We present a generalized framework for $n$-photon processes involving a uniformly accelerated Unruh-DeWitt detector interacting with a massless scalar field. We utilize the $n$th-order Dyson series to derive the final quantum state for an arbitrary number of interactions. Our analysis covers both even-order processes, which return the detector to its initial state, and odd-order processes, which result in a change of the detector’s state. By employing a unified formalism and performing a complete, time-ordered integration, we obtain exact analytical expressions for the $n$-photon states. The results reveal a rich structure of resonant denominators corresponding to multiparticle processes, including new field-mediated resonances independent of the detector’s energy gap for $n>2$. Crucially, the analysis of odd-order transitions reveals an exponential factor, $\exp (-\pi \omega /a)$, characteristic of the Unruh thermal bath. By considering processes starting from the detector’s excited state, we demonstrate that the ratio of excitation to deexcitation amplitudes precisely recovers the Boltzmann factor, providing a higher-order confirmation of thermal detailed balance for the Unruh effect. This work provides a unified tool for studying multipartite entanglement and thermal phenomena in noninertial frames.

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• Quantum fields in curved spacetime
• Unruh effect