Large effects onBsBsmixing by vectorlike quarks

Abstract

We calculate the contributions of the vectorlike quark model to B s B s mixing, taking into account the constraints from the decay B→X s ␥. In this model the neutral bosons mediate flavor-changing interactions at the tree level. However, B s B s mixing is dominated by contributions from the box diagrams with the top quark and the extra up-type quark. In sizable ranges of the model parameters, the mixing parameter x s is much different from the standard model prediction.The standard model ͑SM͒ may have to be extended to describe physics around or above the electroweak scale. Various works have thus discussed phenomena involving the B meson which are sensitive to new physics ͓1͔. For instance, the radiative B-meson decay B→X s ␥ and BB mixing could receive nontrivial contributions from supersymmetry ͓2,3͔. The vectorlike quark model ͑VQM͒ could also affect these processes of flavor-changing neutral currents ͓4,5͔.In this Brief Report we discuss B s B s mixing within the framework of the VQM which is one of the minimal extensions of the SM. The mixing parameter x s is evaluated and its dependencies on the model parameters are analyzed. These model parameters are constrained by the branching ratio of the decay B→X s ␥. Even under these constraints, the value of x s can be much different from the SM prediction.The VQM incorporates extra quarks whose left-handed components, as well as right-handed ones, are singlets under the SU͑2͒ gauge transformation. Then, the interactions of quarks become different from those in the SM. The CabibboKobayashi-Maskawa ͑CKM͒ matrix for the interactions with the W boson is extended and not unitary. The Z boson couples directly to the quarks with different flavors. The neutral Higgs boson also mediates flavor-changing interactions at the tree level.Our study concentrates on B s B s mixing at the one-loop level through box diagrams. The contributions at the tree level have already been analyzed in the literature. The order of these tree-level diagrams is lower than the box diagrams of the SM. However, the experimental bounds on the branching ratio of the decay B→K ϩ Ϫ suggest very weak couplings for the flavor-changing interactions at the tree level. Consequently, the tree-level contributions turn out to be smaller than the one-loop contributions. On the other hand, the new box diagrams in the VQM are expected to contribute at the same order as those of the SM. Although these new contributions do not yield a drastic change from the SM prediction, precise measurements in near-future experiments, such as BTeV and the CERN Large Handron Collider ͑LHCb͒, may be able to distinguish the VQM and the SM. Indeed, the VQM could give sizable new contributions to the decay B→X s ␥ at the one-loop level ͓5͔, imposing non-trivial constraints on the model. We assume, for definiteness, that there exist two vectorlike quarks U and D with electric charge 2/3 and Ϫ1/3, respectively. The CKM matrix V is then enlarged to be a 4 ϫ4 matrix and expressed asA L u and A L d being unitary matrices which diagonalize...

CKM matrix with lattice QCD - the full determination using recent results

“…Two unquenched results agree with each other within errors. These are also consistent with previous quenched calculations [43,44,45,46,47]; at present it is difficult to estimate the effect of the quenching quantitatively because the size of other systematic uncertainties O(10%) is the same as the expected size of the quenching error.…”

Light-cone heavy quark effective theory sum rules for theB→πtransition with1/mQKörner1, Li2, Yan3 2002Phys. Rev. D110150View full textAdd to dashboardCite

“…It should be mentioned that the matching results obtained here correspond to the case of central values of ω c . For further support of our matching procedure we have included in the lattice NRQCD results from the JLQCD collaboration [23]. They can be seen to be well consistent with our matching result.…”

“…The scalar form factor contributes to the decay B → πτ ν τ and also enters the factorized amplitudes in non-leptonic two-body B decays. For comparison, the results from the lattice QCD simulations by APE [30], UKQCD [31], FNAL [32] and JLQCD [23] are also shown in the figures.…”

“…[11] which gave leading order results for L α . In addition to that the analytical expressions of the sum rules differ from ours by a factor of 2, the The form factors f B→π +, 0 (q 2 ) from combining LC-HQET sum rules and HMχPT, and from the lattice QCD simulations by APE [30], UKQCD [31], FNAL [32] and JLQCD [23].…”

Flavour Physics Theory Overview

“…Only two modern unquenched results [51,52] exist so far, so that the average for |V ub | excl takes into account also older quenched results [53]- [56]. It reads…”