Vector-like Down Quark Research Articles

DIRECT CP VIOLATION AND NEW PHYSICS EFFECTS IN THE DECAY MODE B+→ϕK+

We study the direct CP violation effect in the decay mode B+→ϕK+. This decay mode is dominated by the loop induced [Formula: see text] penguin diagram with a tiny contribution from the annihilation diagram. Therefore, the standard model expectation of direct CP violation is negligibly small. Using QCD factorization approach we find the CP asymmetry in the standard model to be at percent level. We consider then two scenarios beyond the standard model, the model with an extra vector-like down quark (VLDQ) and the R-parity violating supersymmetric model (RPV) and show that the direct CP violating asymmetry in B+→ϕK+ could be as large as ~ 85% (70%) in VLDQ (RPV) model.

Probing new physics in B→φπ decay

We analyze the rare decay mode B→φπ, which is a pure penguin induced process, receiving dominant contribution from the electroweak penguins. Thus the Standard Model branching ratio is expected to be very small, which makes it as a sensitive probe of new physics. Using QCD factorization approach, we find the branching ratio in the Standard Model as Br(B−→φπ−)≃5×10−9. Exploring some of the beyond Standard Model scenarios the branching ratio is found to be ∼O(10−8) in the minimal supersymmetric Standard Model (MSSM) with mass insertion approximation and in the extended technicolor model (TC2). The existence of an extra vector-like down quark (VLDQ) model predicts it to be ∼O(10−7). The recent BaBar result on B0→φπ0 might be a strong indication of new physics effect present in the penguin induced process B→φπ.

New physics effects on theCPasymmetries inB→φKSandB→η′KSdecays

Within the standard model (SM), the time dependent CP asymmetries in B -> psi K_S, B -> eta' K_S and B -> phi K_S are expected to give the same result i.e. sin (2 beta). However recent measurements of the mixing induced CP asymmetries in B -> phi K_S and B -> eta' K_S modes give results whose central values differ from SM expectations. We explore the effects of new physics in the two Higgs doublet model (THDM), which allows tree level flavor changing neutral currents (so called Model III), and the model with extra vector like down quark (VLDQ). We find that the observed mixing induced CP asymmetry for B -> phi K_S can not be accommodated by the THDM, but can be explained in the VLDQ model and both models can explain the observed asymmetry for B -> eta' K_S mode.

Vector-like fermion contributions to ε′

We consider extensions to the standard electroweak model which contain new vector-like fermions at the Fermi scale as a source of CP violation. After a detailed calculation of the QCD corrections to leading order, we find that the new contributions to | ε′ ε | range typically from 10 −3 to 10 −2 when we require that the corresponding contributions to ε saturate its experimental value. If, for instance, a new vector-like down-quark exists at the Fermi scale | ε′ ε | is predicted to be ∼×10 −3. These results are within the range of sensitivity of presently planned experiments.

Vector-like fermion contributions to ε′

We consider extensions to the standard electroweak model which contain new vector-like fermions at the Fermi scale as a source of CP violation. After a detailed calculation of the QCD corrections to leading order, we find that the new contributions to |e′/e| range typically from 10 −3 to 10 −2 when we require that the corresponding contributions to e saturate its experimental value. If, for instance, a new vector-like down-quark exists at the Fermi scale |e′/e| is predicted to be ∼2 × 10 −3 . These results are within the range of sensitivity of presently planned experiments.