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We compute branching ratios and invariant mass distributions of the tau decays into four pions. The hadronic matrix elements are obtained by starting from the structure of the hadronic current in chiral limit and then implementing low-lying resonances in the different channels. Reasonable agreement with experiment is obtained both for the $tau to u_{tau} + (4 pi ) $ decay rates and the $e^+e^- to (4 pi ) $ cross sections. Furthermore we supply an interface to use our matrix elements within the Tauola Monte-Carlo program.
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tau -> (3 pions) nu_tau decays are analysed within the framework of the resonance effective theory of QCD. We work out the relevant Lagrangian that describes the axial-vector current hadronization contributing to these processes, in particular the local a_1(1260)-rho(770)-Goldstone interactions. The new coupling constants are constrained by imposing the asymptotic behaviour of the corresponding spectral function within QCD. Hence we compare the theoretical framework with the experimental data, obtaining a good quality fit from the ALEPH spectral function and branching ratio. We also get values for the mass and on-shell width of the a_1(1260) resonance. In this way we are able to provide the structure functions that have been measured by OPAL and CLEO-II and we find an excellent agreement.
We analyse tau -> (3 pions) nu_tau decays within the framework of the resonance chiral theory of QCD. We have worked out the relevant Lagrangian that describes the axial-vector current hadronization contributing to these processes, and the new coupling constants that arise have been constrained by imposing the asymptotic behaviour of the corresponding spectral function within QCD. Hence we compare the theoretical framework with the experimental data, obtaining a good quality fit from the ALEPH spectral function and branching ratio. We also get values for the mass and on-shell width of the a_1(1260) resonance, and provide the tau -> (3 pions) nu_tau structure functions that have been measured by OPAL and CLEO-II finding an excellent agreement.
We search for lepton-flavor-violating tau decays into three leptons (electron or muon) using 535 fb-1 of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. No evidence for these decays is observed, and we set 90% confidence level upper limits on the branching fractions of (2.0-4.1)x10^-8. These results improve upon our previously published upper limits by factors of 4.9 to 10.
Models with extended Higgs boson sectors are of prime importance for investigating the mechanism of electroweak symmetry breaking for Higgs decays into four fermions and for Higgs-production in association with a vector bosons. In the framework of the Two-Higgs-Doublet Model using two scenarios obtained from the experimental measurements we presented next-to-leading-order results on the four-fermion decays of light CP-even Higgs boson, $h rightarrow 4f$. With the help of Monte Carlo program Prophecy 4f 3.0, we calculated the values $Gamma= Gamma_{EW} /left(Gamma_{EW}+Gamma_{SM}right)$ and $Gamma= Gamma_{EW+QCD} /left(Gamma_{EW+QCD}+Gamma_{SM}right)$ for Higgs boson decay channels $ H rightarrow u_{mu} overline{mu} e overline{ u_e}$, $mu overline{mu} e overline{e}$, $e overline{e} e overline{e}$. We didnt find significant difference when accounting QCD corrections to EW processes in the decay modes of Higgs boson. Using computer programs Pythia 8.2 and FeynHiggs we calculated the following values: $sigma(VBH)BR(Hrightarrow ZZ)$ and $sigma(VBF)BR(H rightarrow WW)$ for VBF production processes, $sigma(ggH)BR(H rightarrow WW)$ and $sigma(ggH)BR(H rightarrow ZZ)$ for gluon fusion production process at 13 and 14 TeV and found good agreement with experimental data.
A search for the non-resonant decays $B^0_s rightarrow mu^{+}mu^{-}mu^{+}mu^{-}$ and $B^0 rightarrow mu^{+}mu^{-}mu^{+}mu^{-}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of $1$ and $2~mathrm{fb}^{-1}$ collected at centre-of-mass energies of $7$ and $8~mathrm{TeV}$, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at $95%$ confidence level are determined to be mathcal{B}(B^0_s rightarrow mu^{+}mu^{-}mu^{+}mu^{-}) & < 2.5 times 10^{-9} mathcal{B}(B^0 rightarrow mu^{+}mu^{-}mu^{+}mu^{-}) & < 6.9 times 10^{-10}.
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