Dark matter through the quark vector current portal
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Dark matter through the quark vector current portal DILLON BERGER1 , ARVIND RAJARAMAN1,∗ and JASON KUMAR2 1 Department
of Physics and Astronomy, University of California, Irvine, CA 92697, USA of Physics and Astronomy, University of Hawai’i, Honolulu, HI 96822, USA ∗ Corresponding author. E-mail: [email protected] 2 Department
MS received 6 April 2020; revised 20 May 2020; accepted 18 June 2020 Abstract. We consider models of light dark matter coupled to quarks through a vector current interaction. For low energies, these models must be treated through the effective couplings to mesons, which are implemented here through the chiral Lagrangian. We find the signals of dark matter annihilation and decay to the light mesons, and find the expected photon spectrum from the decay of the hadrons. We compare the current and future observations, and show that there is a significant discovery reach for these models. Keywords. Indirect detection; light dark matter; gamma rays; chiral Lagrangian. PACS Nos 95.35.+d; 95.55.Cs; 11.30.Rd
1. Introduction Recently, there has been significant interest in models of dark matter (DM) in which the DM particle has a mass m X O(GeV). These models can evade the tight constraints on DM placed by direct detection experiments, as these experiments typically lose sensitivity at low mass. If DM with m X O(GeV) annihilates or decays in the cosmos, the photons produced will tend to lie in the current ‘MeV-gap’ in observational sensitivity, but a variety of new instruments (such as e-ASTROGAM [1], AMEGO [2] and APT [3]) are being developed to fill this gap. Such instruments would be well-positioned for indirect detection searches for MeV-range DM. Recently, there has been particular interest in MeVrange DM which couples largely to light quarks [4–10]. The reason is that the hadronic final states which can be produced at such small centre-of-mass energies are largely constrained by kinematics and symmetry. Moreover, several accessible hadrons, such as π 0 and η, produce striking photon signals when they decay. This scenario is thus particularly appealing from the point of view of indirect detection. Recent work has considered the case where DM couples to either scalar, pseudoscalar, or axial-vector quark bilinears [10]. But if DM couples to a quark vector current, then the leading accessible final state (at low centre-of-mass energy) is π + π − , whose decays produce few photons, making this case difficult to probe.
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In this work, we extend this analysis to higher energies, where new final states are allowed. We determine the photon spectrum which will be produced for a variety of choices of the flavour structure of DM–standard model (SM) interactions, and determine the sensitivity of the proposed experiments. We shall be interested in the case where DM appears as a vector spurion. We assume that electroweak couplings are only relevant for the decays of hadrons produced by DM annihilation/decay. As described in [10] (see also [11]), DM–SM inter
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