Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userHorizon thermodynamics in $f(R,R^{mu u}R_{mu u})$ theory
76
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We investigate whether the new horizon first law still holds in $f(R,R^{mu u}R_{mu u})$ theory. For this complicated theory, we first determine the entropy of black hole via Wald method, then we derive the energy by using the new horizon first law, the degenerate Legendre transformation, and the gravitational field equations. For application, we consider the quadratic-curvature gravity and firstly calculate the entropy and the energy for a static spherically symmetric black hole, which reduces to the results obtained in literatures for a Schwarzschild-(A)dS black hole.
rate research
Read More
Dynamical behavior and future singularities of $f(R, T,R_{mu u}T^{mu u})$ gravitational theory are investigated. This gravitational model is a more complete form of the $f(R,T)$ gravity which can offer new dynamics for the universe. We investigate this gravitational theory for the case $f = R + alpha R_{mu u}T^{mu u}$ using the method of autonomous dynamical systems and by assuming an interaction between matter and dark energy. The fixed points are identified and the results are consistent with standard cosmology and show that for small $alpha$, the radiation dominated era is an unstable fixed point of the theory and the universe will continue its procedure toward matter era which is a saddle point of the theory and allows the evolution to dark energy dominated universe. Finally the dark energy dominated epoch is a stable fixed point and will be the late time attractor for the universe. We also consider future singularities for the two $f = R + alpha R_{mu u}T^{mu u}$ and $f = R +alpha RR_{mu u}T^{mu u}$ cases and for $w = 0,dfrac{1}{3},1$ and $-1$. Our results show that for the case of $f = R + alpha R_{mu u}T^{mu u}$, the future singularities of the universe will happen in the same condition as do for the Einstein-Hilbert FRW universe. However, a new type of singularity is obtained for $f = R +alpha RR_{mu u}T^{mu u}$ that is captured by $trightarrow t_s; a rightarrow a_s; rhorightarrow infty;$ and $ |p| rightarrow 0$.
We compute the one-loop divergences in a theory of gravity with Lagrangian of the general form $f(R,R_{mu u}R^{mu u})$, on an Einstein background. We also establish that the one-loop effective action is invariant under a duality that consists of changing certain parameters in the relation between the metric and the quantum fluctuation field. Finally, we discuss the unimodular version of such a theory and establish its equivalence at one-loop order with the general case.
We investigate whether the new horizon first law proposed recently still work in $f(R)$ theory. We identify the entropy and the energy of black hole as quantities proportional to the corresponding value of integration, supported by the fact that the new horizon first law holds true as a consequence of equations of motion in $f(R)$ theories. The formulas for the entropy and energy of black hole found here are in agreement with the results obtained in literatures. For applications, some nontrivial black hole solutions in $f(R)$ theories have been considered, the entropies and the energies of black holes in these models are firstly computed, which may be useful for future researches.
We propose a new model of gravity where the Ricci scalar (R) in Einstein-Hilbert action is replaced by an arbitrary function of R and of the norm of energy-momentum tensor i.e., $f(R,T_{mu u}T^{mu u})$. Field equations are derived in the metric formalism. We find that the equation of motion of massive test particles is non-geodesic and these test particles are acted upon by a force which is orthogonal to the four-velocity of the particles. We also find the Newtonian limit of the model to calculate the extra acceleration which can affect the perihelion of Mercury. There is a deviation from the general relativistic(GR) result unless the energy density of fluid is constant. Arranging $alpha$ parameter gives an opportunity to cure the inconsistency between the observational values for the abundance of light elements and the standard Big Bang Nucleosynthesis results. Even the dust dominated universe undergoes an accelerated expansion without using a cosmological constant in Model II. With this specific choice of $f(R,T_{mu u}T^{mu u})$, we get the a Cardassian-like expansion.
In all $n(ge 3)$-dimensional gravitation theories whose Lagrangians are functions of the Riemann tensor and metric, we prove that static solutions are absent unless the total energy-momentum tensor for matter fields is of type I in the Hawking-Ellis classification. In other words, there is no hypersurface-orthogonal timelike Killing vector in a spacetime region with an energy-momentum tensor of type II, III, or IV. This asserts that ultra-dense regions with a semiclassical type-IV matter field cannot be static even with higher-curvature correction terms.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
