Theoretical overview on tau physics

Precise measurements of the tau lepton properties provide stringent tests of the Standard Model structure and accurate determinations of its parameters. We overview the present status of a few selected topics: lepton universality, QCD tests and the determination of alpha_s, m_s and V_us from hadronic tau decays, and lepton flavor violation phenomena.Comment: Invited talk at the International Workshop on Tau-Charm Physics (Charm2006), Beijing, China, June 5-7, 2006. 8 pages, 2 figure

Determination of MbM_b and αs\alpha_s from the Upsilon System

The mass of the bottom quark (both the pole mass $M_b$ and the \MSb mass $m_b$) and the strong coupling constant $\alpha_s$ have been determined from QCD moment sum rules for the $\Upsilon$ system. In the pole-mass scheme large perturbative corrections resulting from coulombic contributions have been resummed. The results of this analysis are: M_b=4.60 \pm 0.02 \gev, m_b(m_b)=4.13 \pm 0.06 \gev and $\alpha_s(M_Z)=0.119 \pm 0.008$.Comment: 5 pages, 1 Postscript figure Invited talk at the High Energy Conference on Quantum Chromodynamics (QCD'97), Montpellier, July 199

Spectral distribution for the decay tau -> nu_tau K pi

With the newly available data sets on hadronic tau decays from the B-factories BABAR and BELLE, and future data from BESIII, precise information on the decay distributions will soon become available. This calls for an improvement of the decay spectra also on the theoretical side. In this work, the distribution function for the decay tau -> nu_tau K pi will be presented with the relevant K pi vector and scalar form factors being calculated in the framework of the resonance chiral theory, also taking into account additional constraints from dispersion relations and short-distances. As a by-product the slope and curvature of the vector form factor F_+^{K pi}(s) are determined to be lambda_+^' = 25.6 10^{-3} and lambda_+^{''} = 1.31 10^{-3} respectively. From our approach it appears that it should be possible to obtain information on the low lying scalar K_0^*(800) as well as the second vector K^*(1410) resonances from the tau decay data. In particular, the exclusive branching fraction of the scalar component is found to be B[tau -> nu_tau(K pi)_{S-wave}] = (3.88 +- 0.19) 10^{-4}.Comment: 14 pages, 2 figure

Phase diagram and magnons in quasi-one-dimensional dipolar antiferromagnets

We investigate antiferromagnetic spin chains, which are coupled by a weak antiferromagnetic exchange interaction on a hexagonal lattice. We particulary study the role of the dipole-dipole interaction within the framework of a Heisenberg model with nearest-neighbor exchange and additional dipolar interaction. We find several commensurate and incommensurate phases depending on the ratio of dipolar energy to interchain-exchange energy due to their competing qualtity. The ground-state analysis is supplemented by a stability analysis by means of a linear spin-wave theory. In comparison with experiments (CsMnBr_3, RbMnBr_3) we obtain good agreement for the energy gaps. From this we conclude, that the dipolar interaction is the most important source of anisotropy in these Mn-compounds.Comment: 3 pages, 3 Postscript figure

Chiral low-energy constants from tau data

We analyze how the recent precise hadronic tau-decay data on the V-A spectral function and general properties of QCD such as analyticity, the operator product expansion and chiral perturbation theory (ChPT), can be used to improve the knowledge of some of the low-energy constants of ChPT. In particular we find the most precise values of L_{9,10} (or equivalently l_{5,6}) at order p^4 and p^6 and the first phenomenological determination of C_87 (c_50).Comment: Proceedings of the 6th International Workshop on Chiral Dynamics (Bern, Switzerland, July 6-10, 2009). 9 pages, 3 figure

ChPT parameters from tau-decay data

Using the updated ALEPH V-A spectral function from tau decays, we determine the lowest spectral moments of the left-right correlator and extract dynamical information on order parameters of the QCD chiral symmetry breaking. Uncertainties associated with violations of quark-hadron duality are estimated from the data, imposing all known short-distance constraints on a resonance-based parametrization. Employing proper pinched weight functions, we obtain an accurate determination of the effective chiral couplings L10 and C87 and the dimension-six and -eight contributions in the Operator Product Expansion.Comment: 5 pages, 3 figures, QCD2015 Montpellie

V(us) Determination from Hyperon Semileptonic Decays

We analyze the numerical determination of the quark mixing factor V(us) from hyperon semileptonic decays. The discrepancies between the results obtained in two previous studies are clarified. Our fits indicate sizeable SU(3) breaking corrections, which unfortunately can only be fully determined from the data at the first order. The lack of a reliable theoretical calculation of second-order symmetry breaking effects translates into a large systematic uncertainty, which has not been taken into account previously. Our final result, V(us) = 0.226 +/- 0.005, is not competitive with the existing determinations from K(l3), K(l2) and \tau decays.Comment: 16 pages, no figures. References added and other minor change

Hadron structure in tau -> KKpi nu_tau decays

We analyse the hadronization structure of both vector and axial-vector currents leading to tau -> KKpi nu_tau decays. At leading order in the 1/Nc expansion, and considering only the contribution of the lightest resonances, we work out, within the framework of the resonance chiral Lagrangian, the structure of the local vertices involved in those processes. The couplings in the resonance theory are constrained by imposing the asymptotic behaviour of vector and axial-vector spectral functions ruled by QCD. In this way we predict the hadron spectra and conclude that, contrarily to previous assertions, the vector contribution dominates by far over the axial-vector one in all KKpi charge channels.Comment: 32 pages, 7 figure

The B -> Xs gamma Rate and CP Asymmetry within the Aligned Two-Higgs-Doublet Model

In the two-Higgs-doublet model the alignment of the Yukawa matrices in flavour space guarantees the absence of flavour-changing neutral currents at tree level, while introducing new sources for CP violation parametrized in a very economical way. This implies potentially large influence in a number of processes, b -> s gamma being a prominent example where rather high experimental and theoretical precision meet. We analyze the CP rate asymmetry in this inclusive decay and determine the resulting constraints on the model parameters. We demonstrate the compatibility with previously obtained limits. Moreover we extend the phenomenological analysis of the branching ratio, and examine the influence of resulting correlations on the like-sign dimuon charge asymmetry in B decays.Comment: 12 pages, 6 figures. Submitted to Phys.Rev.