Friedmann–Lemaître–Robertson–Walker metric

About: Friedmann–Lemaître–Robertson–Walker metric is a research topic. Over the lifetime, 4113 publications have been published within this topic receiving 87752 citations. The topic is also known as: FLRW metric.

Cosmological perturbations in massive gravity with doubly coupled matter

Abstract: We investigate the cosmological perturbations around FLRW solutions to non- linear massive gravity with a new effective coupling to matter proposed recently. Unlike the case with minimal matter coupling, all five degrees of freedom in the gravity sector propagate on generic self-accelerating FLRW backgrounds. We study the stability of the cosmological solutions and put constraints on the parameters of the theory by demanding the correct sign for the kinetic terms for scalar, vector and tensor perturbations.

Generalized second law of thermodynamics for FRW cosmology with logarithmic correction

Abstract: In the previous analyses in the literature about the generalized second law (GSL) in an accelerated expanding universe the usual relation for the entropy, i.e. , was used for the cosmological horizon entropy. But this entropy relation may be modified due to thermal and quantum fluctuations or corrections motivated by loop quantum gravity giving rise to S=A/4+πα ln(A/4)+γ, where α and γ are some constants whose the values are still in debate in the literature. Our aim is to study the constraints that GSL puts on these parameters. Besides, we investigate the conditions that the presence of such modified terms in the entropy puts on other physical parameters the system such as the temperature of dark energy via requiring the validity of GSL. In our study we consider a spatially flat Friedman-Robertson-Walker universe and assume that it is composed of several interacting components (including dark energy). The model is investigated in the context of thermal equilibrium and non-equilibrium situations. We show that in a (super) accelerated universe the GSL is valid whenever α ( 0 leading to a (negative) positive contribution from logarithmic correction to the entropy. In the case of super acceleration the temperature of the dark energy is obtained to be less than or equal to the Hawking temperature.

Jerk, snap, and the cosmological equation of state

Abstract: Taylor expanding the cosmological equation of state around the current epoch is the simplest model one can consider that does not make any a priori restrictions on the nature of the cosmological fluid. Most popular cosmological models attempt to be ``predictive'', in the sense that once somea priori equation of state is chosen the Friedmann equations are used to determine the evolution of the FRW scale factor a(t). In contrast, a retrodictive approach might usefully take observational dataconcerning the scale factor, and use the Friedmann equations to infer an observed cosmological equation of state. In particular, the value and derivatives of the scale factor determined at the current epoch place constraints on the value and derivatives of the cosmological equation of state at the current epoch. Determining the first three Taylor coefficients of the equation of state at the current epoch requires a measurement of the deceleration, jerk, and snap -- the second, third, and fourth derivatives of the scale factor with respect to time. Higher-order Taylor coefficients in the equation of state are related to higher-order time derivatives of the scale factor. Since the jerk and snap are rather difficult to measure, being related to the third and fourth terms in the Taylor series expansion of the Hubble law, it becomes clear why direct observational constraints on the cosmological equation of state are so relatively weak; and are likely to remain weak for the foreseeable future.

Cosmic acceleration and crossing of w = −1 barrier in non-local Cubic Superstring Field Theory model

Abstract: We show that the rolling of the Cubic Superstring Field Theory (CSSFT) non-local tachyon in the FRW Universe leads to a cosmic acceleration with a periodic crossing of the w = −1 barrier at large time. An asymptotic solution for the tachyon field and Hubble parameter is constructed explicitly linearizing non-local equations of motion. For a small Hubble parameter a period of oscillations is a number entirely determined by parameters of the CSSFT action.

AdS/CFT CORRESPONDENCE, CONFORMAL ANOMALY AND QUANTUM CORRECTED ENTROPY BOUNDS

Abstract: The role of conformal anomaly in AdS/CFT and related issues is clarified. The comparison of holographic and QFT conformal anomalies (with the account of brane quantum gravity contribution) indicates the possibility for brane quantum gravity to occur within the AdS/CFT setup. Three-dimensional quantum induced inflationary (or hyperbolic) brane-world is shown to be realized in the frames of AdS3/CFT2 correspondence where the role of 2d brane cosmological constant is played by effective tension due to two-dimensional conformal anomaly. The dynamical equations to describe 4d FRW universe with the account of quantum effects produced by conformal anomaly are obtained. The quantum corrected energy, pressure and entropy are found. The dynamical evolution of entropy bounds in the inflationary universe is estimated and its comparison with quantum corrected entropy is done. It is demonstrated that entropy bounds for quantum corrected entropy are getting the approximate ones and occur for some limited periods of evolution of the inflationary universe.