Gravitational clustering of relic neutrinos and implications for their detection

Abstract

We study the gravitational clustering of big bang relic neutrinos ontoexisting cold dark matter (CDM) and baryonic structures within the flatΛCDM model, using both numerical simulations and a semi-analytical linear technique, with theaim of understanding the neutrinos’ clustering properties for direct detection purposes. In acomparative analysis, we find that the linear technique systematically underestimates theamount of clustering for a wide range of CDM halo and neutrino masses. This invalidatesearlier claims of the technique’s applicability. We then compute the approximate phasespace distribution of relic neutrinos in our neighbourhood at Earth, and estimate thelarge scale neutrino density contrasts within the local Greisen–Zatsepin–Kuzminzone. With these findings, we discuss the implications of gravitational neutrinoclustering for scattering-based detection methods, ranging from flux detection viaCavendish-type torsion balances, to target detection using accelerator beams and cosmicrays. For emission spectroscopy via resonant annihilation of extremely energeticcosmic neutrinos on the relic neutrino background, we give new estimates for theexpected enhancement in the event rates in the direction of the Virgo cluster.