Browsing by Author "Huang, Da"
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- Anomalies in B-meson decays and the muon g-2 from dark loopsPublication . Huang, Da; Morais, António P.; Santos, RuiWe explore a class of models which can provide a common origin for the recently observed evidence for lepton flavor universality violation in b -> sl(+)l(-) decays, the dark matter (DM) problem, and the long-standing muon (g - 2) anomaly. In particular, both anomalies in the B meson decays and the muon (g - 2) can be explained by the additional one-loop diagrams with DM candidates. We first classify several simple models according to the new fields' quantum numbers. We then focus on a specific promising model and perform a detailed study of both DM and flavor physics. A random scan over the relevant parameter space reveals that there is indeed a large parameter space which can explain the three new physics phenomena simultaneously, while satisfying all other flavor and DM constraints. Finally, we discuss some of the possible new physics signatures at the Large Hadron Collider.
- CP violating hW(+)W(-) coupling in the Standard Model and beyondPublication . Huang, Da; Morais, António P.; Santos, RuiInspired by the recent development in determining the property of the observed Higgs boson, we explore the CP-violating (CPV) -cCPVhW+mu nu Wmu nu-/upsilon coupling in the Standard Model (SM) and beyond, where W-+/- mu nu and W+/- mu nu denote the W-boson field strength and its dual. To begin with, we show that the leading-order SM contribution to this CPV vertex appears at two-loop level. By summing over the quark flavor indices in the two loop integrals analytically, we can estimate the order of the corresponding Wilson coefficient to be cCPVSMsimilar to O10-23, which is obviously too small to be probed at the LHC and planned future colliders. Then we investigate this CPV hW(+)W(-) interaction in two Beyond the Standard Model benchmark models: the left-right model and the complex 2-Higgs doublet model (C2HDM). Unlike what happens for the SM, the dominant contributions in both models arise at the one-loop level, and the corresponding Wilson coefficient can be as large as of O(10(-9)) in the former model and of O(10(-3)) for the latter. In light of such a large CPV effect in the hW(+)W(-) coupling, we also give the formulae for the leading one-loop contribution to the related CPV hZZ effective operator in the complex 2-Higgs doublet model. The order of magnitude of the Wilson coefficients in the C2HDM may be within reach of the high-luminosity LHC or planned future colliders.
- Impact of electroweak group representation in models for B and g − 2 anomalies from dark loopsPublication . Capucha, Rodrigo; Huang, Da; Lopes, Tomás; Santos, RuiWe discuss two models that are part of a class providing a common explanation for lepton flavor universality violation in b→sl+l− decays, the dark matter (DM) problem and the muon (g−2) anomaly. The B meson decays and the muon (g−2) anomalies are explained by additional one-loop diagrams with DM candidates. The models have one extra fermion field and two extra scalar fields relative to the Standard Model. The SU(3) quantum numbers are fixed by the interaction with the Standard Model fermions in a new Yukawa Lagrangian that connects the dark and the visible sectors. We compare two models, one where the fermion is a singlet and the scalars are doublets under SU(2)L and another one where the fermion is a doublet and the scalars are singlets under SU(2)L. We conclude that both models can explain all of the previously mentioned issues imultaneously, while satisfying all other flavor and DM constraints. However, there are crucial differences between how the DM constraints affect the two models leading to a noticeable difference in the allowed DM mass range.
- 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.
- 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.