Precision cosmology provides a sensitive probe of extremely weakly coupled states due to thermal freeze-in production, with subsequent decays impacting physics during well-tested cosmological epochs. We explore the cosmological implications of the freeze-in production of a new scalar S via the superrenormalizable Higgs portal. If the mass of S is at or below the electroweak scale, peak freeze-in production occurs during the electroweak epoch. We improve the calculation of the freeze-in abundance by including all relevant QCD and electroweak production channels. The resulting abundance and subsequent decay of S is constrained by a combination of x-ray data, cosmic microwave background anisotropies and spectral distortions, Neff, and the consistency of big bang nucleosynthesis with observations. These probes constrain technically natural couplings for such scalars from mS∼10 keV all the way to mS∼100 GeV. The ensuing constraints are similar in spirit to typical beam dump limits, but extend to much smaller couplings, down to mixing angles as small as θSh∼10-16, and to masses all the way to the electroweak scale.
Bibliographical noteFunding Information:
We thank Chien-Yi Chen, Robert Lasenby, Subir Sarkar, and Roman Zwicky for helpful discussions. The work of M. P. and A. R. is supported in part by NSERC, Canada, and research at the Perimeter Institute is supported in part by the Government of Canada through NSERC and by the Province of Ontario through Ministry of Economic Development, Job Creation and Trade (Government of Ontario). J. P. is supported by the New Frontiers program of the Austrian Academy of Sciences.
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