RESUMEN
We discuss proton and neutron decays involving three leptons in the final state. Some of these modes could constitute the dominant decay channel because they conserve lepton-flavor symmetries that are broken in all usually considered channels. This includes the particularly interesting and rarely discussed pâe^{+}e^{+}µ^{-} and pâµ^{+}µ^{+}e^{-} modes. As the relevant effective operators arise at dimension 9 or 10, observation of a three-lepton mode would probe energy scales of order 100 TeV. This allows us to connect proton decay to other probes such as rare meson decays or collider physics. UV completions of this scenario involving leptoquarks unavoidably violate lepton-flavor universality and could provide an explanation to the recent bâsµµ anomalies observed in B-meson decays.
RESUMEN
BABAR, Belle, and LHCb Collaborations report evidence for new physics in BâDτν and BâD^{*}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 τâµνν 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 hâµτ. 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 τâµνν 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 tâHc can be in a testable range for the LHC. Effects in hâµτ are also possible, but in this case a simultaneous explanation of the anomalous magnetic moment of the muon is difficult due to the unavoidable τâµÎ³ decay.
RESUMEN
We show that left-right symmetric models can easily accommodate stable TeV-scale dark matter particles without the need for an ad hoc stabilizing symmetry. The stability of a newly introduced multiplet either arises accidentally as in the minimal dark matter framework or comes courtesy of the remaining unbroken Z_{2} subgroup of B-L. Only one new parameter is introduced: the mass of the new multiplet. As minimal examples, we study left-right fermion triplets and quintuplets and show that they can form viable two-component dark matter. This approach is, in particular, valid for SU(2)×SU(2)×U(1) models that explain the recent diboson excess at ATLAS in terms of a new charged gauge boson of mass 2 TeV.
RESUMEN
The LHC has observed, so far, 3 deviations from the Standard Model (SM) predictions in flavor observables: LHCb reported anomalies in BâK*µ(+)µ(-) and R(K)=BâKµ(+)µ(-)/BâKe(+)e(-), while CMS found an excess in hâµτ. We show, for the first time, how these deviations from the SM can be explained within a single well-motivated model: a two-Higgs-doublet model with gauged L(µ)-L(τ) symmetry. We find that, despite the constraints from τâµµµ and B(s)-B¯(s) mixing, one can explain hâµτ, BâK*µ(+)µ(-) and R(K) simultaneously, obtaining interesting correlations among the observables.
RESUMEN
Yes, the photon. While a nonzero photon mass has been under experimental and theoretical study for years, the possible implication of a finite photon lifetime lacks discussion. The tight experimental upper bound of the photon mass restricts the kinematically allowed final states of photon decay to the lightest neutrino and/or particles beyond the standard model. We discuss the modifications of the well-measured cosmic microwave background spectrum of free streaming photons due to photon mass and lifetime and obtain model-independent constraints on both parameters--most importantly a lower direct bound of 3 yr on the photon lifetime, should the photon mass be at its conservative upper limit. In that case, the lifetime of microwave photons will be time-dilated by a factor order 10(15).