Beyond de Sitter: Longitudinal-Mode Instabilities and Spectral Evolution of Massive Vector Fields with Non-Minimal Curvature Coupling during Inflation
Year: 2026
Type: preprint
Abstract: We investigate the inflationary dynamics of a spectator massive vector field with a non-minimal curvature coupling in de Sitter (dS) and quasi-de Sitter (qdS) backgrounds, focusing on the transverse and longitudinal sectors. By solving the mode equations with Bunch-Davies initial conditions, we compute the spectral energy densities and quantify the deviations between the exact dS approximation and the slow-roll-corrected qdS evolution. We find that the coupling parameter xi significantly affects the evolution of the effective mass, the mass-crossing condition, and the behavior of the longitudinal mode. In particular, increasing xi suppresses the vector fluctuations and reduces transient tachyonic effects. We further follow the evolution of the modes into the radiation-dominated era, showing how the inflationary initial conditions determine the subsequent spectral energy densities. Our results identify the parameter regime in which the dS approximation provides an accurate description and determine when slow-roll corrections become relevant.
Source: arXiv (Cornell University)
Authors: Momeni, Ehsan, Shojai, Fatimah
Institutions: University of Padua, University of Tehran
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7204177940