arXiv subjects

M. Muenz

Publications and source records attributed to M. Muenz.

4 recordsLinked to original sources

arXiv1995

Effective Hamiltonian for $B \ra X_s e^+ e^-$ Beyond Leading Logarithms in the NDR and HV Schemes

We calculate the next-to-leading QCD corrections to the effective Hamiltonian for \Bsee in the NDR and HV schemes. We give for the first time analytic expressions for the Wilson Coefficient of the operator $Q_9 = (\bar s b)_{V-A}(\bar e e)_V$ in the NDR and HV schemes. Calculating the relevant matrix elements of local operators in the spectator model we demonstrate the scheme independence of the resulting short distance contribution to the physical amplitude. Keeping consistently only leading and next-to-leading terms, we find an analytic formula for the differential dilepton invariant mass distribution in the spectator model. Numerical analysis of the $\mt$, $\Lms$ and $μ\approx {\cal O}(\mb)$ dependences of this formula is presented. We compare our results with those given in the literature.

hep-ph↗

arXiv1994

Two-loop mixing of dimension-five flavor-changing operators

We calculate the two-loop QCD mixing of the dimension-five flavor-changing operators that arise in the Standard Model after integrating out the $W$, $Z$ and Higgs bosons and the top-quark, i.e.~the mixing among gluonic and photonic magnetic moment operators. Our calculation completes the two-loop anomalous dimension matrix of operators that govern low energy flavor-changing processes. It is an important ingredient of the next-to-leading calculation of the $B \rightarrow X_s γ$ decay rate.

hep-ph↗

arXiv1993

Theoretical Uncertainties and Phenomenological Aspects of $B \rightarrow X_s γ$ Decay

We analyze uncertainties in the theoretical prediction for the inclusive branching ratio $BR[B \rightarrow X_s γ]$. We find that the dominant uncertainty in the leading order expression comes from its $μ$-dependence. We discuss a next-to-leading order calculation of $B \rightarrow X_s γ$ in general terms and check to what extent the $μ$-dependence can be reduced in such a calculation. We present constraints on the Standard and Two-Higgs-Doublet Model parameters coming from the measurement of $b \rightarrow s γ$ decay. The current theoretical uncertainties do not allow one to definitively restrict the Standard Model parameters much beyond the limits coming from other experiments. The bounds on the Two-Higgs-Doublet Model remain very strong, though significantly weaker than the ones present in the recent literature. In the Two-Higgs-Doublet Model case, the $b \rightarrow s γ$, $Z \rightarrow b \bar{b}$ and $b \rightarrow c τ\barν_τ$ processes are enough to give the most restrictive bounds in the $M_{H^{\pm}}-tan β$ plane.

hep-ph↗

arXiv1992

Current correlators to all orders in the quark masses

The contributions to the coefficient functions of the quark and the mixed quark-gluon condensate to mesonic correlators are calculated for the first time to all orders in the quark masses, and to lowest order in the strong coupling constant. Existing results on the coefficient functions of the unit operator and the gluon condensate are reviewed. The proper factorization of short- and long-distance contributions in the operator product expansion is discussed in detail. It is found that to accomplish this task rigorously the operator product expansion has to be performed in terms of non-normal-ordered condensates. The resulting coefficient functions are improved with the help of the renormalization group. The scale invariant combination of dimension 5 operators, including mixing with the mass operator, which is needed for the renormalization group improvement, is calculated in the leading order.

hep-ph↗