Attractive Lagrangians for Noncanonical Inflation

TL;DR

This paper develops a framework for constructing and analyzing noncanonical inflation models with higher-dimensional kinetic operators, showing they can be viable and are attractors in phase space, thus broadening the class of inflationary theories.

Contribution

It introduces a method to construct noncanonical inflationary solutions and identifies conditions for their viability, extending the known landscape of inflationary Lagrangians.

Findings

Noncanonical inflation solutions can be constructed explicitly.

Noncanonical inflation acts as an attractor in phase space.

Certain functional forms of the Lagrangian support successful inflation.

Abstract

Treating inflation as an effective theory, we expect the effective Lagrangian to contain higher-dimensional kinetic operators suppressed by the scale of UV physics. When these operators are powers of the inflaton kinetic energy, the scalar field can support a period of noncanonical inflation which is smoothly connected to the usual slow-roll inflation. We show how to construct noncanonical inflationary solutions to the equations of motion for the first time, and demonstrate that noncanonical inflation is an attractor in phase space for all small- and large-field models. We identify some sufficient conditions on the functional form of the Lagrangian that lead to successful noncanonical inflation since not every Lagrangian with higher-dimensional kinetic operators can support noncanonical inflation. This extends the class of known viable Lagrangians and excludes many Lagrangians which do not work.