\mu\rightarrow e\gamma decay in the left-right supersymmetric model

We calculate the dipole amplitude for the decay and related processes in the left-right supersymmetric model when parity breaking occurs at a considerably large scale. The low-energy flavor violation in the model originates either from the nonvanishing remnants of the left-right symmetry in the slepton mass matrix or from the direct flavor changing lepton-slepton-neutralino interaction. The result is found to be large and already accessible with current experimental accuracy for supersymmetric masses not far above the electroweak scale. It also provides nontrivial constraints on the lepton mixing in the model. Received: 8 June 1998 / Published online: 15 October 1998     

Hara's theorem, quark model, and \gamma _5-dependent renormalization constants

We discuss the applicability of -dependent field renormalization as a means of renormalizing away the apparent violation of Hara's theorem observed in the quark model. It is pointed out that a result totally analogous to the violation of Hara's theorem is predicted by the quark model also for neutral baryons. For neutral baryons, however, such a result cannot be renormalized away. This proves that -dependent renormalization does not provide a proper way for a hadron-level understanding of the violation of Hara's theorem observed in the quark model. Received: 12 November 1997 / Revised version: 17 February 1998 Published online: 9 April 1998     

Isospin constraints on the \tau\to K\bar Kn\pi\nu decay mode

The construction of the complete isospin relations and inequalities between the possible charge configurations of a decay mode is presented. Detailed applications to the cases of two and three pions are given. Received: 3 September 1997 / Published online: 20 February 1998     

Triple pomeron vertex in the limit N_c\rightarrow\infty

In the hard pomeron theory with the number of colours the diffractive amplitude obtained in [3] is compared with the results found for in [1] and in the dipole approach in [5]. It is shown that the double pomeron exchange contribution can be substituted by an equivalent triple pomeron interaction term. After such a substitution the triple pomeron vertices in [1,3,5] essentially coincide. It is demonstrated that, in any form, the triple pomeron vertex is conformal invariant. It is also shown that higher order densities in the dipole approach do not involve 1 to k pomeron verteces with but are rather given by a set of pomeron fan diagrams with only a triple pomeron coupling. Received: 11 December 1997 / Revised version: 6 February 1998 / Published online: 7 August 1998     

Determination of radiative widths of scalar mesons from experimental results on \gamma\gamma\to\pi\pi

The scalar mesons in the 1 GeV region constitute the Higgs sector of the strong interactions. They are responsible for the masses of all light flavour hadrons. However, the composition of these scalar states is far from clear, despite decades of experimental effort. The two photon couplings of the 's are a guide to their structure. Two photon results from Mark II, Crystal Ball and CELLO prompt a new Amplitude Analysis of , cross-sections. Despite their currently limited angular coverage and lack of polarized photons, we use a methodology that provides the nearest one can presently achieve to a model-independent partial wave separation. We find two distinct classes of solutions. Both have very similar two photon couplings for the and . Hopefully these definitive results will be a spur to dynamical calculations that will bring us a better understanding of these important states. Received: 10 Decmeber 1998 / Published online: 27 April 1999     

Polarization in semileptonic \mathrm{B}\rightarrow X\tau decays

The paper gives the polarization of the tau lepton in the semileptonic B decays with respect to the direction of the virtual W boson. The result given includes the nonperturbative HQET corrections. The perturbative QCD corrections are probably negligible, as is suggested by the existing results for the longitudinal polarization of the charged lepton (Jeżabek and Urban, 1998). Received: 14 January 1999 / Revised version: 14 May 1999 / Published online: 14 October 1999     

P-odd observables at the \Upsilon peak

We study the -Z interference in the process as a means to measure the neutral current coupling of the b-quark. The helicity amplitudes are calculated from resonant and background diagrams and the spin density matrix of the final state is discussed. The spin analyzer of the 's is illustrated with the decays and . With a sensitivity to of a few per cent could be reachable. Received: 14 April 1998 / Revised version: 25 August 1998 / Published online: 3 December 1998     

Heavy quark production at a \gamma\gamma collider: the effect of large logarithmic perturbative corrections

We derive the spectral representations of QED 3-point functions and then explicitly calculate the 3-point spectral densities in hard thermal loop approximation within the real time formalism. The Ward identities obeyed by the retarded and advanced 2- and 3-point functions are discussed. We compare our results with those for hot QCD. Received: 12 March 1998 / Published online: 21 September 1998     

The neutral kaon decays to \pi^+ \pi^- \pi^0: a detailed analysis of the CPLEAR data

A detailed analysis of neutral kaons decaying to is presented based on the complete data set containing half a million events. Time-dependent decay rate asymmetries are measured between initially tagged and and for different regions of the phase space. These asymmetries, resulting from the interference between the CP-conserving decay amplitude of and the decay amplitude of – either CP-violating or CP-conserving – allow the determination of the parameters (CP-violating) and (CP-conserving), and also of the main isospin components of the decay amplitude. The branching ratio of (CP-conserving) is deduced directly from . In addition, we extract the slope parameters describing the energy dependence of the Dalitz plot. The whole set of our results fits well within the current phenomenological picture of the neutral-kaon system including CP violation and Chiral Perturbation Theory (ChPT). Received: 13 March 1998 / Published online: 3 September 1998     

Charmed hadron production in \pi p and Kp collisions and leading particle effect by constituent quark-diquark cascade model

We investigate the meson, baryon and anti-baryon productions in and collisions in terms of a constituent cascade model which includes charm flavour. The constituent diquark in an incident baryon has a tendency to get a large momentum fraction, resulting in considerable difference of subenergies for particle productions from quark-diquark and quark-antiquark chains in a meson-baryon collision. As a consequence, the leading particle effects on meson productions are expected to be quite different in and beams at present accelerator energies. Received: 5 November 1996 / Revised version: 30 June 1997 / Published online: 20 February 1998     

An upper limit for the \tau–neutrino mass from \tau\rightarrow 5\pi^{\pm}\nu_{\tau} decays

An upper limit for the –neutrino mass has been determined from the decay using data collected with the OPAL detector from 1991 to 1995 in collisions at . A limit of 43.2 MeV at 95% CL is obtained using a two–dimensional method in the invariant mass and energy distribution from 22 selected events. Combining this result with OPAL's previously published measurement using decays, a new combined limit of MeV (95% CL) is obtained. Received: 15 April 1998 / Published online: 12 August 1998     

The $Z \rightarrow \gamma \gamma,\;gg$ decays in the non-commutative standard model

On non-commutative spacetime, the standard model (SM) allows new, usually SM forbidden, triple gauge boson interactions to occur. In this letter we propose the SM strictly forbidden and decay modes coming from the gauge sector of the non-commutative standard model (NCSM) as a place where non-commutativity could be experimentally discovered. Received: 2 July 2002, Revised: 28 February 2003, Published online: 18 June 2003     

Double-lepton polarization asymmetries in the $B \to K \ell^ + \ell^-$ decaybeyond the standard model

General expressions for the double-lepton polarizations in the decay are obtained, using a model independent effective Hamiltonian, including all possible interactions. Correlations between the averaged double-lepton polarization asymmetries and the branching ratio, as well as the averaged single-lepton polarization asymmetry are studied. It is observed that a study of the double-lepton polarization asymmetries can serve as a good test for establishing new physics beyond the standard model.Received: 23 November 2003, Revised: 8 March 2004, Published online: 30 April 2004     

Isospin amplitudes and CP violation in (B \to K \pi) decays

We present a simple isospin invariant parametrization for decay amplitudes which consistently includes CP violation and (quasi-elastic) hadronic final state interactions. We find that the observed decays do not lead to a significant bound on the angle of the unitarity triangle. On the other hand, we claim that a sizeable CP violation asymmetry in rates is by no means excluded. Received: 9 June 1998 / Published online: 8 September 1998     

Scattering Problem for Local Perturbations\newline of the Free Quantum Gas

A Harnack type inequality is established for solutions to some semilinear elliptic equations in dimension two. The result is motivated by our approach to the study of some semilinear elliptic equations on compact Riemannian manifolds, which originated from some Chern–Simons Higgs model and have been studied recently by various authors. Received: 30 September 1997 / Accepted: 21 July 1998     

One-prong \tau decays with kaons

Cross-sections for hadronic, and lepton pair final states in collisions at =183 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. Forward-backward asymmetries for the leptonic final states have also been measured. Cross-sections and asymmetries are also presented for data recorded in 1997 at =130 and 136 GeV. The results are used to measure the energy dependence of the electromagnetic coupling constant , and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a leptoquark, or of a squark or sneutrino in supersymmetric theories with R-parity violation. Received: 3 July 1998 / Published online: 15 October 1998     

Production of \Xi^* resonances in \Sigma^- induced reactions at 345 GeV/c

The value of the - mixing angle is phenomenologically deduced from a rather exhaustive and up-to-date analysis of data including strong decays of tensor and higher-spin mesons, electromagnetic decays of vector and pseudoscalar mesons, decays into a vector and a pseudoscalar meson, and other transitions. A value of between ° and ° is consistent with the present experimental evidence and the average seems to be favoured. Received: 14 May 1998 / Published online: 6 November 1998     

Damage-spreading in the parallel Bak-Sneppen model

We study the behavior under perturbations of the Parallel Bak-Sneppen model (PBS) in 1+1 dimension, which has been shown to belong to the universality class of Directed Percolation (DP) in 1+1 dimensions [#!SD96!#]. We focus our attention on the damage-spreading features of the PBS model with both random and deterministic updating, which are studied and compared to the known results for the extremal Bak-Sneppen model (BS) and for DP. For both random and deterministic updating, we observe a power law growth of the Hamming distance. In addition, we compute analytically the asymptotic plateau reached by the distance after the growing phase. Received: 24 September 1998 / Revised: 17 November 1998 / Accepted: 19 November 1998     

A-dependences of neutral strange particle yields in \bar p-nuclei collisions at 40 GeV/c

The interactions of with D, Li, C, S, Cu and Pb nuclei at 40 GeV/c were studied by the RISC-streamer chamber spectrometer. The yields of mesons and and hyperons as functions of the target nucleus mass number are investigated. The experimental results are compared with model predictions using the FRITIOF-7.02 program package. Received: 10 October 1998 / Revised version: 1 April 1999 / Published online: 12 August 1999