Cosmological parameter analysis including SDSS Ly-alpha forest and galaxy bias: constraints on the primordial spectrum of fluctuations, neutrino mass, and dark energy

TL;DR

This study reports a joint cosmological parameter analysis that combines WMAP with SDSS Lyα forest data and SDSS bias to constrain the primordial power spectrum, neutrino masses, and dark energy. Using a comprehensive MCMC framework and incorporating nuisance marginalization for Lyα and bias, it finds a nearly scale-invariant spectrum with no detected running or tensors and tight upper bounds on the sum of neutrino masses (∑mν < 0.42 eV for 3 degenerate families). It also constrains dark energy to w ≈ -1 with no significant time evolution and yields σ8 ≈ 0.90 and Ω_m ≈ 0.28, with improved precision over previous analyses. These results reinforce the standard cosmological model and place strong constraints on inflationary models, while highlighting the importance of systematics control in Lyα and bias analyses for robust future refinements.

Abstract

We combine the constraints from the recent Ly-alpha forest and bias analysis of the SDSS with previous constraints from SDSS galaxy clustering, the latest supernovae, and WMAP . Combining WMAP and the lya we find for the primordial slope n_s=0.98\pm 0.02. We see no evidence of running, dn/d\ln k=-0.003\pm 0.010, a factor of 3 improvement over previous constraints. We also find no evidence of tensors, r<0.36 (95% c.l.). A positive correlation between tensors and primordial slope disfavors chaotic inflation type models with steep slopes: V \propto φ^4 is outside the 3-sigma contour. For the amplitude we find sigma_8=0.90\pm 0.03 from the lyaf and WMAP alone. We find no evidence of neutrino mass: for the case of 3 massive neutrino families with an inflationary prior, \sum m_ν<0.42eV and the mass of lightest neutrino is m_1<0.13eV at 95% c.l. For the 3 massless + 1 massive neutrino case we find m_ν<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 Omega_lambda=0.72\pm 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 lyaf 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.

Figures (14)

• Figure 1: 68% (inner, blue) and 95% (outer, red) contours in the plane of $\tau)$ versus $\Omega_m$, $h$, $\sigma_8$ and $n_s$, respectively, using all measurements.
• Figure 2: 68% (inner, dark) and 95% (outer, light) contours in the $(r=T/S,n_s)$ plane with and without SDSS-lya. There is a correlation between tensors and slope $n_s$. Inclusion of the Ly$\alpha$ forest significantly reduces the allowed region in this plane. Also shown are the positions of two chaotic inflation models, $V\propto \phi^2$ with $N=50$ and $V \propto \phi^4$ with $N=60$.
• Figure 3: 68% (inner, dark) and 95% (outer, light) contours in the $(\alpha_s,n_s)$ plane using WMAP+SDSS-lya versus WMAP+SDSS-gal+bias. Adding the SDSS Ly$\alpha$ forest dramatically reduces the allowed region of parameter space in this plane. Note that the simplest model with $n_s=1$ and $\alpha_s=0$ is within 68% interval.
• Figure 4: 68% (inner, dark) and 95% (outer, light) contours in the $(\alpha_s,r)$ plane using WMAP+SDSS-lya versus WMAP+SDSS-gal+bias. Adding the SDSS Ly$\alpha$ forest dramatically reduces the allowed region of parameter space in this plane. Note that the simplest model with $\alpha_s=0$ and $r=0$ is within the 68% interval.
• Figure 5: 68% and 95% contours in the $(\Omega_m, \sigma_8)$ plane showing previous constraints from WMAP and galaxy clustering with the new data.