Abstract
Solar neutrinos can be efficiently upscattered to MeV scale heavy neutral leptons (HNLs) within the Earth's mantle. HNLs can then decay to electron-positron pairs leading to energy deposition inside large-volume detectors. In this paper we consider mass-portal upscattering of solar neutrinos to HNLs of mass 20 MeV $\geq m_N \geq 2 m_e$. The large volume of the Earth compensates for the long decay-length of the HNLs leading to observable rates of $N\rightarrow \nu_\alpha e^+e^-$ in large volume detectors. We find that searches for mantle-upscattered HNLs can set the novel limits on mixing with third generation leptons, $|U_{\tau N}|$ for masses in the MeV regime; sensitivity to mixing with first- and second-generation leptons is not competitive with existing search strategies.
Highlights
Heavy neutral leptons (HNLs) are among the best motivated extensions of the Standard Model (SM), and their phenomenology has been studied extensively for masses in the MeV to the few GeV regime [1,2,3,4,5,6,7,8,9,10,11,12,13,14]
As we show in this paper, the presence of a substantial ντ flux allows us to set new constraints on mass-mixing portals connected to third-generation leptons
The volume of the Earth can serve as a powerful resource for upscattering astrophysical particles that, if they are long lived but unstable, can leave visible imprints in large volume detectors
Summary
Heavy neutral leptons (HNLs) are among the best motivated extensions of the Standard Model (SM), and their phenomenology has been studied extensively for masses in the MeV to the few GeV regime [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. In a related paper [23], we study a neutrino-dipole portal [24,25] and show that the Earth’s mantle can serve as a powerful resource when λ becomes very large ameliorating the naive Oð10 mÞ=λ suppression expected for a Borexinoscale detector and replacing it with the much more favorable Oð5000 kmÞ=λ for λ ≫ R⊕ This is a useful observation when coupled with the solar-neutrino flux which contains sizeable νe, νμ, and ντ components. V, we summarize our results and comment on possible future improved sensitivity at future large-scale detectors
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