37 research outputs found
Can residuals of the Solar system foreground explain low multipole anomalies of the CMB ?
The low multipole anomalies of the Cosmic Microwave Background has received
much attention during the last few years. It is still not ascertained whether
these anomalies are indeed primordial or the result of systematics or
foregrounds. An example of a foreground, which could generate some non-Gaussian
and statistically anisotropic features at low multipole range, is the very
symmetric Kuiper Belt in the outer solar system. In this paper, expanding upon
the methods presented by Maris et al. (2011), we investigate the contributions
from the Kuiper Belt objects (KBO) to the WMAP ILC 7 map, whereby we can
minimize the contrast in power between even and odd multipoles in the CMB,
discussed discussed by Kim & Naselsky (2010). We submit our KBO de-correlated
CMB signal to several tests, to analyze its validity, and find that
incorporation of the KBO emission can decrease the quadrupole-octupole
alignment and parity asymmetry problems, provided that the KBO signals has a
non-cosmological dipole modulation, associated with the statistical anisotropy
of the ILC 7 map. Additionally, we show that the amplitude of the dipole
modulation, within a 2 sigma interval, is in agreement with the corresponding
amplitudes, discussed by Lew (2008).Comment: 24 pages, 9 figures, 5 tables. Matches version in JCA
Thermal history of the plasma and high-frequency gravitons
Possible deviations from a radiation-dominated evolution, occurring prior the
synthesis of light nuclei, impacted on the spectral energy density of
high-frequency gravitons. For a systematic scrutiny of this situation, the
CDM paradigm must be complemented by (at least two) physical
parameters describing, respectively, a threshold frequency and a slope. The
supplementary frequency scale sets the lower border of a high-frequency domain
where the spectral energy grows with a slope which depends, predominantly, upon
the total sound speed of the plasma right after inflation. While the infra-red
region of the graviton energy spectrum is nearly scale-invariant, the expected
signals for typical frequencies larger than 0.01 nHz are hereby analyzed in a
model-independent framework by requiring that the total sound speed of the
post-inflationary plasma be smaller than the speed of light. Current (e.g.
low-frequency) upper limits on the tensor power spectra (determined from the
combined analysis of the three large-scale data sets) are shown to be
compatible with a detectable signal in the frequency range of wide-band
interferometers. In the present context, the scrutiny of the early evolution of
the sound speed of the plasma can then be mapped onto a reliable strategy of
parameter extraction including not only the well established cosmological
observables but also the forthcoming data from wide band interferometers.Comment: 47 pages, 31 included figures, to appear in Classical and Quantum
Gravit
BINGO: A code for the efficient computation of the scalar bi-spectrum
We present a new and accurate Fortran code, the BI-spectra and
Non-Gaussianity Operator (BINGO), for the efficient numerical computation of
the scalar bi-spectrum and the non-Gaussianity parameter f_{NL} in single field
inflationary models involving the canonical scalar field. The code can
calculate all the different contributions to the bi-spectrum and the parameter
f_{NL} for an arbitrary triangular configuration of the wavevectors. Focusing
firstly on the equilateral limit, we illustrate the accuracy of BINGO by
comparing the results from the code with the spectral dependence of the
bi-spectrum expected in power law inflation. Then, considering an arbitrary
triangular configuration, we contrast the numerical results with the analytical
expression available in the slow roll limit, for, say, the case of the
conventional quadratic potential. Considering a non-trivial scenario involving
deviations from slow roll, we compare the results from the code with the
analytical results that have recently been obtained in the case of the
Starobinsky model in the equilateral limit. As an immediate application, we
utilize BINGO to examine of the power of the non-Gaussianity parameter f_{NL}
to discriminate between various inflationary models that admit departures from
slow roll and lead to similar features in the scalar power spectrum. We close
with a summary and discussion on the implications of the results we obtain.Comment: v1: 5 pages, 5 figures; v2: 35 pages, 11 figures, title changed,
extensively revised; v3: 36 pages, 11 figures, to appear in JCAP. The BINGO
code is available online at
http://www.physics.iitm.ac.in/~sriram/bingo/bingo.htm
Confronting hybrid inflation in supergravity with CMB data
-term GUT inflation coupled to N=1 Supergravity is confronted with CMB
data. Corrections to the string mass-per-unit-length away from the Bogomolny
limit are taken into account. We find that a superpotential coupling
10^{-7}/\mcN \lesssim \kappa \lesssim 10^{-2}/\mcN, with \mcN the dimension
of the Higgs-representation, is still compatible with the data. The parameter
space is enlarged in warm inflation, as well as in the curvaton and
inhomogeneous reheat scenario. -strings formed at the end of -term
inflation are also considered. Because these strings satisfy the Bogomolny
bound the bounds are stronger: the gauge coupling is constrained to the range
.Comment: 36 pages, 15 figure
Measuring our Peculiar Velocity by "Pre-deboosting" the CMB
It was recently shown that our peculiar velocity \beta with respect to the
CMB induces mixing among multipoles and off-diagonal correlations at all scales
which can be used as a measurement of \beta, which is independent of the
standard measurement using the CMB temperature dipole. The proposed techniques
rely however on a perturbative expansion which breaks down for \ell \gtrsim
1/(\beta) \approx 800. Here we propose a technique which consists of deboosting
the CMB temperature in the time-ordered data and show that it extends the
validity of the perturbation analysis multipoles up to \ell \sim 10000. We also
obtain accurate fitting functions for the mixing between multipoles valid in a
full non-linear treatment. Finally we forecast the achievable precision with
which these correlations can be measured in a number of current and future CMB
missions. We show that Planck could measure the velocity with a precision of
around 60 km/s, ACTPol in 4 years around 40 km/s, while proposed future
experiments could further shrink this error bar by over a factor of around 2.Comment: 14 pages, 7 figures. Revised projections for ACTPol, SPTPol and
ACBAR; included projections for BICEP2; extended conclusions; typos correcte
Large non-Gaussianities in the Effective Field Theory Approach to Single-Field Inflation: the Bispectrum
The methods of effective field theory are used to study generic theories of
inflation with a single inflaton field and to perform a general analysis of the
associated non-Gaussianities. We investigate the amplitudes and shapes of the
various generic three-point correlators, the bispectra, which may be generated
by different classes of single-field inflationary models. Besides the
well-known results for the DBI-like models and the ghost inflationary theories,
we point out that curvature-related interactions may give rise to large
non-Gaussianities in the form of bispectra characterized by a flat shape which,
quite interestingly, is independently produced by several interaction terms. In
a subsequent work, we will perform a similar general analysis for the
non-Gaussianities generated by the generic four-point correlator, the
trispectrum.Comment: Version matching the one published in JCAP, 2 typos fixed, references
added. 30 pages, 20 figure
Large non-Gaussianities in the Effective Field Theory Approach to Single-Field Inflation: the Trispectrum
We perform the analysis of the trispectrum of curvature perturbations
generated by the interactions characterizing a general theory of single-field
inflation obtained by effective field theory methods. We find that
curvature-generated interaction terms, which can in general give an important
contribution to the amplitude of the four-point function, show some new
distinctive features in the form of their trispectrum shape-function. These
interesting interactions are invariant under some recently proposed symmetries
of the general theory and, as shown explicitly, do allow for a large value of
the trispectrum.Comment: 29 pages, 13 figure
Mixed Wino Dark Matter: Consequences for Direct, Indirect and Collider Detection
In supersymmetric models with gravity-mediated SUSY breaking and gaugino mass
unification, the predicted relic abundance of neutralinos usually exceeds the
strict limits imposed by the WMAP collaboration. One way to obtain the correct
relic abundance is to abandon gaugino mass universality and allow a mixed
wino-bino lightest SUSY particle (LSP). The enhanced annihilation and
scattering cross sections of mixed wino dark matter (MWDM) compared to bino
dark matter lead to enhanced rates for direct dark matter detection, as well as
for indirect detection at neutrino telescopes and for detection of dark matter
annihilation products in the galactic halo. For collider experiments, MWDM
leads to a reduced but significant mass gap between the lightest neutralinos so
that chi_2^0 two-body decay modes are usually closed. This means that dilepton
mass edges-- the starting point for cascade decay reconstruction at the CERN
LHC-- should be accessible over almost all of parameter space. Measurement of
the m_{\tz_2}-m_{\tz_1} mass gap at LHC plus various sparticle masses and cross
sections as a function of beam polarization at the International Linear
Collider (ILC) would pinpoint MWDM as the dominant component of dark matter in
the universe.Comment: 29 pages including 19 eps figure
Exploring the BWCA (Bino-Wino Co-Annihilation) Scenario for Neutralino Dark Matter
In supersymmetric models with non-universal gaugino masses, it is possible to
have opposite-sign SU(2) and U(1) gaugino mass terms. In these models, the
gaugino eigenstates experience little mixing so that the lightest SUSY particle
remains either pure bino or pure wino. The neutralino relic density can only be
brought into accord with the WMAP measured value when bino-wino co-annihilation
(BWCA) acts to enhance the dark matter annihilation rate. We map out parameter
space regions and mass spectra which are characteristic of the BWCA scenario.
Direct and indirect dark matter detection rates are shown to be typically very
low. At collider experiments, the BWCA scenario is typified by a small mass gap
m_{\tilde Z_2}-m_{\tilde Z_1} ~ 20-80 GeV, so that tree level two body decays
of \tilde Z_2 are not allowed. However, in this case the second lightest
neutralino has an enhanced loop decay branching fraction to photons. While the
photonic neutralino decay signature looks difficult to extract at the Fermilab
Tevatron, it should lead to distinctive events at the CERN LHC and at a linear
e^+e^- collider.Comment: 44 pages, 21 figure
Seeking String Theory in the Cosmos
We review the existence, formation and properties of cosmic strings in string
theory, the wide variety of observational techniques that are being employed to
detect them, and the constraints that current observations impose on string
theory models.Comment: 25 pages; contribution for String Cosmology issue of Classical and
Quantum Gravity. References added and other improvements. Matches journal
versio