CERN Theory Division, CH-1211 Geneva 23, Switzerland.
Service de Physique Théorique, Université Libre de Bruxelles, Boulevard du Triomphe, CP225, 1050 Brussels, Belgium.
Phys Rev Lett. 2016 Feb 26;116(8):081801. doi: 10.1103/PhysRevLett.116.081801. Epub 2016 Feb 23.
BABAR, Belle, and LHCb Collaborations report evidence for new physics in B→Dτν and B→D^{}τν of approximately 3.8σ. There is also the long lasting discrepancy of about 3σ in the anomalous magnetic moment of the muon, and the branching ratio for τ→μνν is 1.8σ (2.4σ) above the standard model expectation using the HFAG (PDG) values. Furthermore, CMS Collaboration finds hints for a nonzero decay rate of h→μτ. Interestingly, all these observations can be explained by introducing new scalars. In this Letter we consider these processes within a lepton-specific two-Higgs doublet model (i.e., of type X) with additional nonstandard Yukawa couplings. It is found that one can accommodate τ→μνν with modified Higgs-τ couplings. The anomalous magnetic moment of the muon can be explained if the additional neutral CP-even Higgs boson H is light (below 100 GeV). Also R(D) and R(D^{}) can be easily explained by additional t-c-Higgs couplings. Combining these t-c couplings with a light H the decay rate for t→Hc can be in a testable range for the LHC. Effects in h→μτ are also possible, but in this case a simultaneous explanation of the anomalous magnetic moment of the muon is difficult due to the unavoidable τ→μγ decay.
BABAR、 Belle 和 LHCb 合作组报道了在 B→Dτν 和 B→Dτν 中大约 3.8σ 的新物理证据。μ 子反常磁矩也存在大约 3σ 的长期差异，使用 HFAG（PDG）值，τ→μνν 的分支比比标准模型预期高出 1.8σ（2.4σ）。此外，CMS 合作组发现 h→μτ 的非零衰变率的迹象。有趣的是，所有这些观测结果都可以通过引入新标量来解释。在这封信中，我们考虑了这些过程在具有附加非标准 Yukawa 耦合的轻子特定双 Higgs 二重态模型（即 X 型）内的情况。结果发现，可以通过修改的 Higgs-τ 耦合来容纳 τ→μνν。如果额外的中性 CP 相等 Higgs 玻色子 H 很轻（低于 100GeV），则可以解释μ子的反常磁矩。额外的 t-c-Higgs 耦合也可以解释 μ 子反常磁矩和 R(D)、R(D)。将这些 t-c 耦合与轻的 H 结合起来，t→Hc 的衰变率可以在 LHC 中进行测试。h→μτ 中也可能存在效应，但在这种情况下，由于不可避免的 τ→μγ 衰变，很难同时解释μ子的反常磁矩。
