Coupling Hybrid Inflation to Moduli

TL;DR

Coupling moduli to hybrid inflation in supergravity introduces challenges for slow-roll conditions, but implementing shift symmetries and no-scale moduli sectors can mitigate these issues, though moduli variations still impact inflation dynamics.

Contribution

The paper demonstrates how moduli coupling affects hybrid inflation in supergravity and proposes solutions using shift symmetries and no-scale models to achieve viable inflation.

Findings

Moduli coupling introduces problematic slope and curvature in the inflaton potential.

Shift symmetries and no-scale moduli sectors can alleviate inflationary issues.

Small moduli variations during inflation significantly influence the inflaton potential.

Abstract

Hybrid inflation can be realised in low-energy effective string theory, as described using supergravity. We find that the coupling of moduli to F-term hybrid inflation in supergravity leads to a slope and a curvature for the inflaton potential. The epsilon and eta parameters receive contributions at tree and one loop level which are not compatible with slow roll inflation. Furthermore the coupling to the moduli sector can even prevent inflation from ending at all. We show that introducing shift symmetries in the inflationary sector and taking the moduli sector to be no-scale removes most of these problems. If the moduli fields are fixed during inflation, as is usually assumed, it appears that viable slow-roll inflation can then be obtained with just one fine-tuning of the moduli sector parameters. However, we show this is not a reasonable assumption, and that the small variation of the moduli fields during inflation gives a significant contribution to the effective inflaton potential. This typically implies that eta is approximately -6, although it may be possible to obtain smaller values with heavy fine-tuning.