Monika Blanke

Another look at the flavour structure of the Littlest Higgs model with T-parity

Abstract We discuss the mixing matrix V H d that describes the charged and neutral current interactions between ordinary down-quarks and up- and down-mirror quarks in the Littlest Higgs model with T-parity (LHT). We point out that this matrix in addition to three mixing angles contains three physical complex phases and not only one as used in the present literature. We explain the reason for the presence of two additional phases, propose a new standard parameterization of V H d and briefly comment on the relevance of these new phases for the phenomenology of FCNC processes in the LHT model. In a separate paper we present a detailed numerical analysis, including these new phases, of K and B physics, with particular attention to the most interesting rare decays.

Particle-antiparticle mixing, εK, ΔΓq, ASLq, ACP(Bd→ψKS), ACP(Bs→ψphi) and B→Xs,dγ in the Littlest Higgs model with T-parity

We calculate a number of observables related to particle-antiparticle mixing in the Littlest Higgs model with T-parity (LHT). The resulting effective Hamiltonian for Delta F=2 transitions agrees with the one of Hubisz et al., but our phenomenological analysis goes far beyond the one of these authors. In particular, we point out that the presence of mirror fermions with new flavour and CP-violating interactions allows to remove the possible Standard Model (SM) discrepancy between the CP asymmetry S_{psi K_S} and large values of |V_ub| and to obtain for the mass difference Delta M_s X_s gamma decay and A_CP(B -> X_s gamma) that are presented in the LHT model here for the first time. In another scenario the second, non-SM, value for the angle gamma=-(109+-6) from tree level decays, although unlikely, can be made consistent with all existing data with the help of mirror fermions. We present a number of correlations between the observables in question and study the implications of our results for the mass spectrum and the weak mixing matrix of mirror fermions. In the most interesting scenarios, the latter one turns out to have a hierarchical structure that differs significantly from the CKM one.

Correlations between epsilon-prime / epsilon and rare K decays in the littlest Higgs model with T-parity

We calculate the CP-violating ratio epsilon/epsilon in the Littlest Higgs model with T-parity (LHT) and investigate its correlations with the branching ratios for K_L -> pi^0 nu {bar nu}, K_L -> pi^0 l^+ l^- and K^+ -> pi^+ nu {bar nu}. The resulting correlations are rather strong in the case of K_L decays, but less pronounced in the case of K^+ -> pi^+ nu {bar nu}. Unfortunately, they are subject to large hadronic uncertainties present in epsilon/epsilon, whose theoretical prediction in the Standard Model (SM) is reviewed and updated here. With the matrix elements of Q_6 (gluon penguin) and Q_8 (electroweak penguin) evaluated in the large-N limit and m_s^MS(2 GeV) = 100 MeV from lattice QCD, (epsilon/epsilon)_SM turns out to be close to the data so that significant departures of Br(K_L -> pi^0 nu {bar nu}) and Br(K_L -> pi^0 l^+ l^-) from the SM expectations are unlikely, while Br(K^+ -> pi^+ nu {bar nu}) can be enhanced even by a factor 5. On the other hand, modest departures of the relevant hadronic matrix elements from their large-N values allow for a consistent description of epsilon/epsilon within the LHT model accompanied by large enhancements of Br(K_L -> pi^0 nu {bar nu}) and Br(K_L -> pi^0 l^+ l^-), but only modest enhancements of Br(K^+ -> pi^+ nu {bar nu}).

Minimal flavour violation waiting for precise measurements of ΔMs, Sψϕ, AsSL, |Vub|, γ and B0s,d→μ+μ−

We emphasize that the recent measurements of the B^0_s - bar B^0_s mass difference Delta M_s by the CDF and D0 collaborations offer an important model independent test of minimal flavour violation (MFV). The improved measurements of the angle gamma in the unitarity triangle and of |V_ub| from tree level decays, combined with future accurate measurements of Delta M_s, S_{psi K_S}, S_{psi phi}, Br(B_{d,s} -> mu+ mu-), Br(B -> X_{d,s} nu bar nu), Br(K+ -> pi+ nu bar nu) and Br(K_L -> pi^0 nu bar nu) and improved values of the relevant non-perturbative parameters, will allow to test the MFV hypothesis in a model independent manner to a high accuracy. In particular, the difference between the reference unitarity triangle obtained from tree level processes and the universal unitarity triangle (UUT) in MFV models would signal either new flavour violating interactions and/or new local operators that are suppressed in MFV models with low tan(beta), with the former best tested through S_{psi phi} and K_L -> pi^0 nu bar nu. A brief discussion of non-MFV scenarios is also given. In this context we identify in the recent literature a relative sign error between Standard Model and new physics contributions to S_{psi phi}, that has an impact on the correlation between S_{psi phi} and A^s_SL. We point out that the ratios S_{psi phi}/A^s_SL and (Delta M_s)/(Delta Gamma_s) will allow to determine (Delta M_s)/(Delta M_s)^SM. Similar proposals for the determination of (Delta M_d)/(Delta M_d)^SM are also given.

Particle-antiparticle mixing, ?K, ??q, ASLq, ACP(Bd??KS), ACP(Bs??phi) and B?Xs,d? in the Littlest Higgs model with T-parity

We calculate a number of observables related to particle-antiparticle mixing in the Littlest Higgs model with T-parity (LHT). The resulting effective Hamiltonian for Delta F=2 transitions agrees with the one of Hubisz et al., but our phenomenological analysis goes far beyond the one of these authors. In particular, we point out that the presence of mirror fermions with new flavour and CP-violating interactions allows to remove the possible Standard Model (SM) discrepancy between the CP asymmetry S_{psi K_S} and large values of |V_ub| and to obtain for the mass difference Delta M_s X_s gamma decay and A_CP(B -> X_s gamma) that are presented in the LHT model here for the first time. In another scenario the second, non-SM, value for the angle gamma=-(109+-6) from tree level decays, although unlikely, can be made consistent with all existing data with the help of mirror fermions. We present a number of correlations between the observables in question and study the implications of our results for the mass spectrum and the weak mixing matrix of mirror fermions. In the most interesting scenarios, the latter one turns out to have a hierarchical structure that differs significantly from the CKM one.