Acta Physica Slovaca 49 (1999)
The rho meson - a historical essay
Acta Physica Slovaca 49, vii (1999)
Abstract: The rho meson - a historical essay
The role of qualitative discussion in problem solving
Acta Physica Slovaca 49, xv (1999)
Abstract: The paper contributes to the methodology of problem solving in physics. We argue that the task of solving a problem does not end by obtaing the result. We claim that a question like "Why the result came out as it did?" can be meaningfully posed and that deeper understanding of the subject comes out as a result of a discussion on possible answers to such a question.
A note on the derivation of the boundary conditions for electromagnetic fields
Acta Physica Slovaca 49, xxi (1999)
Abstract: The aim of this note is to point out that some assumptions of the standard derivation of the boundary conditions for electromagnetic fields are not met in some physically relevant situations. In such situations it is better to consider this derivation as not really a derivation, but rather as a motivation for postulating the boundary conditions.
A method for top quark mass determination from a dilepton channel
Acta Physica Slovaca 49, 127 (1999)
Abstract: A new method of top quark mass determination based on full kinematic event reconstruction is presented. Method was tested on Monte Carlo samples produced by event generator PYTHIA in conditions close to ones expected in experiments at TEVATRON. Resolution of the method in case of 5 events sample is in the range of 5-8 GeV/c2.
The LPM effect: Why there is no coherence on the coherence length?
Acta Physica Slovaca 49, 137 (1999)
Abstract: The noncoherence of radiation of a high-energy particle in a medium, down to frequencies at which the coherence length exceeds the mean free path of the particle considerably, is discussed. The noncoherence can be assigned to an interplay between destructive and constructive interference of the radiation coming from separate collisions. In this explanation crucial role is played by the specific form of the law governing the random walk of the particle in a plane perpendicular to initial velocity.
A. Bia as, K. Zalewski
BE condensation and independent emission: statistical physics interpretation
Acta Physica Slovaca 49, 145 (1999)
Abstract: Recent results on effects of Bose-Einstein symmetrization in a system of independently produced particles are interpreted in terms of statistical physics. For a large class of distributions, the effective sizes of the system in momentum and in configuration space are shown to shrink when quantum interference is taken into account.
V. Buzek, R. Derka
Optimal encoding of phase information in trapped ions
Acta Physica Slovaca 49, 151 (1999)
Abstract: We propose a specific preparation of a set of N two-level ions (i.e., the collective state of these ions) in which the information about the phase can be most optimally encoded. The phase in this context refers to a continuous parameter which labels different points along the evolution path of a given state of the N-ion system described by a unitary one-parametric group . The optimality of the preparation of the given quantum system means that using the optimal measurement scheme the phase encoded in the system of N two-level ions can be ``extracted'' (decoded) with the highest mean fidelity.
A. Di Giacomo
Exploring ensembles of instantons
Acta Physica Slovaca 49, 159 (1999)
Abstract: A number of observables is constructed which can give useful information on instanton ensembles. The basic properties used are (1) Istantons are SU(2) configurations. (2) They are self-dual or antiself-dual.
S. Dubnicka, A.Z. Dubnicková, A. Antusek
Prediction of -decay into two pions by more realistic pion electromagnetic form factor model
Acta Physica Slovaca 49, 165 (1999)
Abstract: The unitary and analytic phenomenological pion electromagnetic structure model is constructed for the range of momenta from to which for the first time contains all known theoretical pion electromagnetic form factor properties and describes all existing data. The predicted by means of this model branching ratio of the - decay into two pions coincides just with the experimental value obtained recently by ALEPH in CERN.
M. Faber, J. Greensite, S. Olejník
Evidence for a center vortex origin of the adjoint string tension
Acta Physica Slovaca 49, 177 (1999)
Abstract: Wilson loops in the adjoint representation are evaluated on cooled lattices in SU(2) lattice gauge theory. It is found that the string tension of an adjoint Wilson loop vanishes, if the loop is evaluated in a sub-ensemble of configurations in which no center vortex links the loop. This result supports our recent proposal that the adjoint string tension, in the Casimir-scaling regime, can be attributed to a center vortex mechanism.
H. Grosse, P. Presnajder
Elements of a field theory on a noncommutative cylinder
Acta Physica Slovaca 49, 185 (1999)
Abstract: First we briefly describe the scalar fields on a two dimensional space-time modeled as a standard (commutative) cylinder. Then we construct the noncommutative cylinder, the noncommutative generalization of a noncompact manifold. Free scalar field on a noncommutative cylinder is investigated. Due to the noncommutativity of the underlying space-time the energy frequencies are restricted, the time evolution is discrete. This leads to an UV-regularization of Feynman diagrams. We expect that analogous properties will survive in a more realistic field theoretical models formulated on a noncommutative space-times.
Towards dynamical mass calculations
Acta Physica Slovaca 49, 193 (1999)
Abstract: SU electroweak gauge model without Higgs sector is extended by a new vector field interacting with leptons and quarks of both chiralities. This interaction is treated under a dynamical assumption in a self-consistent approximation. Fermion masses are calculated in terms of new Abelian hypercharges, and the intermediate boson masses are calculated in terms of the fermion masses by sum rules. Self-consistency requires a rich sector of heavy spin-1 collective fermion-antifermion excitations.
Universal features of fluctuations in complex systems
Acta Physica Slovaca 49, 201 (1999)
Abstract: Properties of fluctuations in many complex systems in particle, nuclear, atomic, condensed matter, and statistical physics are examined with the aim of finding possible universal features among them. Two areas of particular interest are phase transitions and chaotic behaviors. Effective measures are found to quantify the universality.
A simple model for transverse energy distribution in heavy ion collisions
Acta Physica Slovaca 49, 209 (1999)
Abstract: A simple geometrical model (often quoted in literature as the Glauber model) of heavy ion collisions is recapitulated. It is shown that the transverse energy distribution of heavy ion collisions follow the geometry of the collision. An extension of the model to include rapidity and transverse mass particle spectra is discussed.
Are the production and decay of a resonance always independent?
Acta Physica Slovaca 49, 215 (1999)
Abstract: The widely accepted assumption that the decay of a resonance proceeds independently of its production, quantitatively expressed as a factorizing formula for the differential cross section in the invariant mass of resonance debris, is put under scrutiny. It is shown that the factorization is always valid for scalar and pseudoscalar resonances, although the usual version of the formula is not entirely correct. For resonances with nonzero spins the factorization does not generally take place. We deal in more detail with the spin-one case, where we show a condition on the decay matrix element that ensures the validity of the same factorizing formula as in the spinless case. This condition is satisfied for but not, e.g., for or . The formalism is applied also to the case when the resonance is produced not in two-body collisions but in the decay of a heavier particle or resonance (chain decay). Application of our formulas to the e+e- production in one-photon approximation agrees with what is known from quantum electrodynamics and thus provides another test of their soundness.
S.V. Molodtsov, A.M. Snigirev, G.M. Zinovjev
Phonon-like excitations of the instanton liqu
Acta Physica Slovaca 49, 231 (1999)
Abstract: The phonon-like excitations of (anti)-instanton liquid ( ) due to adiabatic variations of vacuum wave functions are studied in this paper. The kinetic energy term is found and proper effective Lagrangian for such excitations is evaluated. The properties of their spectrum, while the corresponding masses are defined by with prevailing chromoelectric component, are investigated based on the phenomenology of QCD vacuum already developed.
A. Patkós, Zs. Szép
Landau damping of self-interacting scalar fields in the broken phase
Acta Physica Slovaca 49, 241 (1999)
Abstract: An effective kinetic theory is constructed representing the action of high frequency fluctuations on the low frequency modes. Specifically, the classical statistical expression of the modified mass term in the wave operator of these modes is studied and the Landau damping coefficient is extracted in the broken phase. The domain of validity of the classical approach is found from comparing it with the result of a 1-loop quantum calculation.
B. Tomásik, U. Heinz
Potentials and limits of Bose-Einstein interferometry
Acta Physica Slovaca 49, 251 (1999)
Abstract: We complete the introduction of Yano-Koonin-Podgoretskii (YKP) parametrization of the correlation function by deriving the corrections to the correlation radii which arise from releasing the popular smoothness approximation and approximation of setting the pair momentum on-shell. We investigate the definition range of this parametrization and find kinematic regions in which the YKP parametrization is inapplicable. These problems disappear if the newly proposed Modified Yano-Koonin-Podgoretskii parametrization is used. We then focus on the physical interpretation of the correlation radii obtained in the different parametrizations. While the extraction of the longitudinal source expansion from the YK rapidity is found to be rather robust against variations of the source density profiles, the extracted emission duration is quite sensitive to such variations and cannot be reliably extracted except for the case of extremely long source lifetimes.
Proton spin structure and quark-parton model
Acta Physica Slovaca 49, 273 (1999)
Abstract: The alternative to the standard formulation of the quark-parton model is proposed. Our approach is based on the solution of the master equations relating the structure and distribution functions, which consistently takes into account the intrinsic quark motion - in contradistinction to the standard infinite momentum approach, in which this motion is latently suppressed. The model well reproduces the experimental data on the both polarized and unpolarized structure functions, assuming that only the valence quarks term contributes to the nucleon spin. It is shown, the combined analysis of the polarized and unpolarized data can give an information about the effective masses and intrinsic motion of the quarks inside the nucleon. Simultaneously, it is shown that the rate of the nucleon energy carried by the quarks can be less, than estimated from the standard approach. As an addition, a prediction for the proton spin function g2 is given.