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 ultra high 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 non-thermal dark matter while the tau leptons produced from NLSP decay after passing through the earth can explain the ANITA events. We first show that a purely non-thermal dark matter scenario can not give rise to the required event rates while a hybrid scenario where dark matter can have both thermal as a well non-thermal contribution to its relic abundance, serves the purpose.
Highlights
The ANtarctic Impulsive Transient Antenna (ANITA) Collaboration has reported two anomalous upward-going ultrahigh-energy cosmic-ray (UHECR) air shower events corresponding to deposited energies of 0.6 Æ 0.4 EeV and 0.56þ−00..23 EeV [1,2]
We have proposed a beyond-standard-model framework to explain the two anomalous upward-going ultrahighenergy cosmic-ray air shower events reported by the ANITA Collaboration
While two types of such Z2-odd fields—namely, a scalar doublet and gauge singlet neutral fermions—play the role of generating light neutrino masses at the one-loop level similar to the scotogenic scenarios, the other fields are responsible for generating the anomalous events (AAEs)
Summary
The ANtarctic Impulsive Transient Antenna (ANITA) Collaboration has reported two anomalous upward-going ultrahigh-energy cosmic-ray (UHECR) air shower events corresponding to deposited energies of 0.6 Æ 0.4 EeV and 0.56þ−00..23 EeV [1,2]. Typical FIMP or nonthermal DM models involve tiny couplings of DM with SM or other particles in the thermal bath and often lead to longlived particles Such long-lived charged particles have the potential to pass through the Earth before decaying into DM and a tau lepton, which could explain the anomalous events observed by ANITA [15,16]. The Z2-odd particles, the lightest of which is the DM candidate, give rise to light neutrino masses at one-loop level in this model We extend this model suitably to explain the AAEs. We first consider an extension of this model to incorporate a purely nonthermal or FIMP-type DM and name it as Model I.
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