Light--like propagation of self--interacting Klein--Gordon fields in cosmology

TL;DR

This paper demonstrates that complex scalar fields with self-interactions can propagate along null geodesics in flat FRW cosmologies, regardless of their mass, under certain interaction conditions.

Contribution

It shows that self-interacting Klein-Gordon fields can propagate along null geodesics in cosmological models, extending understanding of scalar field dynamics in the universe.

Findings

Scalar fields can propagate along null geodesics with suitable self-interactions.

Propagation occurs in flat FRW universes with various scale factors.

Massive fields can also follow null geodesics under certain conditions.

Abstract

It is showed that complex scalar fields with a self-interaction potential may propagate along null geodesics on flat Friedmann--Lema\^itre--Robertson--Walker universes with different time-dependent scale factors. This occurs provided they self interact adequately, for different forms of potentials, and even for the massive case.