Partial wave amplitudes and multiparticle production

Recursion relations for integrals of amplitudes over the phase space, i.e. for partial wave amplitudes, are introduced. In their simplest form these integrals are proportional to the s-wave amplitudes and represent rigorous lower bounds on the total cross sections. The connection with classical field equations in $D$ dimensions is established. Previous results on multiparticle amplitudes are easily reproduced.Comment: 7 pages, CERN-TH.6971/93, (typing errors corrected

Soliton-antisoliton pair production in particle collisions

We propose general semiclassical method for computing the probability of soliton-antisoliton pair production in particle collisions. The method is illustrated by explicit numerical calculations in (1+1)-dimensional scalar field model. We find that the probability of the process is suppressed by an exponentially small factor which is almost constant at high energies.Comment: 4 pages, 3 figures, journal versio

Particle decay in false vacuum

We revisit the problem of decay of a metastable vacuum induced by the presence of a particle. For the bosons of the `master field' the problem is solved in any number of dimensions in terms of the spontaneous decay rate of the false vacuum, while for a fermion we find a closed expression for the decay rate in (1+1) dimensions. It is shown that in the (1+1) dimensional case an infrared problem of one-loop correction to the decay rate of a boson is resolved due to a cancellation between soft modes of the field. We also find the boson decay rate in the `sine-Gordon staircase' model in the limits of strong and weak coupling.Comment: 19 pages, 2 figure

Nullification of multi-Higgs threshold amplitudes in the Standard Model

We show that nullification of all tree-order threshold amplitudes involving Higgs particles in the Standard Model occurs, provided that certain equations relating the masses of all existing elementary particles to the mass of the Higgs scalar are satisfied. The possible role of these relations in restoring the high-multiplicity unitarity and their phenomenological relevance are briefly discussed.Comment: CERN-TH.6853/93, 9 pages, Late

Degenerate Domain Wall Solutions in Supersymmetric Theories

A family of degenerate domain wall configurations, partially preserving supersymmetry, is discussed in a generalized Wess-Zumino model with two scalar superfields. We establish some general features inherent to the models with continuously degenerate domain walls. For instance, for purely real trajectories additional "integrals of motion" exist. The solution for the profile of the scalar fields for any wall belonging to the family is found in quadratures for arbitrary ratio of the coupling constants. For a special value of this ratio the solution family is obtained explicitly in terms of elementary functions. We also discuss the threshold amplitudes for multiparticle production generated by these solutions. New unexpected nullifications of the threshold amplitudes are found.Comment: 21 pages, LaTeX, 3 figures using epsf.st

Amplitude Zeroes in Collinear Processes or What Is Left from a Factorizable 2d Model in Higher Dimensions

We show that for collinear processes, i.e. processes where the incoming and outgoing momenta are aligned along the same line, the S-matrix of the tree level 2+1 dimensional Thirring model factorizes: any S - matrix element is a product of $2\rightarrow 2$ elements. In particular this means nullification of all collinear $2 \rightarrow n$ amplitudes for $n > 2$.Comment: latex , 8 pp., 2 fig. not include

New bounds on the neutrino magnetic moment from the plasma induced neutrino chirality flip in a supernova

The neutrino chirality-flip process under the conditions of the supernova core is investigated in detail with the plasma polarization effects in the photon propagator taken into account, in a more consistent way than in earlier publications. It is shown in part that the contribution of the proton fraction of plasma is essential. New upper bounds on the neutrino magnetic moment are obtained: mu_nu < (0.5 - 1.1) 10^{-12} mu_B from the limit on the supernova core luminosity for nu_R emission, and mu_nu < (0.4 - 0.6) 10^{-12} mu_B from the limit on the averaged time of the neutrino spin-flip. The best upper bound on the neutrino magnetic moment from SN1987A is improved by the factor of 3 to 7.Comment: 19 pages, LaTeX, 7 EPS figures, submitted to Journal of Cosmology and Astroparticle Physic

Metastable anisotropy orientation of nematic quantum Hall fluids

We analyze the experimental observation of metastable anisotropy resistance orientation at half filled quantum Hall fluids by means of a model of a quantum nematic liquid in an explicit symmetry breaking potential. We interpret the observed ``rotation'' of the anisotropy axis as a process of nucleation of nematic domains and compute the nucleation rate within this model. By comparing with experiment, we are able to predict the critical radius of nematic bubbles, $R_c\sim 2.6 \mu m$. Each domain contains about $10^4$ electrons.Comment: 10 pages, 8 figures, final version as will appear in PR

Estimates with an Effective Chiral Lagrangian for Heavy Mesons

On the basis of an effective lagrangian incorporating approximate chiral symmetry and heavy-quark spin and flavor symmetries, and by use of information on leptonic decays, we estimate the effective $D^\star D\pi$ coupling.Comment: UGVA-DPT 1992/07-779, BARI-TH/92-117 Revised version, September 1992, LaTeX (style article), 7 page