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- Testing scalar versus vector dark matterPublication . Azevedo, Duarte; Duch, Mateusz; Grzadkowski, Bohdan; Huang, Da; Iglicki, Michal; Santos, RuiWe investigate and compare two simple models of dark matter (DM): a vector and a scalar DM model. Both models require the presence of two physical Higgs bosons h1 and h2 which come from mixed components of the standard Higgs doublet H and a complex singlet S. In the vector model, the extra Uð1Þ symmetry is spontaneously broken by the vacuum of the complex field S. This leads to a massive gauge boson Xμ that is a DM candidate stabilized by the dark charge conjugation symmetry S → S , Xμ → −Xμ. On the other hand, in the scalar model the gauge group remains the standard one. The DM field A is the imaginary component of S and the stabilizing symmetry is also the dark charge conjugation S → S (A → −A). In this case, in order to avoid spontaneous breaking, the Uð1Þ symmetry is broken explicitly, but softly, in the scalar potential. The possibility to disentangle the two models has been investigated. We have analyzed collider, cosmological, DM direct and indirect detection constraints and shown that there are regions in the space spanned by the mass of the nonstandard Higgs boson and the mass of the DM particle where the experimental bounds exclude one of the models. We have also considered possibility to disentangle the models at eþe− collider and concluded that the process eþe− → Z þ DM provides a useful tool to distinguish the models.
- One-loop contribution to dark-matter-nucleon scattering in the pseudo-scalar dark matter modelPublication . Azevedo, Duarte; Duch, Mateusz; Grzadkowski, Bohdan; Huang, Da; Iglicki, Michal; Santos, RuiRecent dark matter (DM) direct searches place very stringent constraints on the possible DM candidates proposed in extensions of the Standard Model. There are however models where these constraints are avoided. One of the simplest and most striking examples comes from a straightforward Higgs-portal pseudo-scalar DM model featured with a softly broken U(1) symmetry. In this model the tree-level DM-nucleon scattering cross section vanishes in the limit of zero momentum transfer. It has also been argued that the leading-order DM-nucleon cross section appears at the one-loop level. In this work we have calculated the exact cross section in the zero momentum transfer at the leading order i.e., at the one-loop level of perturbative expansion. We have concluded that, in agreement with expectations, the amplitude for the scattering process is UV finite and approaches zero in the limit of vanishing DM masses. Moreover, we made clear that the finite DM velocity correction at tree level is subdominant with respect to the one-loop contribution. Based on the analytic formulae, our numerical studies show that, for a typical choice of model parameters, the DM nuclear recoiling cross section is well below OO(10−50 cm2), which indicates that the DM direct detection signal in this model naturally avoids present strong experimental limits on the cross section.