# On scalar radiation

## TL;DR

This paper investigates scalar field radiation, revealing that non-minimal coupling affects energy positivity and Lorentz invariance, with implications for conformal field theories and supersymmetric probes.

## Contribution

It uncovers how non-minimal coupling alters scalar radiation properties and establishes a universal relation in conformal field theories, with evidence for coupling-independent energy-momentum tensor behavior in supersymmetric probes.

## Key findings

- Radiative energy density can be negative with non-minimal coupling.
- Radiated power depends on acceleration derivatives and is not Lorentz invariant.
- Energy-momentum tensor one-point function is coupling-independent for certain supersymmetric probes.

## Abstract

We discuss radiation in theories with scalar fields. Our key observation is that even in flat spacetime, the radiative fields depend qualitatively on the coupling of the scalar field to the Ricci scalar: for non-minimally coupled scalars, the radiative energy density is not positive definite, the radiated power is not Lorentz invariant and it depends on the derivative of the acceleration. We explore implications of this observation for radiation in conformal field theories. First, we find a relation between two coefficients that characterize radiation, that holds in all the conformal field theories we consider. Furthermore, we find evidence that for a $1/2$-BPS probe coupled to ${\cal N}=4$ super Yang-Mills, and following an arbitrary trajectory, the spacetime dependence of the one-point function of the energy-momentum tensor is independent of the Yang-Mills coupling.