Evolution of cosmological perturbations in a renormalization-group-driven inflationary scenario

Abstract

A gauge-invariant, linear cosmological perturbation theory of an almost homogeneous and isotropic universe with dynamically evolving Newton constant G and cosmological constant Λ is presented. The equations governing the evolution of the comoving fractional spatial gradients of the matter density, G and Λ are thus obtained. Explicit solutions are discussed in cosmologies, featuring an accelerated expansion, where both G and Λ vary according to renormalization group equations in the vicinity of an ultraviolet fixed point. Finally, a similar analysis is carried out in the late universe regime described by the part of the renormalization group trajectory close to the gaussian fixed point.

Black Hole Thermodynamics Under the Microscope

“…For asymptotically safe gravity, we find that the entropy at fixed horizon area increases due to quantum corrections, leading to an entropy of the order of a few in the limit where the black hole becomes critical. The thermodynamical definition for entropy agrees with the statistical definition of entropy (71) for all RG scales and black hole masses, which serves as a consistency check. On the other hand, deriving the entropy using Clausius's rule leads to an additional term logarithmic in the area.…”

“…A gravitational fixed point is also consistent with results from holography [60,61], conformal reductions [62], Lorentzian signature [63], and minisuperspace approximations [64]. Phenomenological implications of a gravitational fixed point have been explored for black holes [25][26][27][28][29]31,32], cosmology [65][66][67][68][69][70][71][72][73][74][75][76][77], and particle physics [78][79][80][81][82]. Nonlocal low-energy corrections to the gravitational effective action have equally been addressed [83,84].…”

Asymptotically safe gravity as a scalar-tensor theory and its cosmological implications

“…(35), (36), (38), and (41), we can study the cosmological evolution of the universe once suitable initial conditions are chosen. Relevant topics were discussed in the literature; however, in the current paper, our main purpose is to extend the AS cosmology to the perturbative level.…”

“…Therefore, we expect the cutoff p to be both time and space dependent when cosmological perturbations are considered. See also [38] for an application of the spacedependent cutoff scale to cosmological perturbation theory. From the above generic analysis of cosmological perturbations, this feature is reflected in the perturbed mode pðt;xÞ.…”

On the renormalization group perspective of α-attractors

“…In usual flat space-time quantum field theory µ is usually the external momenta of the interacting particles. In the case of cosmology (and inflation) one can relate µ to the Hubble parameter (or a function of Hubble scale) [46][47][48]. Under such a identification of µ, it is worth investigating the effect of the running of α-parameter on the cosmic evolution.…”