It is notoriously difficult to construct a stable non-singular bouncing cosmology that avoids all possible instabilities throughout the entire evolution of the universe. In this work, we explore whether a non-singular bounce driven by a specific class of modifications of General Relativity, the vector-tensor generalized Proca theories, can be constructed without encountering any pathologies in linear perturbation theory. We find that such models unavoidably lead either to strong coupling in the tensor or the scalar sector, or instabilities in the matter sector during the bouncing phase. As our analysis is performed in a gauge-independent way, this result can be cast in the form of a no-go theorem for non-singular bounces with generalized Proca. In contrast to the no-go theorem found for Horndeski theories, however, it cannot be evaded by considering beyond generalized Proca theory. At the core of our result lies the non-dynamical nature of the temporal component of the vector field, which renders it an ill-suited mediator for a bouncing solution.

Switzerland

Lara Bohnenblust

Germany

Serena Giardino

Lavinia Heisenberg

Nadine Nussbaumer

To bounce or not to bounce in generalized Proca theory and beyond

The Einstein–Euler–Heisenberg (EEH) black hole model represents an extension of classical black hole solutions in general relativity by incorporating quantum electrodynamic (QED) corrections. These corrections are introduced through the inclusion of the Euler–Heisenberg Lagrangian, which accounts for the nonlinear effects of QED in the presence of strong electromagnetic fields. This study investigates the observational properties of a thin accretion disk surrounding the electrically charged rotating EEH black hole. By exploring the influence of the spin parameter and charge on key dynamical quantities – such as the energy, angular momentum, angular velocity, and the innermost stable circular orbit (ISCO) of a test particle – it becomes possible to analyze the radiative flux, temperature distribution, and differential luminosity of the thin accretion disk in the spacetime of the charged rotating EEH black hole. The results are compared to those of Kerr and Kerr–Newman black holes in General relativity, revealing that QED corrections are found to increase the ISCO radius. Specifically, for a fixed electric charge, an increasing spin parameter leads to a larger ISCO radius compared to the standard Kerr black holes, as a result of additional electromagnetic corrections introduced by the Euler–Heisenberg theory. Conversely, when the spin parameter is held constant, an increase in the electric charge reduces the ISCO radius. Additionally, thin accretion disks around charged EEH rotating black holes exhibit higher temperatures and greater efficiency when the spin parameter is fixed and the electric charge is increased. However, for a constant electric charge, increasing the spin parameter results in an accretion disk that is cooler and has lower radiant efficiency. These findings highlight the potential of accretion disk processes as valuable tools for probing Euler–Heisenberg theory through astrophysical observations.

Iran

Kourosh Nozari

Sara Saghafi

Fatemeh Aliyan

Investigating QED effects on the thin accretion disk properties around rotating Euler–Heisenberg black holes

In this paper, we investigate the thermodynamics of charged Brans–Dicke (BD) black holes (BHs) in the presence of Euler-Heisenberg (EH) electrodynamics. We write the action and discuss that the equations of electromagnetic, scalar, and gravitational fields are strongly coupled, which make them difficult to be solved directly. To remove this problem, we use the conformal transformations (CTs) to transfer Jordan frame (JF) action to that of Einstein frame (EF). We solve the equations and introduce two new classes of BHs in the Einstein-dilaton theory. By detailed calculations, we show that if the EH nonlinearity parameter is treated as a conformal-invariant quantity, the first law of thermodynamics (FLT) is violated. To solve this problem, we allow the nonlinear parameter to change under CTs. Then, by using this proposal, we obtain the corrected solutions by exactly solving the field equations. Our solutions are asymptotically unusual and capable of exhibiting extreme and multi-horizon dilaton BHs. Then, we calculate the thermodynamic quantities and show that the FLT holds for the new EH BHs. The thermal stability or phase transition of the BHs is analyzed by using the canonical ensemble method. Finally, we introduce new EH-BD BHs solutions, from their EF counterparts, by reversing the transformations. We explore thermodynamic quantities, FLT and thermal stability of the BD BHs by utilizing the appropriate methods.

A. Haghighi

M. Dehghani

Black hole thermodynamics in the four-dimensional Brans–Dicke–Euler–Heisenberg theory

We develop a relativistic framework of integral quantization applied to the motion of spinless particles in the four-dimensional Minkowski spacetime. The proposed scheme is based on coherent states generated by the action of the Heisenberg–Weyl group and has been motivated by the Hamiltonian description of the geodesic motion in General Relativity. We believe that this formulation should also allow for a generalization to the motion of test particles in curved spacetimes. A key element in our construction is the use of suitably defined positive operator-valued measures. We show that this approach can be used to quantize the one-dimensional nonrelativistic harmonic oscillator, recovering the standard Hamiltonian as obtained by the canonical quantization. A direct application of our model, including a computation of transition amplitudes between states characterized by fixed positions and momenta, is postponed to a forthcoming article.

Poland

Aleksandra Pȩdrak

Andrzej Góźdź

Włodzimierz Piechocki

Patryk Mach

Adam Cieślik

Integral quantization based on the Heisenberg–Weyl group

We explore the ideas of resurgence and Padé–Borel resummation in the Euler–Heisenberg Lagrangian of scalar quantum electrodynamics, which has remained largely unexamined in these contexts. We thereby extend the related seminal works in spinor quantum electrodynamics, while contrasting the similarities and differences in the two cases. We investigate in detail the efficacy of resurgent extrapolations starting from just a finite number of terms in the weak-field expansions of the 1-loop and 2-loop scalar quantum electrodynamics Euler–Heisenberg Lagrangian. While we re-derive some of the well-known 1-loop and 2-loop contributions in representations suitable for Padé–Borel analyses, other contributions have been derived for the first time. For instance, we find a closed analytic form for the one-particle reducible contribution at 2-loop, which until recently was thought to be zero. It is pointed out that there could be an interesting interplay between the one-particle irreducible and one-particle reducible terms in the strong-field limit. The 1-loop scalar electrodynamics contribution may be effectively mapped into two copies of the spinor quantum electrodynamics, and the particle reducible contribution may be mapped to the 1-loop contribution. It is suggested that these mappings cannot be trivially used to map the corresponding resurgent structures. The singularity structures in the Padé–Borel transforms at 1-loop and 2-loop are examined in some detail. Analytic continuation to the electric field case and the generation of an imaginary part is also studied. We compare the Padé–Borel reconstructions to closed analytic forms or to numerically computed values in the full theory.

United States

India

Drishti Gupta

Arun Thalapillil

Resurgence in the scalar quantum electrodynamics Euler–Heisenberg Lagrangian

We extend the black hole solution of Euler-Heisenberg gravitational theory in AdS space-time by introducing quintessence field in it and studied thermodynamics and phase structure using both semi classical analysis and shadow formalism by considering Λ as thermodynamic pressure. We compare the results obtained by these two methods. The N-type change in temperature for <math altimg='si1.svg'><mi>P</mi><mo linebreak='goodbreak' linebreakstyle='after'>&lt;</mo><msub><mrow><mi>P</mi></mrow><mrow><mi>c</mi></mrow></msub></math> can be seen. The nature of Gibbs free energy ensures the second order phase transition for <math altimg='si1.svg'><mi>P</mi><mo linebreak='goodbreak' linebreakstyle='after'>&lt;</mo><msub><mrow><mi>P</mi></mrow><mrow><mi>c</mi></mrow></msub></math>, which agrees with the temperature behaviour and then derived heat capacity, Joule-Thomson coefficient to study local stability and heating (or cooling) effect. Assuming black hole as a thermodynamic engine, we calculate the efficiency of Carnot cycle and Rankin cycle and study the impact of various black hole parameters on them. We also studied Ruppeiner thermodynamic geometry in {S,Q} thermodynamic phase space to study the BH at molecular level.

Debojyoti Mondal

Tanusree Roy

Ujjal Debnath

Thermodynamics of Euler-Heisenberg AdS black hole surrounded by quintessence field using shadow

In this article, motivated by the high interest in Euler–Heisenberg nonlinear electrodynamic theory, we investigated several thermal aspects of the charged Euler–Heisenberg black hole surrounded by perfect fluid dark matter. To ensure the validity of the first law of thermodynamics, we measured the conserved thermal quantities. Furthermore, the local and global thermal stability of the charged Euler–Heisenberg black hole surrounded by perfect fluid dark matter is also discussed in canonical and grand canonical ensembles and reveals how the coupling parameter affects the stability regions. We also examined the extended second-order phase transition via P–V criticality. Finally, we extend our study to the optical features of the charged Euler–Heisenberg black hole surrounded by perfect fluid dark matter, such as the black hole shadow and energy emission rate and observe the impact of the coupling parameter.

Pakistan

M. Shahzad

G. Abbas

China

Tao Zhu

R. Ali

Azerbaijan

Asifa Ashraf

Saudi Arabia

Badr Al-Kahtani

Optical features and thermal properties of charged AdS Euler–Heisenberg black hole surrounded by perfect fluid dark matter

We explore the motion of particles in the vicinity of an Euler-Heisenberg black hole immersed in a cold dark matter halo, focusing on how the black hole parameters influence particle dynamics. This black hole solution is characterized by five parameters, namely, the black hole mass <italic>M</italic>, the feature radius <italic>R</italic>, the parameter <italic>&#961;</italic> describing the density of the cold dark matter halo, the quantum electrodynamics parameter <italic>&#945;</italic>, and the black hole charge <italic>Q</italic>. We confine ourselves to an equatorial plane and examine the stability of equatorial circular orbits with the help of the effective potential. The analytical mathematical expressions for the energy and the angular momentum of circular orbits have been computed. We have also examined the innermost stable circular orbits. The effective force acting on the particles is explored. The epicyclic oscillations of particles in proximity to stable circular orbits have been examined, and the phenomenon of periastron precession has been addressed. Additionally, we examine the collision of particles and the center of mass energy in proximity to the black hole's horizon. The model parameters significantly affect the motion of the particles. Finally, we compare the particle dynamics surrounding a Euler-Heisenberg black hole within a cold dark-matter halo to those around a Schwarzschild black hole within a cold dark-matter halo and a Schwarzschild black hole devoid of a cold dark matter halo.

G. Mustafa

Oman

S.K. Maurya

Tayyab Naseer

Türkiye

Arzu Cilli

Ertan Güdekli

Assmaa Abd-Elmonem

Neissrien Alhubieshi

Particle motion and QPOs around Euler-Heisenberg black hole immersed in cold dark matter halo

Italy

Gabriele Barca

Giovanni Montani

Erratum: Non-singular gravitational collapse through modified Heisenberg algebra

We consider a simplified model of double scaled SYK (DSSYK) in which the Hamiltonian is the position operator of the Harmonic oscillator. This model captures the high temperature limit of DSSYK but could also be defined as a quantum theory in its own right. We study properties of the emergent geometry including its dynamics in response to inserting matter particles. In particular, we find that the model displays de Sitter-like properties such as that infalling matter reduces the rate of growth of geodesic slices between the two boundaries. The simplicity of the model allows us to compute the full generating functional for correlation functions of the length mode or any number of matter operators. We provide evidence that the effective action of the geodesic length between boundary points is non-local. Furthermore, we use the on-shell solution for the geodesic lengths between any two boundary points to reconstruct an effective bulk metric and reverse engineer the dilaton gravity theory that generates this metric as a solution.