Heavy quark-philic scalar dark matter with a vector-like fermion portal

Abstract

The absence of confirmed signal in dark matter (DM) direct detection (DD) may suggest weak interaction strengths between DM and the abundant constituents inside nucleon, i.e. gluons and valence light quarks. In this work we consider a real scalar dark matter S interacting only with SU(2)L singlet Up-type quarks Ui = uR,cR,tR via a vector-like fermion ψ which has the same quantum number as Ui. The DM-nucleon scattering can proceed through both h-mediated Higgs portal (HP) and ψ-mediated vector-like portal (VLP), in which HP can receive sizable radiative corrections through the new fermions. We first study the separate constraints on the new Yukawa couplings yi and find that the constraints of XENON1T results are strong on y1 from VLP scattering and on y3 from its radiative contributions to HP scattering. Since both DM-light quark interactions and HP have been well studied in the existing literature, we move forward to focus on DM-heavy quark interactions. Since there is no valence c,t quark inside nucleons at μhad ∼ 1 GeV, y2,y3 interactions are manifested in DM-gluon scattering at loop level. We find that renormalization group equation (RGE) and heavy quark threshold effects are important if one calculates the DM-nucleon scattering rate σSIp at μhad ∼ 1 GeV while constructing the effective theory at μEFT ∼ mZ. For the benchmarks y3 = 0.5, y2 = 0.5, 1, 3, combined results from ΩDM h2 ≃ 0.12, XENON1T, Fermi-LAT, 13 TeV LHC data have almost excluded mS < mt/2 when only DM-{c,t} interactions are considered. FCNC of top quark can be generated at both tree level t → ψ(*)S → cSS and loop level t → c+γ/g/Z, of which the branching fractions are typically below 10−9 after passing the other constraints, which are still safe from the current top quark width measurements.