Inflation with vector fields revisited: non-Gaussianities
Abstract
{We revisit the resulting bispectrum of inflation with kinetic-coupled vector fields by organizing the dynamics in terms of h, which measures the vector kinetic contribution relative to that of the scalar field. We derive a low-energy effective field theory (EFT) and evaluate the bispectrum of the curvature perturbation for the large-h regime. For h≫1, the entropic perturbation becomes heavy and can be integrated out; the remaining curvature mode has an imaginary sound speed and undergoes transient growth before horizon crossing. In contrast to the h≪1 regime, where transfer from the vector sector persists outside the horizon and produces a local-type contribution enhanced as h2NK3, we find that the bispectrum signals are controlled by the matching parameter x≃1.63Ah, where A<1 is a numerical factor remaining dependent on the UV-to-EFT matching prescription. As a result, in addition to the known flattened-enhanced signals scaling as x3, a flattened-enhanced signal scaling as x2 and a pronounced local projection scaling as x are present. The bispectrum therefore distinguishes vector-supported inflationary dynamics even for an exactly isotropic background.
Versions
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BibTeX
@misc{chen2026inflation,
title = {{Inflation with vector fields revisited: non-Gaussianities}},
author = {Chong-Bin Chen},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2605.28752},
eprint = {2605.28752},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.28752},
}
RIS
TY - UNPB
TI - Inflation with vector fields revisited: non-Gaussianities
AU - Chong-Bin Chen
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2605.28752
UR - https://arxiv.org/abs/2605.28752
AB - {We revisit the resulting bispectrum of inflation with kinetic-coupled vector fields by organizing the dynamics in terms of h, which measures the vector kinetic contribution relative to that of the scalar field. We derive a low-energy effective field theory (EFT) and evaluate the bispectrum of the curvature perturbation for the large-h regime. For h≫1, the entropic perturbation becomes heavy and can be integrated out; the remaining curvature mode has an imaginary sound speed and undergoes transient growth before horizon crossing. In contrast to the h≪1 regime, where transfer from the vector sector persists outside the horizon and produces a local-type contribution enhanced as h^2N_K^3, we find that the bispectrum signals are controlled by the matching parameter x≃1.63Ah, where A<1 is a numerical factor remaining dependent on the UV-to-EFT matching prescription. As a result, in addition to the known flattened-enhanced signals scaling as x^3, a flattened-enhanced signal scaling as x^2 and a pronounced local projection scaling as x are present. The bispectrum therefore distinguishes vector-supported inflationary dynamics even for an exactly isotropic background.
ER -