Luminous solar neutrinos. I. Dipole portals

Ryan Plestid

doi:10.1103/physrevd.104.075027

Abstract

Solar neutrinos upscattering inside the Earth can source unstable particles that can decay inside terrestrial detectors. Contrary to naive expectations we show that when the decay length is much shorter than the radius of the \emph{Earth} (rather than the detector), the event rate is independent of the decay length. In this paper we study a transition dipole operator (neutrino dipole portal) and show that Borexino's existing data probes previously untouched parameter space in the 0.5--20 MeV regime, complementing recent cosmological and supernova bounds. We briefly comment on similarities and differences with luminous dark matter and comment on future prospects for analogous signals stemming from atmospheric neutrinos.

Highlights

The Earth is continuously bombarded by both neutrinos from the Sun and dark matter from our local Galaxy; both can serve as a resource with which to search for new physics
The canonical strategy, as it pertains to dark matter, is to detect particles directly via elastic or inelastic scattering within a detector; this strategy applies well to new physics coupled via some neutrino portal
VI where we summarize our main results, emphasize the overlap between luminous dark matter searches and luminous solar neutrino searches, and comment on qualitative effects that are important for future dedicated analysis

Summary

INTRODUCTION

The Earth is continuously bombarded by both neutrinos from the Sun (among other sources) and dark matter from our local Galaxy; both can serve as a resource with which to search for new physics. Physics potential for detecting upscattered unstable particles sourced by solar neutrinos inside the Earth with a neutrino-dipole portal serving as a useful benchmark example. In both cases pp and/or pA collisions source mesons, which promptly decay, producing a flux of light, long-lived, new physics particles, e.g., heavy neutral leptons [24], light dark matter [27], or millicharged particles [28] Such an indirect production mechanism costs an extra two powers of the coupling constant, such that for a neutrino-dipole portal the flux itself scales as Φ ∼ d2 leading to an event rate that scales as R ∼ d4. Our results are summarized and shown in context with other constraints for a muon-only dipole portal in Fig. 2; constraints derived in this paper for de and dτ are broadly

DIPOLE-PORTAL UPSCATTERING

RADIATIVE STERILE DECAY

SIGNALS AT LARGE-SCALE DETECTORS

NEW CONSTRAINTS ON DIPOLE PORTALS

CONCLUSIONS