arXiv subjects
Publications and source records attributed to B. V. Martemyanov.
We report the observation of calorons with nontrivial holonomy and fractional topological charge objects in cooled lattice samples derived from SU(2) equilibrium ensembles at $T<T_c$.
The omega production in nucleon-nucleon collisions is described through the decay of intermediate nuclear resonances. Close to threshold the pp --> pp omega cross section is dominated by the off-shell production of omega mesons with masses far below the physical omega mass of 782 MeV. A crucial role plays thereby the N^*(1535) resonance. Due to a strong N omega decay mode this resonance leads to off-shell contributions which are in the vicinity of the threshold about one order of magnitude larger than the experimentally measurable contribution from only the omega peak. After a subtraction of the theoretical "background" from off-shell omega production the available data are accurately reproduced over the entire energy range from very close to threshold up to several GeV above threshold. The scenario of a weaker N^*(1535) --> N omega decay mode which is still consistent with electro- and photo-production data is discussed as well. In the latter case the off-shell contributions to the pp --> pp omega cross section are substantially reduced but the description of the experimental cross section is poor above threshold.
With the help of the cooling method applied to SU(2) lattice gauge theory at non-zero $T \le T_c$ we present numerical evidence for the existence of superpositions of Kraan-van Baal caloron (or BPS monopole pair) solutions with non-trivial holonomy, which might constitute an important contribution to the semi-classical approximation of the partition function.
Finite temperature Euclidean SU(2) lattice gauge fields generated in the confinement phase close to the deconfinement phase transition are subjected to cooling. The aim is to identify long-living, almost-classical local excitations which carry (generically non-integer) topological charge. Two kinds of spatial boundary conditions (fixed holonomy and standard periodic boundary conditions) are applied. For the lowest-action almost-classical configurations we find that their relative probability semi-quantitatively agrees for both types of boundary conditions. We find calorons with unit topological charge as well as (anti-)selfdual lumps (BPS-monopoles or dyons) combined in pairs of non-integer (equal or opposite sign) topological charge. For calorons and separated pairs of equal-sign dyons obtained by cooling we have found that (i) the gluon field is well-described by Kraan-van Baal solutions of the Euclidean Yang-Mills field equations and (ii) the lowest Wilson-fermion modes are well-described by analytic solutions of the corresponding Dirac equation. For metastable configurations found at higher action, the multi-center structure can be interpreted in terms of dyons and antidyons, using the gluonic and fermionic indicators as in the dyon-pair case. Additionally, the Abelian monopole structure and field strength correlators between the centers are useful to analyse the configurations in terms of dyonic constituents. We argue that a semi-classical approximation of the non-zero temperature path integral should be built on superpositions of solutions with non-trivial holonomy.
Relativistic, kinematically complete phenomenological expressions for the dilepton decay rates of nucleon resonances with arbitrary spin and parity are derived in terms of the magnetic, electric, and Coulomb transition form factors. The dilepton decay rates of the nucleon resonances with masses below 2 GeV are estimated using the extended vector meson dominance model for the transition form factors. The model provides a unified description of the photo- and electroproduction data, the vector meson decays, and the dilepton decays of the nucleon resonances. The constraints on the transition form factors from the quark counting rules are taken into account. The parameters of the model are fixed by fitting the available photo- and electroproduction data and using results of the multichannel partial-wave analysis of the $πN$ scattering. Where experimental data are not available, predictions of the non-relativistic quark models are used as an input. The vector meson coupling constants of the magnetic, electric, and Coulomb types are determined. The dilepton widths and the dilepton spectra from decays of nucleon resonances with masses below 2 GeV are calculated.
We generate SU(2) lattice gauge fields at finite temperature and cool them in order to characterize the two phases by the occurrence of specific classical solutions.We apply two kinds of spatial boundary conditions: fixed holonomy and standard periodic b.c. For T < T_c our findings concerning classical configurations semi-quantitatively agree for both types of boundary conditions. We find in the confinement phase a mixture of undissociated calorons with lumps of positive or negative half-integer topological charges.
The field strength correlators at zero temperature are semi-classically evaluated fitting the random instanton liquid model to lattice data for quenched SU(3) lattice gauge theory. We restrict ourselves to the lowest order in an instanton density expansion necessary to explain the difference between transverse and longitudinal correlation functions. In the instanton-instanton and instanton-antiinstanton contributions the Schwinger line factors neglected in a previous analysis are numerically taken into account in a weighted Monte Carlo evaluation. This leads to different estimates for instanton size and density. A reasonable description of the correlators within the intermediate range from 0.4 fm to 1 fm is obtained.
The following lectures concern with the quark structure of hadrons made up from light quarks. The symmetries of strong interaction were the only instruments used for the description of this structure. The models of hadrons (there are a lot of them) were not considered. There was not also considered the structure of hadrons with heavy quarks. The first round of problems (models of hadrons) is not considered because of its unexhaustability. The second round of problems (hadrons with heavy quarks) is not considered because of the physics of heavy flavors tends mainly to electroweak interaction and will be considered in the course of electroweak interactions. Therefore, the presented here course, being the self-bounded part of the theory of elementary particles, is considered separately. These lectures were formed from 1989 and are the part of the set of courses on the theory of fundamental interactions for the students of Moscow Physical Technical Institute. The basic source of the lectures was the unpublished manuscript "Hadrons and quarks" by L.B. Okun. Another source was the "Lectures on the theory of unitary symmetry in elementary particle physics" by Nguen Van Hieu (Atomizdat, Moscow 1967). The list of references (due to its smallness) is absent.
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.
Field strength correlators are semi-classically evaluated in the dilute gas model of non-Abelian sources (instantons) and compared with lattice data for QCD at zero temperature. We show that one of the Euclidean invariant, tensorial structures vanishes for configurations being purely selfdual or anti-selfdual. We compute the invariant functions contributing to the correlators within the two lowest orders in an instanton density expansion. Fitting instanton size and density for quenched and full QCD, we obtain a reasonable description.
The effects of the presence of $Δ$-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 $Δ$-isobar self-energy and thereby on the mean-field coupling constants of the scalar and vector mesons with $Δ$-isobars. The range of possible values for the scalar and vector coupling constants of $Δ$-isobars with respect to the nucleon coupling is investigated and compared to recent predictions of QCD sum-rule calculations.
The interaction of dyons in the mean field approximation is considered. The result of interaction is the mass term for dyonic field in the effective Lagrangian. Due to the mass term the profile function of dyon falls off exponentially at large distances.
The possibility for occurrence of a Bose condensate of dibaryons in nuclear matter is investigated within the framework of the Walecka model in the mean-field approximation. Constraints for the omega - and sigma - meson coupling constants with dibaryons following from the requirement of stability of dibaryon matter against compression are derived and the effect of sigma - and pi - meson exchange current contributions to the sigma - dibaryon coupling constant is discussed. The mean-field solutions of the model are constructed. The effective nucleon mass vanishes when the density of dibaryons approaches a critical value about 0.15/fm^3. The Green's functions of the equilibrium binary mixture of nucleons and dibaryons are constructed by solving the Gorkov-Dyson system of equations in the no-loop approximation. We find that when the square of the sound velocity is positive, the dispersion laws for all elementary excitations of the system are real functions. This indicates stability of the ground state of the heterophase nucleon-dibaryon mixture. In the model considered, production of dibaryons becomes energetically favorable at higher densities as compared to estimates based on a model of non-interacting nucleons and dibaryons.
We consider the thermodynamics of the matter made up of equal number of neutrons and protons and of scalar dibaryons. They interact via the exchange of scalar and vector mesons. The interaction is taken into account in the mean field approximation. The condensation of dibaryons in this matter and the phase transition of matter to quark matter are considered. Possible signatures of dibaryons in Heavy Ion Collisions are speculated on.
If sufficiently light dibaryon resonances exist, a Bose condensate of dibaryons can occur in nuclear matter before the quark-hadron phase transition. Within a relativistic mean-field model we show that heterophase nuclear-dibaryon matter is for a wide set of parameters energetically more favorable than normal nuclear matter. Production of dibaryons is, however, relatively suppressed as compared to estimates based on the model of non-interacting nucleons and dibaryons.