362 research outputs found
Quantization of Higher Spin Superfields in the anti-de Sitter Superspace
We describe a Lagrangian quantization of the free massless gauge superfield
theories of higher superspins both in the anti-de Sitter and flat global
superspaces.Comment: 9 pages, LaTe
MSLED, Neutrino Oscillations and the Cosmological Constant
We explore the implications for neutrino masses and mixings within the
minimal version of the supersymmetric large-extra-dimensions scenario (MSLED).
This model was proposed in {\tt hep-ph/0404135} to extract the phenomenological
implications of the promising recent attempt (in {\tt hep-th/0304256}) to
address the cosmological constant problem. Remarkably, we find that the
simplest couplings between brane and bulk fermions within this approach can
lead to a phenomenologically-viable pattern of neutrino masses and mixings that
is also consistent with the supernova bounds which are usually the bane of
extra-dimensional neutrino models. Under certain circumstances the MSLED
scenario can lead to a lepton mixing (PMNS) matrix close to the so-called
bi-maximal or the tri-bimaximal forms (which are known to provide a good
description of the neutrino oscillation data). We discuss the implications of
MSLED models for neutrino phenomenology.Comment: 38 pages, 1 figure; Reposted with a few additional reference
TIME-SYMMETRIC INITIAL DATA SETS IN 4--D DILATON GRAVITY
I study the time--symmetric initial--data problem in theories with a massless
scalar field (dilaton), free or coupled to a Maxwell field in the stringy way,
finding different initial--data sets describing an arbitrary number of black
holes with arbitrary masses, charges and asymptotic value of the dilaton. The
presence of the scalar field gives rise to a number of interesting effects. The
mass and charges of a single black hole are different in its two asymptotically
flat regions across the Einstein--Rosen bridge. The same happens to the value
of the dilaton at infinity. This forbids the identification of these asymptotic
regions in order to build (Misner) wormholes in the most naive way. Using
different techniques, I find regular initial data for stringy wormholes. The
price payed is the existence singularities in the dilaton field. The presence
of a single--valued scalar seems to constrain strongly the allowed topologies
of the initial space--like surface. Other kinds of scalar fields (taking values
on a circle or being defined up to an additive constant) are also briefly
considered.Comment: latex file, 38 pages
Running Spectral Index and Formation of Primordial Black Hole in Single Field Inflation Models
A broad range of single field models of inflation are analyzed in light of
all relevant recent cosmological data, checking whether they can lead to the
formation of long-lived Primordial Black Holes (PBHs). To that end we calculate
the spectral index of the power spectrum of primordial perturbations as well as
its first and second derivatives. PBH formation is possible only if the
spectral index increases significantly at small scales, i.e. large wave number
. Since current data indicate that the first derivative of the
spectral index is negative at the pivot scale , PBH formation
is only possible in the presence of a sizable and positive second derivative
("running of the running") . Among the three small-field and five
large-field models we analyze, only one small-field model, the "running mass"
model, allows PBH formation, for a narrow range of parameters. We also note
that none of the models we analyze can accord for a large and negative value of
, which is weakly preferred by current data.Comment: 26 pages, 5 figures, Refs. added, Minor textual change; version to
appear in JCA
Quintessence Restrictions on Negative Power and Condensate Potentials
We study the cosmological evolution of scalar fields that arise from a phase
transition at some energy scale \Lm_c. We focus on negative power potentials
given by V=c\Lm_c^{4+n}\phi^{-n} and restrict the cosmological viable values
of \Lm_c and . We make a complete analysis of and impose
conditions on the different cosmological parameters. The cosmological
observations ruled out models where the scalar field has reached its attractor
solution. For models where this is not the case, the analytic approximated
solutions are not good enough to determine whether a specific model is
phenomenologically viable or not and the full differential equations must be
numerically solved. The results are not fine tuned since a change of 45% on the
initial conditions does not spoil the final results. We also determine the
values of that give a condensation scale \Lm_c consistent with
gauge coupling unification, leaving only four models that satisfy unification
and SN1a constraints.Comment: 15 pages, LaTeX, 8 Figures. Minor changes in text, a discussion on
initial conditions added (accepted in Phys.Rev.D
DBI Inflation in the Tip Region of a Warped Throat
Previous work on DBI inflation, which achieves inflation through the motion
of a brane as it moves through a warped throat compactification, has
focused on the region far from the tip of the throat. Since reheating and other
observable effects typically occur near the tip, a more detailed study of this
region is required. To investigate these effects we consider a generalized warp
throat where the warp factor becomes nearly constant near the tip. We find that
it is possible to obtain 60 or more e-folds in the constant region, however
large non-gaussianities are typically produced due to the small sound speed of
fluctuations. For a particular well-studied throat, the Klebanov-Strassler
solution, we find that inflation near the tip may be generic and it is
difficult to satisfy current bounds on non-gaussianity, but other throat
solutions may evade these difficulties.Comment: 26 pages, 1 figure. v1. references added, typos corrected v2.
clarifications mad
Observational consequences of the Standard Model Higgs inflation variants
We consider the possibility to observationally differentiate the Standard
Model (SM) Higgs driven inflation with non-minimal couplingto gravity from
other variants of SM Higgs inflation based on the scalar field theories with
non-canonical kinetic term such as Galileon-like kinetic term and kinetic term
with non-minimal derivative coupling to the Einstein tensor. In order to ensure
consistent results, we study the SM Higgs inflation variants by using the same
method, computing the full dynamics of the background and perturbations of the
Higgs field during inflation at quantum level. Assuming that all the SM Higgs
inflation variants are consistent theories, we use the MCMC technique to derive
constraints on the inflationnoary parameters and the Higgs boson mass from
their fit to WMAP7+SN+BAO data set. We conclude that a combination of a Higgs
mass measurement by the LHC and accurate determination by the PLANCK satellite
of the spectral index of curvature perturbations and tensor-to-scalar ratio
will enable to distinguish among these models. We also show that the
consistency relations of the SM Higgs inflation variants are distinct enough to
differentiate the models.Comment: 22 pages, 4 figure
Potential-driven Galileon inflation
For the models of inflation driven by the potential energy of an inflaton
field , the covariant Galileon Lagrangian
generally works to slow down the evolution of the field. On the other hand, if
the Galileon self-interaction is dominant relative to the standard kinetic
term, we show that there is no oscillatory regime of inflaton after the end of
inflation. This is typically accompanied by the appearance of the negative
propagation speed squared of a scalar mode, which leads to the
instability of small-scale perturbations. For chaotic inflation and natural
inflation we clarify the parameter space in which inflaton oscillates
coherently during reheating. Using the WMAP constraints of the scalar spectral
index and the tensor-to-scalar ratio as well, we find that the self coupling
of the potential is constrained to be very
much smaller than 1 and that the symmetry breaking scale of natural
inflation cannot be less than the reduced Planck mass . We also
show that, in the presence of other covariant Galileon Lagrangians, there are
some cases in which inflaton oscillates coherently even for the self coupling
of the order of 0.1, but still the instability associated with
negative is generally present.Comment: 22 pages, 15 figure
Static quantities of the W boson in the SU_L(3) X U_X(1) model with right-handed neutrinos
The static electromagnetic properties of the boson, and
, are calculated in the SU_L(3)} \times U_X(1) model with
right-handed neutrinos. The new contributions from this model arise from the
gauge and scalar sectors. In the gauge sector there is a new contribution from
a complex neutral gauge boson and a singly-charged gauge boson .
The mass of these gauge bosons, called bileptons, is expected to be in the
range of a few hundreds of GeV according to the current bounds from
experimental data. If the bilepton masses are of the order of 200 GeV, the size
of their contribution is similar to that obtained in other weakly coupled
theories. However the contributions to both and are
negligible for very heavy or degenerate bileptons. As for the scalar sector, an
scenario is examined in which the contribution to the form factors is
identical to that of a two-Higgs-doublet model. It is found that this sector
would not give large corrections to and .Comment: New material included. Final version to apppear in Physical Review
- âŠ