Unruh-DeWitt detector in dimensionally-reduced static spherically symmetric spacetimes

Abstract: We study the dynamics of an Unruh-DeWitt detector interacting with a massless scalar field in an arbitrary static spherically symmetric spacetimes whose metric is characterised by a single metric function $f(r)$. In order to obtain clean physical insights, we employ the derivative coupling variant of the Unruh-DeWitt model in (1+1) dimensions where powerful conformal techniques enable closed-form expressions for the vacuum two-point functions. Due to the generality of the formalism, we will be able to study a very general class of static spherically symmetric (SSS) background. We pick three examples to illustrate our method: (1) non-singular Hayward black holes, (2) the recently discovered $D\to 4$ limit of Gauss-Bonnet black holes, and (3) the "black bounce" metric that interpolates Schwarzschild black holes and traversable wormholes. We also show that the derivative coupling Wightman function associated with the generalized Hartle-Hawking vacuum satisfies the KMS property with the well-known temperature $f'(r_\text{H})/(4\pi)$, where $r_\text{H}$ is the horizon radius.