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Probing the relaxed relaxion at the luminosity and precision frontiers

TitleProbing the relaxed relaxion at the luminosity and precision frontiers
Publication TypeJournal Article
Year of Publication2020
AuthorsA. Banerjee, H. Kim, O. Matsedonskyi, ii, G. Perez, and M. S. Safronova
JournalJ. High Energy Phys.
Date PublishedJUL 22
Type of ArticleArticle
KeywordsBeyond Standard Model, Cosmology of Theories beyond the SM

Cosmological relaxation of the electroweak scale is an attractive scenario relaxion, is a light spin-zero field which dynamically relaxes the Higgs mass with respect to its natural large value. We show that the relaxion is generically stabilized at a special position in the field space, which leads to suppression of its mass and potentially unnatural values for the model's effective low-energy couplings. In particular, we find that the relaxion mixing with the Higgs can be several orders of magnitude above its naive naturalness bound. Low energy observers may thus find the relaxion theory being fine-tuned although the relaxion scenario itself is constructed in a technically natural way. More generally, we identify the lower and upper bounds on the mixing angle. We examine the experimental implications of the above observations at the luminosity and precision frontiers. A particular attention is given to the impressive ability of future nuclear clocks to search for rapidly oscillating scalar ultra-light dark matter, where the future projected sensitivity is presented.