139 research outputs found
Ultraviolet properties of f(R)-Gravity
We discuss the existence and properties of a nontrivial fixed point in
f(R)-gravity, where f is a polynomial of order up to six. Within this
seven-parameter class of theories, the fixed point has three
ultraviolet-attractive and four ultraviolet-repulsive directions; this brings
further support to the hypothesis that gravity is nonperturbatively
renormalizabile.Comment: 4 page
Fluid Membranes and 2d Quantum Gravity
We study the RG flow of two dimensional (fluid) membranes embedded in
Euclidean D-dimensional space using functional RG methods based on the
effective average action. By considering a truncation ansatz for the effective
average action with both extrinsic and intrinsic curvature terms we derive a
system of beta functions for the running surface tension, bending rigidity and
Gaussian rigidity. We look for non-trivial fixed points but we find no evidence
for a crumpling transition at . Finally, we propose to identify the
limit of the theory with two dimensional quantum gravity. In
this limit we derive new beta functions for both cosmological and Newton's
constants.Comment: 16 pages, 1 figur
One-loop effective action in quantum gravitation
We present the formalism of computing one-loop effective action for Quantum Gravitation using non-local heat kernel methods. We found agreement with previous old results. In main part of my presentation I considered the system of E-H gravitation and scalar fields. We were able to derive non-local quantum effective action up to the second order in heat kernel generalized curvatures. By going to flat spacetime expressions for gravitational form factors are possible to construct and compare with the results from effective field theory for gravity
The electroweak S and T parameters from a fixed point condition
We consider the standard model without the Higgs boson, where the Goldstone
modes are described by a nonlinear sigma model. We study the renormalization
group flow of the sigma model coupling f and of the electroweak parameters S
and T. The condition that the couplings reach a fixed point at high energy
leaves the low energy values of f and T arbitrary (to be determined
experimentally) and fixes S to a value compatible with electroweak precision
data.Comment: 4 pages, 2 figure
Infrared fixed point in quantum Einstein gravity
We performed the renormalization group analysis of the quantum Einstein
gravity in the deep infrared regime for different types of extensions of the
model. It is shown that an attractive infrared point exists in the broken
symmetric phase of the model. It is also shown that due to the Gaussian fixed
point the IR critical exponent of the correlation length is 1/2. However,
there exists a certain extension of the model which gives finite correlation
length in the broken symmetric phase. It typically appears in case of models
possessing a first order phase transitions as is demonstrated on the example of
the scalar field theory with a Coleman-Weinberg potential.Comment: 9 pages, 7 figures, final version, to appear in JHE
Geometry of the quantum universe
A universe much like the (Euclidean) de Sitter space-time appears as
background geometry in the causal dynamical triangulation (CDT) regularization
of quantum gravity. We study the geometry of such universes which appear in the
path integral as a function of the bare coupling constants of the theory.Comment: 19 pages, 7 figures. Typos corrected. Conclusions unchange
Scale-dependent Planck mass and Higgs VEV from holography and functional renormalization
We compute the scale-dependence of the Planck mass and of the vacuum
expectation value of the Higgs field using two very different renormalization
group methods: a "holographic" procedure based on Einstein's equations in five
dimensions with matter confined to a 3-brane, and a "functional" procedure in
four dimensions based on a Wilsonian momentum cutoff. Both calculations lead to
very similar results, suggesting that the coupled theory approaches a
non-trivial fixed point in the ultraviolet.Comment: 11 pages, 1 figur
Exact Curie temperature for the Ising model on Archimedean and Laves lattices
Using the Feynman-Vdovichenko combinatorial approach to the two dimensional
Ising model, we determine the exact Curie temperature for all two dimensional
Archimedean lattices. By means of duality, we extend our results to cover all
two dimensional Laves lattices. For those lattices where the exact critical
temperatures are not exactly known yet, we compare them with Monte Carlo
simulations.Comment: 10 pages, 1 figures, 3 table
CDT meets Horava-Lifshitz gravity
The theory of causal dynamical triangulations (CDT) attempts to define a
nonperturbative theory of quantum gravity as a sum over space-time geometries.
One of the ingredients of the CDT framework is a global time foliation, which
also plays a central role in the quantum gravity theory recently formulated by
Ho\v{r}ava. We show that the phase diagram of CDT bears a striking resemblance
with the generic Lifshitz phase diagram appealed to by Ho\v{r}ava. We argue
that CDT might provide a unifying nonperturbative framework for anisotropic as
well as isotropic theories of quantum gravity.Comment: 17 pages, 3 figures. Typos corrected, a few remarks added
Fractal space-times under the microscope: A Renormalization Group view on Monte Carlo data
The emergence of fractal features in the microscopic structure of space-time
is a common theme in many approaches to quantum gravity. In this work we carry
out a detailed renormalization group study of the spectral dimension and
walk dimension associated with the effective space-times of
asymptotically safe Quantum Einstein Gravity (QEG). We discover three scaling
regimes where these generalized dimensions are approximately constant for an
extended range of length scales: a classical regime where , a
semi-classical regime where , and the UV-fixed point
regime where . On the length scales covered by
three-dimensional Monte Carlo simulations, the resulting spectral dimension is
shown to be in very good agreement with the data. This comparison also provides
a natural explanation for the apparent puzzle between the short distance
behavior of the spectral dimension reported from Causal Dynamical
Triangulations (CDT), Euclidean Dynamical Triangulations (EDT), and Asymptotic
Safety.Comment: 26 pages, 6 figure
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