Abstract
We investigate direct detection signatures of dark matter particles interacting with quarks via a light spin-0 mediator with general CP phases. Since tree-level scattering may be strongly suppressed in the non-relativistic limit, loop contributions play an important role and can lead to observable signals in near-future experiments. We study the phenomenology of different mediator masses and CP phases with an emphasis on scenarios with maximal CP violation and Higgs portal models. Intriguingly, the sum of the rates obtained at tree- and loop-level can give a characteristic recoil spectrum not obtainable from a single type of interaction. We furthermore develop a novel method for decomposing the two-loop contribution to effective interactions between dark matter and gluons into two separate one-loop diagrams, which in our case substantially simplifies the calculation of the important top-quark contribution.
Highlights
“neutrino floor” which indicates the ultimate reach of direct detection experiments [40]
We investigate direct detection signatures of dark matter particles interacting with quarks via a light spin-0 mediator with general CP phases
We include a trilinear coupling between a and the Standard Model (SM) Higgs boson which generally arises in UV completions of this model and can have important phenomenological consequences
Summary
We investigate a simplified model of a Dirac fermion DM particle χ interacting with SM fermions f through a general spin-0 mediator a with mass ma greater than the bottomquark mass mb:. For φχ = φSM = 0 we recover the well-known simplified model of a scalar mediator, whereas for φχ = φSM = π/2 we obtain a CP-conserving theory with a pseudoscalar mediator [52] In the former case constraints on the model from direct detection experiments are very strong, whereas in the latter case they are almost entirely absent [41, 42, 44]. Note that we neglect additional interaction terms involving two Higgs bosons Such terms are in general expected to be present, they do not give any relevant contribution to the calculation of direct detection signatures. We will not consider Higgs mixing within this work but emphasize that it would be straightforward to include these contributions using the results presented below
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