Abstract
Experimentally, baryon number minus lepton number, $B-L$, appears to be a good global symmetry of nature. We explore the consequences of the existence of gauge-singlet scalar fields charged under $B-L$ -- dubbed lepton-number-charged scalars, LeNCS -- and postulate that these couple to the standard model degrees of freedom in such a way that $B-L$ is conserved even at the non-renormalizable level. In this framework, neutrinos are Dirac fermions. Including only the lowest mass-dimension effective operators, some of the LeNCS couple predominantly to neutrinos and may be produced in terrestrial neutrino experiments. We examine several existing constraints from particle physics, astrophysics, and cosmology to the existence of a LeNCS carrying $B-L$ charge equal to two, and discuss the emission of LeNCS's via "neutrino beamstrahlung," which occurs every once in a while when neutrinos scatter off of ordinary matter. We identify regions of the parameter space where existing and future neutrino experiments, including the Deep Underground Neutrino Experiment, are at the frontier of searches for such new phenomena.
Highlights
The gauge symmetry and particle content of the standard model (SM) are such that, at the renormalizable level, both Uð1ÞB and Uð1ÞL are exact classical global symmetries of the Lagrangian
Because φ carries away lepton number, the neutrino charged-current interaction will lead to wrong-sign charged leptons. This φ radiation would change the charged-lepton energy spectrum and lead to significant missing transverse energy in the event.1. We explore these effects in a few accelerator neutrino experiments, including NOMAD, MiniBooNE, MINOS, the NuMI Off-Axis νe Appearance (NOνA) experiment, and the Deep Underground Neutrino Experiment (DUNE)
We explored the hypothesis that B − L is a conserved global symmetry of nature and that there are new SM gauge-singlet scalar fields with integer nonzero B − L charge
Summary
The gauge symmetry and particle content of the standard model (SM) are such that, at the renormalizable level, both Uð1ÞB (baryon number) and Uð1ÞL (lepton number) are exact classical global symmetries of the Lagrangian. If Uð1ÞB−L is a fundamental symmetry of nature, nonzero neutrino masses require the existence of new fermions charged under Uð1ÞB−L. We are interested in the consequences of allowing for the existence of new degrees of freedom charged under Uð1ÞB−L, assuming B − L is conserved even if one allows for higher-dimensional operators. We expand the physical Higgs boson field h around its vacuum expectation value v up to linear order In this simple setup, the new scalar φ couples predominantly to SM neutrinos, and we will demonstrate that it could lead to interesting, observable effects in neutrino experiments. The equivalent coupling λ for a Majoron is related to the observed neutrino masses, λ ∼ mν=f, where f is the spontaneous lepton number breaking scale. Have to be very low, f ∼ OðeVÞ; under these circumstances, it would be inconsistent to talk about Majorons with masses above a MeV
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