A novel formulation of Cabibbo–Kobayashi–Maskawa matrix renormalization

We present a gauge-independent quark mass counterterm for the on-shell renormalization of the Cabibbo–Kobayashi–Maskawa (CKM) matrix in the Standard Model that is directly expressed in terms of the Lorentz-invariant self-energy functions, and automatically satisfies the hermiticity constraints of the mass matrix. It is very convenient for practical applications and leads to a gauge-independent CKM counterterm matrix that preserves unitarity and satisfies other highly desirable theoretical properties, such as flavor democracy.     

A new approach to a global fit of the CKM matrix

We report on a new approach to a global CKM matrix analysis taking into account most recent experimental and theoretical results. The statistical framework (Rfit) developed in this paper advocates frequentist statistics. Other approaches, such as Bayesian statistics or the 95% CL scan method are also discussed. We emphasize the distinction of a model testing and a model dependent, metrological phase in which the various parameters of the theory are estimated. Measurements and theoretical parameters entering the global fit are thoroughly discussed, in particular with respect to their theoretical uncertainties. Graphical results for confidence levels are drawn in various one and two-dimensional parameter spaces. Numerical results are provided for all relevant CKM parameterizations, the CKM elements and theoretical input parameters. Predictions for branching ratios of rare K and B meson decays are obtained. A simple, predictive SUSY extension of the Standard Model is discussed. Received: 18 April 2001 / Published online: 10 August 2001     

The masses of the neutral {\cal CP}-even Higgs bosons in the MSSM: Accurate analysis at the two-loop level

We present detailed results of a diagrammatic calculation of the leading two-loop QCD corrections to the masses of the neutral -even Higgs bosons in the Minimal Supersymmetric Standard Model (MSSM). The two-loop corrections are incorporated into the full diagrammatic one-loop result and supplemented with refinement terms that take into account leading electroweak two-loop and higher-order QCD contributions. The dependence of the results for the Higgs-boson masses on the various MSSM parameters is analyzed in detail, with a particular focus on the part of the parameter space accessible at LEP2 and the upgraded Tevatron. For the mass of the lightest Higgs boson, , a parameter scan has been performed, yielding an upper limit on which depends only on . The results for the Higgs-boson masses are compared with results obtained by renormalization group methods. Good agreement is found in the case of vanishing mixing in the scalar quark sector, while sizable deviations occur if squark mixing is taken into account. Received: 11 January 1999 / Published online: 28 May 1999     

Simple approach to renormalize the Cabibbo-Kobayashi-Maskawa matrix

We present an on-shell scheme to renormalize the Cabibbo-Kobayashi-Maskawa (CKM) matrix. It is based on a novel procedure to separate the external-leg mixing corrections into gauge-independent self-mass and gauge-dependent wave function renormalization contributions, and to implement the on-shell renormalization of the former with nondiagonal mass counterterm matrices. Diagonalization of the complete mass matrix leads to an explicit CKM counterterm matrix, which automatically satisfies all the following important properties: it is gauge independent, preserves unitarity, and leads to renormalized amplitudes that are nonsingular in the limit in which any two fermions become mass degenerate.     

Physics program of open charm and heavy cc states at the BES-Ⅲ experiment

We present the physics program of the open charm and heavy cc states above the DD production energy threshold, which will be studied with the BES-Ⅲ detector at the BEPC- Ⅱ collider in the coming years. Based on some full Monte Carlo simulations with the BES-Ⅲ detector, we predict the accuracy levels on measuring some physical quantities related to D^0, D^＋ and Ds^＋ decays as well as some non-charmed decays of the heavy cc states.     

Are CP Violating Effects in the Standard Model Really Tiny?

We derive an effective action of the bosonic sector of the Standard Model by integrating out the fermionic degrees of freedom in the worldline approach. The CP violation due to the complex phase in the CKM matrix gives rise to CP-violating operators in the effective action. We calculate the prefactor of the appropriate next-to-leading order operators and give general estimates of CP violation in the bosonic sector of the Standard Model. In particular, we show that the effective CP violation for weak gauge fields is not suppressed by the Yukawa couplings of the light quarks and is much larger than the bound given by the Jarlskog determinant.     

Energy-scale dependence of the lepton flavor-mixing matrix

We study an energy-scale dependence of the lepton flavor-mixing matrix in the minimal supersymmetric standard model with the effective dimension-five operators, which give Majorana masses of neutrinos. We analyze the renormalization group equations of the coefficients () of these effective operators under an approximation that neglects terms of order . We find that only (where is the generation number) real independent parameters in the lepton flavor-mixing matrix depend on the energy scale. In particular, all the phases in are scale-independent. Received: 10 April 1999 / Revised version: 23 May 1999 / Published online: 28 September 1999     

General scan in flavor parameter space in models with vector quark doublets and an enhancement in the B→X_sγ process

In models with vector-like quark doublets, the mass matrices of up and down type quarks are related.Precise diagonalization of the mass matrices has become an obstacle in numerical studies. In this work we first propose a diagonalization method. As its application, in the Standard Model with one vector-like quark doublet we present the quark mass spectrum and Feynman rules for the calculation of B → X_sγ. We find that i) under the constraints of the CKM matrix measurements, the mass parameters in the bilinear term are constrained to a small value by the small deviation from unitarity; ii) compared with the fourth generation extension of the Standard Model, there is an enhancement to the B → X_sγ process in the contribution of vector-like quarks, resulting in a non-decoupling effect in such models.     

A possible hidden symmetry and geometrical source of the phase in the CKM matrix

Based on the present data, the three Cabibbo–Kobayashi–Maskawa (CKM) angles may construct a spherical surface triangle whose area automatically provides a “holonomy” phase. By assuming this geometrical phase to be that in the CKM matrix determined by an unknown hidden symmetry, we compare the theoretical prediction on with experimental data and find the two are consistent within error range. The predicted from this symmetry are also consistent with data. Further applications to the B-physics are briefly discussed. We also suggest restrictions for the Wolfenstein parameters explicitly; the agreement will be tested by more precise measurements in the future. Received: 7 September 1998 / Revised version: 4 January 1999 / Published online: 28 May 1999     

CP in R-parity violating models

It is shown that in R-parity violating models of supersymmetry, the CP violation observed in the kaon system could arise purely from the R-parity violating scalar interactions (A-terms), with no CP violation in the CKM matrix. The direct CP violating parameter, ′, could be as large or larger than that expected in the Standard Model. CP violation in the B system however is expected to be negligible.     

Quark mixing,CKM unitarity

In the Standard Model of elementary particles, quark-mixing is expressed in terms of a 3 x 3 unitary matrix V, the so called Cabibbo-Kobayashi-Maskawa (CKM) matrix. Significant unitarity checks are so far possible for the first row of this matrix. This article reviews the experimental and theoretical information on these matrix elements. On the experimental side, we find a 2.2 to 2.7 deviation from unitarity, which conflicts with the Standard Model.Received: 25 October 2003, Published online: 29 January 2004F. Glück: Present address: Johannes Gutenberg University Mainz, Inst. Physics, WA EXAKT, 55099 Mainz, GermanyA. Serebrov: Also: Paul Scherrer Institut, 5232 Villigen PSI, Switzerland     

Neutralino mass matrix in the nonminimal supersymmetric Standard Model

We study in detail the neutralino mass matrix in the minimal extension of the minimal supersymmetric Standard Model. The model contains a Higgs singlet besides the two Higgs doublets of the minimal model. A number of limiting cases are considered wherein the neutralino mass spectrum can be analytically obtained. Based on these analytical results several useful approximation formulas for the neutralino masses are obtained. Using the constraints from the renormalization group analysis of the model, we obtain the spectrum numerically and study the dependence of the neutralino masses on the parameters of the model. We compare the results of the approximation formulas with the numerical results, and thereby establish the applicability of the these formulae in the different regions of the parameter space.     

Maximal neutrino mixing from an attractive infrared fixed point

In the Standard Model (and MSSM), renormalization effects on neutrino mixing are generally very small and the attractive fixed points are at vanishing neutrino mixing. However for multi-Higgs extensions of the Standard Model, renormalization effects on neutrino mixing can be large and nontrivial fixed points are possible. Here we examine a simple two-Higgs model. For two flavors, maximal mixing is an attractive infrared fixed point. For three flavors, the neutrino mass matrix evolves towards large off-diagonal elements at low energies. The experimentally suggested bimaximal neutrino mixing pattern is one possible attractive infrared fixed point.     

The Higgs boson sector of the complex MSSM in the Feynman-diagrammatic approach

In the Minimal Supersymmetric Standard Model with complex parameters (cMSSM) we calculate higher order corrections to the Higgs boson sector in the Feynman-diagrammatic approach using the on-shell renormalization scheme. The application of this approach to the cMSSM, being complementary to existing approaches, is analyzed in detail. Numerical examples for the leading fermionic corrections, including the leading two-loop effects, are presented. Numerical agreement within 10% with other approaches is found for small and moderate mixing in the scalar top sector. The leading fermionic corrections, supplemented by the full logarithmic one-loop and the leading two-loop contributions are implemented into the public Fortran code FeynHiggsFastC. Received: 6 August 2001 / Revised version: 8 October 2001 / Published online: 21 November 2001     

Decay widths of the neutral \mathcal{CP}-even MSSM Higgs bosons in the Feynman-diagrammatic approach

In the Minimal Supersymmetric Standard Model (MSSM) we incorporate the Higgs-boson propagator corrections, evaluated up to two-loop order, into the prediction of and for . The propagator corrections consist of the full one-loop contribution, including the effects of non-vanishing external momentum, and corrections of at the two-loop level. The results are supplemented with the dominant one-loop QED corrections and final state QCD corrections from both gluons and gluinos. The effects of the two-loop propagator corrections and of the one-loop gluino contributions are investigated in detail. Our results are compared with the result obtained within the renormalization group approach. Agreement within 10% is found for most parts of the MSSM parameter space. Received: 9 March 2000 / Published online: 14 April 2000     

Higgs production in association with squark pairs in the Minimal Supersymmetric Standard Model at future hadron colliders

We study neutral and charged Higgs boson production in association with stop and sbottom squarks at the Large Hadron Collider, within the Supergravity inspired Minimal Supersymmetric Standard Model. The phenomenological relevance of such reactions is twofold. Firstly, they constitute a novel production mechanism of Higgs particles, either through a decay of a heavier (anti)squark into a lighter one or via a Higgs bremsstrahlung process. Secondly, their production rates are extremely sensitive to the values assumed by the five input parameters of the model, this possibly allowing one to put stringent constraints on the latter. After an exhaustive scan of the parameter space, we find that the majority of such processes could be detectable at high luminosity, provided is large, (except in the case of and final states, whose detection is also possible for smaller values), that the universal soft Supersymmetric breaking masses are in the ranges GeV and GeV, and that the trilinear couplings are negative, . We also point out some sizable decay signatures and discuss their Standard Model (SM) backgrounds. Finally, we derive compact analytical formulae of the corresponding scattering matrix elements. Received: 11 May 1999 / Published online: 3 August 1999     

Gluino contribution to the 3-loop quark mass anomalous dimension in the minimal supersymmetric standard model

We deduce the gluino contribution to the three-loop QCD quark mass anomalous dimension function within the minimal supersymmetric Standard Model (MSSM) from its standard QCD expression. This work is a continuation of the program of computation of MSSM renormalization group functions.     

Resummation of angular dependent corrections in spontaneously broken gauge theories

Recent investigations of electroweak radiative corrections have revealed the importance of higher order contributions in high energy processes, where the size of typical corrections can exceed those associated with QCD considerably. Beyond one loop, only universal (angular independent) corrections are known to all orders except for massless processes, where also angle dependent corrections exist in the literature. In this paper we present general arguments for the consistent resummation of angle dependent subleading (SL) logarithmic corrections to all orders in the regime where all invariants are still large compared to the gauge boson masses. We discuss soft isospin correlations, fermion mass and gauge boson mass gap effects, the longitudinal and Higgs boson sector as well as mixing contributions including CKM effects for massive quarks. Two loop results for the right handed Standard Model are generalized in the context of the high energy effective theory based on the standard model Lagrangian in the symmetric basis with the appropriate matching conditions to include the soft QED regime. The result is expressed in exponentiated operator form in a CKM extended isospin space in the symmetric basis. Thus, a full electroweak SL treatment based on the infrared evolution equation method is formulated for arbitrary high energy processes at future colliders. Comparisons with known results are presented. Received: 12 February 2002 / Revised version: 7 March 2002 / Published online: 8 May 2002     

Renormalization of non-semisimple gauge models with the background field method

We study the renormalization of non-semisimple gauge models quantized in the 't Hooft-background gauge to all orders. We analyze the normalization conditions for masses and couplings compatible with the Slavnov-Taylor and Ward-Takahashi Identities and with the IR constraints. We take into account both the problem of renormalization of CKM matrix elements and the problem of CP violation and we show that the Background Field Method (BFM) provides proper normalization conditions for fermion, scalar and gauge field mixings. We discuss the hard and the soft anomalies of the Slavnov-Taylor Identities and the conditions under which they are absent.