This work presents a unified semiclassical framework for understanding vacuum instability and particle production in curved spacetime. Building on established methods from quantum field theory in external fields and cosmological backgrounds, the paper synthesizes several traditionally distinct phenomena into a single conceptual and computational “dictionary.” The analysis connects nonperturbative Schwinger pair production in external electric fields, cosmological gravitational particle production in time-dependent (FLRW and de Sitter) spacetimes, and vacuum decay via Coleman and Coleman–De Luccia (CDL) bubble nucleation. A central idea is that these processes share a common geometric structure at the level of leading semiclassical exponents, governed by a competition between “cost” and “gain” contributions. Within this framework, worldline instantons describing Schwinger pair production are mapped onto thin-wall bubble solutions describing vacuum decay. This correspondence is made explicit through a parameter dictionary linking particle mass and electric field strength to domain-wall tension and vacuum energy differences. The result is a coherent interpretation of seemingly different phenomena as manifestations of a single underlying semiclassical mechanism. The framework is further extended to holonomy–radion effective field theories motivated by Kaluza–Klein constructions. In this setting, the paper highlights a mechanism of modulus-assisted vacuum decay, in which radion dynamics effectively reduce the domain-wall tension and can lead to an exponential enhancement of decay rates within controlled semiclassical regimes. The analysis also clarifies the role of gravitational backreaction and identifies the conditions under which Coleman–De Luccia effects become important. In addition, the work discusses the relationship between different diagnostic tools, such as the imaginary part of the in–out effective action and Bogoliubov coefficients, and clarifies their interpretation in curved spacetimes where the notion of particles is not unique. By organizing these perspectives within a single notation and conceptual structure, the paper provides a consolidated and application-oriented view of semiclassical vacuum instability. Overall, the manuscript offers a systematic synthesis of semiclassical methods and establishes a bridge between tunneling phenomena, particle production, and effective field theory descriptions in curved backgrounds, with an emphasis on conceptual clarity and cross-domain applicability. From a phenomenological perspective, the unified treatment of pair production mechanisms developed here provides a rigorous theoretical foundation that may open new pathways for addressing astrophysical puzzles, such as the generation of positron fluxes related to the anomalous 511 keV galactic emission.
dariusz Staniszewski (Fri,) studied this question.