Abstract
We study the self-energies of weakly interacting scalar fields in de Sitter space with one field much lighter than the Hubble scale. We argue that self-energies drastically simplify in this light limit. We illustrate this in theories with two scalar fields, one heavy and one light, interacting with one another through either cubic or quartic interactions. To regulate infrared divergences, we compute these self-energies in Euclidean de Sitter space and then carefully analytically continue to Lorentzian signature. In particular, we do this for the most general renormalizable theory of two scalar fields with even interactions to leading order in the coupling and the mass of the light field. These self-energies are determined by de Sitter sunset diagrams, whose analytic structure and UV divergences we derive. Even at very weak couplings, the light field can substantially change how the heavy field propagates over long distances. The light field’s existence may then be inferred from how it modifies the heavy field’s oscillatory contribution to the primordial bispectrum in the squeezed limit, i.e. its cosmological collider signal.
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Acknowledgments
We would like to thank Arindam Bhattacharya, Michael Geller, Cody Long, Qianshu Lu, Austin Joyce, Rashmish Mishra, Matt Reece, and Lian-Tao Wang for very helpful discussions. We would especially like to thank Qianshu Lu and Matt Reece for comments on the draft. The work of both PC and JS is supported by the DOE grant DE-SC0013607, while the work of JS is also supported NASA Grant 80NSSC20K0506. This work was performed in part at Aspen Center for Physics, which is supported by National Science Foundation grant PHY-2210452.
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Chakraborty, P., Stout, J. Light scalars at the cosmological collider. J. High Energ. Phys. 2024, 21 (2024). https://doi.org/10.1007/JHEP02(2024)021
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DOI: https://doi.org/10.1007/JHEP02(2024)021