2,340 research outputs found
Inflation in asymptotically safe f(R) theory
We discuss the existence of inflationary solutions in a class of
renormalization group improved polynomial f(R) theories, which have been
studied recently in the context of the asymptotic safety scenario for quantum
gravity. These theories seem to possess a nontrivial ultraviolet fixed point,
where the dimensionful couplings scale according to their canonical
dimensionality. Assuming that the cutoff is proportional to the Hubble
parameter, we obtain modified Friedmann equations which admit both power law
and exponential solutions. We establish that for sufficiently high order
polynomial the solutions are reliable, in the sense that considering still
higher order polynomials is very unlikely to change the solution.Comment: Presented at 14th Conference on Recent Developments in Gravity: NEB
14, Ioannina, Greece, 8-11 Jun 201
Dynamical System Analysis of Cosmologies with Running Cosmological Constant from Quantum Einstein Gravity
We discuss a mechanism that induces a time-dependent vacuum energy on
cosmological scales. It is based on the instability induced renormalization
triggered by the low energy quantum fluctuations in a Universe with a positive
cosmological constant. We employ the dynamical systems approach to study the
qualitative behavior of Friedmann-Robertson-Walker cosmologies where the
cosmological constant is dynamically evolving according with this
nonperturbative scaling at low energies. It will be shown that it is possible
to realize a "two regimes" dark energy phases, where an unstable early phase of
power-law evolution of the scale factor is followed by an accelerated expansion
era at late times.Comment: 26 pages, 4 figures. To appear in New Journal of Physic
Improved Action Functionals in Non-Perturbative Quantum Gravity
Models of gravity with variable G and Lambda have acquired greater relevance
after the recent evidence in favour of the Einstein theory being
non-perturbatively renormalizable in the Weinberg sense. The present paper
builds a modified Arnowitt-Deser-Misner (ADM) action functional for such models
which leads to a power-law growth of the scale factor for pure gravity and for
a massless phi**4 theory in a Universe with Robertson-Walker symmetry, in
agreement with the recently developed fixed-point cosmology. Interestingly, the
renormalization-group flow at the fixed point is found to be compatible with a
Lagrangian description of the running quantities G and Lambda.Comment: Latex file. Record without file already exists on SLAC-SPIRES, and
hence that record and the one for the present arxiv submission should become
one record onl
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
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
Flow Equations for U_k and Z_k
By considering the gradient expansion for the wilsonian effective action S_k
of a single component scalar field theory truncated to the first two terms, the
potential U_k and the kinetic term Z_k, I show that the recent claim that
different expansion of the fluctuation determinant give rise to different
renormalization group equations for Z_k is incorrect. The correct procedure to
derive this equation is presented and the set of coupled differential equations
for U_k and Z_k is definitely established.Comment: 5 page
Recurrence and algorithmic information
In this paper we initiate a somewhat detailed investigation of the
relationships between quantitative recurrence indicators and algorithmic
complexity of orbits in weakly chaotic dynamical systems. We mainly focus on
examples.Comment: 26 pages, no figure
Spacetime Structure of an Evaporating Black Hole in Quantum Gravity
The impact of the leading quantum gravity effects on the dynamics of the
Hawking evaporation process of a black hole is investigated. Its spacetime
structure is described by a renormalization group improved Vaidya metric. Its
event horizon, apparent horizon, and timelike limit surface are obtained taking
the scale dependence of Newton's constant into account. The emergence of a
quantum ergosphere is discussed. The final state of the evaporation process is
a cold, Planck size remnant.Comment: 23 pages, BibTeX, revtex4, 7 figure
Primordial Entropy Production and Lambda-driven Inflation from Quantum Einstein Gravity
We review recent work on renormalization group (RG) improved cosmologies
based upon a RG trajectory of Quantum Einstein Gravity (QEG) with realistic
parameter values. In particular we argue that QEG effects can account for the
entire entropy of the present Universe in the massless sector and give rise to
a phase of inflationary expansion. This phase is a pure quantum effect and
requires no classical inflaton field.Comment: 12 pages, 4 figures, IGCG-07 Pun
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