KeV scale new fermion from a hidden sector

Abstract

We studied a simple model of hidden sector that consists of a Dirac fermion χ and a spontaneously broken U (1) s symmetry. The dark sector is connected to the Standard Model(SM) via three righthanded SM singlet neutrinos, N R 's, and the kinetic mixing between U (1) s and U (1) Y . A mixing between the scalar φ that breaks U (1) s and the SM Higgs boson, H, is implemented via the term φ † φH † H and this provides a third connection to the SM. Integrating out the N R at a high scale not only gives the active neutrinos, ν, masses but generates effective Dirac-type couplings between ν and χ. This changes the usual Type-I seesaw results for active neutrino masses and makes χ behave like a sterile neutrino even though its origin is in the hidden sector. Note that χ is also split into a pair of Majorana fermions. The amount of splitting depends on the parameters. If the lighter of the pair has a mass around keV, its lifetime is longer than the age of the Universe and it can be a warm dark matter candidate. Signatures of χ in high precision Kurie plots of nuclei β decays and low energy neutrino nuclei coherent scatterings are discussed. The model also induces new invisible Z decay modes that can be searched for in future Z factories. * Electronic address: wfchang@phys.nthu.edu.tw † Electronic address: misery@triumf.ca

Constraints on light singlet fermion interactions from coherent elastic neutrino-nucleus scattering

“…Also, from Eq. (14) and the flux given in Eq. (9), we know that for m χ ¼ 40 MeV, the νN → χN process at COHERENT is dominated by theν μ events.…”

“…Moreover, the additional interactions are not necessarily negligible comparing to the dominate two, χ-ν-Z 0 and χ-l − -W þ ðl ¼ e; μ; τÞ, through the χ-ν mixings. As an example, the new χ-ν interactions emerge in a 3-portal model recently discussed in [14]. This simple model consists of a pair of vector fermions, χ L=R , and a singlet scalar, ϕ x .…”

Constraints on light singlet fermion interactions from coherent elastic neutrino-nucleus scattering

“…As an example, the new χ-ν interactions emerge in a 3-portal model recently discussed in [14]. This simple model consists a pair of vector fermion, χ L/R , and a singlet scalar, φ x .…”

Constraints on general neutrino interactions with exotic fermion from neutrino-electron scattering experiments

“…The couplings between the neutrinos and sub-GeV DM through the scattering off nucleus have been studied in refs. [2][3][4][5][6][7][8][9]. There are also plenty of novel models and signatures proposed to search for sub-GeV DM through the scattering off electrons [10][11][12][13][14][15].…”