A crucial ingredient of inflation

TL;DR

This paper discusses the importance of nonminimal coupling in inflationary models, analyzing the determination of coupling constants, the slow-roll approximation, and perturbations, highlighting open problems in the generalized inflation paradigm.

Contribution

It advances the understanding of nonminimal coupling effects in inflation, including the determination of coupling constants and the behavior of perturbations.

Findings

Coupling constant values critically influence inflation success.

Slow-roll approximation is extended to include nonminimal coupling.

Open problems remain in scalar and tensor perturbation analysis.

Abstract

Nonminimal coupling of the inflaton field to the Ricci curvature of spacetime is generally unavoidable, and the paradigm of inflation should be generalized by including the corresponding term in the Lagrangian of the inflationary theory. This paper reports on the status of the programme of generalizing inflation. First, the problem of finding the correct value (or set of values) of the coupling constant is analyzed; the result has important consequences for the success or failure of inflationary scenarios. Then, the slow-roll approximation to generalized inflation is studied. Both the unperturbed inflating universe models and scalar/tensor perturbations are discussed, and open problems are pointed out.