Enhancement and suppression of decay rates in an accelerated fermionic cavity coupled to a massive field

We study a (1+1)-dimensional model in which a massless Dirac field, initially in an excited state inside a uniformly accelerated cavity, decays to its ground state, accompanied by the excitation of an external massive Dirac field of mass M, through a local coupling confined to the physical extent of the cavity. The confinement mechanism is modeled via MIT bag boundary conditions and their probabilistic extensions, which depend on a boundary angle θ ∈ [ 0, 2 π ) and s ∈ (0, 1). For intermediate-sized cavities (a l ∼ c 2) with light external massive Dirac field (M c 2 ≪ ℏ a / c), we demonstrate that the total long-time asymptotic decay rate factorizes as Γ acc / Γ in ∼ F g F T with Γ in the inertial decay rate. Here, F g = a l / c 2 ln ⁡ (1 + a l / c 2) is a geometric factor, and F T = (1 + e − 2 π β) − 1 is the thermal stimulation factor from the Unruh bath (β = Ω 1 c a = ( 1 + s) π ln ⁡ (1 + a l / c 2)). Crucially, in this regime, the thermal factor F T remains approximately unity for all admissible boundary conditions, while the geometric factor a l / c 2 ln ⁡ (1 + a l / c 2) produces measurable enhancements up to 26% for realistic parameters (a = 10 20ms⁻², l = 500 μm), and represents a measurable signature accessible through quantum simulation platforms. In contrast, for heavy external fermionic fields (such as the electron field), the condition M c 2 ≫ ℏ a / c is satisfied at all achievable accelerations, placing the system in a regime of exponential suppression, Γ acc / Γ in ∼ exp ⁡ (− 2 M c 2 / ( ℏ a / c) ), for all cavity sizes. This suggests that, within this specific model, the observable decay signatures of acceleration are strongly suppressed, rendering Unruh-induced enhancements highly improbable in experiments involving heavy fermions under these conditions.