25 research outputs found
Higher derivative quantum gravity near four dimensions
We investigate the role of the Gauss-Bonnet term for the n = 4 and n = 4-e renormalization group, for both conformal and general versions of the theory. The cancellation of the quantum effects of the Gauss-Bonnet term in the n = 4 limit represents an efficient test for the correctness of previous calculations and also resolves two long-standing problems concerning quantum corrections in quantum gravity. In the case of n = 4-e renormalization group there is a number of new nontrivial fixed points, that may indicate to a rich nonperturbative structure of the theory. At the same time, if we do not treat e as a small parameter, the renormalization group is spoiled by an extensive gauge fixing ambiguity.
On the cosmological effects of the Weyssenhoff spinning fluid in the Einstein-Cartan framework
The effects of non-Riemannian structures in Cosmology have been studied long
ago and are still a relevant subject of investigation. In the seventies, it was
discovered that singularity avoidance and early accelerated expansion can be
induced by torsion in the Einstein-Cartan theory. In this framework, torsion is
not dynamical and is completely expressed by means of the spin sources. Thus,
in order to study the effects of torsion in the Einstein-Cartan theory, one has
to introduce matter with spin. In principle, this can be done in several ways.
In this work we consider the cosmological evolution of the universe in the
presence of a constant isotropic and homogeneous axial current and the
Weyssenhoff spinning fluid. We analyse possible solutions of this model, with
and without the spinning fluid.Comment: Work presented at the 7th Alexander Friedmann International Seminar
on Gravitation and Cosmology, Joao Pessoa, Brazil, 29 Jun - 5 Jul 2008. No
figures, 5 pages. New version with dynamical equation corrected, new
reference and a brief comparison with its experimental bound
Trajectories in a space with a spherically symmetric dislocation
We consider a new type of defect in the scope of linear elasticity theory,
using geometrical methods. This defect is produced by a spherically symmetric
dislocation, or ball dislocation. We derive the induced metric as well as the
affine connections and curvature tensors. Since the induced metric is
discontinuous, one can expect ambiguity coming from these quantities, due to
products between delta functions or its derivatives, plaguing a description of
ball dislocations based on the Geometric Theory of Defects. However, exactly as
in the previous case of cylindric defect, one can obtain some well-defined
physical predictions of the induced geometry. In particular, we explore some
properties of test particle trajectories around the defect and show that these
trajectories are curved but can not be circular orbits.Comment: 11 pages, 3 figure
Efeitos quânticos de vácuo - energia escura e matéria escura
-Nesta apresentação, descrevemos a eletrodinâmica na forma covariante. Isto é possÃvel devido ao fato de que a teoria é uma teoria relativÃstica,
podendo inclusive ser formulada no espaço curvo, junto com uma teoria de gravitação. Iniciaremos com as transformações de Lorentz a
apresentaremos a formulação covariante de uma teoria clássica de campo, através de objetos tensoriais (e.g., quadrivetor). Em seguida, após
introduzir o conceito de tensor campo eletromagnético, apresentaremos as equações de Maxwell em termos desse tensor e estudaremos o
comportamento da teoria sob uma transformação de Lorentz
On the renormalization of CPT/Lorentz violating QED in curved space
We consider the one-loop renormalization of QED in curved space-time with
additional Lorentz and/or CPT breaking terms. The renormalization group
equations in the vacuum sector are derived. In the special case of Minkowski
metric and with constant Lorentz and CPT breaking terms these equations reduce
to the ones obtained earlier by other authors. The necessary form of the vacuum
counterterms indicate possible violations of the space or time homogeneity or
space isotropy in the gravitational phenomena. However, the necessity of the
phenomenologically most interesting terms such as linear in the space-time
curvature or torsion, is related to the non-constant nature of the
dimensionless Lorentz and CPT breaking parameters.Comment: 11 pages, LaTeX file. Minor improvements and new references added.
Accepted in Physics Letters
Universality and ambiguity in fermionic effective actions
We discuss an ambiguity in the one-loop effective action of massive fields
which takes place in massive fermionic theories. The universality of
logarithmic UV divergences in different space-time dimensions leads to the
non-universality of the finite part of effective action, which can be called
the non-local multiplicative anomaly. The general criteria of existence of this
phenomena are formulated and applied to fermionic operators with different
external fields.Comment: 13 pages, no figure
Higher Derivative Quantum Gravity with Gauss-Bonnet Term
Higher derivative theory is one of the important models of quantum gravity,
renormalizable and asymptotically free within the standard perturbative
approach. We consider the renormalization group for this theory,
an approach which proved fruitful in models. A consistent
formulation in dimension requires taking quantum effects of the
topological term into account, hence we perform calculation which is more
general than the ones done before. In the special case we confirm a known
result by Fradkin-Tseytlin and Avramidi-Barvinsky, while contributions from
topological term do cancel. In the more general case of
renormalization group equations there is an extensive ambiguity related to
gauge-fixing dependence. As a result, physical interpretation of these
equations is not universal unlike we treat as a small parameter. In
the sector of essential couplings one can find a number of new fixed points,
some of them have no analogs in the case.Comment: LaTeX file, 30 pages, 5 figures. Several misprints in the
intermediate expressions correcte