Floquet resonances and redshift-enhanced acceleration radiation from vibrating atoms in Schwarzschild spacetime

Abstract: We study acceleration radiation from a two-level Unruh-DeWitt detector that undergoes small-amplitude radial oscillations at fixed mean radius $R_0$ outside a Schwarzschild black hole. The massless scalar field is quantized in the Boulware vacuum to isolate curvature-modulated acceleration effects without a thermal Hawking background. Working in a (1+1) radial reduction and using first-order time-dependent perturbation, we evaluate the period-averaged transition rate (or the "Floquet" transition rate). The resulting particle emission spectrum exhibits a thermal Bose-Einstein-type profile with periodic trajectory yielding a Floquet resonance condition $n\Omega > \omega_0$ and a closed-form expression for the Floquet transition rate $\overline{P}n$ which reduces to the flat Minkowski spacetime result as $R_0\to\infty$. Near the horizon, $f(R_0)<1$ enhances the effective Bessel argument by $1/\sqrt{f(R_0)}$, providing a simple analytic demonstration of curvature/redshift amplification of acceleration radiation. In particular, the spectrum weighted by Bessel function becomes ill-defined near the black hole horizon as $R{0}\rightarrow 2M$, possibly manifesting the well-known pathological behavior of Boulware vacuum state. We discuss the regime of validity (small amplitude, $R_0$ away from the horizon) and outline the extensions to (3+1) dimensions, including density-of-states and greybody factors, and to alternative vacuum choices. Our results offer an analytically tractable link between flat-space "vibrating atom" proposals and black-hole spacetimes.