Calculating the squeezed bispectrum in stochastic inflation by Monte Carlo simulation

@misc{miyamoto2026calculating,
  title = {{Calculating the squeezed bispectrum in stochastic inflation by Monte Carlo simulation}},
  author = {Koichi Miyamoto and Yuichiro Tada},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.02076},
  eprint = {2609.02076},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.02076},
}

TY  - UNPB
TI  - Calculating the squeezed bispectrum in stochastic inflation by Monte Carlo simulation
AU  - Koichi Miyamoto
AU  - Yuichiro Tada
PY  - 2026
DA  - 2026/09/02
PB  - arXiv
DO  - 10.48550/arxiv.2609.02076
UR  - https://arxiv.org/abs/2609.02076
AB  - The bispectrum of cosmological perturbations is an important probe of inflation and the underlying particle physics. However, calculating it becomes challenging in inflation models where inflaton dynamics is dominated by quantum diffusion rather than slow-roll, especially in the multi-field case. In this paper, employing the stochastic-δ𝒩 formalism, we propose a Monte Carlo-based method to calculate the bispectrum in the squeezed limit, as an extension of the method for the power spectrum that we previously proposed. Our method involves generating paths of inflatons' time evolution that branch only several times, avoiding nested path generation, which incurs a prohibitive computational cost. As numerical demonstrations, we apply the proposed method to single- and double-field chaotic inflation for validation, and to hybrid inflation with mild waterfall, for which, to the best of our knowledge, the bispectrum is calculated for the first time in this work.
ER  -