Distinguishing Dirac vs. Majorana Neutrinos: a Cosmological Probe

Understand

Cosmic background neutrinos ($C_{\nu}B)$ helicity composition is different for Dirac or Majorana neutrinos making detectors based on $C_{\nu}B$ capture sensitive to the nature of neutrinos.

• We calculate, for the first time, the helicity changes of neutrinos crossing dark matter fields, to quantitatively calculate this effect on the capture rate.
• We show that a fraction of neutrinos change their helicity, regardless of them being deflected by a void or a dark matter halo.
• The average signal from the 100 most massive voids or halos in a Gpc$^3$ gives a prediction that if neutrinos are Dirac, the density of the $C_{\nu} B$ background measured on Earth should be 48 cm${^{-3}}$ for left-helical neutrinos, a decrease of 15% (53.6 cm${^{-3}}$; 5%) for a halo (void) with respect to the standard calculation without including gravitational effects due to large scale structures.