Predictions on the second-class current decays $tau^{-}topi^{-}eta^{(prime)} u_{tau}$

We analyze the second-class current decays $tau^{-}topi^{-}eta^{(prime)} u_{tau}$ in the framework of Chiral Perturbation Theory with resonances. Taking into account $pi^{0}$-$eta$-$eta^{prime}$ mixing, the $pi^{-}eta^{(prime)}$ vector form factor is extracted, in a model-independent way, using existing data on the $pi^{-}pi^{0}$ one. For the participant scalar form factor, we have considered different parameterizations ordered according to their increasing fulfillment of analyticity and unitarity constraints. We start with a Breit-Wigner parameterization dominated by the $a_{0}(980)$ scalar resonance and after we include its excited state, the $a_{0}(1450)$. We follow by an elastic dispersion relation representation through the Omn`{e}s integral. Then, we illustrate a method to derive a closed-form expression for the $pi^{-}eta$, $pi^{-}eta^{prime}$ (and $K^{-}K^{0}$) scalar form factors in a coupled-channels treatment. Finally, predictions for the branching ratios and spectra are discussed emphasizing the error analysis. An interesting result of this study is that both $tau^{-}topi^{-}eta^{(prime)} u_{tau}$ decay channels are promising for the soon discovery of second-class currents at Belle-II. We also predict the relevant observables for the partner $eta^{(prime)}_{ell 3}$ decays, which are extremely suppressed in the Standard Model.

The $eta^prime$ transition form factor from space- and time-like experimental data

The $eta^prime$ transition form factor is reanalyzed in view of the recent BESIII first observation of the Dalitz decay $eta^primetogamma e^+e^-$ in both space- and time-like regions at low and intermediate energies using the Pade approximants method. The present analysis provides a suitable parameterization for reproducing the measured form factor in the whole energy region and allows to extract the corresponding low-energy parameters together with a prediction of its values at the origin, related to $Gamma_{eta^primetogammagamma}$, and the asymptotic limit. The $eta$-$eta^prime$ mixing is reassessed within a mixing scheme compatible with the large-$N_c$ chiral perturbation theory at next-to-leading order, with particular attention to the OZI-rule--violating parameters. The $J/psi$, $Ztoeta^{(prime)}gamma$ decays are also considered and predictions reported.

Combined analysis of the decays $tau^{-}to K_{S}pi^{-} u_{tau}$ and $tau^{-}to K^{-}eta u_{tau}$

The potential of performing a combined analysis of the strangeness-changing decays $tau^{-}to K_{S}pi^{-} u_{tau}$ and $tau^{-}to K^{-}eta u_{tau}$ for unveiling the $K^{*}(1410)$ resonance pole parameters is illustrated. Our study is carried out within the framework of Chiral Perturbation Theory, including resonances as explicit degrees of freedom. Resummation of final state interactions are considered through a dispersive parameterization of the required form factors. A considerable improvement in the determination of the pole position with mass $M_{K^{*}(1410)}=1304pm17$ MeV and width $Gamma_{K^{*}(1410)}=171pm62$ MeV is obtained.

Jet energy loss in the quark-gluon plasma by stream instabilities

We study the evolution of the plasma instabilities induced by two jets of particles propagating in opposite directions and crossing a thermally equilibrated non-Abelian plasma. In order to simplify the analysis we assume that the two jets of partons can be described with uniform distribution functions in coordinate space and by Gaussian distribution functions in momentum space. We find that while crossing the quark-gluon plasma, the jets of particles excite unstable chromomagnetic and chromoelectric modes. These fields interact with the particles (or hard modes) of the plasma inducing the production of currents; thus, the energy lost by the jets is absorbed by both the gauge fields and the hard modes of the plasma. We compare the outcome of the numerical simulations with the analytical calculation performed assuming that the jets of particles can be described by a tsunami-like distribution function. We find qualitative and semi-quantitative agreement between the results obtained with the two methods.