cosmic microwave background and large scale structure missions have played a crucial role in constructing the standard model of cosmology. The upcoming missions in astrophysics and cosmology are going to explore the Universe over a wide range of redshifts using both electromagnetic waves and gravitational waves. I will introduce a few new frontiers in cosmology which will open-up from the...

45. New solutions in tensor-multi-scalar theories of gravity

Stoytcho Yazadjiev (Sofia University)

Poster

In this talk I will present new solutions describing neutron stars and black holes in the tensor-multi-scalar theories of gravity. Some astrophysical implications of the solutions will be also discussed.

52. Novel Wormhole Solutions in Einstein-Scalar-Gauss-Bonnet Theories

Mr Georgios Antoniou ( University of Nottingham )

Poster

Novel wormholes are obtained in Einstein-scalar-Gauss-Bonnet theory for several coupling functions. The wormholes may feature a single-throat or a double-throat geometry. The scalar field may asymptotically vanish or be finite, and it may possess radial excitations. The domain of existence is fully mapped out for several forms of the coupling function.

13. Physics Beyond General Relativity: Theoretical and Observational Constraints.

Prof. Sudipta Sarkar (IIT Gandhinagar)

Poster

The study of the effects of higher curvature terms is a major research theme of contemporary gravitational physics. In this talk, I will present a comprehensive study of the higher curvature gravity and various observational & theoretical constraints. The inclusion of these terms leads to exciting new possibilities, e.g., gravitational and electromagnetic perturbations following different...

37. Probing black holes with X-rays and gravitational waves

Sourabh Nampalliwar (Eberhard Karls University of Tuebingen)

Poster

Einstein’s theory has been the standard theory of gravity for nearly a century. Alternatives to and extensions of it have been proposed to address various issues. With advances in technology, these theories are becoming testable, especially in the strong field regime around black holes. In this talk, I will describe a theory agnostic approach to probe the nature of black holes. I will provide...

69. Quantum constitutive equations for finite temperature Dirac fermions under rotation

Victor Eugen Ambrus (West University of Timisoara)

Poster

The experimental confirmation of the polarization of the Lambda hyperons observed in relativistic heavy ion collisions experiments [1] has renewed the interest in anomalous transport of fermions due to the spin-orbit coupling (e.g., through the chiral vortical effect [2]). Using a non-perturbative technique [3], exact expressions are derived for the thermal expectation values of the...

7. Rotating and non rotating, non singular compact objects

Prof. Anupam Mazumdar

Poster

I will discuss the physics of non singular compact objects which is primrily made up of gravitons, and it is as compact as that of the Buchdahl star. I will discuss how to construct such a system within higher derivative theories of gravity which incorporates nonlocal effects at the level of gravitational ingeractions. I will construct in fact both static and rotating solutions in this regard...

46. Rotating Solitonic Vacuum in TMST

Lucas Gardai Collodel

Poster

In the context of a special class of tensor-multi-scalar theories of gravity for which the target-space metric admits as a Killing field a generator of a one-parameter group of point transformations under which the theory is invariant, we present rotating vacuum solutions, namely with no matter fields. These objects behave like nontopological solitons, whose primary stability is due to the...

86. Searching tidally disrupted white dwarfs to find intermediate mass black holes

Mrs Martina Toscani

Poster

My poster is focused on two topics. The main one is related to intermediate mass black holes (IMBHs). Some recent observations suggest that IMBHs exist in our Universe. Yet, none of them has been confirmed so far. A possible way to prove the existence of these elusive objects can be the study of tidal disruption events of white dwarfs (WDs). Indeed, if a WD wanders too close to an IMBH, it...

72. Signatures of Unimodular Gravity

Raquel Santos Garcia

Poster

Unimodular Gravity is an infrared modification of General Relativity where the cosmological constant is replaced by an integration constant, thus free from radiative corrections and effectively solving one piece of the cosmological constant problem. Apart from this, both theories enjoy the same classical
dynamics, dictated by Einstein equations, and they were thought to be equivalent for any...

56. Smarr formulas for Einstein-Maxwell-dilaton stationary spacetimes with line singularities

Igor Bogush (Lomonosov Moscow State University)

Poster

We generalize the recent derivation http://arxiv.org/abs/arXiv:1908.10617 of the Smarr formulas for Einstein-Maxwell stationary axisymmetric asymptotically locally flat spacetimes with line singularities to the Einstein-Maxwell-dilaton (EMD) theory with an arbitrary dilaton coupling constant. The line singularities include the Dirac and Misner strings for spacetimes with magnetic and NUT...

38. Stationary vector clouds around Kerr black holes

Mr Nuno M. Santos (CENTRA, Instituto Superior Técnico, Universidade de Lisboa)

Poster

Kerr black holes are known to support massive bosonic test fields whose phase angular velocity fulfills the synchronization condition, i.e. the threshold of superradiance. The presence of these real-frequency bound states at the linear level, commonly dubbed stationary clouds, is intimately linked to existence of Kerr black holes with bosonic hair at the non-linear level. These configurations...

59. Strong cosmic censorship in charged black holes with a positive cosmological constant

Kyriakos Destounis (Theoretical Astrophysics, University of Tübingen)

Poster

The strong cosmic censorship conjecture has recently regained a lot of attention in charged and rotating black holes immersed in de Sitter space. Such spacetimes possess Cauchy horizons in the internal region of the black hole. The stability of Cauchy horizons is intrinsically connected to the decay of small perturbations
exterior to the event horizon. As such, the validity of strong cosmic...

65. The Ultra-relativistic Expansion of General Relativity

Dennis Hansen (ETH Zürich)

Poster

In this talk I will discuss the ultra-relativistic expansion of general relativity. The ultra-relativistic expansion in the speed of light captures very strong gravitational field effects and extreme astrophysical phenomena in a simplifying setting compared to full GR. Surprisingly it also turns out that the ultra-relativistic expansion is closely related to the non-relativistic expansion,...

15. Thermally Quasi-stable Radiant Black Holes

Partha Sarathi Majumdar (School of Physical Sciences, Indian Association for the Cultivation of Science)

Poster

We use loop quantum gravity inspired holographic thermal stability criteria to establish the existence of regions in parameter space of charged rotating black holes away from extremality, where partial fulfillment of the stability criteria is possible. Physical implications of our results will be discussed.

60. Tidal effect on scalar cloud:numerical simulations

Taishi Ikeda (Instituto Superior Tecnico)

Poster

Axion and axion-like particle are the candidates of the dark matter. Due to the super-radiant instability, these fields are amplified, and can localize around Kerr BH, as axion clouds. Since the axion clouds emit gravitational waves, it is important to analyze several properties of the axion cloud around BHs. Here, we study the axion cloud around binary BH (BBH). The axion cloud around a BH of...

39. Time-domain metric reconstruction using the Hertz potential

Mr Oliver Long (University of Southampton)

Poster

Historically the Teukolsky equation corresponding to gravitational perturbations is solved for the Weyl scalars. However, reconstructing the metric from these scalars involves solving a fourth order PDE to obtain the Hertz potential and then another second order PDE to construct the metric perturbation. Solving the (adjoint) Teukolsky equation for the Hertz potential directly simplifies the...

67. Total probability for fermion pair production in external fields on de Sitter space-time

Diana-Cristiana Popescu (West University of Timisoara)

Poster

We are illustrating a procedure for computing the total probabilities corresponding to the processes of fermion pair production in electric fields and in the field of a magnetic dipole on de Sitter space-time. The total probabilities are preserving the dependence on the expansion parameter, proving the fact that the results are consistent with the ones obtained for probability densities. The...

2. Wormholes in $R^2$-gravity

Pradyumn Sahoo (Birla Institute of Technology and Science-Pilani, Hyderabad Campus)

Poster

We propose, as a novelty in the literature, the modelling of wormholes within the particular case of the $f(R,T)$ gravity, namely $f(R,T)=R+\alpha R^{2}+\lambda T$, with $R$ and $T$ being the Ricci scalar and trace of the energy-momentum tensor, respectively, while $\alpha$ and $\lambda$ are constants. Although such a functional form application can be found in the literature, those concern to...