Exploring top quark FCNC within 2HDM type III in association with flavor physics

Abstract

Abstract:The top quark flavor changing neutral current (FCNC) process is an excellent probe to search for new physics in top sector since the Standard Model expectation is extremely suppressed. We explore Higgs-mediated top quark FCNC, focusing on H-tc Yukawa coupling λ ct within the general two Higgs doublet model. After electroweak symmetry breaking the top quark FCNC couplings are included in the charged Higgs Yukawa sector so that they contribute to various processes in flavor physics. To probe λ ct , we study anomalous single top production and the same sign top pair production at the LHC in association with flavor physics from the tree-level processes B → D ( * ) τ ν, B → τ ν as well as from the loop-level processes B d → X s γ, B d,s − B d,s mixing. We perform combined analysis of all the constraints regarding the fine-tuning argument to fit the data and discuss future prospect. The recently updated measurements on B → D ( * ) τ ν still prefer large λ ct , but we show that the current bound on the same sign top pair production at the LHC gives the most significant upper bound on λ ct to be less than 10 ∼ 30 depending on neutral heavy Higgs masses. We also find that for the given upper bound on λ ct , B → D ( * ) τ ν put significant lower bound on H-τ -τ Yukawa coupling, and the bound is proportional to the charged Higgs mass.

High-scale validity of a two-Higgs-doublet scenario: metastability included

“…This particular scheme can be implemented by introducing a Z 2 symmetry that demands 1 → − 1 and 2 → 2 . While the primary motivation of the above is to suppress flavour changing neutral currents (FCNC) [20][21][22], it reduces the number of free parameters in the Yukawa sector 1 As a consequence, it becomes easier to throw light on the scalar sector in an analysis using the renormalisation group equations (RGEs).…”

Lifetime of Bc− Mesons Constrains Explanations for Anomalies in B→D(*)Alonso1, Grinstein2, Camalich3 2017Phys. Rev. Lett.29982972View full textAdd to dashboardCite

“…In fact, this type of scenario encompasses models of NP that have been popular in the interpretation of the R D ðÃÞ , such as the 2HDM [28][29][30][31][32][33][34][35][36][37][38]. In light of the constraint from the B c lifetime, any of the 2HDM interpretations of R D à is ruled out, in particular, those realizations of the model based on the so-called type III, with general Yukawa couplings to the different fermions [65], which can explain simultaneously R D and R D à [32,[34][35][36][37][38] Interplay between P à L and R D ðÃÞ .-The analysis of the B c lifetime leaves only ϵ L and ϵ T as possible mechanisms to explain the R D à anomaly.…”

“…In light of the constraint from the B c lifetime, any of the 2HDM interpretations of R D à is ruled out, in particular, those realizations of the model based on the so-called type III, with general Yukawa couplings to the different fermions [65], which can explain simultaneously R D and R D à [32,[34][35][36][37][38] Interplay between P à L and R D ðÃÞ .-The analysis of the B c lifetime leaves only ϵ L and ϵ T as possible mechanisms to explain the R D à anomaly. As discussed succinctly above, the left-handed scenario leads to a universal enhancement with respect to the SM of all the b → cτν decay rates by the very same ∼30% that is required to simultaneously explain R D and R à D .…”

Rare top decays as probes of flavorful Higgs bosons

“…In our flavorful 2HDMs, 50% of the time the final state will be same-sign tops, in contrast to 2HDMs with natural flavor conservation that only produce opposite sign tops. Same-sign tops have been identified as important probes in a number of new physics scenarios, including RPV SUSY [56], 2HDMs [35,57,58], additional scalars [59,60], colored vectors [61], and effective field theories [62]. The cross section of same-sign tops in our scenario is shown in the left plot of In [55] searches for same-sign leptons are interpreted in a benchmark model in which same-sign tops are created by a neutral spin-1 mediator.…”