Weak K-amplitudes in the chiral and 1/Nc-expansions

It is shown that there exist symmetry constraints for non-leptonic weak amplitudes which emerge when the 1/N-c-expansion restricted to the leading and next-to-leading approximations only is systematically combined with chi PT limited to the lowest non-trivial order. We discuss these constraints for the couplings g(8) and g(27) of Delta S = 1 transitions and the B-K-parameter of K-0-K-0 mixing

Strangeness changing scalar form factors

We derive expressions for strangeness-changing scalar form factors, which incorporate known theoretical constraints both at low and high energies. Their leading behaviour in the limit of a large number of colours is calculated from the resonance chiral Lagrangian, and a set of short-distance constraints on the scalar resonance couplings is obtained, imposing the form factors to vanish at infinite momentum transfer. The important effects of meson rescattering are taken into account by exploiting unitarity and analyticity. Making use of previous results on S-wave Kpi scattering [1], and a coupled-channel dispersion-relation analysis, the Kpi, Keta and Keta' scalar form factors are calculated up to 2 GeV These scalar form factors are a key ingredient in the determination of the corresponding scalar spectral function which is important in the extraction of the mass of the strange quark from QCD sum rules as well as hadronic tau decays

LHC constraints on two-Higgs doublet models

A new Higgs-like boson with mass around 126 GeV has recently been discovered at the LHC. The available data on this new particle is analyzed within the context of two-Higgs doublet models without tree-level flavour-changing neutral currents. Keeping the generic Yukawa structure of the Aligned Two-Higgs Doublet Model framework, we study the implications of the LHC data on the allowed scalar spectrum. We analyze both the CP-violating and CP-conserving cases, and a few particular limits with a reduced number of free parameters, such as the usual models based on discrete Z2 symmetries

Towards a general analysis of LHC data within two-Higgs-doublet models

The data accumulated so far confirm the Higgs-like nature of the new boson discovered at the LHC. The Standard Model Higgs hypothesis is compatible with the collider results and no significant deviations from the Standard Model have been observed neither in the flavour sector nor in electroweak precision observables. We update the LHC and Tevatron constraints on CP-conserving two-Higgs-doublet models without tree-level flavour-changing neutral currents. While the relative sign between the top Yukawa and the gauge coupling of the 126 GeV Higgs is found be the same as in the SM, at 90% CL, there is a sign degeneracy in the determination of its bottom and tau Yukawa couplings. This results in several disjoint allowed regions in the parameter space. We show how generic sum rules governing the scalar couplings determine the properties of the additional Higgs bosons in the different allowed regions. The role of electroweak precision observables, low-energy flavour constraints and LHC searches for additional scalars to further restrict the available parameter space is also discussed

Physics at BES_III

There has recently been a dramatic renewal of interest in the subjects of hadron spectroscopy and charm physics. This renaissance has been driven in part by experimental reports of D-0(D) over bar (0) mixing and the discovery of narrow D-sJ states and a plethora of charmonium-like XY Z states at the B factories, and the observation of an intriguing proton-antiproton threshold enhancement and the possibly related X(1835) meson state at BESII. At the same time, lattice QCD is now coming of age, and we are entering a new era when precise, quantitative predictions from lattice QCD can be tested against experimental measurements. For example, the High Precision QCD (HPQCD) and United Kingdom QCD (UKQCD) collaboration's recent high-precision, unquenched calculation of f(D+) = 208 +/- 4 MeV has been found to agree with the CLEO-c collaboration measurement of f(D+) = 223 +/- 17 +/- 8 MeV - a precision level of similar to 8%. Intriguingly, this agreement does not extend to f(Ds), where the HPQCD + UKQCD result f(Ds) = 241 +/- 3 MeV is more than three standard deviations below the current world average experimental value f(Ds) = 276 +/- 9 MeV. Precision improvements, especially on the experimental measurements, are called for and will be of extreme interest. The BES-III experiment at BEPCII in Beijing, which will start operation in summer 2008, will accumulate huge data samples of 10 x 10(9) J/psi, 3 x 10(9) psi(2S), 30 million D (D) over bar or 2 million DS+DS--pairs per running year, respectively, running in the tau-charm theshold region. Coupled with currently available results from CLEO-c, BES-III will make it possible to study in detail, and with unprecedentedly high precision, light hadron spectroscopy in the decays of charmonium states and charmed mesons. In addition, about 90 million D (D) over bar pairs will be collected at BES-III in a three-year run at the psi(3770) peak. Many high precision measurements, including CKM matrix elements related to charm weak decays, decay constants f(D+) and f(Ds), Dalitz decays of three-body D meson decays, searches for CP violation in the charmed-quark sector, and absolute decay branching fractions, will be accomplished. BES-III analyses are likely to be essential in deciding if recently observed signs of mixing in the D-0(D) over bar (0) meson system are actually due to new physics or not. BES-III measurements of f(D+) and f(Ds) at the similar to 1% precision level will match the precision of lattice QCD calculations and provide the opportunity to probe the charged Higgs sector in some mass ranges that will be inaccessible to the LHC. With modern techniques and huge data samples, searches for rare, lepton-number violating, flavor violating and/or invisible decays of D-mesons, charmonium resonances, and tau-leptons will be possible. Studies of tau-charm physics could reveal or indicate the possible presence of new physics in the low energy region. This physics book provides detailed discussions on important topics in tau-charm physics that will be explored during the next few years at BES-III. Both theoretical and experimental issues are covered, including extensive reviews of recent theoretical developments and experimental techniques. Among the subjects covered are: innovations in Partial Wave Analysis (PWA), theoretical and experimental techniques for Dalitz-plot analyses, analysis tools to extract absolute branching fractions and measurements of decay constants, form factors, and CP-violation and D-0(D) over bar (0)-oscillation parameters. Programs of QCD studies and near-threshold tau-lepton physics measurements are also discussed

Tau Decays

The following sections are included: Hadronic τ Decays Leptonic Tau Decays Semileptonic Decays Search for CP Violation in τ Decays

Large-N-c naturalness in coupled-channel meson-meson scattering

The analysis of hadronic interactions with effective field theory techniques is complicated by the appearance of a large number of low-energy constants, which are usually fitted to data. On the other hand, the large-Nc limit helps to impose natural short-distance constraints on these low-energy constants, providing a parameter reduction. A Bayesian interpretation of the expected 1/Nc accuracy allows for an easy and efficient implementation of these constraints, using an augmented χ2. We apply this approach to the analysis of meson-meson scattering, in conjunction with chiral perturbation theory to one loop and coupled-channel unitarity, and show that it helps to largely reduce the many existing ambiguities and simultaneously provide an acceptable description of the available phase shifts

The tau lepton and its associated neutrino

The present knowledge of the τ-lepton and the prospects for future improvements are discussed. It is shown how a better understanding of the τ properties could be used for testing fundamental aspects of the electroweak and strong interactions

QCD duality analysis of B0-B0 mixing

Using finite energy sum rules, the hadronic matrix element of the DeltaB=2 operator governing the mixing between the B 0 and overlineB0 mesons is evaluated. The result is very sensitive to the input value of the bottom quark mass. Allowing it to vary in the range mb=4.70±0.14 GeV, one finds xi B|f B| |B B| =0.13±0.05 GeV