Constraining The Universal Lepton Asymmetry

The relic cosmic background neutrinos accompanying the cosmic microwave background (CMB) photons may hide a universal lepton asymmetry orders of magnitude larger than the universal baryon asymmetry. At present, the only direct way to probe such an asymmetry is through its effect on the abundances of the light elements produced during primordial nucleosynthesis. The relic light element abundances also depend on the baryon asymmetry, parameterized by the baryon density parameter (eta_B = n_B/n_gamma = 10^(-10)*eta_10), and on the early-universe expansion rate, parameterized by the expansion rate factor (S = H'/H) or, equivalently by the effective number of neutrinos (N_nu = 3 + 43(S^2 - 1)/7). We use data from the CMB (and Large Scale Structure: LSS) along with the observationally-inferred relic abundances of deuterium and helium-4 to provide new bounds on the universal lepton asymmetry, finding for eta_L, the analog of eta_B, 0.072 +/- 0.053 if it is assumed that N_nu = 3 and, 0.115 +/- 0.095 along with N_nu = 3.3^{+0.7}_{-0.6}, if N_nu is free to vary

An Accelerating Cosmology Without Dark Energy

The negative pressure accompanying gravitationally-induced particle creation can lead to a cold dark matter (CDM) dominated, accelerating Universe (Lima et al. 1996) without requiring the presence of dark energy or a cosmological constant. In a recent study Lima et al. (2008, LSS) demonstrated that particle creation driven cosmological models are capable of accounting for the SNIa observations of the recent transition from a decelerating to an accelerating Universe. Here we test the evolution of such models at high redshift using the constraint on z_eq, the redshift of the epoch of matter radiation equality, provided by the WMAP constraints on the early Integrated Sachs-Wolfe effect. Since the contribution of baryons and radiation was ignored in the work of LSS, we include them in our study of this class of models. The parameters of these more realistic models with continuous creation of CDM is tested and constrained at widely-separated epochs (z = z_eq and z = 0) in the evolution of the Universe. This comparison reveals a tension between the high redshift CMB constraint on z_eq and that which follows from the low redshift SNIa data, challenging the viability of this class of models.Comment: 12 pages, 8 figure

WMAP 5-year constraints on lepton asymmetry and radiation energy density: Implications for Planck

In this paper we set bounds on the radiation content of the Universe and neutrino properties by using the WMAP-5 year CMB measurements complemented with most of the existing CMB and LSS data (WMAP5+All),imposing also self-consistent BBN constraints on the primordial helium abundance. We consider lepton asymmetric cosmological models parametrized by the neutrino degeneracy parameter and the variation of the relativistic degrees of freedom, due to possible other physical processes occurred between BBN and structure formation epochs. We find that WMAP5+All data provides strong bounds on helium mass fraction and neutrino degeneracy parameter that rivals the similar bounds obtained from the conservative analysis of the present data on helium abundance. We also find a strong correlation between the matter energy density and the redshift of matter-radiation equality, z_re, showing that we observe non-zero equivalent number of relativistic neutrinos mainly via the change of the of z_re, rather than via neutrino anisotropic stress claimed by the WMAP team. We forecast that the CMB temperature and polarization measurements observed with high angular resolutions and sensitivities by the future Planck satellite will reduce the errors on these parameters down to values fully consistent with the BBN bounds

The Atacama Cosmology Telescope: Cosmological Parameters from the 2008 Power Spectra

We present cosmological parameters derived from the angular power spectrum of the cosmic microwave background (CMB) radiation observed at 148 GHz and 218 GHz over 296 deg^2 with the Atacama Cosmology Telescope (ACT) during its 2008 season. ACT measures fluctuations at scales 500<l<10000. We fit a model for the lensed CMB, Sunyaev-Zel'dovich (SZ), and foreground contribution to the 148 GHz and 218 GHz power spectra, including thermal and kinetic SZ, Poisson power from radio and infrared point sources, and clustered power from infrared point sources. The power from thermal and kinetic SZ at 148 GHz is estimated to be B_3000 = 6.8+-2.9 uK^2, where B_l=l(l+1)C_l/2pi. We estimate primary cosmological parameters from the 148 GHz spectrum, marginalizing over SZ and source power. The LCDM cosmological model is a good fit to the data, and LCDM parameters estimated from ACT+WMAP are consistent with the 7-year WMAP limits, with scale invariant n_s = 1 excluded at 99.7% CL (3sigma). A model with no CMB lensing is disfavored at 2.8sigma. By measuring the third to seventh acoustic peaks, and probing the Silk damping regime, the ACT data improve limits on cosmological parameters that affect the small-scale CMB power. The ACT data combined with WMAP give a 6sigma detection of primordial helium, with Y_P = 0.313+-0.044, and a 4sigma detection of relativistic species, assumed to be neutrinos, with Neff = 5.3+-1.3 (4.6+-0.8 with BAO+H0 data). From the CMB alone the running of the spectral index is constrained to be dn/dlnk = -0.034 +- 0.018, the limit on the tensor-to-scalar ratio is r<0.25 (95% CL), and the possible contribution of Nambu cosmic strings to the power spectrum is constrained to string tension Gmu<1.6 \times 10^-7 (95% CL).Comment: 20 pages, 13 figures. Submitted to ApJ. This paper is a companion to Hajian et al. (2010) and Das et al. (2010