Massive exchange and the sign of the equilateral bispectrum
- 1Indian Institute of Science Education and Research
- 2International Centre for Theoretical Sciences-TIFR
Abstract
We study the inflationary bispectrum generated by the tree-level exchange of a massive hidden-sector scalar during inflation. When the interaction between the inflaton and the hidden sector arises only from the leading boost-breaking operator of the Effective Field Theory (EFT) of inflation, the equilateral bispectrum for principal-series scalar exchange is known to be universally negative, independent of the sign of the coupling. We revisit this result within the full EFT operator basis. Using bootstrap methods, we construct the de Sitter-invariant seed four-point function and obtain the inflationary bispectrum via weight-shifting operators and a soft-limit procedure. While the equilateral bispectrum remains strictly negative when only the leading interaction is present, additional operators generate independent cubic structures whose contributions compete in the equilateral configuration. As a result, the sign of the bispectrum is no longer universal. We derive a critical ratio of interaction coefficients that separates regions of positive and negative equilateral bispectrum. We further study the effects of reduced sound speed cs < 1 and the exchange of multiple particles. In both cases the critical ratio is modified, and for multi-particle exchange a positive equilateral bispectrum can arise even when the higher-order operator is subdominant. Our results show that the negativity of the equilateral bispectrum from massive exchange is not generic, but reflects a restricted operator structure in the EFT of inflation.
Related
- Calculating the squeezed bispectrum in stochastic inflation by Monte Carlo simulation
- Stochastic Bubble Completion in de Sitter Space: Power Spectrum, Bispectrum, and Infrared Moment Hierarchies
- Cosmological inference from a joint DESI DR1 full-shape power spectrum and bispectrum analysis
- 2+1 is not 3: Angular bispectrum and Super-Sample Covariance on the light cone
- Cross-Bispectrum Constraints from HI Intensity Mapping and Galaxy Surveys
BibTeX
@article{ghosh2026massive,
title = {{Massive exchange and the sign of the equilateral bispectrum}},
author = {Diptimoy Ghosh and Suvashis Maity and Farman Ullah},
journal = {Journal of High Energy Physics},
year = {2026},
month = nov,
doi = {10.1007/jhep11(2026)022},
url = {https://link.springer.com/article/10.1007/JHEP11(2026)022},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Massive exchange and the sign of the equilateral bispectrum
AU - Diptimoy Ghosh
AU - Suvashis Maity
AU - Farman Ullah
PY - 2026
DA - 2026/11/04
JO - Journal of High Energy Physics
DO - 10.1007/jhep11(2026)022
UR - https://link.springer.com/article/10.1007/JHEP11(2026)022
AB - We study the inflationary bispectrum generated by the tree-level exchange of a massive hidden-sector scalar during inflation. When the interaction between the inflaton and the hidden sector arises only from the leading boost-breaking operator of the Effective Field Theory (EFT) of inflation, the equilateral bispectrum for principal-series scalar exchange is known to be universally negative, independent of the sign of the coupling. We revisit this result within the full EFT operator basis. Using bootstrap methods, we construct the de Sitter-invariant seed four-point function and obtain the inflationary bispectrum via weight-shifting operators and a soft-limit procedure. While the equilateral bispectrum remains strictly negative when only the leading interaction is present, additional operators generate independent cubic structures whose contributions compete in the equilateral configuration. As a result, the sign of the bispectrum is no longer universal. We derive a critical ratio of interaction coefficients that separates regions of positive and negative equilateral bispectrum. We further study the effects of reduced sound speed cs < 1 and the exchange of multiple particles. In both cases the critical ratio is modified, and for multi-particle exchange a positive equilateral bispectrum can arise even when the higher-order operator is subdominant. Our results show that the negativity of the equilateral bispectrum from massive exchange is not generic, but reflects a restricted operator structure in the EFT of inflation.
SN - 1029-8479
ER -