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PreprintarXiv licencearXiv

Primordial tensor mode from the neutrino sector

  • Shohei Saga
  • Shuichiro Yokoyama
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Abstract

We show that a regular solution for primordial tensor fluctuations can arise from the higher-order multipoles of the collisionless neutrino distribution after neutrino decoupling. Focusing on the leading case with the neutrino octupole mode (tensor-octupole mode), we derive the initial conditions for the Einstein-Boltzmann system and calculate angular power spectra for the cosmic microwave background (CMB) anisotropies. Compared with the standard gravitational-wave mode, the tensor-octupole mode has a weaker large-scale metric response. It therefore gives a suppressed reionization bump and a different oscillation phase in the tensor CMB power spectra, providing a way to separate it from the standard tensor mode.

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Cite

BibTeXRIS
BibTeX
@misc{saga2026primordial,
  title = {{Primordial tensor mode from the neutrino sector}},
  author = {Shohei Saga and Shuichiro Yokoyama},
  howpublished = {arXiv},
  year = {2026},
  month = nov,
  doi = {10.48550/arxiv.2607.15335},
  eprint = {2607.15335},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2607.15335},
}
RIS
TY  - UNPB
TI  - Primordial tensor mode from the neutrino sector
AU  - Shohei Saga
AU  - Shuichiro Yokoyama
PY  - 2026
DA  - 2026/11/06
PB  - arXiv
DO  - 10.48550/arxiv.2607.15335
UR  - https://arxiv.org/abs/2607.15335
AB  - We show that a regular solution for primordial tensor fluctuations can arise from the higher-order multipoles of the collisionless neutrino distribution after neutrino decoupling. Focusing on the leading case with the neutrino octupole mode (tensor-octupole mode), we derive the initial conditions for the Einstein-Boltzmann system and calculate angular power spectra for the cosmic microwave background (CMB) anisotropies. Compared with the standard gravitational-wave mode, the tensor-octupole mode has a weaker large-scale metric response. It therefore gives a suppressed reionization bump and a different oscillation phase in the tensor CMB power spectra, providing a way to separate it from the standard tensor mode.
ER  -