Towards the Theory of Non--Abelian Tensor Fields I

We present a triangulation--independent area--ordering prescription which naturally generalizes the well known path ordering one. For such a prescription it is natural that the two--form ``connection'' should carry three ``color'' indices rather than two as it is in the case of the ordinary one--form gauge connection. To define the prescription in question we have to define how to {\it exponentiate} a matrix with three indices. The definition uses the fusion rule structure constants.Comment: 22 pages, 18 figure

Effects of spin polarization on resonant photoemission from d-f states in TbNi2Mnx compounds

Resonant photoemission in narrow-band materials is described by the sum of first-and secondorder transitions, their quantum-mechanical interference leads to an increase in the spectrum from the valence bands and the appearance of an asymmetric dependence on the photon energy. These effects are studied theoretically and experimentally using the example of three-component intermetallic compounds TbNi2Mnx. The competition between the elastic and inelastic photoemission channels leads to a different dependence of photoemission spectra from nickel and manganese on photon energy. The elastic channel is realized on atoms with large magnetic moments, the inelastic Auger decay occurs on atoms with small moments. © 2018 The Authors, published by EDP Sciences.The research was carried out within the state assignment of FASO of Russia (theme uQ" ant" No. 01201463332), supported in part by RFBR (No. 18-02-00060) and UD RAS (No.15 -8 2-10). The authors express their gratitude to A. Preobrazhenskii and N. Vinogradov (synchrotron MAX-Lab, Lund, Sweden) for their assistance in carrying out experiments

String theory and classical integrable systems

We discuss different formulations and approaches to string theory and $2d$ quantum gravity. The generic idea to get a unique description of {\it many} different string vacua altogether is demonstrated on the examples in $2d$ conformal, topological and matrix formulations. The last one naturally brings us to the appearance of classical integrable systems in string theory. Physical meaning of the appearing structures is discussed and some attempts to find directions of possible generalizations to ``higher-dimensional" models are made. We also speculate on the possible appearence of quantum integrable structures in string theory.Comment: lecture given at III Baltic Rim student seminar, Helsinki, September 1993} 33pp, late

Quantum matter wave dynamics with moving mirrors

When a stationary reflecting wall acting as a perfect mirror for an atomic beam with well defined incident velocity is suddenly removed, the density profile develops during the time evolution an oscillatory pattern known as diffraction in time. The interference fringes are suppressed or their visibility is diminished by several effects such as averaging over a distribution of incident velocities, apodization of the aperture function, atom-atom interactions, imperfect reflection or environmental noise. However, when the mirror moves with finite velocity along the direction of propagation of the beam, the visibility of the fringes is enhanced. For mirror velocities below beam velocity, as used for slowing down the beam, the matter wave splits into three regions separated by space-time points with classical analogues. For mirror velocities above beam velocity a visibility enhancement occurs without a classical counterpart. When the velocity of the beam approaches that of the mirror the density oscillations rise by a factor 1.8 over the stationary value.Comment: 5.2 pages, 6 figure

Magnetic and magnetocaloric properties of (MnCo)1-xGe compounds

The crystal structure, magnetic properties, and heat capacity of the (MnCo)1-xGe compounds with x ≤ 0.05 have been studied. It was found that, as the deviation from the MnCoGe stoichiometric composition increases, the temperature of structural transition from the low-temperature phase with the orthorhombic TiNiSi-type structure to the high-temperature phase with the hexagonal Ni2In-type phase decreases rapidly, whereas the magnetic ordering temperature varies slightly. The temperature of structural transition for the composition with x = 0.02 approximately coincides with the Curie temperature of the hexagonal phase, and the transition is accompanied by a significant entropy change, namely, ΔS = 34 J/(kg K). The application of high magnetic field in the transition-temperature range causes an increase in the relative volume of the orthorhombic phase. An analysis of magnetocaloric properties of these compounds, which was performed with the formal application of the Maxwell's relationship near the temperature of first-order structural phase transition, is shown to give overestimated values of the entropy change. © Pleiades Publishing, Ltd., 2013

Search for NN-decoupled dibaryons using the process pp→γγXpp \to \gamma \gamma X below the pion production threshold

The energy spectrum for high energy $\gamma$-rays ($E_\gamma \geq 10$ MeV) from the process $pp \to \gamma \gamma X$ emitted at $90^0$ in the laboratory frame has been measured at an energy below the pion production threshold, namely, at 216 MeV. The resulting photon energy spectrum extracted from $\gamma-\gamma$ coincidence events consists of a narrow peak at a photon energy of about 24 MeV and a relatively broad peak in the energy range of (50 - 70) MeV. The statistical significances for the narrow and broad peaks are 5.3$\sigma$ and 3.5$\sigma$, respectively. This behavior of the photon energy spectrum is interpreted as a signature of the exotic dibaryon resonance $d^\star_1$ with a mass of about 1956 MeV which is assumed to be formed in the radiative process $pp \to \gamma d^\star_1$ followed by its electromagnetic decay via the $d^\star_1 \to pp \gamma$ mode. The experimental spectrum is compared with those obtained by means of Monte Carlo simulations.Comment: 14 pages, LaTex, 6 eps-figures, accepted for publication in Phys.Rev.

Fragmentation channels of relativistic 7^7Be nuclei in peripheral interactions

Nuclei of $^7$Li were accelerated at the JINR Nuclotron. After the charge-exchange reaction involving these nuclei at an external target a second $^7$Be beam of energy 1.23A GeV was formed. This beam was used to expose photo-emulsion chambers. The mean free path for inelastic $^7$Be interactions in emulsion $\lambda$=14.0$\pm$0.8 cm coincides within the errors with those for $^6$Li and $^7$Li nuclei. More than 10% of the $^7$Be events are associated with the peripheral interactions in which the total charge of the relativistic fragments is equal to the charge of the $^7$Be and in which charged mesons are not produced. An unusual ratio of the isotopes is revealed in the composition of the doubly charged $^7$Be fragments: the number of $^3$He fragments is twice as large as that of $^4$He fragments. In 50% of peripheral interactions, a $^7$Be nucleus decays to two doubly charged fragments. The present paper gives the channels of the $^7$Be fragmentation to charged fragments. In 50% of events, the $^7$Be fragmentation proceeds only to charged fragments involving no emission of neutrons. Of them, the $^3$He+$^4$He channel dominates, the $^4$He+d+p and $^6$Li+pchannels constitute 10% each. Two events involving no emission of neutrons are registered in the 3-body $^3$He+t+p and $^3$He+d+d channels. The mean free path for the coherent dissociation of relativistic $^7$Be nuclei to $^3$He+$^4$He is 7$\pm$1 m. The particular features of the relativistic $^7$Be fragmentation in such peripheral interactions are explained by the $^3$He+$^4$He 2-cluster structure of the $^7$Be nucleus.Comment: 10 pages, 3 figures, 3 tables, conference: Conference on Physics of Fundamental Interactions, Moscow, Russia, 5-9 Dec 200