2,981 research outputs found
Cosmological Perturbations in Renormalization Group Derived Cosmologies
A linear cosmological perturbation theory of an almost homogeneous and
isotropic perfect fluid Universe with dynamically evolving Newton constant
and cosmological constant is presented. A gauge-invariant formalism
is developed by means of the covariant approach, and the acoustic propagation
equations governing the evolution of the comoving fractional spatial gradients
of the matter density, , and are thus obtained. Explicit solutions
are discussed in cosmologies where both and vary according to
renormalization group equations in the vicinity of a fixed point.Comment: 22 pages, revtex, subeqn.sty, to appear on IJMP
Quantum Gravity effects near the null black hole singularity
The structure of the Cauchy Horizon singularity of a black hole formed in a
generic collapse is studied by means of a renormalization group equation for
quantum gravity. It is shown that during the early evolution of the Cauchy
Horizon the increase of the mass function is damped when quantum fluctuations
of the metric are taken into account.Comment: 15 Pages, one figure. Minor changes in the presentation, to appear on
Phys.Rev.
Noether symmetry approach to scalar-field-dominated cosmology with dynamically evolving G and Lambda
This paper studies the cosmological equations for a scalar field Phi in the
framework of a quantum gravity modified Einstein--Hilbert Lagrangian where G
and Lambda are dynamical variables. It is possible to show that there exists a
Noether symmetry for the point Lagrangian describing this scheme in a FRW
universe. Our main result is that the Noether Symmetry Approach fixes both
Lambda = Lambda(G) and the potential V = V(Phi) of the scalar field. The method
does not lead, however, to easily solvable equations, by virtue of the higher
dimensionality of the reduced configuration space involved, the additional
variable being the running Newton coupling.Comment: 10 pages, Revtex
Towards Nonperturbative Renormalizability of Quantum Einstein Gravity
We summarize recent evidence supporting the conjecture that four-dimensional
Quantum Einstein Gravity (QEG) is nonperturbatively renormalizable along the
lines of Weinberg's asymptotic safety scenario. This would mean that QEG is
mathematically consistent and predictive even at arbitrarily small length
scales below the Planck length. For a truncated version of the exact flow
equation of the effective average action we establish the existence of a
non-Gaussian renormalization group fixed point which is suitable for the
construction of a nonperturbative infinite cutoff-limit. The cosmological
implications of this fixed point are discussed, and it is argued that QEG might
solve the horizon and flatness problem of standard cosmology without an
inflationary period.Comment: 10 pages, latex, 1 figur
The role of Background Independence for Asymptotic Safety in Quantum Einstein Gravity
We discuss various basic conceptual issues related to coarse graining flows
in quantum gravity. In particular the requirement of background independence is
shown to lead to renormalization group (RG) flows which are significantly
different from their analogs on a rigid background spacetime. The importance of
these findings for the asymptotic safety approach to Quantum Einstein Gravity
(QEG) is demonstrated in a simplified setting where only the conformal factor
is quantized. We identify background independence as a (the ?) key prerequisite
for the existence of a non-Gaussian RG fixed point and the renormalizability of
QEG.Comment: 2 figures. Talk given by M.R. at the WE-Heraeus-Seminar "Quantum
Gravity: Challenges and Perspectives", Bad Honnef, April 14-16, 2008; to
appear in General Relativity and Gravitatio
An effective action for asymptotically safe gravity
Asymptotically safe theories of gravitation have received great attention in
recent times. In this framework an effective action embodying the basic
features of the renormalized flow around the non-gaussian fixed point is
derived and its implications for the early universe are discussed. In
particular, a "landscape" of a countably infinite number of cosmological
inflationary solutions characterized by an unstable de Sitter phase lasting for
a large enough number of e-folds is found.Comment: 5 pages, to appear as a Rapid Communication in Physical Review
A Class of Renormalization Group Invariant Scalar Field Cosmologies
We present a class of scalar field cosmologies with a dynamically evolving
Newton parameter and cosmological term . In particular, we discuss
a class of solutions which are consistent with a renormalization group scaling
for and near a fixed point. Moreover, we propose a modified
action for gravity which includes the effective running of and
near the fixed point. A proper understanding of the associated variational
problem is obtained upon considering the four-dimensional gradient of the
Newton parameter.Comment: 10 pages, RevTex4, no figures, to appear on GR
Running Gauge Coupling in Asymptotically Safe Quantum Gravity
We investigate the non-perturbative renormalization group behavior of the
gauge coupling constant using a truncated form of the functional flow equation
for the effective average action of the Yang-Mills-gravity system. We find a
non-zero quantum gravity correction to the standard Yang-Mills beta function
which has the same sign as the gauge boson contribution. Our results fit into
the picture according to which Quantum Einstein Gravity (QEG) is asymptotically
safe, with a vanishing gauge coupling constant at the non-trivial fixed point.Comment: 27 page
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