Nonminimally coupled scalar field in Schwarzschild--de Sitter spacetime: Geodesic synchrotron radiation

TL;DR

This paper investigates scalar radiation emitted by a source near a black hole in de Sitter space, revealing how nonminimal coupling affects emission patterns and power, with implications for understanding quantum fields in curved spacetime.

Contribution

It provides a detailed analysis of scalar radiation in Schwarzschild--de Sitter spacetime considering nonminimal coupling, highlighting the impact on emission characteristics and multipole contributions.

Findings

Synchrotron radiation occurs near the photon sphere for all parameter values.

Emitted power depends strongly on the scalar-curvature coupling.

Lower multipole contributions are suppressed with conformal coupling.

Abstract

We analyze the scalar radiation emitted by a source interacting with a nonminimally coupled scalar field in four-dimensional Schwarzschild--de Sitter spacetime. We obtain the emission probability using quantum field theory in curved spacetimes at tree level. We find that the source emits synchrotron-type radiation for orbits near the photon sphere for all allowed values of the parameters. We also find that the emitted power strongly depends on the coupling to the curvature scalar. In particular, the previously observed enhancement in the contribution of lower multipoles to the emitted power in this spacetime with minimal coupling is absent when conformal coupling is considered.