\tau\rightarrow\omegA3\pi\nu decays

A theoretical study of the anomalous decay mode is presented. The theoretical value of the branching ratio of agrees well with the data. The branching ratio of is predicted. It is found that the vertices of and play a dominant role in these two decay modes. CVC is satisfied, and there is no adjustable parameter. Received: 30 July 2001 / Published online: 21 November 2001     

Testing non-commutative QED \gamma\gamma\gamma and \gamma\gamma\gamma\gamma couplings at LHC

In this work, we investigate the sensitivity of the process at LHC for the photonic 3- and 4-point functions that appear in non-commutative QED. We show that this process serves to study the behavior of the space-space as well as of the space-time non-commutativity. We also show that this process can probe the non-commutative scale in the range of a few TeV.Received: 9 February 2004, Revised: 27 February 2004, Published online: 8 April 2004     

The process\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma as an alternative to\pi ^0 \to v\bar v

The process \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) is investigated as an alternative to \(\pi ^0 \to v\bar v\) . It is shown that the experimental bound on the branching fraction for missing energy (in the form of \(\lambda _\gamma \bar \lambda _\gamma \) and/or \(v\bar v\) ) may be understood in terms of \(\pi ^0 \to \lambda _\gamma \bar \lambda _\gamma \) for the kinematically allowed photino mass, if the squark mass is >8 GeV.     

Process $$\gamma \gamma \to \nu \bar \nu$$ in a strong magnetic field

The three-vertex loop amplitude in a strong magnetic field are analyzed in a general form by using the asymptotic behavior of the electron propagator in an external field. The process \(\gamma \gamma \to \nu \bar \nu\) is studied in terms of the scalar-vector-vector (SVV), pseudoscalar-vector-vector (PVV), vector-vector-vector (VVV), and axial-vector-vector-vector (AVV) combinations of couplings. It is shown that only in the case of the SVV combination does the amplitude grow linearly with increasing magnetic-field strength, the amplitudes evaluated with the other combinations of couplings (PVV, VVV, and AVV) featuring no linearly increasing terms. The process \(\gamma \gamma \to \nu \bar \nu\) is also studied within the left-right model, which is an extension of the Standard Model of electroweak interactions and which may involve an effective scalar ννee coupling. Possible astrophysical manifestations of this process are discussed.     

Analyticity of \eta \pi isospin-violating form factors and the \tau \rightarrow \eta \pi \nu second-class decay

We consider the evaluation of the \(\eta \pi \) isospin-violating vector and scalar form factors relying on a systematic application of analyticity and unitarity, combined with chiral expansion results. It is argued that the usual analyticity properties do hold (i.e. no anomalous thresholds are present) in spite of the instability of the \(\eta \) meson in QCD. Unitarity relates the vector form factor to the \(\eta \pi \rightarrow \pi \pi \) amplitude: we exploit progress in formulating and solving the Khuri–Treiman equations for \(\eta \rightarrow 3\pi \) and in experimental measurements of the Dalitz plot parameters to evaluate the shape of the \(\rho \) -meson peak. Observing this peak in the energy distribution of the \(\tau \rightarrow \eta \pi \nu \) decay would be a background-free signature of a second-class amplitude. The scalar form factor is also estimated from a phase dispersive representation using a plausible model for the \(\eta \pi \) elastic scattering \(S\) -wave phase shift and a sum rule constraint in the inelastic region. We indicate how a possibly exotic nature of the \(a_0(980)\) scalar meson manifests itself in a dispersive approach. A remark is finally made on a second-class amplitude in the \(\tau \rightarrow \pi \pi \nu \) decay.     

\left\langle {:\bar \psi \psi :} \right\rangle and three-point functions in QCD

We calculate the coefficients of to leading order in _s in the operator product expansion of the fundamental three-point functions of QCD in the deep Euclidean region. We demonstrate that these coefficients satisfy the Ward identities.Supported by BMFT 0233 REB4     

Dispersion relations for $$\eta '\rightarrow \eta \pi \pi $$

We present a dispersive analysis of the decay amplitude for \(\eta '\rightarrow \eta \pi \pi \) that is based on the fundamental principles of analyticity and unitarity. In this framework, final-state interactions are fully taken into account. Our dispersive representation relies only on input for the \({\pi \pi }\) and \({\pi }\eta \) scattering phase shifts. Isospin symmetry allows us to describe both the charged and neutral decay channel in terms of the same function. The dispersion relation contains subtraction constants that cannot be fixed by unitarity. We determine these parameters by a fit to Dalitz-plot data from the VES and BES-III experiments. We study the prediction of a low-energy theorem and compare the dispersive fit to variants of chiral perturbation theory.     

Partial wave analysis of $\bar pp \to \bar \Lambda \Lambda$

A partial wave analysis of PS185 data for is presented. A ³ S ₁ cusp is identified in the inverse process at threshold, using detailed balance to deduce cross sections from . Partial wave amplitudes for ³ P ₀, ³ F ₃, ³ D ₃ and ³ G ₃ exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the data then provide evidence for a new I = 0, J ^PC = 1^- resonance with mass MeV, MeV, coupling to both ³ S ₁ and ³ D ₁.Received: 4 June 2004, Published online: 9 July 2004     

B\to \pi \rho, \pi \omega decays in perturbative QCD approach

We calculate the branching ratios and CP-asymmetries for , and decays, in the perturbative QCD approach. In this approach, we calculate non-factorizable and annihilation type contributions, in addition to the usual factorizable contributions. Our result is in agreement with the branching ratio of , measured by the CLEO and BABAR collaborations. We also predict large CP-asymmetries in these decays. These channels are useful to determine the CKM angle . Received: 5 November 2001 / Published online: 8 February 2002     

Study of anomalous couplings of gauge bosons in the reaction e^ - \gamma \to W^ - \nu \to \ell \bar \nu \nu

The possibility of observing an anomaly in triple interactions of a W boson and a photon in the process eγ → Wν is considered in the leptonic mode of W-boson decay. It is shown that, in some cases, the use of a bounded phase-space domain instead of the total phase space improves upper limits on the anomalous couplings. The estimates obtained in the above mode under conditions of the TESLA project are poorer than analogous current estimates for all modes of the e ⁺ e ^? channel.     

Incomplete GIM cancellation inK_L \to \bar \mu \mu decay

Weak contributions to the decay \(K_L \to \bar \mu \mu \) are evaluated over the whole energy spectrum and it is found that terms which survive the GIM cancellation because of the size of the top quark mass are comparable in size to the ones previously kept. Corresponding bounds on the K-M mixing matrix elements are given.