arXiv subjects

Efraín Rojas

Publications and source records attributed to Efraín Rojas.

17 recordsLinked to original sources

arXiv2026

Classical emergence of the quantum-backreacted BTZ black hole from exponential electrodynamics

In this work, we revisit a recently reported generalization of the Bañados-Teitelboim-Zanelli black hole arising in New Massive Gravity sourced by the quantum fluctuations of scalar matter, now examined through the lens of a purely classical framework. We show that the same geometry, distinguished by its logarithmic asymptotic structure, emerges as the unique static solution of Einstein gravity coupled to an exponential nonlinear electrodynamics. We trace the origin of this correspondence and prove that this geometry belongs to a unique class of metrics constituting the intersection of the moduli spaces of the static and circularly symmetric sectors of the two theories, thereby revealing a dynamical equivalence between them. An explicit mapping is established between the global charges of the nonlinearly charged black holes and the parameters governing the quantum backreaction in New Massive Gravity, allowing for a natural reinterpretation of the quantum imprints in terms of classical charges. A detailed analysis of the horizon structure of these spacetimes is presented. In addition, the full thermodynamics of the more general configurations is constructed using the Iyer-Wald formalism, from which we derive the first law and the associated Smarr relation. Altogether, our results provide a classical realization of a semiclassical spacetime and point toward a broader correspondence between higher-curvature corrections in quantum gravity and nonlinear effects in self-gravitating electrodynamics in three dimensions.

gr-qc↗

arXiv2026

Mimetic gravity in the extended objects framework

Starting from the most general second-order in derivatives theories describing extended objects of arbitrary dimension evolving geodetically in a codimension-one flat ambient space-time, we determine the subset of models yielding second-order equations of motion, forming an intriguing theory known as Lovelock-type brane gravity (LBG). These models further extend the so-called geodetic brane gravity (GBG) approach, thereby naturally promoting the GBG geometric properties, allowing LBG to be reformulated as a mimetic embedding gravity and, in turn, the possibility of introducing fictional matter through a peculiar current $\mathcal{T}^{a\,μ}$. Grounded in the elasticity theory, we provide a possible origin of such a current. Finally, variational techniques are employed to elucidate the mechanical function of both the dark current $\mathcal{T}^{a\,μ}$ and its tangential components $\mathcal{T}^{ab}$; these serve as the constituents of a fictional energy-momentum tensor that shares characteristics with a perfect fluid.

gr-qc↗

arXiv2026

Thermodynamics of Geodetic Brane Gravity

In this work, we explore the effect at cosmological level of the extra contribution arising from the Geodetic Brane Gravity model within a thermodynamical perspective. As already known, the universe seen as an extended object embedded within a higher dimensional space time, modifies the dynamical background equations, which in turn results in correction contributions to the entropy and temperature of the apparent horizon. Additionally, we investigate the possibility that the apparent horizon and the bulk remain in thermal equilibrium across various matter contents, demonstrating that such properties are highly sensitive to the equation-of-state parameter.

hep-th↗

arXiv2025

Lovelock type brane cosmology

The cosmological implications of the geodetic brane gravity model, enhanced by geometrical terms of Gibbons-Hawking-York (GHY) type and Gibbons-Hawking-York-Myers type (GHYM), carefully constructed as combinations of intrinsic and extrinsic curvatures, are examined. All the geometrical terms under study belong to a set named Lovelock-type brane models. The combined model gives rise to a second-order differential equation of motion. Under a Friedmann-Robertson-Walker (FRW) geometry defined on a $(3+1)$-dimensional world volume, together with a perfect fluid matter content, the emerging universe of this model evolves in a 5-dimensional Minkowski background, yielding peculiar facts. The resulting Friedmann-type equation is written in terms of energy density parameters, where fine-tuning is needed to probe interesting cosmological processes close to the current data. In this sense, Lovelock-type brane models might underlie the cosmic acceleration. Indeed, we find that these correction terms become significant at low energies/late times. The model exhibits self-accelerating (non-self-accelerating) behavior for the brane expansion, and in the case where the radiation-like contribution due to the existence of the extra dimension vanishes its behavior is the same as the Dvali-Gabadadze-Porrati (DGP) brane cosmology and its generalization to the Gauss-Bonnet (GB) brane gravity. Likewise, Einstein cosmology is recovered when the radiation-like contribution fades away along with the odd polynomials in brane extrinsic curvature.

gr-qc↗

arXiv2025

Lovelock type brane gravity from a minimal surface perspective

We explore the correspondence between the parallel surfaces framework, and the minimal surfaces framework, to uncover and apply new aspects of the geometrical and mechanical content behind the so-called Lovelock-type brane gravity (LBG). We show how this type of brane gravity emerges naturally from a Dirac-Nambu-Goto (DNG) action functional built up from the volume element associated with a world volume shifted a distance $α$ along the normal vector of a germinal world volume, and provide all known geometric structures for such a theory. Our development highlights the dependence of the geometry for the displaced world volume on the fundamental forms, as well as on certain conserved tensors, defined on the outset world volume. Based on this, LBG represents a natural and elegant generalization of the DNG theory to higher dimensions. Moreover, our development allows for exploring disformal transformations in Lovelock brane gravity and analyzing their relations with scalar-tensor theories defined on the brane trajectory. Likewise, this geometrical correspondence would enable us to establish contact with tractable Hamiltonian approximations for this brane gravity theory, by exploiting the linkage with a DNG model, and thus start building a suitable quantum version.

hep-th↗

arXiv2024

Regge-Teitelboim cosmology driven by a curved background

We derive the dynamic equations governing a Regge Teitelboim (RT) brane that represents our universe considering that its degrees of freedom are the embedding functions, evolving in a five dimensional curved spacetime. Within this framework, we investigate the effects of embedding a Friedmann Robertson Walker (FRW) metric into a specific curved ambient spacetime. This approach allows us to analyze in detail how the ambient spacetime's curvature influences the brane universe's dynamics. Specifically, we examine the relationship between the Hubble parameter $H$ and the redshift $z$, demonstrating that our results significantly agree with actual observational data. This is contrasted and compared with other approaches.

hep-th↗

arXiv2024

Dark energy as a geometrical effect in geodetic brane gravity

Within the framework of the modified geodetic brane gravity, conformed by the Regge-Teitelboim model and enhanced with a linear term in the extrinsic curvature of the brane, the possibility that under an FRW geometry this theory emulates the so-called dark energy is discussed. The cosmological behavior of this model displays a self-(non-self)-accelerated expansion of this universe which is caused by a combination of usual matter and gravitational geometric effects controlled by a $β$ parameter that accompanies the correction $K$ term. Indeed, the self-accelerated branch, provided by the trace $K$ model raises the question of whether the extrinsic curvature correction terms might be suitable for dark energy candidates. We discuss the analytical expression obtained for $\rd$ in addition to the main cosmological parameters such as the state parameter $ω_{\text{\tiny eff}}$ and the deceleration parameter $q$. Moreover, when we call for the contribution of dark radiation-like energy to be switched off, $\Odr \to 0$, we find the same acceleration behavior, as well as the same dark energy content provided by the DGP theory. The relationship of our findings to the analysis for $\rd$ performed by Davidson and Gurwich within the unified brane cosmology is briefly discussed.

gr-qc↗

arXiv2022

Jacobi equations of geodetic brane gravity

We consider brane gravity as described by the Regge-Teitelboim geometric model, in any codimension. In brane gravity our spacetime is modeled as the time-like world volume spanned by a space-like brane in its evolution, seen as a manifold embedded in an ambient background Minkowski spacetime of higher dimension. Although the equations of motion of the model are well known, apparently their linearization has not been considered before. Using a direct approach, we linearize the equations of motion about a solution, obtaining the Jacobi equations of the Regge- Teitelboim model. They take a formidable aspect. Some of their features are commented upon. By identifying the Jacobi equations, we derive an explicit expression for the Morse index of the model. To be concrete, we apply the Jacobi equations to the study of the stability of a four-dimensional Schwarzschild spacetime embedded in a six-dimensional Minkowski spacetime. We find that it is unstable under small linear deformations.

hep-th↗

arXiv2021

Ostrogradsky-Hamilton approach to geodetic brane gravity

We develop the Ostrogradsky-Hamilton formalism for geodetic brane gravity, described by the Regge-Teitelboim geometric model in higher codimension. We treat this gravity theory as a second-order derivative theory, based on the extrinsic geometric structure of the model. As opposed to previous treatments of geodetic brane gravity, our Lagrangian is linearly dependent on second-order time derivatives of the field variables, the embedding functions. The difference resides in a boundary term in the action, usually discarded. Certainly, this suggests applying an appropriate Ostrogradsky-Hamiltonian approach to this type of theories. The price to pay for this choice is the appearance of second class constraints. We determine the full set of phase space constraints, as well as the gauge transformations they generate in the reduced phase space. Additionally, we compute the algebra of constraints and explain its physical content. In the same spirit, we deduce the counting of the physical degrees of freedom. We comment briefly on the naive formal canonical quantization emerging from our development.

hep-th↗

arXiv2021

Hamilton-Jacobi approach for linearly acceleration-dependent Lagrangians

We develop a constructive procedure for arriving at the Hamilton-Jacobi framework for the so-called affine in acceleration theories by analysing the canonical constraint structure. We find two scenarios in dependence of the order of the emerging equations of motion. By properly defining generalized brackets, the non-involutive constraints that originally arose, in both scenarios, may be removed so that the resulting involutive Hamiltonian constraints ensure integrability of the theories and, at the same time, lead to the right dynamics in the reduced phase space. In particular, when we have second-order in derivatives equations of motion we are able to detect the gauge invariant sector of the theory by using a suitable approach based on the projection of the Hamiltonians onto the tangential and normal directions of the congruence of curves in the configuration space. Regarding this, we also explore the generators of canonical and gauge transformations of these theories. Further, we briefly outline how to determine the Hamilton principal function $S$ for some particular setups. We apply our findings to some representative theories: a Chern-Simons-like theory in $(2+1)$-dim, an harmonic oscillator in $2D$ and, the geodetic brane cosmology emerging in the context of extra dimensions.

hep-th↗

arXiv2018

Stealth's cosmologies

We present a novel approach to construct cosmological models endowed with a particular scalar field, the stealth. The model is constructed by studying a scalar field no-minimally coupled to the gravitational field with sources; as sources, we used a perfect fluid and analyzed the simplest case of dust and the power-law cosmology. Surprisingly, we find that these stealth fields, which have no back-reaction to background space-time, have a contribution to cosmological dynamics. Furthermore, we provide analytic expressions of the stealth's contributions to the energy density in both cases, and for the pressure in the power-low cosmology, which means that such contributions to cosmological evolution are quantifiable. Additionally, we discuss the behaviors of the self-interaction potential for some cases.

gr-qc↗

arXiv2016

Stealths on $(1+1)$-dimensional dilatonic gravity

We study gravitational stealth configurations emerging on a charged dilatonic $(1+1)$-D black hole spacetime. We accomplish this by considering the coupling of a non-minimally scalar field $ϕ$ and a self-interacting scalar field $Ψ$ living in a $(1+1)$-D charged black hole background. In addition, the self-interacting potential for $Ψ$ is obtained which exhibits transitions for some specific values of the non-minimal parameter. Atypically, we found that the solutions for these stealth scalar fields do not have a dependence on the temporal coordinate.

gr-qc↗

arXiv2015

Deformation quantization of the Pais-Uhlenbeck fourth order oscillator

We analyze the quantization of the Pais-Uhlenbeck fourth order oscillator within the framework of deformation quantization. Our approach exploit the Noether symmetries of the system by proposing integrals of motion as the variables to obtain a solution to the -genvalue equation, namely the Wigner function. We also obtain, by means of a quantum canonical transformation the wave function associated to the Schrödinger equation of the system. We show that unitary evolution of the system is guaranteed by means of the quantum canonical transformation and via the properties of the constructed Wigner function, even in the so called equal frequency limit of the model, in agreement with recent results.

quant-ph↗

arXiv2015

A possible geometrical origin of the accelerated expansion of the universe

The modified geodetic brane cosmology (MGBC) is tested with observational data. The MGBC is derived from the geodetic brane gravity action corrected by the extrinsic curvature of the braneworld. The density parameter coming from this additional term produces an accelerated expansion of geometrical origin. Subject to the Supernovae Ia, Observable Hubble parameter, Baryon Acoustic Oscillations and Cosmic Microwave Background probes, the obtained fit provides enough evidence in the sense that the extrinsic curvature effect is able to reproduce the accelerated expansion of the universe without need of invoking dark energy, exotic matter or cosmological constant. Moreover the MGBC is free of the problems present in other braneworld models.

astro-ph.CO↗

arXiv2014

Quantum modified Regge-Teitelboim cosmology

The canonical quantization of the modified geodetic brane cosmology which is implemented from the Regge-Teitelboim model and the trace of the extrinsic curvature of the brane trajectory, K, is developed. As a second-order derivative model, on the grounds of the Ostrogradski Hamiltonian method and the Dirac's scheme for constrained systems, we find suitable first- and second-class constraints which allow for a proper quantization. We also find that the first-class constraints obey a sort of truncated Virasoro algebra. The effective quantum potential emerging in our approach is exhaustively studied where it shows that an embryonic epoch is still present. The quantum nucleation is sketched where we observe that it is driven by an effective cosmological constant.

gr-qc↗

arXiv2013

Born-Infeld extension of Lovelock brane gravity

We present a Born-Infeld type theory to describe the evolution of p-branes propagating in an N = (p+2)-dimensional Minkowski spacetime. The expansion of the BI-type volume element gives rise to the (p+1) Lovelock brane invariants associated with the worldvolume swept out by the brane. Contrary to the Lovelock theory in gravity, the number of Lovelock brane Lagrangians differs in this case, depending on the dimension of the worldvolume as a consequence that we consider the embedding functions, instead of the metric, as the field variables. This model depends on the intrinsic and the extrinsic geometries of the worldvolume and in consequence is a second-order theory as shown in the main text. A classically equivalent action is discussed and we comment on its Weyl invariance in any dimension which naturally requires the introduction of some auxiliary fields.

gr-qc↗

arXiv2012

Modified geodetic brane cosmology

We explore the cosmological implications provided by the geodetic brane gravity action corrected by an extrinsic curvature brane term, describing a codimension-1 brane embedded in a 5D fixed Minkowski spacetime. In the geodetic brane gravity action, we accommodate the correction term through a linear term in the extrinsic curvature swept out by the brane. We study the resulting geodetic-type equation of motion. Within a Friedmann-Robertson-Walker metric, we obtain a generalized Friedmann equation describing the associated cosmological evolution. We observe that, when the radiation-like energy contribution from the extra dimension is vanishing, this effective model leads to a self-(non-self)-accelerated expansion of the brane-like universe in dependence on the nature of the concomitant β-parameter associated with the correction, which resembles an analogous behaviour in the DGP brane cosmology. Several possibilities in the description for the cosmic evolution of this model are embodied and characterized by the involved density parameters related in turn to the cosmological constant, the geometry characterizing the model, the introduced β-parameter as well as the dark like-energy and the matter content on the brane.

gr-qc↗