Hybrid seesaw leptogenesis and TeV singlets

Author(s)

Agashe, Kaustubh ^[1] ; Du, Peizhi ^[1] ; Ekhterachian, Majid ^[1] ; Fong, Chee Sheng ^{[2, 3]} ; Hong, Sungwoo ^[4] ; Vecchi, Luca ^[5]

Affiliation

^[1] Univ Maryland, Dept Phys, Maryland Ctr Fundamental Phys, College Pk, MD 20742 - USA

^[2] Univ Sao Paulo, Inst Fis, Sao Paulo - Brazil

^[3] Pontificia Univ Catolica Rio de Janeiro, Dept Fis, Rio De Janeiro - Brazil

^[4] Cornell Univ, Dept Phys, LEPP, Ithaca, NY 14853 - USA

^[5] Ecole Polytech Fed Lausanne, Theoret Particle Phys Lab, Inst Phys, Lausanne - Switzerland

• Document type: Journal article
• Source: Physics Letters B; v. 785, p. 489-497, OCT 10 2018.
• Web of Science Citations: 6

Abstract

The appealing feature of inverse seesaw models is that the Standard Model (SM) neutrino mass emerges from the exchange of TeV scale singlets with sizable Yukawa couplings, which can be tested at colliders. However, the tiny Majorana mass splitting between TeV singlets, introduced to accommodate small neutrino masses, is left unexplained. Moreover, we argue that these models suffer from a structural limitation that prevents a successful leptogenesis if one insists on having unsuppressed Yukawa couplings and TeV scale singlets. In this work we propose a hybrid seesaw model, where we replace the mass splitting with a coupling to a high scale seesaw module including a TeV scalar. We show that this structure achieves the goal of filling both the above gaps with couplings of order unity. The necessary structure automatically arises embedding the seesaw mechanism in composite Higgs models, but may also be enforced by new gauge symmetries in a weakly-coupled theory. Our hybrid seesaw models have distinguishing features compared to the standard high scale type-I seesaw and inverse seesaw. Firstly, they have much richer phenomenology. Indeed, they generally predict new TeV scale physics (including scalars) potentially accessible at present and future colliders, whereas weakly-coupled versions may also have cosmological signature due to the presence of a light Nambu-Goldstone boson coupled to neutrinos. Secondly, our scenario features an interesting interplay between high scale and TeV scale physics in leptogenesis and enlarges the range of allowed high scale singlet masses beyond the usual similar to 10(9)-10(15) GeV, without large hierarchies in the Yukawa couplings nor small mass splitting among the singlets. (C) 2018 The Authors. Published by Elsevier B.V. (AU)

• FAPESP's process: 17/02747-7 - Confronting physics puzzles in the Mirror Twin Higgs models
• Grantee: Chee Sheng Fong
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• FAPESP's process: 12/10995-7 - Particle physics phenomenology
• Grantee: Gustavo Alberto Burdman
• Support Opportunities: Research Projects - Thematic Grants