Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1401.7549

Generalized second law of thermodynamics in scalar-tensor gravity

A. Abdolmaleki·T. Najafi·K. Karami
View original source ↗Read source document ↗Export metadata ↓

Abstract

Within the context of scalar-tensor gravity, we explore the generalized second law (GSL) of gravitational thermodynamics. We extend the action of ordinary scalar-tensor gravity theory to the case in which there is a non-minimal coupling between the scalar field and the matter field (as chameleon field). Then, we derive the field equations governing the gravity and the scalar field. For a FRW universe filled only with ordinary matter, we obtain the modified Friedmann equations as well as the evolution equation of the scalar field. Furthermore, we assume the boundary of the universe to be enclosed by the dynamical apparent horizon which is in thermal equilibrium with the Hawking temperature. We obtain a general expression for the GSL of thermodynamics in the scalar-tensor gravity model. For some viable scalar-tensor models, we first obtain the evolutionary behaviors of the matter density, the scale factor, the Hubble parameter, the scalar field, the deceleration parameter as well as the effective equation of state (EoS) parameter. We conclude that in most of the models, the deceleration parameter approaches a de Sitter regime at late times, as expected. Also the effective EoS parameter acts like the LCDM model at late times. Finally, we examine the validity of the GSL for the selected models.

Explore related subjects

gr-qchep-th

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

A. Abdolmaleki, T. Najafi, K. Karami. 2014-05-26. Generalized second law of thermodynamics in scalar-tensor gravity. https://doi.org/10.1103/physrevd.89.104041

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

General Relativistic Chronometry with Clocks on Ground and in Space

One of the main tasks of geodesy is to determine the gravity field of the Earth from measurements performed on ground and in space. High-precision clock comparison has the potential to provide a new observable for the global determination of the Earth's gravitational potential through the gravitational redshift. Towards such a global chronometric geodesy, we derive a general relativistic framework beyond the post-Newtonian level for the relativistic redshift and the timing between observers in stationary spacetimes. These observers are equipped with standard clocks and may move along arbitrary worldlines. The redshift is factorized into geometric, transversal-Doppler, and longitudinal-Doppler contributions, providing a transparent separation of gravitational and kinematic effects. We then show how redshift measurements involving clocks on ground and/or in space can, in principle, be used to determine the mass multipole moments of the underlying spacetime. In the weak field limit, our results recover the corresponding Newtonian and post-Newtonian expressions. The framework is illustrated for different exact vacuum spacetimes and provides a theoretical basis for using clock comparisons as an additional observable for gravity-field recovery and future relativistic geodesy missions.

gr-qc↗
arXiv2026

DESI DR2 Constraints on Coupled Hu--Sawicki $f(R)$ Gravity with Interacting Neutrinos: Implications for the Hubble and \(S_8\) Tensions

We investigate the cosmological implications of viable Hu--Sawicki \(f(R)\) gravity models and their extension through an effective interaction with the neutrino sector. Motivated by the persistent \(H_0\) and \(S_8\) tensions, we explore whether the combined effects of modified gravity, neutrino free-streaming, and dark-sector interaction can alleviate these discrepancies while remaining consistent with current cosmological observations. Starting from the metric formulation of \(f(R)\) gravity, we derive the modified background and perturbation equations and implement the resulting cosmological scenario within the {MontePython}/{hi\_class} framework. A comprehensive Bayesian MCMC analysis is performed using combinations of Planck 2018 CMB data, CMB lensing, DESI DR2 BAO measurements, Cosmic Chronometers, and Pantheon supernova observations. Our results show that the interacting Hu--Sawicki scenario provides a noticeable improvement over both the standard \(Λ\)CDM cosmology and the non-interacting \(f(R)\) framework. In particular, the interacting model shifts the inferred Hubble constant toward larger values, yielding \(H_0 = 70.21 \pm 1.60~{\rm km~s^{-1}Mpc^{-1}}\), while simultaneously lowering the clustering amplitude to \(S_8 = 0.796 \pm 0.009\). Consequently, the residual tensions with SH0ES R22 and DES-Y6 are reduced to nearly the \(1σ\) level. From the statistical perspective, the interacting model provides the best overall fit according to the Akaike Information Criterion, with \(Δχ^2 \simeq -45\) relative to \(Λ\)CDM. The obtained neutrino mass constraints remain fully consistent with current cosmological bounds, with \(\sum m_ν< 0.122~{\rm eV}\). These results suggest that interacting modified-gravity scenarios offer a viable route to moderately easing both late-time tensions at once.

gr-qc↗
arXiv2026

Decoherence of ergotropy of a relativistic battery as a probe of motion-selected Unruh thermality in Minkowski spacetime

We put forward a physical model of a relativistic Unruh-DeWitt battery moving along a general accelerated trajectory, including a linear motion and a circular motion with a reflecting boundary. The maximal amount of quantum work extraction, defined as the ergotropy, serves as a witness to Unruh effect modified by motion trajectories. It is found out that for a very low Unruh temperature, linear motion yields a high amount of ergotropy, while for a high temperature, circular motion becomes optimal for estimating the Unruh effect. For a specific acceleration, the ergotropy is the same for two different trajectories. The behavior demonstrates that, in a certain condition, one can simulate the work extraction of the accelerated battery in a linear motion by exploring the battery in circular motion. The observed ergotropy for the thermality is closely related to quantum coherence affected by spacetime vacuum fluctuations. In the presence of a reflecting boundary plane, we study different ways for the dynamics of the ergotropy. When the battery moves near the boundary, the prominent oscillation of the ergotropy will happen and exhibit some large instantaneous peaks. The interesting phenomenon results from the protection of quantum coherence for the accelerated battery in the vicinity of the boundary. Far away from the boundary, the oscillation behavior can be suppressed and the ergotropy rapidly arrives at a steady value. By contrast, the circular motion contributes to prolonging the oscillation evolution. The asymptotic amount of the ergotropy can rise progressively up to a saturation value with increasing the distance from the circular trajectory to the boundary plane. From the perspective of energy transfer, optimized quantum work extraction for the accelerated battery moving along a selected motion with a boundary plane is advantageous for probing Unruh thermality.

gr-qc↗