scholarly journals Physical Hamiltonian for mimetic gravity

2020 ◽  
Vol 102 (10) ◽  
Author(s):  
Marco de Cesare ◽  
Viqar Husain
Keyword(s):  
Mimetic Gravity

scholarly journals Reconstruction of Mimetic Gravity in a Non-Singular Bouncing Universe from Quantum Gravity

Universe ◽  
2019 ◽  
Vol 5 (5) ◽  
pp. 107 ◽  
Author(s):  
Marco de Cesare
Keyword(s):  
Field Theory ◽  
Quantum Gravity ◽  
Effective Field ◽  
Time Varying ◽  
Reconstruction Procedure ◽  
Cosmological Background ◽  
Bouncing Universe ◽  
Physical Information ◽  
Group Field Theory ◽  
Mimetic Gravity

We illustrate a general reconstruction procedure for mimetic gravity. Focusing on a bouncing cosmological background, we derive general properties that must be satisfied by the function f(□ϕ) implementing the limiting curvature hypothesis. We show how relevant physical information can be extracted from power-law expansions of f in different regimes, corresponding e.g., to the very early universe or to late times. Our results are then applied to two specific models reproducing the cosmological background dynamics obtained in group field theory and in loop quantum cosmology, and we discuss the possibility of using this framework as providing an effective field theory description of quantum gravity. We study the evolution of anisotropies near the bounce, and discuss instabilities of scalar perturbations. Furthermore, we provide two equivalent formulations of mimetic gravity: one in terms of an effective fluid with exotic properties, the other featuring two distinct time-varying gravitational “constants” in the cosmological equations.

Braneworld mimetic f(R) gravity

2019 ◽  
Vol 16 (03) ◽  
pp. 1950042 ◽  
Author(s):  
Kourosh Nozari ◽  
Naser Sadeghnezhad
Keyword(s):  
Scalar Field ◽  
Recent Work ◽  
Friedmann Equation ◽  
Equation Of Motion ◽  
Einstein’S Field Equations ◽  
Field Equations ◽  
Einstein's Field Equations ◽  
Bulk Scalar Field ◽  
Codazzi Equations ◽  
Mimetic Gravity

Following our recent work on braneworld mimetic gravity, in this paper, we study an extension of braneworld mimetic gravity to the case that the gravitational sector on the brane is modified in the spirit of [Formula: see text] theories. We assume the physical 5D bulk metric in the Randall–Sundrum II braneworld scenario consists of a 5D scalar field (which mimics the dark sectors on the brane) and an auxiliary 5D metric. We find the 5D Einstein’s field equations and the 5D equation of motion of the bulk scalar field in this setup. By using the Gauss–Codazzi equations, we obtain the induced Einstein’s field equations on the brane. Finally, by adopting the FRW background, we find the Friedmann equation on the brane in this [Formula: see text] mimetic braneworld setup.

scholarly journals Energy–Momentum Pseudotensor and Superpotential for Generally Covariant Theories of Gravity of General Form

Universe ◽  
2020 ◽  
Vol 6 (10) ◽  
pp. 173
Author(s):  
Roman Ilin ◽  
Sergey Paston
Keyword(s):  
General Relativity ◽  
Conservation Laws ◽  
Wide Class ◽  
Equations Of Motion ◽  
General Covariance ◽  
Independent Variables ◽  
Theories Of Gravity ◽  
Generally Covariant ◽  
Derivatives Of ◽  
Mimetic Gravity

The current paper is devoted to the investigation of the general form of the energy–momentum pseudotensor (pEMT) and the corresponding superpotential for the wide class of theories. The only requirement for such a theory is the general covariance of the action without any restrictions on the order of derivatives of the independent variables in it or their transformation laws. As a result of the generalized Noether procedure, we obtain a recurrent chain of the equations, which allows one to express canonical pEMT as a divergence of the superpotential. The explicit expression for this superpotential is also given. We discuss the structure of the obtained expressions and the conditions for the derived pEMT conservation laws to be satisfied independently (fully or partially) by the equations of motion. Deformations of the superpotential form for theories with a change in the independent variables in action are also considered. We apply these results to some interesting particular cases: general relativity and its modifications, particularly mimetic gravity and Regge–Teitelboim embedding gravity.

scholarly journals Nonconservative traceless type gravity

2019 ◽  
Vol 28 (15) ◽  
pp. 1950175 ◽  
Author(s):  
Mahamadou Daouda ◽  
J. C. Fabris ◽  
A. M. Oliveira ◽  
F. Smirnov ◽  
H. E. S. Velten
Keyword(s):  
Cosmological Constant ◽  
Type Theory ◽  
Energy Momentum Tensor ◽  
Coupling Parameter ◽  
Momentum Tensor ◽  
Gravity Theory ◽  
Field Equations ◽  
Cosmological Constant Problem ◽  
Interesting Approach ◽  
Mimetic Gravity

Extensions of the gravity theory in order to obtain traceless field equations have been widely considered in the literature. The leading example of such class of theories is the unimodular gravity, but there are other possibilities like the mimetic gravity and the Rastall gravity with a coupling parameter [Formula: see text]. The unimodular gravity proposal is a very interesting approach in order to address the cosmological constant problem. When coupled to matter, such theories may imply that the energy–momentum tensor is not divergence free anymore. In this paper, a unimodular type theory will be developed by evading the conservation [Formula: see text]. The cosmological consequences of the later, both at background as well as for scalar and tensor perturbations, are explored. Possible further extensions of this approach are discussed as well as its connection with the traditional unimodular gravity.

scholarly journals Mimetic gravity as DHOST theories

2019 ◽  
Vol 2019 (02) ◽  
pp. 036-036 ◽  
Author(s):  
David Langlois ◽  
Michele Mancarella ◽  
Karim Noui ◽  
Filippo Vernizzi
Keyword(s):  
Mimetic Gravity

Thermodynamics of apparent horizon in mimetic cosmology

2019 ◽  
Vol 28 (03) ◽  
pp. 1950057 ◽  
Author(s):  
Ahmad Sheykhi
Keyword(s):  
Apparent Horizon ◽  
Local Equilibrium ◽  
Second Law Of Thermodynamics ◽  
High Energy ◽  
Frw Universe ◽  
Generalized Second Law ◽  
Friedmann Equations ◽  
New Perspective ◽  
Friedmann Robertson Walker ◽  
Mimetic Gravity

A new perspective toward Einstein’s theory of general relativity, called mimetic gravity, was suggested in [A. H. Chamseddine and V. Mukhanov, J. High Energy Phys. 1311 (2013) 135] by isolating the conformal degree of freedom in a covariant fashion through a re-parametrization of the physical metric in terms of an auxiliary metric and a mimetic field. In this paper, we first derive the Friedmann equations of the Friedmann–Robertson–Walker (FRW) universe with any spatial curvature in mimetic gravity. Then, we disclose that one can always rewrite the Friedmann equations of mimetic cosmology in the form of the first law of thermodynamics, [Formula: see text], on the apparent horizon. We confirm that the entropy associated with the apparent horizon in mimetic cosmology still obeys the area law of entropy which is useful in studying the thermodynamical properties of the black holes in mimetic gravity. We also examine the time evolution of the total entropy in mimetic cosmology and show that, with the local equilibrium assumption, the generalized second law of thermodynamics is fulfilled in a region enclosed by the apparent horizon. Our study further supports the viability of the mimetic gravity from a thermodynamic viewpoint and provides a strong consistency check of this model.

scholarly journals Hamiltonian analysis of Mimetic gravity with higher derivatives

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Yunlong Zheng
Keyword(s):  
Hamiltonian Formalism ◽  
Ricci Scalar ◽  
Gravity Models ◽  
Jordan Frame ◽  
Cosmological Perturbation ◽  
Unitary Gauge ◽  
Dirac Matrix ◽  
Higher Derivatives ◽  
Mimetic Gravity ◽  
Hamiltonian Analysis

Abstract Two types of mimetic gravity models with higher derivatives of the mimetic field are analyzed in the Hamiltonian formalism. For the first type of mimetic gravity, the Ricci scalar only couples to the mimetic field and we demonstrate the number of degrees of freedom (DOFs) is three. Then in both Einstein frame and Jordan frame, we perform the Hamiltonian analysis for the extended mimetic gravity with higher derivatives directly coupled to the Ricci scalar. We show that different from previous studies working at the cosmological perturbation level, where only three propagating DOFs show up, this generalized mimetic model, in general, has four DOFs. To understand this discrepancy, we consider the unitary gauge and find out that the number of DOFs reduces to three. We conclude that the reason why this system looks peculiar is that the Dirac matrix of all secondary constraints becomes singular in the unitary gauge, resulting in extra secondary constraints and thus reducing the number of DOFs. Furthermore, we give a simple example of a dynamic system to illustrate how gauge choice can affect the number of secondary constraints as well as the DOFs when the rank of the Dirac matrix is gauge dependent.

Spherically symmetric black hole solution in mimetic gravity and anti-evaporation

2018 ◽  
Vol 15 (09) ◽  
pp. 1850154 ◽  
Author(s):  
G. G. L. Nashed
Keyword(s):  
Black Hole ◽  
Black Hole Solution ◽  
Spherically Symmetric ◽  
Mimetic Theory ◽  
Event Horizons ◽  
Flat Spacetime ◽  
Symmetric Black Hole ◽  
The Stability ◽  
Mimetic Gravity ◽  
Black Hole Solutions

In this paper, we study the mimetic theory and derive a new spherically symmetric black hole solution. The asymptotic behavior of this solution behaves as a flat spacetime. This black hole is characterized by the fact that it has different components of [Formula: see text] and [Formula: see text]. Nevertheless, both of these components have a coinciding Killing and event horizons. Furthermore, this black hole has curvature singularities which are stronger than those of the known black hole solutions in general relativity. This feature can be shown by calculating some invariants of curvature. We study the stability of the perturbation and the related anti-evaporation of the Nariai spacetime.

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