Indirect and direct signatures of Higgs portal decaying vector dark matter for positron excess in cosmic rays

Abstract

We investigate the indirect signatures of the Higgs portal U(1)X vector dark matter (VDM) Xμ from both its pair annihilation and decay. The VDM is stable at renormalizable level by Z2 symmetry, and thermalized by Higgs-portal interactions. It can also decay by some nonrenormalizable operators with very long lifetime at cosmological time scale. If dim-6 operators for VDM decays are suppressed by 1016 GeV scale, the lifetime of VDM with mass ∼ 2 TeV is just right for explaining the positron excess in cosmic ray observed by PAMELA and AMS02 Collaborations. The VDM decaying into μ+μ- can fit the data, evading various constraints on cosmic rays. We give one UV-complete model as an example. This scenario for Higgs portal decaying VDM with mass around ∼ 2 TeV can be tested by DM direct search at XENON1T, and also at the future colliders by measuring the Higgs self-couplings.