Hybrid cosmological attractors

TL;DR

This paper develops hybrid inflation models with $ extit{ extbf{α}}$-attractor properties, showing how parameters influence spectral index predictions and providing flexible models adaptable to precise cosmological data.

Contribution

It introduces $ extit{ extbf{α}}$-attractor hybrid inflation models with adjustable predictions, applicable to a broad class of uplifted inflationary scenarios.

Findings

In the large $N$ limit, models reproduce universal $ extit{ extbf{α}}$-attractor predictions.

Adjusting parameters $V_{up}$ and $ extphi_c$ interpolates between different spectral index predictions.

Models offer flexibility to match evolving cosmological observational constraints.

Abstract

We construct $\alpha$-attractor versions of hybrid inflation models. In these models, the potential of the inflaton field $\varphi$ is uplifted by the potential of the second field $\chi$. This uplifting ends due to a tachyonic instability with respect to the field $\chi$, which appears when $\varphi$ becomes smaller than some critical value $\varphi_{c}$. In the large $N$ limit, these models have the standard universal $\alpha$-attractor predictions. In particular, $n_{s }= 1- {2 \over N}$ for the exponential attractors. However, in some special cases the large $N$ limit is reached only beyond the horizon, for $N \gtrsim 60$. This may change predictions for the cosmological observations. For any fixed $N$, in the limit of large uplift $V_{\rm up}$, or in the limit of large $\varphi_{c}$, we find another attractor prediction, $ n_s = 1$. By changing the parameters $V_{\rm up}$ and $\varphi_{c}$ one can continuously interpolate between the two attractor predictions $n_{s }= 1- {2 \over N}$ and $n_{s} = 1$. This provides significant flexibility, which can be very welcome in view of the rapidly growing amount and precision of the cosmological data. Our main result is not specific to the hybrid inflation models. Rather, it is generic to any inflationary models where the inflaton potential, for some reasons, is uplifted, and inflation ends prematurely.