The everpresent eta-problem: knowledge of all hidden sectors required

TL;DR

This paper demonstrates that solving the eta-problem in supergravity inflation requires detailed knowledge of hidden sectors and their supersymmetry breaking scales, affecting inflaton dynamics and potentially necessitating multifield models.

Contribution

It shows that the eta-problem cannot be addressed without understanding hidden sectors' ground states and their supersymmetry breaking, highlighting the importance of sector interactions during inflation.

Findings

Hidden sectors influence the inflaton's eta parameter.

Neglecting hidden sectors can lead to inaccurate inflation models.

Multifield models may be necessary to resolve the eta-problem.

Abstract

We argue that the eta-problem in supergravity inflation cannot be solved without knowledge of the ground state of hidden sectors that are gravitationally coupled to the inflaton. If the hidden sector breaks supersymmetry independently, its fields cannot be stabilized during cosmological evolution of the inflaton. We show that both the subsequent dynamical mixing between sectors as well as the lightest mass of the hidden sector are set by the scale of supersymmetry breaking in the hidden sector. The true cosmological eta-parameter arises from a linear combination of the lightest mode of the hidden sector with the inflaton. Generically, either the true eta deviates considerably from the na\"ive eta implied by the inflaton sector alone, or one has to consider a multifield model. Only if the lightest mass in the hidden sector is much larger than the inflaton mass and if the inflaton mass is much larger than the scale of hidden sector supersymmetry breaking, is the effect of the hidden sector on the slow-roll dynamics of the inflaton negligible.