Gauge-field energy density in inflationary kinetic-coupling models: QFT regularization versus horizon cutoffs
Abstract
Coupling gauge fields to the inflaton can amplify their quantum fluctuations during inflation, with potential applications to a range of cosmological phenomena. A central challenge is to define finite and physically meaningful observables, such as the gauge-field energy density. In this work, we study an Abelian gauge field kinetically coupled to the inflaton through f2(ϕ)FμνFμν in a de Sitter background with f∝ aγ1, and compare conventional quantum-field-theoretic regularization with horizon-cutoff prescriptions. Using a hard physical-momentum cutoff and dimensional regularization, we derive the ultraviolet divergences in closed form and fix the remaining one-parameter finite-part ambiguity by requiring the coupling-induced total energy density to be nonnegative. We then examine five horizon-cutoff prescriptions based on characteristic scales of the mode equations. Their predictions depend sensitively on the choice of horizon scale and, for weak gauge-field production, can deviate substantially from the regularized result; for the adopted finite-part prescription, the minimal horizon agrees best with the regularized total energy density. As |γ1|→ 2, where infrared modes dominate, the relative deviation of all prescriptions from the regularized result vanishes, independently of the finite-part prescription. Outside this regime, the separate electric and magnetic contributions, which can become negative after regularization, are not reliably reproduced by any of the horizon-cutoff prescriptions.
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BibTeX
@misc{naidenko2026gaugefield,
title = {{Gauge-field energy density in inflationary kinetic-coupling models: QFT regularization versus horizon cutoffs}},
author = {A. O. Naidenko and O. O. Sobol and S. I. Vilchinskii},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.32599},
eprint = {2610.32599},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.32599},
}
RIS
TY - UNPB
TI - Gauge-field energy density in inflationary kinetic-coupling models: QFT regularization versus horizon cutoffs
AU - A. O. Naidenko
AU - O. O. Sobol
AU - S. I. Vilchinskii
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.32599
UR - https://arxiv.org/abs/2610.32599
AB - Coupling gauge fields to the inflaton can amplify their quantum fluctuations during inflation, with potential applications to a range of cosmological phenomena. A central challenge is to define finite and physically meaningful observables, such as the gauge-field energy density. In this work, we study an Abelian gauge field kinetically coupled to the inflaton through f^2(ϕ)F_μνF^μν in a de Sitter background with f∝ a^γ_1, and compare conventional quantum-field-theoretic regularization with horizon-cutoff prescriptions. Using a hard physical-momentum cutoff and dimensional regularization, we derive the ultraviolet divergences in closed form and fix the remaining one-parameter finite-part ambiguity by requiring the coupling-induced total energy density to be nonnegative. We then examine five horizon-cutoff prescriptions based on characteristic scales of the mode equations. Their predictions depend sensitively on the choice of horizon scale and, for weak gauge-field production, can deviate substantially from the regularized result; for the adopted finite-part prescription, the minimal horizon agrees best with the regularized total energy density. As |γ_1|→ 2, where infrared modes dominate, the relative deviation of all prescriptions from the regularized result vanishes, independently of the finite-part prescription. Outside this regime, the separate electric and magnetic contributions, which can become negative after regularization, are not reliably reproduced by any of the horizon-cutoff prescriptions.
ER -