Scalar-tensor theories of gravity from a thermodynamic viewpoint

Abstract In any diffeomorphism invariant theory of gravity, one can define a Noether charge arising from the invariance of the Lagrangian under diffeomorphisms. We have determined the Noether charge for scalar-tensor theories of gravity, in which case the gravity is mediated by the metric tensor as...

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Main Authors: Krishnakanta Bhattacharya, Sumanta Chakraborty
Format: Article
Language:English
Published: SpringerOpen 2025-01-01
Series:Journal of High Energy Physics
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Online Access:https://doi.org/10.1007/JHEP01(2025)037
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author Krishnakanta Bhattacharya
Sumanta Chakraborty
author_facet Krishnakanta Bhattacharya
Sumanta Chakraborty
author_sort Krishnakanta Bhattacharya
collection DOAJ
description Abstract In any diffeomorphism invariant theory of gravity, one can define a Noether charge arising from the invariance of the Lagrangian under diffeomorphisms. We have determined the Noether charge for scalar-tensor theories of gravity, in which case the gravity is mediated by the metric tensor as well as by a scalar degree of freedom. In particular, we demonstrate that the total Noether charge within an appropriate spatial volume can be related to the heat content of the boundary surface. For static spacetimes, in these theories, there exist an “equipartition” between properly defined bulk and surface degrees of freedom. While the dynamical evolution of spacetime in these theories of scalar-tensor gravity arises due to the departure from the equipartition regime. These results demonstrate that thermodynamical interpretations for gravitational theories transcend Einstein and Lovelock theories of gravity, holding true for theories with additional scalar degrees of freedom as well. Moreover, they hold in both the Jordan and the Einstein frames. However, it turns out that there are two dynamically equivalent representations of the scalar-tensor theory in the Jordan frame, differing by total derivatives in the action, which are thermodynamically inequivalent. This depicts the importance of having a thermodynamic description, which can be used in distinguishing various dynamically equivalent representations of gravity theories beyond Einstein.
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spelling doaj-art-3072e93151d748e68a9b9f0fe7306b6b2025-01-19T12:07:13ZengSpringerOpenJournal of High Energy Physics1029-84792025-01-012025112810.1007/JHEP01(2025)037Scalar-tensor theories of gravity from a thermodynamic viewpointKrishnakanta Bhattacharya0Sumanta Chakraborty1Department of General Science, BITS PilaniSchool of Physical Sciences, Indian Association for the Cultivation of ScienceAbstract In any diffeomorphism invariant theory of gravity, one can define a Noether charge arising from the invariance of the Lagrangian under diffeomorphisms. We have determined the Noether charge for scalar-tensor theories of gravity, in which case the gravity is mediated by the metric tensor as well as by a scalar degree of freedom. In particular, we demonstrate that the total Noether charge within an appropriate spatial volume can be related to the heat content of the boundary surface. For static spacetimes, in these theories, there exist an “equipartition” between properly defined bulk and surface degrees of freedom. While the dynamical evolution of spacetime in these theories of scalar-tensor gravity arises due to the departure from the equipartition regime. These results demonstrate that thermodynamical interpretations for gravitational theories transcend Einstein and Lovelock theories of gravity, holding true for theories with additional scalar degrees of freedom as well. Moreover, they hold in both the Jordan and the Einstein frames. However, it turns out that there are two dynamically equivalent representations of the scalar-tensor theory in the Jordan frame, differing by total derivatives in the action, which are thermodynamically inequivalent. This depicts the importance of having a thermodynamic description, which can be used in distinguishing various dynamically equivalent representations of gravity theories beyond Einstein.https://doi.org/10.1007/JHEP01(2025)037Black HolesClassical Theories of GravityBlack Holes in String Theory
spellingShingle Krishnakanta Bhattacharya
Sumanta Chakraborty
Scalar-tensor theories of gravity from a thermodynamic viewpoint
Journal of High Energy Physics
Black Holes
Classical Theories of Gravity
Black Holes in String Theory
title Scalar-tensor theories of gravity from a thermodynamic viewpoint
title_full Scalar-tensor theories of gravity from a thermodynamic viewpoint
title_fullStr Scalar-tensor theories of gravity from a thermodynamic viewpoint
title_full_unstemmed Scalar-tensor theories of gravity from a thermodynamic viewpoint
title_short Scalar-tensor theories of gravity from a thermodynamic viewpoint
title_sort scalar tensor theories of gravity from a thermodynamic viewpoint
topic Black Holes
Classical Theories of Gravity
Black Holes in String Theory
url https://doi.org/10.1007/JHEP01(2025)037
work_keys_str_mv AT krishnakantabhattacharya scalartensortheoriesofgravityfromathermodynamicviewpoint
AT sumantachakraborty scalartensortheoriesofgravityfromathermodynamicviewpoint