# On backreaction effects in geometrical destabilisation of inflation

## TL;DR

This paper investigates how geometrical destabilisation in multi-field inflation models with negatively curved field space affects the inflationary trajectory, revealing a backreaction mechanism that prevents premature ending of inflation.

## Contribution

It demonstrates that a kinematical backreaction halts the instability in simple models, allowing inflation to continue along a modified trajectory.

## Key findings

- Backreaction effects shut off the instability.
- Unstable fluctuations assist backreaction but stay perturbative.
- Inflation proceeds along a sidetracked trajectory, not ending prematurely.

## Abstract

We study the geometrical instability arising in multi-field models of inflation with negatively-curved field space. We analyse how the homogeneous background evolves in presence of geometrical destabilisation, and show that, in simple models, a kinematical backreaction effect takes place that shuts off the instability. We also follow the evolution of the unstable scalar fluctuations. We show that they assist the kinematical backreaction while remaining in the perturbative regime. We conclude that, in the simplest models of geometrical destabilisation, inflation does not end prematurely, but rather proceeds along a modified, sidetracked, field-space trajectory.