# Massive spin zero fields in cosmology and the tail-free property

## TL;DR

This paper explores the behavior of spin zero fields in cosmology, demonstrating that scalar radiation tails are unavoidable unless specific unnatural conditions are met, which has implications for inflaton fields in de Sitter space.

## Contribution

It generalizes the Huygens principle theorem to spin zero fields and applies it to cosmological inflaton fields, revealing the inevitability of radiation tails under realistic conditions.

## Key findings

- Scalar radiation tails are unavoidable in de Sitter-like space.
- Removing tails requires unnatural fine-tuning of parameters.
- The theorem extension clarifies wave propagation for spin zero fields.

## Abstract

Fields of spin $s \geq 1/2$ satisfying wave equations in a curved space obey the Huygens principle under certain conditions clarified by a known theorem. Here this theorem is generalized to spin zero and applied to an inflaton field in de Sitter-like space, showing that tails of scalar radiation are an unavoidable physical feature. Requiring the absence of tails, on the contrary, necessarily implies an unnatural tuning between cosmological constant, scalar field mass, and coupling constant to the curvature.