49 research outputs found
QCD contributions to the thermal history of the early Universe
We discuss the deviations from the ideal relativistic thermal bath. These
deviations are dominated from quantum chromodynamic (QCD) corrections in the
most part of the parameter space of the Standard Model (SM) and the Minimal
Supersymmetric Standard Model (MSSM). These effects are relevant for
astrophysical precision measurements and dynamics of scalar tensor theories
(SST).Comment: To appear in the AIP proceedings of "Quark Confinement and Hadron
Spectrum IX" (QCHSIX), Madrid 30th August-3rd September 2010. 3 page
R^2 Dark Matter
There is a non-trivial four-derivative extension of the gravitational
spectrum that is free of ghosts and phenomenologically viable. It is the so
called -gravity since it is defined by the only addition of a term
proportional to the square of the scalar curvature. Just the presence of this
term does not improve the ultraviolet behaviour of Einstein gravity but
introduces one additional scalar degree of freedom that can account for the
dark matter of our Universe.Comment: 6 pages, 1 figure, to appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
New torsion black hole solutions in Poincar\'e gauge theory
We derive a new exact static and spherically symmetric vacuum solution in the
framework of the Poincar\'e gauge field theory with dynamical massless torsion.
This theory is built in such a form that allows to recover General Relativity
when the first Bianchi identity of the model is fulfilled by the total
curvature. The solution shows a Reissner-Nordstr\"om type geometry with a
Coulomb-like curvature provided by the torsion field. It is also shown the
existence of a generalized Reissner-Nordstr\"om-de Sitter solution when
additional electromagnetic fields and/or a cosmological constant are coupled to
gravity.Comment: 14 pages, 0 figures, minor changes, references adde
Extended Reissner-Nordstr\"om solutions sourced by dynamical torsion
We find a new exact vacuum solution in the framework of the Poincar\'e Gauge
field theory with massive torsion. In this model, torsion operates as an
independent field and introduces corrections to the vacuum structure present in
General Relativity. The new static and spherically symmetric configuration
shows a Reissner-Nordstr\"om-like geometry characterized by a spin charge. It
extends the known massless torsion solution to the massive case. The
corresponding Reissner-Nordstr\"om-de Sitter solution is also compatible with a
cosmological constant and additional U(1) gauge fields.Comment: 12 pages, 0 figures, minor changes, references adde
Correspondence between Einstein-Yang-Mills-Lorentz systems and dynamical torsion models
In the framework of Einstein-Yang-Mills theories, we study the gauge Lorentz
group and establish a particular correspondence between this case and a certain
class of theories with torsion within Riemann-Cartan space-times. This relation
is specially useful in order to simplify the problem of finding exact solutions
to the Einstein-Yang-Mills equations. The applicability of the method is
divided into two approaches: one associated with the Lorentz group SO(1,n-1) of
the space-time rotations and another one with its subgroup SO(n-2). Solutions
for both cases are presented by the explicit use of this correspondence and,
interestingly, for the last one by imposing on our ansatz the same kind of
rotation and reflection symmetry properties as for a nonvanishing space-time
torsion. Although these solutions were found in previous literature by a
different approach, our method provides an alternative way to obtain them and
it may be used in future research to find other exact solutions within this
theory.Comment: 10 pages, 0 figures, minor changes, references added. It matches the
version published in Phys. Rev.
Dark Matter from R^2-gravity
The modification of Einstein gravity at high energies is mandatory from a
quantum approach. In this work, we point out that this modification will
necessarily introduce new degrees of freedom. We analyze the possibility that
these new gravitational states can provide the main contribution to the
non-baryonic dark matter of the Universe. Unfortunately, the right ultraviolet
completion of gravity is still unresolved. For this reason, we will illustrate
this idea with the simplest high energy modification of the Einstein-Hilbert
action: R^2-gravity.Comment: 5 pages, 2 figure
Magnetic dipole moments for composite dark matter
We study neutral dark matter candidates with a nonzero magnetic dipole
moment. We assume that they are composite states of new fermions related to the
strong phase of a new gauge interaction. In particular, invoking a dark flavor
symmetry, we analyze the composition structure of viable candidates depending
on the assignations of hypercharge and the multiplets associated to the
fundamental constituents of the extended sector. We determine the magnetic
dipole moments for the neutral composite states in terms of their constituents
masses.Comment: 22 pages, 3 figure