Recently, the LHCb collaboration has reported the excesses in the b → sll processes. One of the promising candidates for new physics to explain the anomalies is the extended Standard Model (SM) with vector-like quarks and leptons. In that model, Yukawa couplings between the extra fermions and SM fermions are introduced, adding extra scalars. Then, the box diagrams involving the extra fields achieve the b → sll anomalies. It has been known that the excesses require the large Yukawa couplings of leptons, so that this kind of model can be tested by studying correlations with other observables. In this paper, we consider the extra scalar to be a dark matter (DM) candidate, and investigate DM physics as well as the flavor physics and the LHC physics. The DM relic density and the direct-detection cross section are also dominantly given by the Yukawa couplings, so that we find some explicit correlations between DM physics and the flavor physics. In particular, we find the predictions of the b → sll anomalies against the direct detection of DM. arXiv:1706.04344v2 [hep-ph] 1 Nov 2017Recently, the LHCb collaboration has reported that there are deviations from the Standard Model (SM) predictions in the b → sll processes. In the experiment, the branching fractions of B → K ( * ) ll (l = e, µ) are measured, and lepton universalities and angular distributions are studied in each process. One excess is reported in the ratio between BR(B + → K + µµ) and BR(B + → K + ee) in the region with 1 GeV 2 ≤ q 2 ≤ 6 GeV 2 , where q 2 is the invariant mass of two leptons in the final state [1]. The experimental result suggests the smaller value of BR(B + → K + µµ) than the SM prediction, and the deviation is about 2.6σ [1]. Recently, a similar deviation is discovered in B → K * µµ [2]. The B decay to µ pair in this process is again smaller than the SM prediction. Similar indications are also reported in B → φ µµ [3] and Λ b → Λ µµ [4] in the same q 2 region. Moreover, the disagreement between the experimental results and the SM prediction of the angular distribution in B → K * µµ is also one of the longstanding issues [5,6]. The CMS collaboration has shown the result that may be consistent with the SM prediction, but the deviation is still large in the LHCb experiment and the others. Thus, there might be some issues in the b → s transition associated with µ.The SM predicts that namely C 7 , C 9 and C 10 operators contribute to the b → sll processes. C 7 can not give sizable contributions to the processes, because it corresponds to the electric dipole operator that is strictly constrained by B → X s γ. In the region with 1 GeV 2 ≤ q 2 ≤ 6 GeV 2 , the C 9 and C 10 operators dominantly contribute to the branching ratios. The Wilson coefficients, C l 9 and C l 10 , are defined as follows:
In this paper, we summarize phenomenology in lepton portal dark matter (DM) models, where DM couples to leptons and extra leptons/sleptons. There are several possible setups: a DM field is either a complex/real scalar or a Dirac/Majorana fermion, and chiralities of leptons that couple to the DM are different according to the spin of the DM. We discuss the prediction of each model and compare it with the latest experimental constraints from the DM detections, the LHC, and the flavor experiments. We also propose simple setups to resolve the discrepancy in the anomalous magnetic moment of muon.
The relic abundance of the dark matter (DM) particle d is studied in a secluded DM scenario, in which the d number decreasing process dominantly occurs not through the pair annihilation of d into the standard model particles, but via the dd → mm scattering process with a subsequently decaying mediator particle m. It is pointed out that the cosmologically observed relic abundance of DM can be accomplished even with a massive mediator having a mass mm non-negligibly heavy compared with the DM particle mass m d . In the degenerated d-m case (m d = mm), the DM relic abundance is realized by adjusting the dd → mm scattering amplitude large enough and by choosing an appropriate mediator particle life-time. The DM evolution in the early universe exhibits characteristic "terrace" behavior, or two-step number density decreasing behavior, having a "fake" freeze-out at the first step. Based on these observations, a novel possibility of the DM model buildings is introduced in which the mediator particle m is unified with the DM particle d in an approximate dark symmetry multiplet. A pionic DM model is proposed to illustrate this idea in a renormalizable field theory framework.PACS numbers: 12.60. 12.60.Rc, 95.35.+d
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