Lepton-mass effects in the decays H→ZZ∗→ℓ+ℓ−τ+τ−H \to ZZ^{\ast} \to \ell^{+} \ell^{-} \tau^{+} \tau^{-} and H→WW∗→ℓντντH \to WW^{\ast} \to \ell \nu \tau \nu_{\tau}

We consider lepton-mass effects in the cascade decays $H\to Z(\to \ell^{+} \ell^{-})+Z^{\ast}(\to \tau^{+}\tau^{-})$ and $H\to W^{-}(\to \ell^{-}\bar \nu_{\ell})+W^{+\ast}(\to \tau^{+}\nu_{\tau})$. Since the scale of the problem is set by the off-shellness $q^{2}$ of the respective gauge bosons in the limits $(m_{\ell}+m_{\ell'})^{2} \le q^{2} \le (m_{H}-m_{W,Z})^{2}$ and not by $m_{W,Z}^{2}$, lepton-mass effects are non-negligible for the $\tau$ modes in particular close to the threshold of the off-shell decays. Lepton-mass effects show up e.g.\ in the three-fold joint angular decay distribution for the decays. Nonzero lepton masses lead to leptonic helicity-flip contributions which in turn can generate novel angular dependencies in the respective three-fold angular decay distributions. Lepton-mass effects are more pronounced in the $H \to Z(\to \ell\ell)Z^{\ast}(\to\tau\tau)$ mode which, in part, is due to the fact that the ratio of lepton helicity flip/nonflip contributions in the decay $Z^{\ast} \to \ell^{+}\ell^{-}$ is four times larger than in the decay $W^{+\ast}\to \ell^{+}\nu$. We also briefly consider the corresponding off-shell -- off-shell decays $H\to Z^{\ast}(\to \ell^{+}\ell^{-})+Z^{\ast}(\to \tau^{+}\tau^{-})$ and $H\to W^{-\ast}(\to \ell^{-}\bar \nu_{\ell})+W^{+\ast}(\to \tau^{+}\nu_{\tau})$.Comment: 45 pages, 9 figures and 6 tables, published versio

One-photon decay of the tetraquark state X(3872)→γ+J/ψX(3872) \to \gamma + J/\psi in a relativistic constituent quark model with infrared confinement

We further explore the consequences of treating the X(3872) meson as a tetraquark bound state by analyzing its one-photon decay X => \gamma + J/psi in the framework of our approach developed in previous papers which incorporates quark confinement in an effective way. To introduce electromagnetism we gauge a nonlocal effective Lagrangian describing the interaction of the X(3872) meson with its four constituent quarks by using the P-exponential path-independent formalism. We calculate the matrix element of the transition X => \gamma+ J/psi and prove its gauge invariance. We evaluate the X=> \gamma + J/psi decay width and the longitudinal/transverse composition of the J/psi in this decay. For a reasonable value of the size parameter of the X(3872) meson we find consistency with the available experimental data. We also calculate the helicity and multipole amplitudes of the process, and describe how they can be obtained from the covariant transition amplitude by covariant projection.Comment: 13 pages, 5 figures. Typos corrected, version matching the one published in PR

Semileptonic decays of double heavy baryons in a relativistic constituent three-quark model

We study the semileptonic decays of double heavy baryons using a manifestly Lorentz covariant constituent three-quark model. We present complete results on transition form factors between double-heavy baryons for finite values of the heavy quark/baryon masses and in the heavy quark symmetry limit which is valid at and close to zero recoil. Decay rates are calculated and compared to each other in the full theory, keeping masses finite, and also in the heavy quark limit.Comment: 20 pages, 2 figure

Physical observables in the decay Λb→Λc(→Λ+π)+τ−+νˉτ\Lambda_b \to \Lambda_c (\to \Lambda+\pi)+\tau^{-}+\bar \nu_{\tau}

We analyze the tauonic semileptonic baryon decays $\Lambda^0_b \to \Lambda^+_c + \tau^{-} +\bar \nu_{\tau}$ with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the $\Lambda^+_c$ and the $\tau^-$, and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.Comment: 6 pages, 1 figure. Talk given by Nurgul Habyl at the 9th joint International HADRON STRUCTURE'15 Conference, GRAND HOTEL BELLEVUE, Horny Smokovec, Slovak Republic, 29 June - 3 July, 201