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Register a new user$tau to f_1 (1285)pi^{-} u_{tau}$ decay in the extended Nambu -- Jona-Lasinio model
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Within the framework of the extended Nambu -- Jona-Lasinio model, we calculate the matrix element of the $tau to f_1(1285) pi^{-} u_{tau}$ decay, obtain the invariant mass distribution of the $f_1pi$ -system and estimate the branching ratio Br$(tau to f_1 pi^{-} u_{tau})=4.0times 10^{-4}$. The two types of contributions are considered: the contact interaction, and the axial-vector $I^G(J^{PC})=1^-(1^{++})$ resonance exchange. The latter includes the ground $a_1(1260)$ state, and its first radially excited state, $a_1(1640)$. The corrections caused by the $pi -a_1$ transitions are taken into account. Our estimate is in a good agreement with the latest empirical result Br$(tau to f_1 pi^{-} u_{tau})=(3.9pm 0.5)times 10^{-4}$. The distribution function obtained for the decay $tau to f_1(1285) pi^{-} u_{tau}$ shows a clear signal of $a_1(1640)$ resonance which should be compared with future experimental data including our estimate of the decay width $Gamma (a_1(1640) to f_1 pi )=14.1,mbox{MeV}$.
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Using the Nambu--Jona-Lasinio model with the $U(2)times U(2)$ chiral symmetric effective four-quark interactions, we derive the amplitude of the radiative decay $f_1(1285) topi^+pi^-gamma$, find the decay width $Gamma (f_1topi^+pi^-gamma)=346,mbox{keV}$ and obtain the spectral di-pion effective mass distribution. It is shown that in contrast to the majority of theoretical estimates (which consider the $a_1(1260)$ meson exchange as the dominant one), the most relevant contribution to this process comes out from the $rho^0$-resonance exchange related with the triangle $f_1rho^0gamma$ anomaly. The spectral function is obtained to be confronted with the future empirical data.
The anomalous decays $f_1(1285)torho^0pi^+pi^-$ and $a_1(1260)toomegapi^+pi^-$ violating natural parity for vectors and axial-vectors are studied in the framework of the Nambu -- Jona-Lasinio model. We consider the Lagrangian with $U(2)_Ltimes U(2)_R$ chiral symmetric four quark interactions. The theory is bosonized and corresponding effective meson vertices are obtained in the leading order of $1/N_c$ and derivative expansions. The uncertainties related with the surface terms of anomalous quark triangle diagrams are fixed by the corresponding symmetry requirements. We make a numerical estimate of the decay widths $Gamma (f_1(1285)torho^0pi^+pi^-)=2.78, mbox{MeV}$ and $Gamma (a_1(1260)toomegapi^+pi^-)=87, mbox{keV}$. Our result on the $f_1(1285)torho^0pi^+pi^-$ decay rate is in a good agreement with experiment. It is shown that a strong suppression of the $a_1(1260)toomega pipi$ decay is a direct consequence of destructive interference between box and triangle anomalies.
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.
Within the context of an extended Nambu - Jona-Lasinio model, we analyze the role of the axial-vector $a_1(1260)$ and $a_1(1640)$ mesons in the decay $tauto u_tau rho^0pi^-$. The contributions of pseudoscalar $pi$ and $pi (1300)$ states are also considered. The form factors for the decay amplitude are determined in terms of the masses and widths of these states. To describe the radial excited states $pi (1300)$ and $a_1(1640)$ we introduce two additional parameters which can be estimated theoretically, or fixed from experiment. The decay rate and $rhopi$ mass spectrum are calculated.
We calculate the thermal evolution of $pi-pi$ scattering lengths, in the frame of the Nambu--Jona-Lasinio model. The thermal corrections were calculated at the one loop level using Thermofield Dynamics. We present also results for the pion thermal mass. Our procedure implies the modeling of a propagating scalar meson as a resumation of chains of quark bubbles, which is presented explicitly. We compare our results with previous analysis of this problem in the frame of different theoretical approaches.
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