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.

FRW Cosmological Model with Modified Chaplygin Gas and Dynamical System

Abstract: The Friedmann-Robertson-Walker (FRW) model with dynamical Dark Energy (DE) in the form of modified Chaplygin gas (MCG) has been investigated. The evolution equations are reduced to an autonomous system on the two dimensional phase plane and it can be interpreted as the motion of the particle in an one dimensional potential. Also the dynamical system analysis has been extended to examine the critical points at infinity with will exist provided the equation of state parameter \(\omega<-\frac{1}{3}\). Finally, theoretical points are asymptotically stable or unstable.

Oscillatory Attractors: A New Cosmological Phase

Abstract: In expanding FRW spacetimes, it is usually the case that homogeneous scalar fields redshift and their amplitudes approach limiting values: Hubble friction usually ensures that the field relaxes to its minimum energy configuration, which is usually a static configuration. Here we discover a class of relativistic scalar field models in which the attractor behavior is the field oscillating indefinitely, with finite amplitude, in an expanding FRW spacetime, despite the presence of Hubble friction. This is an example of spontaneous breaking of time translation symmetry. We find that the effective equation of state of the field has average value $\langle w\rangle=-1$, implying that the field itself could drive an inflationary or dark energy dominated phase. This behavior is reminiscent of ghost condensate models, but in the new models, unlike in the ghost condensate models, the energy-momentum tensor is time dependent, so that these new models embody a more definitive breaking of time translation symmetry. We explore (quantum) fluctuations around the homogeneous background solution, and find that low $k$-modes can be stable, while high $k$-modes are typically unstable. We discuss possible interpretations and implications of that instability.

On Shear-free perturbations of f(R) gravity

Abstract: Recently it was shown that if the matter congruence of a general relativistic perfect fluid flow in an almost FLRW universe is shear-free, then it must be either expansion or rotation-free. Here we generalize this result for a general f(R) theory of gravity and show there exist scenarios where this result can be avoided. This suggests that there are situations where linearized forth-order gravity shares properties with Newtonian theory not valid in General Relativity.

f(R) gravities, Killing spinor equations, “BPS” domain walls and cosmology

Abstract: We derive the condition on f(R) gravities that admit Killing spinor equations and construct explicit such examples. The Killing spinor equations can be used to reduce the fourth-order differential equations of motion to the first order for both the domain wall and FLRW cosmological solutions. We obtain exact “BPS” domain walls that describe the smooth Randall-Sundrum II, AdS wormholes and the RG flow from IR to UV. We also obtain exact smooth cosmological solutions that describe the evolution from an inflationary starting point with a larger cosmological constant to an ever-expanding universe with a smaller cosmological constant. In addition, We find exact smooth solutions of pre-big bang models, bouncing or crunching universes. An important feature is that the scalar curvature R of all these metrics is varying rather than a constant. Another intriguing feature is that there are two different f(R) gravities that give rise to the same “BPS” solution. We also study linearized f(R) gravities in (A)dS vacua.