Neutrino masses and cosmology with Lyman-alpha forest power spectrum (1506.05976v3)

Abstract: We present constraints on neutrino masses, the primordial fluctuation spectrum from inflation, and other parameters of the $\Lambda$CDM model, using the one-dimensional Ly$\alpha$-forest power spectrum measured by Palanque-Delabrouille et al. (2013) from SDSS-III/BOSS, complemented by Planck 2015 cosmic microwave background (CMB) data and other cosmological probes. This paper improves on the previous analysis by Palanque-Delabrouille et al. (2015) by using a more powerful set of calibrating hydrodynamical simulations that reduces uncertainties associated with resolution and box size, by adopting a more flexible set of nuisance parameters for describing the evolution of the intergalactic medium, by including additional freedom to account for systematic uncertainties, and by using Planck 2015 constraints in place of Planck 2013. Fitting Ly$\alpha$ data alone leads to cosmological parameters in excellent agreement with the values derived independently from CMB data, except for a weak tension on the scalar index $n_s$. Combining BOSS Ly$\alpha$ with Planck CMB constrains the sum of neutrino masses to $\sum m_\nu < 0.12$ eV (95\% C.L.) including all identified systematic uncertainties, tighter than our previous limit (0.15 eV) and more robust. Adding Ly$\alpha$ data to CMB data reduces the uncertainties on the optical depth to reionization $\tau$, through the correlation of $\tau$ with $\sigma_8$. Similarly, correlations between cosmological parameters help in constraining the tensor-to-scalar ratio of primordial fluctuations $r$. The tension on $n_s$ can be accommodated by allowing for a running ${\mathrm d}n_s/{\mathrm d}\ln k$. Allowing running as a free parameter in the fits does not change the limit on $\sum m_\nu$. We discuss possible interpretations of these results in the context of slow-roll inflation.

• The paper presents improved constraints on neutrino masses, tightening the limit to ∑ mν < 0.12 eV with extensive hydrodynamical simulations.
• The analysis employs refined intergalactic medium models and systematic uncertainty treatments to harmonize Lyα forest and CMB data.
• The study demonstrates the complementarity of Lyα and Planck observations, offering new insights into reionization history and inflationary dynamics.

Neutrino Mass Constraints and Cosmological Insights from the Lyman-alpha Forest Power Spectrum

The paper "Neutrino masses and cosmology with Lyman-alpha forest power spectrum" presents an in-depth analysis of cosmological parameters, particularly focusing on constraining the sum of neutrino masses ($\sum m_\nu$), using the Lyman-alpha (Ly$\alpha$) forest data from the Baryon Oscillation Spectroscopic Survey (BOSS). This paper is augmented by complementary data from the Planck cosmic microwave background (CMB) observations and other cosmological probes.

Significant improvements over previous analyses are achieved through a more extensive set of hydrodynamical simulations, allowing reduced uncertainties associated with resolution and box size. The paper employs a refined model for the intergalactic medium (IGM) temperature and incorporates a comprehensive set of systematic uncertainties. When Ly$\alpha$ forest data is independently analyzed, the resulting cosmological parameters align well with those derived from CMB data, except for slight tension with the scalar index $n_s$.

When combining Ly$\alpha$ data with the Planck CMB results, the constraint on the sum of neutrino masses tightens to $\sum m_\nu < 0.12$ eV at 95% confidence level, surpassing the prior limit of 0.15 eV and offering a more robust estimate. This enhancement in precision largely stems from improved simulation calibration and expanded redshift coverage in the analysis.

Through correlation analyses, it is demonstrated how Ly$\alpha$ data bolsters constraints on other cosmological parameters such as the optical depth to reionization $\tau$. Reduction in uncertainty on this parameter is achieved through synergy with the measurement of $\sigma_8$ from Ly$\alpha$ data, highlighting the complementarity of these datasets. Additionally, there is a noted but small tension in $n_s$, which is partly addressed by introducing a running of the scalar spectral index ${\mathrm d}n_s/{\mathrm d}\ln k$. However, the negative running derived appears statistically significant mainly because of the systematic-level misalignment between the Ly$\alpha$ and CMB datasets.

In the exploration of potential deviations from the standard $\Lambda$CDM model, the paper investigates the implications of non-zero ${\mathrm d}n_s/{\mathrm d}\ln k$ and its modest impact on the neutrino mass limit, emphasizing that constraints on $\sum m_\nu$ remain robust irrespective. The introduction of tensor to scalar ratio $r$ and its interplay with Ly$\alpha$ data provides additional insights into inflationary models.

The results, including stringent limits on neutrino masses and insights into the early universe's reionization history, have profound implications for structure formation and the role of neutrinos in cosmology. Future directions could involve refined datasets and methodological advances that further elucidate the physics underpinning these critical cosmological parameters. This analysis underscores the power of combining independent observational data to sharpen our understanding of fundamental cosmological properties and inflationary dynamics.