Bounds on decaying sterile neutrinos via magnetic dipole moment from COB intensity

TL;DR

This paper investigates how radiatively decaying sterile neutrinos with keV masses could explain the anomalous cosmic optical background intensity, deriving bounds on their magnetic transition moments based on recent observations.

Contribution

It provides new upper bounds on the magnetic transition moments of keV-scale sterile neutrinos using COB data, linking dark matter properties to observable cosmic background anomalies.

Findings

Sterile neutrinos with keV mass can explain the observed excess intensity.

Transition magnetic moments are constrained to the range 3×10^{-13} to 10^{-9} eV^{-1}.

Future telescopes may improve bounds on sterile neutrino properties.

Abstract

A recent observation by Long Range Reconnaissance Imager (LORRI) mounted on NASA's New Horizons yielded the most accurate measurement of the cosmic optical background (COB). The reported COB intensity is $11.16\pm 1.35$ $\mathrm{nW/m^2/sr}$ at a pivot wavelength $ \lambda_{piv} = 0.608 \, \mu\mathrm{m}$ observed in the range \( 0.4 \, \mu\mathrm{m} \lesssim \lambda \lesssim 0.9 \, \mu\mathrm{m} \). After subtracting the measured intensity from the deep Hubble Space Telescope count, diffused galactic light, and scattered light from bright star foregrounds, an anomalous intensity of $2.99 \pm 2.03~\mathrm{nW/m^2/sr}$ has been found. We considered radiatively decaying sterile neutrinos of keV mass scale, as dark matter candidate, that could contribute to this anomalous reported intensity. Using this, we derive upper bounds on the sterile-to-sterile transition magnetic moment. We find that sterile neutrinos with mass of $\mathcal{O}(\rm keV)$ scale take values of the transition magnetic moment in the range $ 3\times 10^{-13}\,\rm eV^{-1} - 10^{-9}\,\rm eV^{-1}$ to explain the anomalous intensity of $2.99\pm 2.03\,\rm nW/m^2/sr$. % Future experiments such as, Cosmological Advanced Survey Telescope for Optical-UV Research (CASTOR), James Web Space Telescope (JWST), and Spectro-Photometer for the history of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) might help us derive a better bound on the sterile neutrinos.