Current and Future constraints on single-field $\alpha$-Attractor model

TL;DR

This paper forecasts how upcoming CMB experiments, especially CMB-S4, can constrain parameters of single-field $oldsymbol{ extalpha}$-attractor inflation models, improving understanding of inflationary energy scales and potential shapes.

Contribution

It provides detailed forecasts for constraints on $ extalpha$-attractor inflation parameters from future CMB data, including the impact of neutrino sector extensions.

Findings

Current CMB data tightly constrain $r/\alpha$ and $\alpha_S$.

CMB-S4 can measure $oldsymbol{ extalpha}$ with about 15% precision in optimistic detection scenarios.

Including neutrino sector slightly reduces parameter accuracy, but main conclusions remain valid.

Abstract

We study here the observational constraints on single-field inflationary models achievable with the next generation of CMB experiments. We particularly focus on a Stage-IV like experiment and forecasts its constraints on inflationary parameters in the context of $\alpha$-attractor inflation comprising a large class of single-field models. To tailor our forecasts we use as a fiducial model the results obtained with current CMB and LSS data, assuming the $\alpha$-model a priori. We found that current CMB data are able to place a tight bound on the ratio of the tensor-to-scalar ratio with the alpha parameter $r/\alpha = 3.87^{+0.78}_{-0.94}\cdot 10^{-3}$ and on the running of the scalar index $\alpha_S = -6.4^{+1.6}_{-1.3}\cdot 10^{-4}$ with a value of the scalar index consistent with current constraints. In the optimistic scenario of detection of primordial gravitational waves in the CMB B-mode polarization power spectra, we found that CMB-S4 will be able to achieve a $15\%$ bound on the value of the parameter $\alpha = 1.01^{+0.14}_{-0.18}$. This bound clearly show the ability of CMB-S4 to constrain not only the energy scale of inflation but also the shape of its potential. Enlarging the baseline model to also include the neutrino sector merely reduce the accuracy of $5\%$ leading to $\alpha = 1.07^{+0.18}_{-0.23}$ so that our main conclusions are still valid.