Probing the Relaxed Relaxion at the Luminosity and Precision Frontiers

Abhishek Banerjee, Hyungjin Kim, Oleksii Matsedonskyi, Gilad Perez, Marianna S. Safronova

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

Cosmological relaxation of the electroweak scale is an attractive scenario addressing the gauge hierarchy problem. Its main actor, the 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.
Original languageEnglish
Article number153
Number of pages30
JournalJournal of High Energy Physics
Volume2020
Issue number7
DOIs
Publication statusPublished Online - 22 Jul 2020

Funding

We would like to thank Nitzan Akerman, David Leibrandt, David Hume, Yevgeny V. Stadnik, and Jun Ye for useful discussions. We would also like to thank Diego Redigolo and Lorenzo Ubaldi for initial collaboration on this project. The work of OM is supported by the Foreign Postdoctoral Fellowship Program of the Israel Academy of Sciences and Humanities. The work of GP is supported by grants from The U.S.-Israel Binational Science Foundation (BSF), European Research Council (ERC), Israel Science Foundation (ISF), Yeda-Sela-SABRA-WRC, and the Segre Research Award. The work of MS is supported by European Research Council (ERC).

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