6,383 research outputs found
Moduli as Inflatons in Heterotic M-theory
We consider different cosmological aspects of Heterotic M-theory. In
particular we look at the dynamical behaviour of the two relevant moduli in the
theory, namely the length of the eleventh segment (pi rho) and the volume of
the internal six manifold (V) in models where supersymmetry is broken by
multiple gaugino condensation. We look at different ways to stabilise these
moduli, namely racetrack scenarios with or without non-perturbative corrections
to the Kahler potential. The existence of different flat directions in the
scalar potential, and the way in which they can be partially lifted, is
discussed as well as their possible role in constructing a viable model of
inflation. Some other implications such as the status of the moduli problem
within these models are also studied.Comment: 16 pages, 8 Postscript figures. Final version to appear in JHE
Cosmological Aspects of Heterotic M-theory
In this talk we discuss a few relevant aspects of heterotic M-theory. These
are the stabilization of the two relevant moduli (the length of the eleventh
segment (pi rho) and the volume of the internal six manifold (V)) in models
where supersymmetry is broken by multiple gaugino condensation and
non-perturbative corrections to the Kahler potential; the existence of almost
flat directions in the scalar potential; the possibility of lifting them, and
their role in constructing a viable model of inflation. Finally, we review the
status of the moduli problem within these models. TComment: LaTeX, 8 pages, 4 eps figures, uses ws-p8-50x6-00.cls; invited talk
at the International Workshop on Particle Physics and the Early Universe
(COSMO-99), Trieste, Italy, September 27 - October 2, 199
Stabilizing the Dilaton in Superstring Cosmology
We address the important issue of stabilizing the dilaton in the context of
superstring cosmology. Scalar potentials which arise out of gaugino condensates
in string models are generally exponential in nature. In a cosmological setting
this allows for the existence of quasi scaling solutions, in which the energy
density of the scalar field can, for a period, become a fixed fraction of the
background density, due to the friction of the background expansion. Eventually
the field can be trapped in the minimum of its potential as it leaves the
scaling regime. We investigate this possibility in various gaugino condensation
models and show that stable solutions for the dilaton are far more common than
one would have naively thought.Comment: 13 pages, LaTex, uses psfig.sty with 3 figure
Moduli Evolution in Heterotic Scenarios
We discuss several aspects of the cosmological evolution of moduli fields in
heterotic string/M-theory scenarios. In particular we study the equations of
motion of both the dilaton and overall modulus of these theories in the
presence of an expanding Universe and under different assumptions. First we
analyse the impact of their couplings to matter fields, which turns out to be
negligible in the string and M-theory scenarios. Then we examine in detail the
possibility of scaling in M-theory, i.e. how the moduli would evolve naturally
to their minima instead of rolling past them in the presence of a dominating
background. In this case we find interesting and positive results, and we
compare them to the analogous situation in the heterotic string.Comment: 12 pages, 4 postscript figure
The effect of the linear term on the wavelet estimator of primordial non-Gaussianity
In this work we present constraints on different shapes of primordial
non-Gaussianity using the Wilkinson Microwave Anisotropy Probe (WMAP) 7-year
data and the spherical Mexican hat wavelet fnl estimator including the linear
term correction. In particular we focus on the local, equilateral and
orthogonal shapes. We first analyse the main statistical properties of the
wavelet estimator and show the conditions to reach optimality. We include the
linear term correction in our estimators and compare the estimates with the
values already published using only the cubic term. The estimators are tested
with realistic WMAP simulations with anisotropic noise and the WMAP KQ75 sky
cut. The inclusion of the linear term correction shows a negligible improvement
(< 1 per cent) in the error-bar for any of the shapes considered. The results
of this analysis show that, in the particular case of the wavelet estimator,
the optimality for WMAP anisotropy levels is basically achieved with the mean
subtraction and in practical terms there is no need of including a linear term
once the mean has been subtracted. Our best estimates are now: local fnl = 39.0
+/ 21.4, equilateral fnl = -62.8 +/- 154.0 and orthogonal fnl = -159.8 +/-
115.1 (all cases 68 per cent CL). We have also computed the expected linear
term correction for simulated Planck maps with anisotropic noise at 143 GHz
following the Planck Sky Model and including a mask. The improvement achieved
in this case for the local fnl error-bar is also negligible (0.4 per cent).Comment: 8 pages, 5 figures, 4 tables. Minor revision, one figure added,
accepted for publication in MNRA
Geometrical estimators as a test of Gaussianity in the CMB
We investigate the power of geometrical estimators on detecting
non-Gaussianity in the cosmic microwave background. In particular the number,
eccentricity and Gaussian curvature of excursion sets above (and below) a
threshold are studied. We compare their different performance when applied to
non-Gaussian simulated maps of small patches of the sky, which take into
account the angular resolution and instrumental noise of the Planck satellite.
These non-Gaussian simulations are obtained as perturbations of a Gaussian
field in two different ways which introduce a small level of skewness or
kurtosis in the distribution. A comparison with a classical estimator, the
genus, is also shown. We find that the Gaussian curvature is the best of our
estimators in all the considered cases. Therefore we propose the use of this
quantity as a particularly useful test to look for non-Gaussianity in the CMB.Comment: 9 pages, 6 postscript figures, submitted to MNRA
On the recovery of ISW fluctuations using large-scale structure tracers and CMB temperature and polarization anisotropies
In this work we present a method to extract the signal induced by the
integrated Sachs-Wolfe (ISW) effect in the cosmic microwave background (CMB).
It makes use of the Linear Covariance-Based filter introduced by Barreiro et
al., and combines CMB data with any number of large-scale structure (LSS)
surveys and lensing information. It also exploits CMB polarization to reduce
cosmic variance. The performance of the method has been thoroughly tested with
simulations taking into account the impact of non-ideal conditions such as
incomplete sky coverage or the presence of noise. In particular, three galaxy
surveys are simulated, whose redshift distributions peak at low (), intermediate () and high redshift (). The
contribution of each of the considered data sets as well as the effect of a
mask and noise in the reconstructed ISW map is studied in detail. When
combining all the considered data sets (CMB temperature and polarization, the
three galaxy surveys and the lensing map), the proposed filter successfully
reconstructs a map of the weak ISW signal, finding a perfect correlation with
the input signal for the ideal case and around 80 per cent, on average, in the
presence of noise and incomplete sky coverage. We find that including CMB
polarization improves the correlation between input and reconstruction although
only at a small level. Nonetheless, given the weakness of the ISW signal, even
modest improvements can be of importance. In particular, in realistic
situations, in which less information is available from the LSS tracers, the
effect of including polarisation is larger. For instance, for the case in which
the ISW signal is recovered from CMB plus only one survey, and taking into
account the presence of noise and incomplete sky coverage, the improvement in
the correlation coefficient can be as large as 10 per cent.Comment: 17 pages, 15 figures, accepted for publication in MNRA
A Bayesian approach to filter design: detection of compact sources
We consider filters for the detection and extraction of compact sources on a
background. We make a one-dimensional treatment (though a generalization to two
or more dimensions is possible) assuming that the sources have a Gaussian
profile whereas the background is modeled by an homogeneous and isotropic
Gaussian random field, characterized by a scale-free power spectrum. Local peak
detection is used after filtering. Then, a Bayesian Generalized Neyman-Pearson
test is used to define the region of acceptance that includes not only the
amplification but also the curvature of the sources and the a priori
probability distribution function of the sources. We search for an optimal
filter between a family of Matched-type filters (MTF) modifying the filtering
scale such that it gives the maximum number of real detections once fixed the
number density of spurious sources. We have performed numerical simulations to
test theoretical ideas.Comment: 10 pages, 2 figures. SPIE Proceedings "Electronic Imaging II", San
Jose, CA. January 200
A linear filter to reconstruct the ISW effect from CMB and LSS observations
The extraction of a signal from some observational data sets that contain
different contaminant emissions, often at a greater level than the signal
itself, is a common problem in Astrophysics and Cosmology. The signal can be
recovered, for instance, using a simple Wiener filter. However, in certain
cases, additional information may also be available, such as a second
observation which correlates to a certain level with the sought signal. In
order to improve the quality of the reconstruction, it would be useful to
include as well this additional information. Under these circumstances, we have
constructed a linear filter, the linear covariance-based filter, that extracts
the signal from the data but takes also into account the correlation with the
second observation. To illustrate the performance of the method, we present a
simple application to reconstruct the so-called Integrated Sachs-Wolfe effect
from simulated observations of the Cosmic Microwave Background and of
catalogues of galaxies.Comment: 8 pages, 6 figures, accepted for publication in the IEEE Journal of
Selected Topics in Signal Processin
- âŠ