Unsterile-Active Neutrino Mixing

TL;DR

This paper explores the mixing of an unparticle-like sterile neutrino with active neutrinos, revealing unique spectral properties, non-unitary mixing, and implications for dark matter detection constraints.

Contribution

It introduces the concept of an unsterile neutrino as an unparticle, analyzes its mixing with active neutrinos, and discusses the impact on decay widths and observational bounds.

Findings

Unsterile neutrino exhibits a resonance for anomalous dimensions between 0 and 1/3.

The complex pole of the unsterile mode disappears when the anomalous dimension exceeds 1/3.

Decay width of unsterile neutrino into active neutrino and photon is suppressed, affecting dark matter detection bounds.

Abstract

We consider a sterile neutrino to be an unparticle, namely an "unsterile" neutrino, and study its mixing with a canonical active neutrino via a see-saw mass matrix. There is no unitary transformation that diagonalizes the mixed propagator and a field redefinition is required. The unsterile-like propagating mode features a resonance for anomalous dimension between 0 and 1/3, but the complex pole disappears when the anomalous dimension is larger than 1/3. The active-like propagating mode is described by a stable pole, but inherits a non-vanishing spectral density above the unparticle threshold. We also find that the radiative decay width of the unsterile neutrino into the active neutrino (and a photon) via charged current loops is suppressed, and this suppression weakens the bound from the X-ray or soft gamma-ray background when one considers the unsterile neutrino to be a dark matter candidate.