Abstract
Right-handed neutrinos (νR) are often considered as a portal to new hidden physics. It is tempting to consider a gauge singlet scalar (ϕ) that exclusively couples to νR via a νRνRϕ term. Such a νR-philic scalar does not interact with charged fermions at tree level but loop-induced effective interactions are inevitable, which are systematically investigated in this work. The magnitude of the loop-induced couplings coincidentally meets the current sensitivity of fifth-force searches. In particular, the loop-induced coupling to muons could be tested in the recent LIGO observations of neutron star mergers as there might be a sizable Yukawa force in the binary system mediated by the νR-philic scalar.
Highlights
Such a νR† α (σμ)αβ i∂μ (νR)-philic scalar does not interact with charged fermions at tree level but loop-induced effective interactions are inevitable, which are systematically investigated in this work
The suppression can be understood from that in the zero limit of neutrino masses, which corresponds to vanishing couplings of the SM Higgs to νR and left-handed neutrinos, the νR sector would be entirely decoupled from the SM content
In light of the frontiers of precision and novel tests of gravity and gravity-like forces, it is important to perform an in-depth study on the loop-induced interactions of the νRphilic scalar, which is the main goal of this work
Summary
Throughout this paper, Weyl spinors are frequently used in our discussions for simplicity. For Feynman diagram calculations, Dirac or Majorana spinors are more convenient due to a variety of techniques and especially many modern computation packages that have been developed. As both will used in this paper, it is necessary to clarify our notations regarding Weyl spinors versus Dirac/Majorana spinors. All four-component Dirac/Majorana spinors in this paper are denoted by ψX with some interpretative subscripts X ΝL and R are Weyl spinors of a left-handed neutrino and a right-handed charged lepton, respectively. Ψ is a Dirac spinor of a charged lepton containing both left- and right-handed components.
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