Fermionic bubble loop in cosmological collider revisited: exact signals from spectral and Mellin-Barnes methods
5 affiliations
- 1RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS)
- 2Tsinghua University
- 3Cosmology, Gravity and Astroparticle Physics Group, Center for Theoretical Physics of the Universe, Institute for Basic Science
- 4Institute of Science Tokyo
- 5Yonsei University
Abstract
A bstract : Fermionic degrees of freedom are essential ingredients in cosmological collider physics and are well motivated by many phenomenological models beyond the Standard Model, but their signals remain largely unexplored due to the difficulty of computing loop diagrams. In this work, we ask how fermionic bubble loops contribute to cosmological collider signals and provide an exact answer for arbitrary couplings. We develop two parallel analytical methods whose agreement provides a non-trivial check of the result. The first method is similar in spirit to spectral decomposition and is built directly from an identity for the product of propagators, which turns the bubble signal into an infinite sum of tree-level exchange signals. The second method is based on the Mellin-Barnes representation, where the result is reconstructed from the residues of distinct families of poles. We also show that the fermionic bubble can be generated from the scalar bubble by the action of appropriate differential operators. As a phenomenologically important application, we consider Yukawa interactions between fermions and the inflaton, finding that the resulting bispectrum signal vanishes identically. Through the spectral decomposition, this vanishing can be traced to a field redefinition of the associated tree-level counterparts.
Related
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BibTeX
@article{aoki2026fermionic,
title = {{Fermionic bubble loop in cosmological collider revisited: exact signals from spectral and Mellin-Barnes methods}},
author = {Shuntaro Aoki and Zhehan Qin and Masahide Yamaguchi and Yuhang Zhu},
journal = {Journal of High Energy Physics},
year = {2026},
month = nov,
doi = {10.1007/jhep11(2026)023},
url = {https://link.springer.com/article/10.1007/JHEP11(2026)023},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Fermionic bubble loop in cosmological collider revisited: exact signals from spectral and Mellin-Barnes methods
AU - Shuntaro Aoki
AU - Zhehan Qin
AU - Masahide Yamaguchi
AU - Yuhang Zhu
PY - 2026
DA - 2026/11/04
JO - Journal of High Energy Physics
DO - 10.1007/jhep11(2026)023
UR - https://link.springer.com/article/10.1007/JHEP11(2026)023
AB - A bstract : Fermionic degrees of freedom are essential ingredients in cosmological collider physics and are well motivated by many phenomenological models beyond the Standard Model, but their signals remain largely unexplored due to the difficulty of computing loop diagrams. In this work, we ask how fermionic bubble loops contribute to cosmological collider signals and provide an exact answer for arbitrary couplings. We develop two parallel analytical methods whose agreement provides a non-trivial check of the result. The first method is similar in spirit to spectral decomposition and is built directly from an identity for the product of propagators, which turns the bubble signal into an infinite sum of tree-level exchange signals. The second method is based on the Mellin-Barnes representation, where the result is reconstructed from the residues of distinct families of poles. We also show that the fermionic bubble can be generated from the scalar bubble by the action of appropriate differential operators. As a phenomenologically important application, we consider Yukawa interactions between fermions and the inflaton, finding that the resulting bispectrum signal vanishes identically. Through the spectral decomposition, this vanishing can be traced to a field redefinition of the associated tree-level counterparts.
SN - 1029-8479
ER -