Mass limits for heavy neutrinos

TL;DR

This paper investigates the potential role of heavy neutrinos with masses between 100 and 200 GeV in contributing to cosmic gamma ray background and dark matter, using numerical evolution models and observational data comparison.

Contribution

It provides a new numerical model for heavy neutrino density evolution and constrains their mass range and contribution to dark matter based on gamma ray observations.

Findings

Heavy neutrinos with masses 100-200 GeV are excluded as major dark matter contributors.

The contribution of heavy neutrinos to dark matter is at most 15%.

Gamma ray spectra from neutrino annihilation are consistent with EGRET data within constraints.

Abstract

Neutrinos heavier than $M_Z/2\sim 45$ GeV are not excluded by particle physics data. Stable neutrinos heavier than this might contribute to the cosmic gamma ray background through annihilation in distant galaxies as well as to the dark matter content of the universe. We calculate the evolution of the heavy neutrino density in the universe as a function of its mass, $M_N$, and then the subsequent gamma ray spectrum from annihilation of distant $N\bar{N}$ (from $0<z<5$). The evolution of the heavy neutrino density in the universe is calculated numerically. In order to obtain the enhancement due to structure formation in the universe, we approximate the distribution of $N$ to be proportional to that of dark matter in the GalICS model. The calculated gamma ray spectrum is compared to the measured EGRET data. A conservative exclusion region for the heavy neutrino mass is 100 to 200 GeV, both from EGRET data and our re-evalutation of the Kamiokande data. The heavy neutrino contribution to dark matter is found to be at most 15%.