15 research outputs found
Constraints on ultracompact minihalos from extragalactic {\gamma}-ray background
It has been proposed that ultracompact minihalos (UCMHs) might be formed in
earlier epoch. If dark matter consists of Weakly Interacting Massive Particles
(WIMPs), UCMHs can be treated as the {\gamma}-ray sources due to dark matter
annihilation within them. In this paper, we investigate the contributions of
UCMHs formed during three phase transi- tions (i.e., electroweak symmetry
breaking, QCD confinement and e+ e- annihilation) to the extragalactic
{\gamma}-ray background. Moreover, we use the Fermi-LAT observation data of the
extragalactic {\gamma}-ray background to get the constraints on the current
abundance of UCMHs produced during these phase transitions. We also compare
these results with those obtained from Cosmic Microwave Background (CMB)
observations and find that the constraints from the Fermi-LAT are more
stringent than those from CMBComment: 13 pages, 4 figures, 1 tabl
Cosmological CPT Violation and CMB Polarization Measurements
In this paper we study the possibility of testing Charge-Parity-Time Reversal
(CPT) symmetry with cosmic microwave background (CMB) experiments. We consider
two kinds of Chern-Simons (CS) term, electromagnetic CS term and gravitational
CS term, and study their effects on the CMB polarization power spectra in
detail. By combining current CMB polarization measurements, the seven-year
WMAP, BOOMERanG 2003 and BICEP observations, we obtain a tight constraint on
the rotation angle deg (), indicating a
detection of the CPT violation. Here, we particularly take the
systematic errors of CMB measurements into account. After adding the QUaD
polarization data, the constraint becomes deg at 95%
confidence level. When comparing with the effect of electromagnetic CS term,
the gravitational CS term could only generate TB and EB power spectra with much
smaller amplitude. Therefore, the induced parameter can not be
constrained from the current polarization data. Furthermore, we study the
capabilities of future CMB measurements, Planck and CMBPol, on the constraints
of and . We find that the constraint of
can be significantly improved by a factor of 15. Therefore, if this rotation
angle effect can not be taken into account properly, the constraints of
cosmological parameters will be biased obviously. For the gravitational CS
term, the future Planck data still can not constrain very well, if
the primordial tensor perturbations are small, . We need the more
accurate CMBPol experiment to give better constraint on .Comment: 11 pages, 5 figures, 4 tables, Accepted for publication in JCA
Neutrino mass from cosmology: Impact of high-accuracy measurement of the Hubble constant
Non-zero neutrino mass would affect the evolution of the Universe in
observable ways, and a strong constraint on the mass can be achieved using
combinations of cosmological data sets. We focus on the power spectrum of
cosmic microwave background (CMB) anisotropies, the Hubble constant H_0, and
the length scale for baryon acoustic oscillations (BAO) to investigate the
constraint on the neutrino mass, m_nu. We analyze data from multiple existing
CMB studies (WMAP5, ACBAR, CBI, BOOMERANG, and QUAD), recent measurement of H_0
(SHOES), with about two times lower uncertainty (5%) than previous estimates,
and recent treatments of BAO from the Sloan Digital Sky Survey (SDSS). We
obtained an upper limit of m_nu < 0.2eV (95% C.L.), for a flat LambdaCDM model.
This is a 40% reduction in the limit derived from previous H_0 estimates and
one-third lower than can be achieved with extant CMB and BAO data. We also
analyze the impact of smaller uncertainty on measurements of H_0 as may be
anticipated in the near term, in combination with CMB data from the Planck
mission, and BAO data from the SDSS/BOSS program. We demonstrate the
possibility of a 5 sigma detection for a fiducial neutrino mass of 0.1eV or a
95% upper limit of 0.04eV for a fiducial of m_nu = 0eV. These constraints are
about 50% better than those achieved without external constraint. We further
investigate the impact on modeling where the dark-energy equation of state is
constant but not necessarily -1, or where a non-flat universe is allowed. In
these cases, the next-generation accuracies of Planck, BOSS, and 1% measurement
of H_0 would all be required to obtain the limit m_nu < 0.05 - 0.06eV (95%
C.L.) for the fiducial of m_nu = 0eV. The independence of systematics argues
for pursuit of both BAO and H_0 measurements.Comment: 22 pages, 6 figures, 12 table
Probing the primordial power spectra with inflationary priors
We investigate constraints on power spectra of the primordial curvature and
tensor perturbations with priors based on single-field slow-roll inflation
models. We stochastically draw the Hubble slow-roll parameters and generate the
primordial power spectra using the inflationary flow equations. Using data from
recent observations of CMB and several measurements of geometrical distances in
the late Universe, Bayesian parameter estimation and model selection are
performed for models that have separate priors on the slow-roll parameters. The
same analysis is also performed adopting the standard parameterization of the
primordial power spectra. We confirmed that the scale-invariant
Harrison-Zel'dovich spectrum is disfavored with increased significance from
previous studies. While current observations appear to be optimally modeled
with some simple models of single-field slow-roll inflation, data is not enough
constraining to distinguish these models.Comment: 23 pages, 3 figures, 7 tables, accepted for publication in JCA
Estimating the tensor-to-scalar ratio and the effect of residual foreground contamination
We consider future balloon-borne and ground-based suborbital experiments
designed to search for inflationary gravitational waves, and investigate the
impact of residual foregrounds that remain in the estimated cosmic microwave
background maps. This is achieved by propagating foreground modelling
uncertainties from the component separation, under the assumption of a
spatially uniform foreground frequency scaling, through to the power spectrum
estimates, and up to measurement of the tensor to scalar ratio in the parameter
estimation step. We characterize the error covariance due to subtracted
foregrounds, and find it to be subdominant compared to instrumental noise and
sample variance in our simulated data analysis. We model the unsubtracted
residual foreground contribution using a two-parameter power law and show that
marginalization over these foreground parameters is effective in accounting for
a bias due to excess foreground power at low . We conclude that, at least
in the suborbital experimental setups we have simulated, foreground errors may
be modeled and propagated up to parameter estimation with only a slight
degradation of the target sensitivity of these experiments derived neglecting
the presence of the foregrounds.Comment: 19 pages, 12 figures, accepted for publication in JCA
SPIDER: Probing the Early Universe with a Suborbital Polarimeter
We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a
divergence-free polarization pattern ("B-modes") in the Cosmic Microwave
Background (CMB). In the inflationary scenario, the amplitude of this signal is
proportional to that of the primordial scalar perturbations through the
tensor-to-scalar ratio r. We show that the expected level of systematic error
in the SPIDER instrument is significantly below the amplitude of an interesting
cosmological signal with r=0.03. We present a scanning strategy that enables us
to minimize uncertainty in the reconstruction of the Stokes parameters used to
characterize the CMB, while accessing a relatively wide range of angular
scales. Evaluating the amplitude of the polarized Galactic emission in the
SPIDER field, we conclude that the polarized emission from interstellar dust is
as bright or brighter than the cosmological signal at all SPIDER frequencies
(90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the
"Southern Hole." We show that two ~20-day flights of the SPIDER instrument can
constrain the amplitude of the B-mode signal to r<0.03 (99% CL) even when
foreground contamination is taken into account. In the absence of foregrounds,
the same limit can be reached after one 20-day flight.Comment: 29 pages, 8 figures, 4 tables; v2: matches published version, flight
schedule updated, two typos fixed in Table 2, references and minor
clarifications added, results unchange
Reconstruction of the Primordial Power Spectrum using Temperature and Polarisation Data from Multiple Experiments
We develop a method to reconstruct the primordial power spectrum, P(k), using
both temperature and polarisation data from the joint analysis of a number of
Cosmic Microwave Background (CMB) observations. The method is an extension of
the Richardson-Lucy algorithm, first applied in this context by Shafieloo &
Souradeep. We show how the inclusion of polarisation measurements can decrease
the uncertainty in the reconstructed power spectrum. In particular, the
polarisation data can constrain oscillations in the spectrum more effectively
than total intensity only measurements. We apply the estimator to a compilation
of current CMB results. The reconstructed spectrum is consistent with the
best-fit power spectrum although we find evidence for a `dip' in the power on
scales k ~ 0.002 Mpc^-1. This feature appears to be associated with the WMAP
power in the region 18 < l < 26 which is consistently below best--fit models.
We also forecast the reconstruction for a simulated, Planck-like survey
including sample variance limited polarisation data.Comment: 8 pages, 5 figures, comments welcom
Brane inflation revisited after WMAP five-year results
In this paper, we revisit brane inflation models with the WMAP five-year
results. The WMAP five-year data favor a red-tilted power spectrum of
primordial fluctuations at the level of two standard deviations, which is the
same as the WMAP three-year result qualitatively, but quantitatively the
spectral index is slightly greater than the three-year value. This result can
bring impacts on brane inflation models. According to the WMAP five-year data,
we find that the KKLMMT model can survive at the level of one standard
deviation, and the fine-tuning of the parameter can be alleviated to a
certain extent at the level of two standard deviations.Comment: 23 pages, 11 figure
Cosmological Constraints on Decaying Dark Matter
We present a complete analysis of the cosmological constraints on decaying
dark matter. Previous analyses have used the cosmic microwave background and
Type Ia supernova. We have updated them with the latest data as well as
extended the analysis with the inclusion of Lyman- forest, large scale
structure and weak lensing observations. Astrophysical constraints are not
considered in the present paper. The bounds on the lifetime of decaying dark
matter are dominated by either the late-time integrated Sachs-Wolfe effect for
the scenario with weak reionization, or CMB polarization observations when
there is significant reionization. For the respective scenarios, the lifetimes
for decaying dark matter are Gyr and Gyr (at 95.4% confidence level), where the
phenomenological parameter is the fraction of the decay energy deposited in
baryonic gas. This allows us to constrain particle physics models with dark
matter candidates through investigation of dark matter decays into Standard
Model particles via effective operators. For decaying dark matter of
GeV mass, we found that the size of the coupling constant in the effective
dimension-4 operators responsible for dark matter decay has to generically be . We have also explored the implications of our analysis for
representative models in theories of gauge-mediated supersymmetry breaking,
minimal supergravity and little Higgs.Comment: 29 pages, 6 figures. Added references and corrected typos as well as
grammatical oversight