How robust are inflation model and dark matter constraints from cosmological data?

TL;DR

The paper probes how robust inflationary and dark-sector constraints are when expanding the cosmological parameter space beyond the vanilla ΛCDM model to include parameters like a nonzero neutrino mass, curvature, and a dynamic dark energy equation of state. Using CosmoMC with data from WMAP3, SDSS LRG, BAO, and SNLS, the authors reveal strong degeneracies, particularly between the tensor-to-scalar ratio $r$, the neutrino fraction $f_ν$, and the dark energy equation of state $w$, which can mask inflationary signals and relax dark-matter constraints. They show that λφ^4 chaotic inflation remains compatible with current data within this extended framework and, conversely, that if λφ^4 is correct it favours a quasi-degenerate neutrino mass sum of about $0.3$–$0.5$ eV, revealing a deep connection between inflationary physics and neutrino properties. The study also finds that the allowed dark-matter density bound broadens to $0.094<\Omega_c h^2<0.136$ (95% CL) when curvature and other parameters are allowed to vary, underscoring the need to account for extended cosmological models when interpreting particle-physics implications in cosmology.

Abstract

High-precision data from observation of the cosmic microwave background and the large scale structure of the universe provide very tight constraints on the effective parameters that describe cosmological inflation. Indeed, within a constrained class of LambdaCDM models, the simple lambda phi^4 chaotic inflation model already appears to be ruled out by cosmological data. In this paper, we compute constraints on inflationary parameters within a more general framework that includes other physically motivated parameters such as a nonzero neutrino mass. We find that a strong degeneracy between the tensor-to-scalar ratio r and the neutrino mass prevents lambda phi^4 from being excluded by present data. Reversing the argument, if lambda phi^4 is the correct model of inflation, it predicts a sum of neutrino masses at 0.3-0.5 eV, a range compatible with present experimental limits and within the reach of the next generation of neutrino mass measurements. We also discuss the associated constraints on the dark matter density, the dark energy equation of state, and spatial curvature, and show that the allowed regions are significantly altered. Importantly, we find an allowed range of 0.094 < Omega_c h^2 < 0.136 for the dark matter density, a factor of two larger than that reported in previous studies. This expanded parameter space may have implications for constraints on SUSY dark matter models.

Figures (9)

• Figure 1: Two-dimensional $68\ \%$ and $95 \ \%$ C.L. contours for the inflationary parameters $n_s$, $r$, and $\alpha_s$, using the full data set and parameter set B, and marginalised over the other $(10-2)$ parameters.
• Figure 2: Degeneracies between $r$ and $f_\nu,w$ for the full data set and parameter set B, marginalised over $(10-2)$ parameters.
• Figure 3: Two-dimensional $68 \ \%$ and $95 \ \%$ C.L. contours for $n_s$ and $r$, using parameter set C (consistent with predictions of chaotic inflation), and marginalised over $(9-2)$ parameters. The upper panel uses WMAP+SDSS data and the lower the full data set. The two short black/solid lines with boxes at the ends correspond to predictions of $\lambda \phi^4$ (top left) and $m^2 \phi^2$ models of inflation, with 46 to 60 $e$-foldings (left to right).
• Figure 4: Degeneracies between between $r$ and $f_\nu,w$ for the full data set and parameter set C, marginalised over $(9-2)$ parameters.
• Figure 5: Two-dimensional marginalised constraints on $n_s$ and $r$ for the parameter set C, but with the restriction $w=-1$.