N
-point functions of strongly coupled fluids dual to generalized higher-derivative theories of gravity

In this work, we present some cosmologically relevant solutions using the spatially flat Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime in metric f ( R ) gravity where the form of the gravitational Lagrangian is given by 1 α e α R . In the low curvature limit this theory reduces to ordinary Einstein-Hilbert Lagrangian together with a cosmological constant term. Precisely because of this cosmological constant term this theory of gravity is able to support nonsingular bouncing solutions in both matter and vacuum background. Since for this theory of gravity f ′ and f ″ is always positive, this is free of both ghost instability and tachyonic instability. Moreover, because of the existence of the cosmological constant term, this gravity theory also admits a de-Sitter solution. Lastly we hint towards the possibility of a new type of cosmological solution that is possible only in higher derivative theories of gravity like this one.

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Selected topics in scalar–tensor theories and beyond

International Journal of Modern Physics D ◽

10.1142/s021827181930012x ◽

2019 ◽

Vol 28 (07) ◽

pp. 1930012 ◽

Cited By ~ 23

Author(s):

Israel Quiros

Keyword(s):

Theoretical Perspective ◽

Scalar Fields ◽

Theory Of Relativity ◽

Postgraduate Students ◽

Higher Derivative ◽

Long Time ◽

Theories Of Gravity ◽

Weyl Symmetry ◽

Stability Issues ◽

First Time

Scalar fields have played an important role in the development of the fundamental theories of physics as well as in other branches of physics such as gravitation and cosmology. For a long time, these escaped detection until 2012 when the Higgs boson was observed for the first time. Since then, alternatives to the general theory of relativity like the Brans–Dicke (BD) theory, scalar–tensor theories of gravity and their higher derivative generalizations — collectively known as Horndeski theories — have acquired renewed interest. In the present review, we discuss several selected topics regarding these theories, mainly from the theoretical perspective but with due mention of the observational aspect. Among the topics covered in this review, we pay special attention to the following: (1) the asymptotic dynamics of cosmological models based on the BD, scalar–tensor and Horndeski theories, (2) inflationary models, extended quintessence and the Galileons, with emphasis in causality and stability issues, (3) the chameleon and Vainshtein screening mechanisms that may allow the elusive scalar field to evade the tight observational constraints implied by the solar system experiments, (4) the conformal frames conundrum with a brief discussion on the disformal transformations and (5) the role of Weyl symmetry and scale invariance in the gravitation theories. The review is aimed at specialists as well as at nonspecialists in the subject, including postgraduate students.

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Higher-derivative f(R,□R,T) theories of gravity

International Journal of Modern Physics D ◽

10.1142/s0218271817500249 ◽

2017 ◽

Vol 26 (03) ◽

pp. 1750024 ◽

Cited By ~ 13

Author(s):

M. J. S. Houndjo ◽

M. E. Rodrigues ◽

N. S. Mazhari ◽

D. Momeni ◽

R. Myrzakulov

Keyword(s):

Modified Gravity ◽

Equations Of Motion ◽

Momentum Tensor ◽

De Sitter ◽

Higher Derivative ◽

Stress Energy ◽

Derivative Term ◽

Theories Of Gravity ◽

Tensor Formula ◽

Stress Energy Momentum Tensor

In literature, there is a model of modified gravity in which the matter Lagrangian is coupled to the geometry via trace of the stress–energy–momentum tensor [Formula: see text]. This type of modified gravity is denoted [Formula: see text] in which [Formula: see text] is Ricci scalar [Formula: see text]. We extend manifestly this model to include the higher derivative term [Formula: see text]. We derived equations of motion (EOM) for the model by starting from the basic variational principle. Later we investigate FLRW cosmology for our model. We show that de Sitter (dS) solution is unstable for a generic type of [Formula: see text] model. Furthermore we investigate an inflationary scenario based on this model. A graceful exit from inflation is guaranteed in this type of modified gravity.

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ASYMPTOTIC FLATNESS AND BIRKHOFF'S THEOREM IN HIGHER-DERIVATIVE THEORIES OF GRAVITY

The Eleventh Marcel Grossmann Meeting ◽

10.1142/9789812834300_0117 ◽

2008 ◽

Cited By ~ 1

Author(s):

T. CLIFTON

Keyword(s):

Asymptotic Flatness ◽

Higher Derivative ◽

Theories Of Gravity ◽

Birkhoff's Theorem ◽

Birkhoff’S Theorem

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Generalised boundary terms for higher derivative theories of gravity

Journal of High Energy Physics ◽

10.1007/jhep08(2016)144 ◽

2016 ◽

Vol 2016 (8) ◽

Cited By ~ 12

Author(s):

Ali Teimouri ◽

Spyridon Talaganis ◽

James Edholm ◽

Anupam Mazumdar

Keyword(s):

Boundary Terms ◽

Higher Derivative ◽

Theories Of Gravity

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Backreaction effects due to matter coupled higher derivative gravity

Modern Physics Letters A ◽

10.1142/s0217732315500650 ◽

2015 ◽

Vol 30 (16) ◽

pp. 1550065 ◽

Cited By ~ 2

Author(s):

Lata Kh Joshi ◽

P. Ramadevi

Keyword(s):

Shear Viscosity ◽

Quark Gluon Plasma ◽

Transport Coefficients ◽

Gluon Plasma ◽

Entropy Density ◽

Flow Measurements ◽

Strongly Coupled ◽

Higher Derivative ◽

Scalar Matter ◽

Dimensional Spacetime

AdS-hydrodynamics has proven to be a useful tool for obtaining transport coefficients observed in the collective flow of strongly coupled fluids like quark gluon plasma (QGP). Particularly, the ratio of shear viscosity to entropy density η/s obtained from elliptic flow measurements can be matched with the computation done in the dual gravity theory. The experimentally observed temperature dependence of η/s requires the study of scalar matter coupled AdS gravity including higher derivative curvature corrections. We obtain the backreaction to the metric for such a matter coupled AdS gravity in D-dimensional spacetime due to the higher derivative curvature corrections. Then, we present the backreaction corrections to shear viscosity η and entropy density s.

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THE SHEAR VISCOSITY TO ENTROPY RATIO: A STATUS REPORT

Modern Physics Letters B ◽

10.1142/s0217984911027315 ◽

2011 ◽

Vol 25 (23) ◽

pp. 1867-1888 ◽

Cited By ~ 89

Author(s):

SERA CREMONINI

Keyword(s):

Lower Bound ◽

Shear Viscosity ◽

Entropy Density ◽

Status Report ◽

Strongly Coupled ◽

Higher Derivative ◽

Universal Ratio ◽

Gauge Gravity ◽

Gravity Duality ◽

Insight Into

This review highlights some of the lessons that the holographic gauge/gravity duality has taught us regarding the behavior of the shear viscosity to entropy density in strongly coupled field theories. The viscosity to entropy ratio has been shown to take on a very simple universal value in all gauge theories with an Einstein gravity dual. Here we describe the origin of this universal ratio, and focus on how it is modified by generic higher derivative corrections corresponding to curvature corrections on the gravity side of the duality. In particular, certain curvature corrections are known to push the viscosity to entropy ratio below its universal value. This disproves a longstanding conjecture that such a universal value represents a strict lower bound for any fluid in nature. We discuss the main developments that have led to insight into the violation of this bound, and consider whether the consistency of the theory is responsible for setting a fundamental lower bound on the viscosity to entropy ratio.

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An entropy current and the second law in higher derivative theories of gravity

Journal of High Energy Physics ◽

10.1007/jhep09(2021)169 ◽

2021 ◽

Vol 2021 (9) ◽

Author(s):

Sayantani Bhattacharyya ◽

Prateksh Dhivakar ◽

Anirban Dinda ◽

Nilay Kundu ◽

Milan Patra ◽

...

Keyword(s):

Black Hole ◽

Equilibrium Configuration ◽

Second Law Of Thermodynamics ◽

Alternative Proof ◽

Second Law ◽

Higher Derivative ◽

Entropy Current ◽

Theories Of Gravity ◽

Dynamical Fluctuations ◽

Set Up

Abstract We construct a proof of the second law of thermodynamics in an arbitrary diffeomorphism invariant theory of gravity working within the approximation of linearized dynamical fluctuations around stationary black holes. We achieve this by establishing the existence of an entropy current defined on the horizon of the dynamically perturbed black hole in such theories. By construction, this entropy current has non-negative divergence, suggestive of a mechanism for the dynamical black hole to approach a final equilibrium configuration via entropy production as well as the spatial flow of it on the null horizon. This enables us to argue for the second law in its strongest possible form, which has a manifest locality at each space-time point. We explicitly check that the form of the entropy current that we construct in this paper exactly matches with previously reported expressions computed considering specific four derivative theories of higher curvature gravity. Using the same set up we also provide an alternative proof of the physical process version of the first law applicable to arbitrary higher derivative theories of gravity.

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