Soft Scalars don't decouple

TL;DR

This paper shows that massless scalar particles can exhibit infrared behavior similar to gauge theories without gauge invariance, and unlike photons or gravitons, they do not decouple from dressed states, affecting the understanding of soft particle interactions.

Contribution

It introduces a field theory with massless scalars mimicking gauge theory infrared structure without gauge invariance or asymptotic symmetries.

Findings

Soft scalars do not decouple from dressed states.

Soft scalars are produced during interactions of hard dressed particles.

Entanglement between hard and soft scalars is negligible.

Abstract

It is demonstrated that it is possible to find a field theory containing massless scalar particles which has infrared structure closely resembling that of quantum electrodynamics and perturbative quantum gravity but exhibiting no gauge invariance or internal symmetries at all, and in particular, no apparent asymptotic symmetry. It is shown that, unlike soft photons and gravitons, the soft scalars do not decouple from dressed states and they are generically produced when hard dressed particles interact. However, the entanglement of the hard and resulting soft particles is vanishingly small.