Search

Topological lumps are known to be present in gluonic fields of SU(3) gluodynamics. Near the transition temperature they were classified either as constituents of nondissociated (anti)calorons, or as constituents of (anti)dyon pairs, or as isolated (anti)dyons. In this paper we study the density and correlation functions of these objects at temperature T/T_c=0.96., Comment: 5 pages, 1 figure. arXiv admin note: text overlap with arXiv:1309.7850

The paper considers the problem of non-visual data recovery from images acquired by land-survey satellites. Such non-visual data include: dynamics and parameters of land-survey satellite angular motion along an underlying surface, an underlying surface elevation, etc.

The effective method (referred to as an image functionalization method) of an optical flow evaluation is stated in the report. The functionalization method differs from the well know gradient method in operating not upon the image intensity functions but upon values of a special functional, determined on a set of the image intensity functions. On the base of that approach a functional relation equation is derived. That equation is an analogue of a brightness constancy constraint equation used in the gradient method of image registration, but it does not hold spatial derivatives of image density functions. That brings considerably new features of universality and accuracy to the technique of the image motion parameters estimation as the equation encloses spatial derivatives of the applied functional kernel only. The functional relation equation establishes a fundamental linkage between measurable characteristics of dynamic images and its motion parameters. It represents a generalization of gradient group methods. This method is free from main principal shortcomings of the ordinary gradient method. As a result the method gives an opportunity to solve different difficult problems of registration such as varying brightness images registration, different color images interconnecting and others.)

We study lattice QCD with $N_f=2$ Wilson fermions at nonzero imaginary chemical potential and nonzero temperature. We relate the Roberge - Weiss phase transition to the properties of dyons which are constituents of the KvBLL calorons. We present numerical evidence that the characteristic features of the spectral gap of the overlap Dirac operator as function of an angle modifying the boundary condition are determined by the $Z_3$ sector of the respective imaginary chemical potential. We then demonstrate that dyon excitations in thermal configurations could be responsible (in line with perturbative excitations) for these phenomena., Comment: 10 pages, 5 figures, Contribution to XIIth Quark Confinement and the Hadron Spectrum

We study the topological structure of $SU(3)$ lattice gluodynamics by cluster analysis. This methodological study is meant as preparation for full QCD. The topological charge density is becoming visible in the process of overimproved gradient flow, which is monitored by means of the the Inverse Participation Ratio (IPR). The flow is stopped at the moment when calorons dissociate into dyons due to the overimproved character of the underlying action. This gives the possibility to simultaneously detect all three dyonic constituents of KvBLL calorons in the gluonic field. The behaviour of the average Polyakov loop under (overimproved) gradient flow could be also (as its value) a diagnostics for the actual phase the configuration is belonging to. Timelike Abelian monopole currents and specific patterns of the local Polyakov loop are correlated with the topological clusters.The spectrum of reconstructed cluster charges $Q_{cl}$ corresponds to the phases. It is scattered around $Q_{cl} \approx \pm 1/3$ in the confined phase, whereas it is $Q_{cl} \approx \pm 0.5 ��0.7$ for heavy dyons and $|Q_{cl}| < 0.3$ for light dyons in the deconfined phase. Heavy dyons are increasingly suppressed with increasing temperature. The paper is dedicated to the memory of Michael Mueller-Preussker who was a member of our research group for more than twenty years., 7 pages, 6 figures

We study the topological structure of QCD by cluster analysis. The fermionic topological charge density is constructed from low lying modes of overlap Dirac operator for three types of temporal boundary conditions for fermion field. This gives the possibility to mark all three dyon constitutents of KvBLL caloron in gluonic fields. The gluonic topological charge density is appearing in the process of overimproved gradient flow process stopped at the moment when it maximally matches the fermionic topological charge density. This corresponds to the smearing of gluonic fields up to the scale set by dyon size. The time-like Abelian monopoles and specific KvBLL pattern of Polyakov line correlate with topological clusters., 12 pages, 6 figures. Corrected HUB preprint number, restored missing temperature scale, changed subsections of section III. arXiv admin note: text overlap with arXiv:1410.4632

Dileptons represent a unique probe for nuclear matter under extreme conditions reached in heavy ion collisions. They allow the study of meson properties, like mass and decay width, at various density and temperature regimes. Up to now, in the Tubingen model for dilepton production, modification of meson properties in nuclear medium has been accounted for by allowing a density dependence of the mass (Brown-Rho scaling) together with an ad hoc dependence of the meson decay widths on the same variable. We use the extended vector meson dominance (eVMD) model to extract meson properties in nuclear matter by computing the in-medium meson spectral functions. Dilepton spectra for C+C at 1.0 and 2.0 AGeV are calculated and compared with previous results.

We study the properties of configurations from which P-vortices on one hand or Abelian monopoles on the other hand have been removed. We confirm the loss of confinement in both cases and investigate in what respect the modified ensembles differ from the confining ones from the point of view of the complementary confinement scenario.

This article in honor of Yurii Antonovich Simonov’s 70th birthday reviews some recent work related to the semiclassical approach to QCD at finite temperature based on classical solutions with nontrivial holonomy. By cooling Monte Carlo generated lattice SU(2) gauge fields, we investigate approximate solutions of the classical field equations as a possible starting point for rethinking the semiclassical approximation of the path integral. We show that old findings of cooling have to be reinterpreted in terms of Kraan-van Baal solutions with generically nontrivial holonomy instead of Harrington-Shepard caloron solutions with trivial holonomy. The latter represent only a subclass of possible topological configurations and for T < Tc seem to become suppressed due to quantum fluctuations.

We discuss recent solutions for SU(2) calorons with non-trivial holonomy at higher charge, both through analytic means and using cooling, as well as extensive lattice studies for SU(3)., 12 pages, 16 figures in 34 parts, 4 talks presented at Lattice 2004(topology)

Weak radiative decay Λ → ne+e− depends in general on four independent electromagnetic transition form factors. These form factors can be fixed in an extended model of dominance of vector mesons, where the asymptotic behavior of form factors is in agreement with quark counting rules. The dependence of the branching ratio of the Λ → ne+e− decay on the relative weight of four electromagnetic form factors is investigated.

The Dalitz plot distribution of the $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ decay is determined by using a data sample of $1.2\ifmmode\times\else\texttimes\fi{}{10}^{7}$ $\ensuremath{\eta}$ mesons from the $pd\ensuremath{\rightarrow}^{3}\mathrm{He}\ensuremath{\eta}$ reaction at 1 GeV collected by the WASA detector at COSY.

The topological structure of lattice gluodynamics is studied at intermediate resolution scale in the deconfining phase with the help of a cluster analysis. UV filtered topological charge densities are determined from a fixed number of low-lying eigenmodes of the overlap Dirac operator with three types of temporal boundary conditions applied to the valence quark fields. This method usually allows to find all three distinguished (anti)dyon constituents in the gauge field of Kraan-van Baal-Lee-Lu (anti)caloron solutions. The clustering of the three topological charge densities in Monte Carlo generated configurations is then used to mark the positions of anticipated (anti)dyons of the corresponding type. In order to support this interpretation, inside these clusters, we search also for time-like Abelian monopole currents (defined in the maximally Abelian gauge) as well as for local holonomies with at least two approximately degenerated eigenvalues. Our results support the view that light dyon-antidyon pairs - in contrast to the heavy (anti)caloron dyon constituents - contribute dominantly to thermal Yang-Mills fields in the deconfinement phase. This paper is dedicated to the memory of Pierre van Baal and Dmitri Igorevich Diakonov who have influenced our work very much., 15 pages, 10 figures

The production of d' dibaryons in heavy ion collisions due to the elementary process NN -> d' + pion is considered. The cross section NN -> d' + pion is estimated using the vacuum d' width = 0.5 MeV extracted from data on the double charge exchange reactions on nuclei. The d' production rate per single collision of heavy ions is estimated at an incident beam energy of 1 A GeV within the framework of the Quantum Molecular Dynamics transport model. We suggest to analyse the invariant mass spectrum of the NN + pion system in order to search for an abundance of events with the invariant mass of the d' dibaryon. The d' peak is found to exceed the statistical fluctuations of the background at a level of 6 standard deviations for 2 10^5 A central collisions of heavy ions with the atomic number A., 29 pages including 7 figures, REVTeX

The hypothesis of leptonic charge raises the problem of its neutralization, which is crucial for the stability of material bodies. The screening of the leptonic charge by a charged bosonic condensate is considered. The screening length and the structure of the skin layer are investigated in both the nonrelativistic and relativistic regimes.

The effects of the presence of $\Delta$-isobars in nuclear matter are studied in the framework of relativistic mean-field theory. The existence of stable nuclei at saturation density imposes constraints on the $\Delta$-isobar self-energy and thereby on the mean-field coupling constants of the scalar and vector mesons with $\Delta$-isobars. The range of possible values for the scalar and vector coupling constants of $\Delta$-isobars with respect to the nucleon coupling is investigated and compared to recent predictions of QCD sum-rule calculations., Comment: 8 pages, Latex using Elsevier style, 2 PS figures, minor changes in revised version

Topological objects of $SU(3)$ gluodynamics are studied at the infrared scale near the transition temperature with the help of zero and near-zero modes of the overlap Dirac operator. We construct UV filtered topological charge densities corresponding to three versions of the temporal boundary condition applied to this operator, for which the zero mode is known to be located on corresponding three constituent dyons (antidyons) in the reference case of an analytical (anti)caloron solution. The clustering of the three topological charge densities marks the positions of three types of dyons and antidyons which can therefore be considered as present in equilibrium (Monte Carlo) gluonic fields at the given resolution scale. We classify them either as constituents of nondissociated (anti)calorons or as constituents of (anti)dyon pairs or as isolated (anti)dyons. The pattern of the Polyakov loop describing the centers and the interior of these clusters is observed after a limited number of overimproved cooling steps and resembles the description known from analytical caloron solutions., 12 pages, 9 figures; revised version accepted by Phys. Rev. D

Gluodynamics and two-flavor QCD at non-zero temperature are studied with the so-called overimproved cooling technique under which caloron solutions may remain stable. We consider topological configurations either at the first occuring stable plateau of topological charge or at the first (anti)selfdual plateau and find the corresponding topological susceptibility at various temperatures on both sides of the thermal transition or crossover. In pure gluodynamics the topological susceptibility drops sharply at the deconfinement temperature while in full QCD it decreases smoothly at temperatures above the pseudocritical one. The results are close to those calculated by other methods. We interpret our findings in terms of the (in)stability of calorons with non-trivial holonomy and their dyon constituents against overimproved cooling., 10 pages, 9 figures

An experimental Dalitz plot distribution for the decay η → π+π−π0 is fitted by the theoretical one obtained in chiral perturbation theory with unitarity corrections taken into account. The fit shows that the difference of light-quark masses is larger than is expected from electromagnetic mass differences of neutral and charged kaons.

Using a standard cooling method for SU(3) lattice gauge fields constant Abelian magnetic field configurations are extracted after dyon-antidyon constituents forming metastable Q=0 configurations have annihilated. These so-called Dirac sheets, standard and non-standard ones, corresponding to the two U(1) subgroups of the SU(3) group, have been found to be stable if emerging from the confined phase, close to the deconfinement phase transition, with sufficiently nontrivial Polyakov loop values. On a finite lattice we find a nice agreement of the numerical observations with the analytic predictions concerning the stability of Dirac sheets depending on the value of the Polyakov loop.

We reveal the center vortex content of SU(2) calorons and ensembles of them. While one part of the vortex connects the constituent dyons of a single caloron, another part is predominantly spatial and can be related to the twist that exists in the caloron gauge field. The latter part depends strongly on the caloron holonomy and degenerates to a plane between the dyons when the asymptotic Polyakov loop is traceless. Correspondingly, the spatial vortex in caloron ensembles is percolating in this case. This finding fits perfectly in the confinement scenario of vortices and shows that calorons are suitable to facilitate the vortex (de)confinement mechanism., AIP Conf. Proc. 1343

The extended vector meson dominance model, which allows one to describe the electromagnetic form factors of nucleons obeying the asymptotic quark counting rule prescriptions and contains the minimal number of free parameters, is presented. We obtain a reasonable fit of form factors over the experimentally available spacelike region of momentum transfer and reasonable results in the timelike region.

We reveal the center vortex content of SU(2) calorons and ensembles of them. We use Laplacian center gauge as well as maximal center gauges to show that the vortex in a single caloron consists of two parts. The first one connects the constituent dyons of the caloron (which are monopoles in Laplacian Abelian gauge) and extends in time. The second part is predominantly spatial, encloses one of the dyons and can be related to the twist in the caloron gauge field. This part depends strongly on the caloron holonomy and degenerates to a plane when the holonomy is maximally nontrivial, i.e. when the asymptotic Polyakov loop is traceless. Correspondingly, we find the spatial vortices in caloron ensembles to percolate in this case. This finding fits perfectly in the confinement scenario of vortices and shows that calorons are suitable to facilitate the vortex confinement mechanism.

In the deconfinement phase of quenched SU(2) Yang-Mills theory the spectrum and localization properties of the eigenmodes of the overlap Dirac operator with antiperiodic boundary conditions are strongly dependent on the sign of the average Polyakov loop, $$. For $ > 0$ a gap appears with only few, highly localized topological zero and near-zero modes separated from the rest of the spectrum. Instead of a gap, for $ < 0$ a high spectral density of relatively delocalized near-zero modes is observed. In an ensemble of positive $$, the same difference of the spectrum appears under a change of fermionic boundary conditions. We argue that this effect and other properties of near-zero modes can be explained through the asymmetric properties and the different abundance of dyons and antidyons -- topological objects also known to appear, however in a symmetric form, in the confinement phase at $T < T_c$ as constituents of calorons with maximally nontrivial holonomy., Comment: 12 pages, 7 figures. Clarifying changes in the introduction, no results changed; data added, 1 figure added, last changes to match article in Phys.Rev. D

We study the properties of configurations from which P-vortices on one hand or Abelian monopoles on the other hand have been removed. We find that the zero modes and the band of nonzero modes close to zero disappear from the spectrum of the overlap Dirac operator, confirming the absence of topological charge and quark condensate. The different behavior of the modified ensembles under smearing compared to the unmodified Monte Carlo ensemble corroborates these findings. The gluonic topological susceptibility rapidly approaches zero in accordance with ${Q}_{\mathrm{index}}=0$. The remaining (ultraviolet) monopoles without vortices and\char22{}to a less extent\char22{}the remaining vortices without monopoles are unstable under smearing whereas smearing of the unmodified Monte Carlo ensemble affects the monopoles and vortices only by smoothing, reducing the density only slightly.

The in-medium spectral functions of $\rho$ and $\omega$ mesons and the broadening of the nucleon resonances at finite baryon density are calculated self-consistently by combining a resonance dominance model for the vector meson production with an extended vector meson dominance model. The influence of the in-medium modifications of the vector meson properties on the dilepton spectrum in heavy-ion collisions is investigated. The dilepton spectrum is generated for the C+C reaction at 2.0$A$ GeV and compared with recent HADES Collaboration data. The collision dynamics is then described by the T\"ubingen relativistic quantum molecular dynamics transport model. We find that an iterative calculation of the vector meson spectral functions that takes into account the broadening of the nucleon resonances due to their increased in-medium decay branchings is convergent and provides a reasonable description of the experimental data in the mass region $0.45\leq M \leq 0.75$ GeV. On the other side, the theoretical calculations slightly underestimate the region $m_\pi\leq M \leq 0.4$ GeV. Popular in-medium scenarios such as a schematic collisional broadening and dropping vector mesons masses are discussed as well., Comment: v2: some references, comments and one Fig. added; accepted for publication in Phys. Rev. C

We report on a self-consistent calculation of the in-medium spectral functions of the rho and omega mesons at finite baryon density. The corresponding in-medium dilepton spectrum is generated and compared with HADES data. We find that an iterative calculation of the vector meson spectral functions provides a reasonable description of the experimental data., Comment: Talk given at International School of Nuclear Physics, 30th Course, "Heavy Ion Collisions from the Coulomb Barrier to the Quark Gluon Plasma", Erice, Italy, 16-24 Sep 2008

We describe classical spinning particles in external fields. This formalism is extended to spinning particles localized at the ends of open Nambu strings. We consider the relations between the frequencies of spin precession and the energy of spin-orbit splitting.

The phase-space paths introduced by Cheuk-Yin Wong in Phys. Rev.C25, 1460 (1982) and discussed recently in the literature can be used for calculation of evolution of the Wigner function to first order in the time increments only. The first-order solutions are helpful to determine the phase-space Green function in the framework of the phase-space path integral method., 2 pages, accepted to publication in PRC, section Comments

In a pilot study, we use the topological charge density defined by the eigenmodes of the overlap Dirac operator (with ultraviolet filtering by mode-truncation) to search for lumps of topological charge in SU(2) pure gauge theory. Augmenting this search with periodic and antiperiodic temporal boundary conditions for the overlap fermions, we demonstrate that the lumps can be classified either as calorons or as separate caloron constituents (dyons). Inside the topological charge clusters the (smeared) Polyakov loop is found to show the typical profile characteristic for calorons and dyons. This investigation, motivated by recent caloron/dyon model studies, is performed at the deconfinement phase transition for SU(2) gluodynamics on 20^3 x 6 lattices described by the tadpole improved L\"uscher-Weisz action. The transition point has been carefully located. As a necessary condition for the caloron/dyon detection capability, we check that the LW action, in contrast to the Wilson action, generates lattice ensembles, for which the overlap Dirac eigenvalue spectrum smoothly behaves under smearing and under the change of the boundary conditions., Comment: 17 pages, 8 figures, minor changes (typos, grants, ..)

In this talk, relying on experience with various lattice filter techniques, we argue that the semiclassical structure of finite temperature gauge fields for T < T_c is dominated by calorons with non-trivial holonomy. By simulating a dilute gas of calorons with identical holonomy, superposed in the algebraic gauge, we are able to reproduce the confining properties below T_c up to distances r = O(4 fm} >> ��(the caloron size). We compute Polyakov loop correlators as well as space-like Wilson loops for the fundamental and adjoint representation. The model parameters, including the holonomy, can be inferred from lattice results as functions of the temperature., Talk by M. M\"uller-Preussker at "Quark Confinement and Hadron Structure VII", Ponta Delgada, Azores, Portugal, September 2 - 7, 2006, 4 pages, 2 figures, to appear in the Proceedings

Institute for Theoretical and Experimental Physics,B. Cheremushkinskaya 25, Moscow 117259, RussiaIn equilibrium, at finite temperature below and above the deconfining phase transition, we havegenerated lattice SU(2) gauge fields and have exposed them to smearing in order to investigate theemerging clusters of topological charge. Analysing in addition the monopole clusters according tothe maximally Abelian gauge, we have been able to characterize part of the topological clusters tocorrespond either to non-static calorons or static dyons in the context of Kraan-van Baal caloronsolutions with non-trivial holonomy. We show that the relative abundance of these calorons anddyons is changing with temperature and offer an interpretation as dissociation of calorons into dyonswith increasing temperature. The profile of the Polyakov loop inside the topological clusters and the(model-dependent) accumulated topological cluster charges support this interpretation. Above thedeconfining phase transition light dyons (according to Kraan-van Baal caloron solutions with almosttrivial holonomy) become the most abundant topological objects. They are presumably responsiblefor the magnetic confinement in the deconfined phase.

We calculate the in-medium $D$ meson self-energies in a hot pion gas induced by resonance interactions with pions. The appropriate resonances in the {\it s},~ {\it p} and {\it d} waves of the $D$ meson-pion pair are represented by low lying scalar, vector and tensor $D^*$ mesons. At temperatures around 200 MeV the D-meson mass drops by $30~ \rm {MeV}$ and the scattering width grows up to $60~ \rm {MeV}$. Similar medium effects are found for the $D^*$ vector mesons. This opens and/or enhances the decay and/or dissociation channels of the charmonium states $\Psi^\prime$, $\chi_c$ and $J/\Psi$ to $D \bar D,~D^* \bar D,~D \bar D^* ,~D^* \bar D^*$ pairs in pion matter., Comment: 5 pages Revtex, 4 eps figures, final version accepted for publication in PRC

We report on our search for Kraan-van Baal calorons in finite temperature SU(2) lattice ensembles. We also discuss recent progress made in developing a caloron-anticaloron gas model decribing confinement and deconfinement in the context of trivial and non-trivial holonomy.

Using smearing of equilibrium lattice fields generated at finite temperature in the confined phase of $SU(2)$ lattice gauge theory, we have investigated the emerging topological objects (clusters of topological charge). Analyzing their monopole content according to the Polyakov gauge and the maximally Abelian gauge, we characterize part of them to correspond to nonstatic calorons or static dyons in the context of Kraan-van Baal caloron solutions with nontrivial holonomy. The behavior of the Polyakov loop inside these clusters and the (model-dependent) topological charges of these objects support this interpretation.

We consider the {theta}{sup +}(1540) pentaquark in the string model that correctly reproduces the linear Regge trajectories for the case of orbtal excitations of light qq mesons and qqq baryons. Assuming (and arguing in favor of) the diquark-antiquark-diquark ([ud]s[ud]) clustering of this orbitally excited object we found its mass about 290 MeV above the experimental value 1540 MeV. In the model considered this discrepancy could be attributed to the change of the constituent mass of s antiquark as compared to that of s quark localized at the string end.

We present a unified description of the vector meson and dilepton production in elementary and in heavy ion reactions. The production of vector mesons is described via the excitation of nucleon resonances. Medium effects in heavy ion reactions are discussed., 4 pages, LaTeX, 4 eps figures. Talk given at 10th International Conference on the Structure of Baryons (Baryon 2004) at Palaiseau (France), 25-29 October 2004

The mean field (MF) approximation for the pion matter, being equivalent to the leading ChPT order, involves no dynamical loops and, if self-consistent, produces finite renormalizations only. The weight factor of the Haar measure of the pion fields, entering the path integral, generates an effective Lagrangian $\delta \mathcal{L}_{H}$ which is generally singular in the continuum limit. There exists one parameterization of the pion fields only, for which the weight factor is equal to unity and $\delta \mathcal{L}_{H}=0$, respectively. This unique parameterization ensures selfconsistency of the MF approximation. We use it to calculate thermal Green functions of the pion gas in the MF approximation as a power series over the temperature. The Borel transforms of thermal averages of a function $\mathcal{J}(\chi ^{\alpha}\chi ^{\alpha})$ of the pion fields $\chi ^{\alpha}$ with respect to the scalar pion density are found to be $\frac{2}{\sqrt{\pi}}\mathcal{J}(4t)$. The perturbation series over the scalar pion density for basic characteristics of the pion matter such as the pion propagator, the pion optical potential, the scalar quark condensate $$, the in-medium pion decay constant ${\tilde{F}}$, and the equation of state of pion matter appear to be asymptotic ones. These series are summed up using the contour-improved Borel resummation method. The quark scalar condensate decreases smoothly until $T_{max}\simeq 310$ MeV. The temperature $T_{max}$ is the maximum temperature admissible for thermalized non-linear sigma model at zero pion chemical potentials. The estimate of $T_{max}$ is above the chemical freeze-out temperature $T\simeq 170$ MeV at RHIC and above the phase transition to two-flavor quark matter $T_{c} \simeq 175$ MeV, predicted by lattice gauge theories., Comment: Replaced with revised and extended version. Results are compared to lattice gauge theories. 16 pages REVTeX, 13 eps figures

We use $\ensuremath{\epsilon}$-cooling, adjusting at will the order ${a}^{2}$ corrections to the lattice action, to study the parameter space of instantons in the background of nontrivial holonomy and to determine the presence and nature of constituents with fractional topological charge at finite and zero temperature for SU(2). As an additional tool, zero-temperature configurations were generated from those at finite temperature with well-separated constituents. This is achieved by ``adiabatically'' adjusting the anisotropic coupling used to implement finite temperature on a symmetric lattice. The action and topological charge density, as well as the Polyakov loop and chiral zero-modes are used to analyze these configurations. We also show how cooling histories themselves can reveal the presence of constituents with fractional topological charge. We comment on the interpretation of recent fermion zero-mode studies for thermalized ensembles at small temperatures.

The pion optical potential generated by the hypothetical pi-NN-coupled NN-decoupled dibaryon resonance d'(2065) is calculated to the lowest order in nuclear matter density. The contribution to the pion optical potential is found to be within the empirical errors, so the d'(2065) existence currently does not contradict to the observed properties of the pi-nucleus bound states. Future progress in the pionic X-ray spectroscopy can reveal contributions of pi-NN resonances to energy levels and widths of the pionic atoms., 3 pages REVTEX, 1 ps figure

The resonance model is used to analyze the omega- and phi-meson angular distributions in proton-proton collisions at sqrt{s} = 2.83 and 2.98 GeV. The assumption of dominant contributions from N^*(1720)3/2+ and N^*(1900)3/2+ resonances which both have, according to the pi N scattering multichannel partial-wave analysis and/or quark models predictions, dominant p_{1/2} N-omega decay modes yields the right pattern of the omega angular distribution at sqrt{s} = 2.83 GeV. The angular distribution at sqrt{s} = 2.98 GeV can be reproduced assuming the dominance of N^*(2000)5/2+ and N^*(1900)3/2+. The experimental phi-meson angular distributions do not shown any asymmetry which requires the existence of a massive negative-parity spin-half resonance. This resonance could be identified with the N^*(2090)1/2-., 7 pages, 4 eps-figures, to appear in PRC

Using cooling for SU(2) lattice configurations, purely Abelian constant magnetic-field configurations were left over after the annihilation of constituents that formed metastable $Q=0$ configurations. These so-called Dirac sheet configurations were found to be stable if emerging from the confined phase, close to the deconfinement phase transition, provided their Polyakov loop was sufficiently nontrivial. Here we show how this is related to the notion of marginal stability of the appropriate constant magnetic-field configurations. We find a perfect agreement between the analytic prediction for the dependence of stability on the value of the Polyakov loop (the holonomy) in a finite volume and the numerical results studied on a finite lattice in the context of the Dirac sheet configurations.

We consider the exclusive reaction $pp\ensuremath{\rightarrow}pp{\ensuremath{\pi}}^{0}{e}^{+}{e}^{\ensuremath{-}}$ at energies near the $\ensuremath{\eta}$ production threshold. Different channels contribute to this reaction. One of them\char22{}the production of $\ensuremath{\eta}$ mesons and its subsequent rare decay $\ensuremath{\eta}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{e}^{+}{e}^{\ensuremath{-}}$\char22{}is considered as a signal to which the other channels constitute the background. The conditions under which the signal can be larger than background are investigated.

By cooling of equilibrium lattice fields at finite temperature in SU(2) gauge theory it has been shown that topological objects (calorons) observed on the lattice in the confined phase possess a dyonic substructure which becomes visible under certain circumstances. Here we show that, with decreasing temperature of the equilibrium ensemble, the distribution in the caloron parameter space is modified such that the calorons appear non-dissociated into constituent dyons. Still the calorons have nontrivial holonomy which is demonstrated by the Polyakov line behaviour for these configurations. At vanishing temperature (on a symmetric lattice) topological lumps obtained by cooling possess rotational symmetry in 4D and a characteristic double peak structure of Polyakov lines (defined with respect to temporal and spatial directions) with non-trivial asymptotics.

The exclusive $\phi$ meson production in proton-proton reactions is calculated within the resonance model. The considered model was already successfully applied to the description of $\pi$, $\eta$, $\rho$, $\omega$, $\pi\pi$ production in proton-proton collisions. The only new parameter entering into the model is the $\omega-\phi$ mixing angle $\theta_{mix}$ which is taken equal to $\theta_{mix} \approx 3.7^o$., Comment: 7 pages, 1 figure, to appear in the brief report section of PRC

Finite temperature Euclidean SU(2) lattice gauge fields close to the deconfinement phase transition are subjected to cooling. We find relatively stable or absolutely stable configurations with an action below the one-instanton action $S_{inst}=2\pi^2$ both in the deconfinement and the confinement phases. In this paper we attempt an interpretation of these lowest action configurations. Their action is purely magnetic and amounts to $S/S_{inst} \approx N_t/N_s$, where $N_t$ ($N_s$) is the timelike (spacelike) lattice size, while the topological charge vanishes. In the confined phase part of the corresponding lattice configurations turns out to be absolutely stable with respect to the cooling process in which case Abelian projection reveals a homogeneous, purely Abelian magnetic field closed over the "boundary" in one of the spatial directions. Referring to the dyonic structure established for the confinement phase near $T_c$ and based on the observation made for this phase that such events below the instanton action $S_{inst}$ emerge from dyon-antidyon annihilation, the question of stability (metastability) is discussed for both phases. The hypothetically different dyonic structure of the deconfinement phase, inaccessible by cooling, could explain the metastability., Comment: 14 pages, 7 figures

We present a unified description of the vector meson and dilepton production in elementary and in heavy ion reactions. The production of vector mesons ($\rho,\omega$) is described via the excitation of nuclear resonances ($R$). The theoretical framework is an extended vector meson dominance model (eVMD). The treatment of the resonance decays $R\longmapsto NV$ with arbitrary spin is covariant and kinematically complete. The eVMD includes thereby excited vector meson states in the transition form factors. This ensures correct asymptotics and provides a unified description of photonic and mesonic decays. The resonance model is successfully applied to the $\omega$ production in $p+p$ reactions. The same model is applied to the dilepton production in elementary reactions ($p+p, p+d$). Corresponding data are well reproduced. However, when the model is applied to heavy ion reactions in the BEVALAC/SIS energy range the experimental dilepton spectra measured by the DLS Collaboration are significantly underestimated at small invariant masses. As a possible solution of this problem the destruction of quantum interference in a dense medium is discussed. A decoherent emission through vector mesons decays enhances the corresponding dilepton yield in heavy ion reactions. In the vicinity of the $\rho/\omega$-peak the reproduction of the data requires further a substantial collisional broadening of the $\rho$ and in particular of the $\omega$ meson., Comment: 32 pages revtex, 19 figures, to appear in PRC