We use the Ly-α forest power spectrum measured by the Sloan Digital Sky Survey (SDSS) and high-resolution spectroscopy observations in combination with cosmic microwave background and galaxy clustering constraints to place limits on a sterile neutrino as a dark matter candidate in the warm dark matter (WDM) scenario. Such a neutrino would be created in the early universe through mixing with an active neutrino and would suppress structure on scales smaller than its free streaming scale. We ran a series of high-resolution hydrodynamic simulations with varying neutrino mass to describe the effect of a sterile neutrino on the Ly-α forest power spectrum. We find that the mass limit is ms > 14keV at 95% c.l. (10keV at 99.9%), which is nearly an order of magnitude tighter constraint than previously published limits and is above the upper limit allowed by X-ray constraints, excluding this candidate as dark matter in this model. The corresponding limit for a neutrino that decoupled early while in thermal equilibrium is 2.5keV (95 % c.l.). One of the major unsolved mysteries in cosmology is the nature of the dark matter in the universe. Observational evidence points towards cold dark matter (CDM), for which random velocities are negligible. Two of the leading particle physics candidates, the lightest supersymmetric partner and axions, both require extensions beyond the standard model. At the same time, neutrino experiments over the past decade have shown that neutrinos oscillate from one flavor to another, which is only possible if they have mass. Current data from atmospheric and solar neutrino experiments [1,2] are compatible with mixing between the three active neutrino families. Perhaps the simplest way to incorporate these neutrino phenomena into the standard model is to add right-handed neutrinos, just as for other fermions.Given this extension of the standard model it is natural to ask if these (almost) sterile right-handed neutrinos can also explain the dark matter [3]. At least two sterile neutrinos are required to explain the origin of neutrino mass and existence of different mass mixing scales in solar and atmospheric neutrinos, so in a model with three families of sterile neutrinos a third one can act as dark matter [4]. Such neutrinos free stream and erase all fluctuations on scales smaller than the free streaming length. This length is roughly proportional to the temperature and inversely proportional to the mass of neutrinos. Thus if the neutrino mass is sufficiently high, or the temperature sufficiently low, then it acts just like CDM and can satisfy all of the observational constraints from structure formation. Current constraints require the neutrino mass to be above 1.8keV [5,6]. This is below the 5-8keV upper limits from the absence of detection of X-ray photons from radiative decays [7,8,9,10]. A massive neutrino in the keV range has also been suggested as a possible explanation for high pulsar velocities [11] and such a model can possibly explain baryon asymmetry in the universe [12].A sterile neutri...

We combine the measurements of luminosity dependence of bias with the luminosity dependent weak lensing analysis of dark matter around galaxies to derive the galaxy bias and constrain amplitude of mass fluctuations. We take advantage of theoretical and simulation predictions that predict that while halo bias is rapidly increasing with mass for high masses, it is nearly constant in low mass halos. We use a new weak lensing analysis around the same SDSS galaxies to determine their halo mass probability distribution. We use these halo mass probability distributions to predict the bias for each luminosity subsample. Galaxies below L * are antibiased with b < 1 and for these galaxies bias is only weakly dependent on luminosity. In contrast, for galaxies above L * bias is rapidly increasing with luminosity. These observations are in an excellent agreement with theoretical predictions based on weak lensing halo mass determination combined with halo bias-mass relations. We find that for standard cosmological parameters theoretical predictions are able to explain the observed luminosity dependence of bias over 6 magnitudes in absolute luminosity. We combine the bias constraints with those from the WMAP and the SDSS power spectrum analysis to derive new constraints on bias and σ8. For the most general parameter space that includes running and neutrino mass we find σ8 = 0.88 ± 0.06 and b * = 0.99 ± 0.07. In the context of spatially flat models we improve the limit on the neutrino mass for the case of 3 degenerate families from mν < 0.6eV without bias to mν < 0.18eV with bias (95% c.l.), which is weakened to mν < 0.24eV if running is allowed. The corresponding limit for 3 massless + 1 massive neutrino is 1.37eV.

We combine the constraints from the recent Ly-α forest analysis of the Sloan Digital Sky Survey (SDSS) and the SDSS galaxy bias analysis with previous constraints from SDSS galaxy clustering, the latest supernovae, and 1st year WMAP cosmic microwave background anisotropies. We find significant improvements on all of the cosmological parameters compared to previous constraints, which highlights the importance of combining Lyα forest constraints with other probes. Combining WMAP and the Lyα forest we find for the primordial slope ns = 0.98 ± 0.02. We see no evidence of running, dn/d ln k = −0.003 ± 0.010, a factor of 3 improvement over previous constraints. We also find no evidence of tensors, r < 0.36 (95% c.l.). Inflationary models predict the absence of running and many among them satisfy these constraints, particularly negative curvature models such as those based on spontaneous symmetry breaking. A positive correlation between tensors and primordial slope disfavors chaotic inflation type models with steep slopes: while the V ∝ φ 2 model is within the 2-sigma contour, V ∝ φ 4 is outside the 3-sigma contour. For the amplitude we find σ8 = 0.90 ± 0.03 from the Lyα forest and WMAP alone. We find no evidence of neutrino mass: for the case of 3 massive neutrino families with an inflationary prior, mν < 0.42eV and the mass of lightest neutrino is m1 < 0.13eV at 95% c.l. For the 3 massless + 1 massive neutrino case we find mν < 0.79eV for the massive neutrino, excluding at 95% c.l. all neutrino mass solutions compatible with the LSND results. We explore dark energy constraints in models with a fairly general time dependence of dark energy equation of state, finding Ω λ = 0.72 ± 0.02, w(z = 0.3) = −0.98 +0.10 −0.12 , the latter changing to w(z = 0.3) = −0.92 +0.09 −0.10 if tensors are allowed. We find no evidence for variation of the equation of state with redshift, w(z = 1) = −1.03 +0.21 −0.28 . These results rely on the current understanding of the Lyα forest and other probes, which need to be explored further both observationally and theoretically, but extensive tests reveal no evidence of inconsistency among different data sets used here.

We present the 3D real-space clustering power spectrum of a sample of ∼600 000 luminous red galaxies measured by the Sloan Digital Sky Survey, using photometric redshifts. These galaxies are old, elliptical systems with strong 4000-Å breaks, and have accurate photometric redshifts with an average error of z = 0.03. This sample of galaxies ranges from redshift z = 0.2 to 0.6 over 3528 deg 2 of the sky, probing a volume of 1.5 h −3 Gpc 3 , making it the largest volume ever used for galaxy clustering measurements. We measure the angular clustering power spectrum in eight redshift slices and use well-calibrated redshift distributions to combine these into a high-precision 3D real-space power spectrum from k = 0.005 to k = 1 h Mpc −1 . We detect power on gigaparsec scales, beyond the turnover in the matter power spectrum, at a ∼2σ significance for k < 0.01 h Mpc −1 , increasing to 5.5σ for k < 0.02 h Mpc −1 . This detection of power is on scales significantly larger than those accessible to current spectroscopic redshift surveys. We also find evidence for baryonic oscillations, both in the power spectrum, as well as in fits to the baryon density, at a 2.5 σ confidence level. The large volume and resulting small statistical errors on the power spectrum allow us to constrain both the amplitude and the scale dependence of the galaxy bias in cosmological fits. The statistical power of these data to constrain cosmology is ∼1.7 times better than previous clustering analyses. Varying the matter density and baryon fraction, we find M = 0.30 ± 0.03, and b / M = 0.18 ± 0.04, for a fixed Hubble constant of 70 km s −1 Mpc −1 and a scale-invariant spectrum of initial perturbations. The detection of baryonic oscillations also allows us to measure the comoving distance to E-mail: NPadmanabhan@lbl.gov C 2007 The Authors. Journal compilation C 2007 RASClustering of LRGs in the SDSS data 853 z = 0.5; we find a best-fitting distance of 1.73 ± 0.12 Gpc, corresponding to a 6.5 per cent error on the distance. These results demonstrate the ability to make precise clustering measurements with photometric surveys.

The large scale anisotropies of WMAP data have attracted a lot of attention and have been a source of controversy, with many of favourite cosmological models being apparently disfavoured by the power spectrum estimates at low ℓ. All of the existing analyses of theoretical models are based on approximations for the likelihood function, which are likely to be inaccurate on large scales. Here we present exact evaluations of the likelihood of the low multipoles by direct inversion of the theoretical covariance matrix for low resolution WMAP maps. We project out the unwanted galactic contaminants using the WMAP derived maps of these foregrounds. This improves over the template based foreground subtraction used in the original analysis, which can remove some of the cosmological signal and may lead to a suppression of power. As a result we find an increase in power at low multipoles. For the quadrupole the maximum likelihood values are rather uncertain and vary between 140-220µK 2 . On the other hand, the probability distribution away from the peak is robust and, assuming a uniform prior between 0 and 2000µK 2 , the probability of having the true value above 1200µK 2 (as predicted by the simplest ΛCDM model) is 10%, a factor of 2.5 higher than predicted by WMAP likelihood code. We do not find the correlation function to be unusual beyond the low quadrupole value. We develop a fast likelihood evaluation routine that can be used instead of WMAP routines for low ℓ values. We apply it to the Markov Chain Monte Carlo analysis to compare the cosmological parameters between the two cases. The new analysis of WMAP either alone or jointly with SDSS and VSA reduces the evidence for running to less than 1-σ, giving αs = −0.022 ± 0.033 for the combined case. The new analysis prefers about 1-σ lower value of Ωm, a consequence of an increased ISW contribution required by the increase in the spectrum at low ℓ. These results suggest that the details of foreground removal and full likelihood analysis are important for the parameter estimation from WMAP data. They are robust in the sense that they do not change significantly with frequency, mask or details of foreground template marginalization. The marginalization approach presented here is the most conservative method to remove the foregrounds and should be particularly useful in the analysis of polarization, where foreground contamination may be much more severe.