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

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 $\ell$. 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

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 $\beta$ can be alleviated to a certain extent at the level of two standard deviations.Comment: 23 pages, 11 figure