Hybrid cosmological attractors

Abstract

We construct α-attractor versions of hybrid inflation models. In these models, the potential of the inflaton field φ is uplifted by the potential of the second field χ. This uplifting ends due to a tachyonic instability with respect to the field χ, which appears when φ becomes smaller than some critical value φc. In the large N limit, these models have the standard universal α-attractor predictions. In particular, ns=1-2N for the exponential attractors. However, in some special cases, the large N limit is reached only beyond the horizon, for N≳60. This may change predictions for the cosmological observations. For any fixed N, in the limit of large uplift Vup, or in the limit of large φc, we find another attractor prediction, ns=1. By changing the parameters, Vup and φc, one can continuously interpolate between the two attractor predictions ns=1-2N and ns=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 reason, is uplifted, and inflation ends prematurely.