4th Valencia Winter Workshop on Theoretical Physics

14 Dec 2020, 09:00 → 17 Dec 2020, 18:50 Europe/Madrid

Online

Gonzalo Olmo Alba (IFIC)

Description

The fourth edition of the Valencia Winter Workshop on Theoretical Physics will take place online due to the COVID19 pandemics. Physical displacements must be reduced for sanitary reasons, but Physics must go on .

Like in previous editions, this meeting is intended to bring together researchers with common interests on the geometric structure of space-time, quantum properties of gravity, cosmology, and astrophysics who collaborate with the host group via active projects (H2020-MSCA-RISE project FunFiCO-777740 or the i-COOP20462) or have close ties with them.

Fundamental questions about the geometric foundations of gravitation, the role of quantized fields in curved space-times, cosmological and astrophysical signatures of gravity within and beyond General Relativity, and recent developments on other topics, will be reviewed in a series of talks with a high dosis of discussions.

The idea of the workshop is to encourage everyone, from seniors to new students, to present some results obtained during the year 2020 that they find particularly relevant/interesting/easy to discuss in a relaxed way, possibly using the pdf of a paper already on arXiv or some scanned handwritten notes of a current work in progress, and addressing a few simple questions:

What is it about?
Why is it important? (An explanation of what is unique and/or timely about this topic and the difference it might make with respect to previous work).
Perspectives.

The contributions are NOT expected to last 60 minutes. Rather 15-25 minute conceptual presentations with minimal calculations are encouraged for everyone. The subsequent discussion and questions could extend up to 60' (in the case of senior researchers) or even more if necessary. For students we expect talks of about 20' (+10' of discussion), and for postdocs up to 30'(+15' of discussion) at most. All non-essential calculations could be provided to those interested for their individual analysis. The idea is to have talks not too focused on technicalities but have more discussions which could lead to new works/collaborations in 2021 and beyond.

This meeting is organized by the Quantum Black Holes, Supergravity and Cosmology group at the Department of Theoretical Physics & IFIC of the University of Valencia & CSIC, Spain.

Monday, 14 December
- 09:45 → 10:00
  
  Opening 15m
- 10:15 → 11:15
  
  Luis C.B. Crispino (UFPA,Brazil) 1h
  
  The first attempts to measure light deflection by the Sun.
- 11:20 → 11:50
  
  Adrià Delhom(UV, Valencia) 30m
  
  title: Inconsistencies in four-dimensional Einstein-Gauss-Bonnet gravity
  
  abstract:We will outline several inconsistencies about the recently proposed four-dimensional Einstein-Gauss-Bonnet theory.
- 12:00 → 12:30
  
  Mercè Guerrero (UCM, Madrid) 30m
  
  Double shadows of asymmetric wormhole in Palatini f(R)
  
  Abstract: We discuss the stability and appearance of an asymmetric thin shell wormhole within the Palatini
  f(R) gravity matching two Reissner-Nordström space-times with different masses and charges via
  suitable junction conditions.
- 12:40 → 13:10
  
  Fabrizio Di Giovanni (UV, Valencia) 30m
  
  On the dynamical bar-mode instability of spinning bosonic stars
  
  Abstract:We report results from three-dimensional numerical-relativity simulations of spinning bosonic stars, both considering a scalar field or a vector (Proca) field. In both cases, the bosonic field is assumed complex and massive. The scalar star is always affected by the growth of a non-axisymmetric instability which triggers the loss of angular momentum and its migration to a non-spinning boson star. For $m=1$ Proca stars, however, no such instability was observed. We tentatively related the different stability properties to the different toroidal/spheroidal topology of the scalar/Proca models. we qualitatively study the instability of SBSs through the analysis of the growth rate of azimuthal density modes and the search of a corotation point in the unstable models. This allows us to put forward a parallelism with rotating neutron stars affected by dynamical bar-mode instabilities. We compute the gravitational wave emission through the mode decomposition of the Newman-Penrose scalar. We compute the characteristic GW strain for some of our models and we compare it with the sensitivity curves of ground-based detectors, space detectors and PTAs. For the ranges of masses in the sensitivity range of each detector we compute the SNR and we evaluate the horizon distance, as the distance at which the SNR is equal to a certain threshold value.
- 13:10 → 15:00
  
  Lunch break 1h 50m
- 15:00 → 15:30
  
  Silvia Pla García (UV, Valencia) 30m
  
  Particle creation by electric and gravitational fields
- 15:40 → 16:10
  
  Llorenç Espinosa Portalés (IFT, Madrid) 30m
  
  Long range enhanced mutual information from inflation
- 16:20 → 16:50
  
  Robert Santacruz Zaragoza (U. New Brunswick, Canada) 30m
  
  Black Hole collapse and bounce in effective loop quantum gravity
- 17:00 → 17:45
  
  Iarley P. Lobo (UFLA/UFPB,Brasil) 45m
  
  Reaching Planck scale sensitivity with muon lifetimes from Finsler measures.
  
  Abstract: Planck scale modified dispersion relations are one way how to capture the influence of quantum gravity on the propagation of fundamental point particles effectively. We derive the time dilation between an observer's or particle's proper time, given by a Finslerian length measure induced from a modified dispersion relation, and a reference laboratory time. To do so, the Finsler length measure for general first order perturbations of the general relativistic dispersion relation is constructed explicitly. From this we then derive the time dilation formula for the κ-Poincaré dispersion relation in several momentum space bases, as well as for modified dispersion relations considered in the context of loop quantum gravity and Hořava-Lifshitz gravity. Most interestingly we find that the momentum Lorentz factor in the present and future colliders can, in principle, become large enough to constrain the κ-Poincaré dispersion relation in the bicrossproduct basis with Planck scale sensitivity with help of the muon's lifetime.
- 17:55 → 18:55
  
  Carolina Benone (UFPA, Brasil) 1h
Tuesday, 15 December
- 10:00 → 10:45
  
  Adrian Del Río (IST, Lisboa) 45m
  
  Gravitational-wave signatures of quantum gravity.
  
  Abstract: We show that gravitational-wave astronomy has the potential to inform us on quantum aspects of black holes. Based on Bekenstein's quantization, we find that black hole area discretization could impart observable imprints to the gravitational-wave signal from a pair of merging black holes, affecting their absorption properties during inspiral and their late-time relaxation after merger. Black hole rotation, ubiquitous in astrophysics, improves our ability to probe these quantum effects. Our analysis shows that gravitational-wave echoes and suppressed tidal heating are signs of new physics from which the fundamental quantum of black hole area can be measured, and which are within reach of future detectors. Our results also highlight the need to derive predictions from specific quantum gravity proposals.
- 10:50 → 11:20
  
  Adrián Casado Turrión (UCM, Madrid) 30m
  
  Accelerating towards an ambidextrous world: chiral symmetry restoration by the Unruh effect
  
  Abstract:In this presentation we shall consider the possibility of triggering the chiral phase transition of QCD through uniform acceleration, i.e. by the Unruh effect. Using Chiral Perturbation Theory at leading order and in the large N limit (with N being the number of pions) as the effective description of low-energy QCD, and the Thermalization Theorem formalism to compute the relevant partition function for the accelerated observer, we are able to find that chiral symmetry is restored for accelerations higher than the critical value a_c = 4 π f_π, where f_π is the pion decay constant. Therefore, our results are in complete agreement with those obtained in the inertial, finite-temperature case.
- 11:30 → 12:00
  
  Sérgio Vinicius Monteiro Castelo Branco Xavier 30m
  
  Shadows of charged rotating black holes: Kerr-Newman versus Kerr-Sen
- 12:05 → 12:50
  
  Matheus A. Marquez (UFPB,Brasil) 45m
  
  New results on magnetic monopoles.
- 12:55 → 13:25
  
  Adrià Delhom (UV) 30m
  
  title: Ghosts in metric-affine higher order curvature gravity
  
  abstract: We disprove the widespread belief that higher order curvature theories of gravity in the metric-affine formalism are generally ghost-free. This is clarified by considering a sub-class of theories constructed only with the Ricci tensor and showing that the non-projectively invariant sector propagates ghost-like degrees of freedom. We also explain how these pathologies can be avoided either by imposing a projective symmetry or additional constraints in the gravity sector. Our results put forward that higher order curvature gravity theories generally remain pathological in the metric-affine (and hybrid) formalisms and highlight the key importance of the projective symmetry and/or additional constraints for their physical viability and, by extension, of general metric-affine theories.
- 13:30 → 15:00
  
  Lunch break 1h 30m
- 15:00 → 16:00
  
  Francisco S.N. Lobo 1h
  
  Thin-shell and and black-bounce traversable wormholes.
- 16:05 → 16:35
  
  Alfredo Delgado Miravet (UCM, Madrid) 30m
  
  The imprint of ultralight vector fields on gravitational wave propagation.
  
  Abstract: We study the effects of ultralight vector field (ULVF) dark matter on gravitational wave propagation. We find that the coherent oscillations of the vector field suppress the amplitude of gravity waves as compared to the $\Lambda$CDM prediction. The effect is enhanced for smaller vector field masses and peaks for modes around $k=H_0/\sqrt{a(H=m)}$. The suppression is negligible for astrophysically generated gravitational waves but could be sizeable for primordial gravity waves. We discuss the possibility of detecting such an effect on the CMB B-mode power spectrum with the sensitivity of future detectors. We find that the upcoming LiteBird mission would be sensitive to ULVF dark matter with masses $m\lsim 10^{-26}$ eV for sufficiently large abundances.
- 17:00 → 18:00
  
  Diego Rubiera-Garcia (UCM, Madrid) 1h
  
  Testing modified gravity with relativistic and non-relativistic stars.
  
  Abstract: I will discuss the most promising opportunities for testing modified gravity effects using models of stellar structure for both relativistic (neutron stars) and non-relativistic (brown, red, white) stars.
- 18:00 → 19:00
  
  Caio F.B. Macedo (UFPA,Brasil) 1h
Wednesday, 16 December
- 10:00 → 10:45
  
  João Luis Rosa (U. Tartu, Estonia) 45m
  
  Existence and stability of relativistic fluid spheres supported by thin-shells.
- 10:50 → 11:20
  
  Avishek Dusoye (UCT, Cape Town) 30m
  
  Disformal couplings in a CDM background cosmology.
  
  Abstract: The coupled quintessence model with disformal couplings is treated here to mimic the LCDM background. Using this approach, the quintessence potential does not have to be specified. The model considers a generic fluid coupled to the quintessence, which is specified to be either dark matter or a relativistic fluid. The LCDM background consists of a cosmological constant and another uncoupled generic fluid, to cater for three studied scenarios (I, II, III). The cosmological dynamics is investigated for the coupled quintessence model, whose disformal couplings depend on the equation of state of both generic fluids. The scenario I, whereby both generic fluids are dark matter was further analysed for an expansion history of the mimicking model. The analysis confirms that the mass scale of the quintessence influences the disformal characteristics of the dynamical system, which is portrayed by the evolution of an effective conformal coupling.
- 11:30 → 12:00
  
  Marco Aurélio Abreu de Paula 30m
  
  Electrically charged black holes in linear and nonlinear electrodynamics: Geodesic analysis and scalar absorption.
- 12:10 → 12:40
  
  Francisco José Maldonado Torralba (UCT and U.Groningen) 30m
- 13:00 → 15:00
  
  Lunch break 2h
- 15:05 → 15:35
  
  Renan Batalha Magalhaes 30m
  
  Persistence of wormholes in Palatini gravity
- 15:40 → 16:10
  
  Haroldo Cilas Duarte Lima Junior 30m
  
  4D Einstein-Gauss-Bonnet gravity: Massless particles and absorption of planar spin-0 waves.
- 16:20 → 16:50
  
  Gerardo Mora 30m
- 17:00 → 17:30
  
  Sergi Navarro-Albalat (University of Texas) 30m
  
  Modelling extreme mass ratio inspirals
- 17:40 → 18:10
  
  João Paulo Bessa Brito 30m
  
  Synchrotron geodesic radiation in Schwarzschild-de Sitter spacetime.
- 18:20 → 18:50
  
  Andreu Masó (UV, València) 30m
  
  Boson Stars in Palatini f(R) gravity
Thursday, 17 December
- 10:00 → 10:45
  
  Aneta Wojnar (U. Tartu, Estonia) 45m
  
  Title: Low-mass stars in modified gravity
  
  Abstract:
  
  I will present modified gravity impacts on stars' early evolution, such as Hayashi tracks and radiative core development, together with the measured quantities such as effective temperature, masses, luminosities, and abundance of light elements. The last one introduces an additional uncertainty to age determination techniques of young stars and globular clusters since they rely on a lithium depletion.
- 10:50 → 11:20
  
  Sergi Nadal (UV) 30m
  
  Title: Renormalization, running couplings, and decoupling for the Yukawa model in curved spacetime
- 11:30 → 12:00
  
  Simon Boudet (University of Trento, Italy) 30m
  
  "Super-entropic black hole with Immirzi hair"
  
  Abstract: "In the context of f(R) generalizations to the Holst action, endowed with a dynamical Immirzi field, we derive an analytic solution describing asymptotically Anti-de Sitter black holes with hyperbolic horizon. These exhibit a scalar hair of the second kind, which ultimately depends on the Immirzi field radial behaviour. In particular, we show how the Immirzi field modifies the usual entropy law associated to the black hole. We also verify that the Immirzi field boils down to a constant value in the asymptotic region, thus restoring the standard Loop Quantum Gravity picture. We finally prove the violation of the reverse isoperimetric inequality, resulting in the super-entropic nature of the black hole, and we discuss in detail the thermodynamic stability of the solution."
- 12:05 → 12:50
  
  Rafael Bernar (UFPA, Brasil) 45m
  
  Quantum superradiance of a charged scalar field in Reissner-Nordström
  spacetime.
  
  Abstract: We analyze the quantum version of charge superradiance for a massless scalar field in Reissner-Nordström spacetime. We compute the expectation
  values of the operators associated to the fluxes of charge and energy
  from the black hole in the vacuum state which has no particles as past
  null infinity. We show that these expectation values are nonvanishing
  and, therefore, that there is an outgoing flux of superradiant particles
  at future null infinity.
- 13:00 → 13:30
  
  Albert Petrov (UFPB, João Pessoa) 30m
  
  Metric-affine bumblebee gravity: quantum aspects, based on https://arxiv.org/abs/2010.06391
- 13:30 → 15:00
  
  Lunch break 1h 30m
- 15:00 → 15:45
  
  Juan Margalef (UC3M/PennState) 45m
  
  The geometric formulation of the covariant Phase Space with boundaries.
  
  Abstract: In this talk, I will introduce the relative bicomplex framework, a new formalism which is the natural one to deal with the covariant phase space of theories with boundaries. I will show that it provides a formal equivalence between the relative version of a theory with boundary and the non-relative version of the same theory with no boundary. With these tools at hand, we can build over the space of solutions a (pre)symplectic structure canonically associated with the action. I will provide a brief summary of other geometric objects that can be derived, such as symmetries, Noether currents, and charges. Likewise, I will characterize the arbitrariness of these constructions which has been a matter of confusion in the past.
- 15:50 → 16:35
  
  Flavio Bombacigno (UV, Valencia) 45m
  
  Gravitational Landau damping for massive scalar modes.
  
  Abstract: We establish the possibility of Landau damping for gravitational scalar waves which propagate in a non-collisional gas of particles. In particular, under the hypothesis of homogeneity and isotropy, we describe the medium at the equilibrium with a J\"uttner-Maxwell distribution, and we analytically determine the damping rate from the Vlasov equation. We find that damping occurs only if the phase velocity of the wave is subluminal throughout the propagation within the medium. Finally, we investigate relativistic media in cosmological settings by adopting numerical techniques.
- 16:45 → 17:45
  
  Param Singh (LSU, USA) 1h
  
  Starting low energy scale inflation in closed universes.Title: Onset of Starobinsky inflation in spatially closed FLRW model
  
  Abstract: Recent CMB data favors a spatially closed FLRW model and low energy inflation such as sourced by the Starobinsky potential. An age old problem with the latter models is that they result in a recollapse of the universe and a big crunch singularity before inflation can even set in. To resolve this problem it is essential to work with a framework which is non-singular. We explore the resolution of this problem in loop quantum cosmology where results in the last decade suggest a generic resolution of singularity. We show that quantum gravity effects result in an onset of inflation even for those initial conditions where it is classically impossible. Interestingly, a key role is played by a hysteresis-like phenomena in the early universe resulting from non-singular dynamics
- 17:50 → 18:50
  
  J. Fernando Barbero G. (IEM, Madrid) 1h
  
  A concise symplectic formulation for tetrad gravity.
  
  Abstract: I will discuss a simple symplectic formulation for tetrad gravity that leads to the real Ashtekar variables in a direct and
  transparent way. It also sheds light on the role of the Immirzi
  parameter and the time gauge.

4th Valencia Winter Workshop on Theoretical Physics

Online

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