20-030 Connecting ANITA anomalous events to a nonthermal dark matter scenario
Debasish Borah, Arnab Dasgupta, Ujjal Kumar Dey, Gaurav Tomar
Physical Review D 101, 075039 (2020)
https://doi.org/10.1103/PhysRevD.101.075039
Abstract
The ANtarctic Impulsive Transient Antenna (ANITA) Collaboration has observed two EeV-energy, upward-going events originating from below the horizon. As no standard-model (SM) particles propagating through the Earth at such energy and exit angles can give rise to the required survival probability for the observed events, several beyond-standard-model (BSM) proposals have come up. We propose a scenario where a Z_{2-} odd sector is responsible for such anomalous events. The next-to-lightest Z_{2-} odd particle or the next-to-lightest stable particle (NLSP), created from ultrahigh-energy neutrino interactions with nucleons, can pass through the Earth and then decay into the lightest Z_{2-} odd particle or the lightest stable particle (LSP) and a tau lepton. The long-lived nature of the NLSP requires its coupling with the LSP to be very small, keeping the LSP out of thermal equilibrium in the early Universe. The LSP can then be a nonthermal dark matter, while the tau leptons produced from NLSP decay after passing through Earth can explain the ANITA events. We first show that a purely nonthermal dark matter scenario cannot give rise to the required event rates, while a hybrid scenario where dark matter can have thermal as well as nonthermal contribution to its relic abundance serves the purpose.