Baby Skyrmion chains

Previous results on multi-charged Baby Skyrmion solutions have pointed to a modular structure, comprised of charge two rings and single charge one Skyrmions, which combine to form higher charged structures. In this paper we present numerical evidence which shows an alternative finite chain, multi-charged global energy minimum Baby Skymion solution. We then proceed from the infinite plane, to Baby Skyrmions on a cylinder and then a torus, to obtain the solutions of periodic Baby Skyrmions, of which periodic segments will correspond to sections of large charge Baby Skyrmions in the plane

Resonances, and mechanisms of Theta-production

After explaining necessity of exotic hadrons, we discuss mechanisms which could determine production of the exotic Theta-baryon. A possible important role of resonances (producing the Theta in real or virtual decays) is emphasized for various processes. Several experimental directions for studies of such resonances, and the Theta itself, are suggested. We briefly discuss also recent negative results on the Theta-baryon.Comment: 6 page

Spectra of Free Diquark in the Bethe-Salpeter Approach

In this work, we employ the Bethe-Salpeter (B-S) equation to investigate the spectra of free diquarks and their B-S wave functions. We find that the B-S approach can be consistently applied to study the diqaurks with two heavy quarks or one heavy and one light quarks, but for two light-quark systems, the results are not reliable. There are a few free parameters in the whole scenario which can only be fixed phenomenologically. Thus, to determine them, one has to study baryons which are composed of quarks and diquarks.Comment: 16 pages, no figure

1+11+1-Dimensional Large NN QCD coupled to Adjoint Fermions

We consider 1+1-dimensional QCD coupled to Majorana fermions in the adjoint representation of the gauge group $SU(N)$. Pair creation of partons (fermion quanta) is not suppressed in the large-$N$ limit, where the glueball-like bound states become free. In this limit the spectrum is given by a linear \lc\ Schr\" odinger equation, which we study numerically using the discretized \lcq. We find a discrete spectrum of bound states, with the logarithm of the level density growing approximately linearly with the mass. The wave function of a typical excited state is a complicated mixture of components with different parton numbers. A few low-lying states, however, are surprisingly close to being eigenstates of the parton number, and their masses can be accurately calculated by truncated diagonalizations.Comment: 22 pages + 9 figures (available by request from [email protected]), uses phyzzx.tex + tables.tex PUPT-1413, IASSNS-HEP-93/4

Brane Gases in the Early Universe

Over the past decade it has become clear that fundamental strings are not the only fundamental degrees of freedom in string theory. D-branes are also part of the spectrum of fundamental states. In this paper we explore some possible effects of D-branes on early Universe string cosmology, starting with two key assumptions: firstly that the initial state of the Universe corresponded to a dense, hot gas in which all degrees of freedom were in thermal equilibrium, and secondly that the topology of the background space admits one-cycles. We argue by t-duality that in this context the cosmological singularities are not present. We derive the equation of state of the brane gases and apply the results to suggest that, in an expanding background, the winding modes of fundamental strings will play the most important role at late times. In particular, we argue that the string winding modes will only allow four space-time dimensions to become large. The presence of brane winding modes with $p > 1$ may lead to a hierarchy in the sizes of the extra dimensions.Comment: 8 pages, 1 figure; typos corrected; published in PR

Small Momentum Evolution of the Extended Drell--Hearn--Gerasimov Sum Rule

We investigate the momentum dependence of the extended Drell-Hearn-Gerasimov sum rule. An economical formalism is developed which allows to express the extended DHG sum rule in terms of a single virtual Compton amplitude in forward direction. Rigorous results for the small momentum evolution are derived from chiral perturbation theory within the one-loop approximation. Furthermore, we evaluate some higher order contributions arising from $\Delta(1232)$ intermediate states and relativistic corrections. (2 figures available upon request).Comment: 12 pages, TeX, BUTP-92/51 and CRN-92-5

Updated resonance photo-decay amplitudes to 2 GeV

We present the results of an energy-dependent and set of single-energy partial-wave analyses of single-pion photoproduction data. These analyses extend from threshold to 2 GeV in the laboratory photon energy, and update our previous analyses to 1.8 GeV. Photo-decay amplitudes are extracted for the baryon resonances within this energy range. We consider two photoproduction sum rules and the contributions of two additional resonance candidates found in our most recent analysis of $\pi N$ elastic scattering data. Comparisons are made with previous analyses.Comment: Revtex, 26 pages, 3 figures. Postscript figures available from ftp://clsaid.phys.vt.edu/pub/pr or indirectly from http://clsaid.phys.vt.edu/~CAPS

Polarization Phenomena in Small-Angle Photoproduction of e+e- Pairs and the Gerasimov-Drell-Hearn Sum Rule

Photoproduction of $e^+e^-$ pairs at small angles is investigated as a tool to determine the functions $f_1$ and $f_2$ entering the real-photon forward Compton scattering amplitude. The method is based on an interference of the Bethe-Heitler and the virtual Compton scattering mechanisms, generating an azimuthal asymmetry in the $e^+$ versus $e^-$ yield. The general case of a circularly polarized beam and a longitudinally polarized target allows one to determine both the real and imaginary parts of $f_1$ as well as $f_2$. The imaginary part of $f_2$ requires target polarization only. We calculate cross sections and asymmetries of the reaction $p(\gamma,e^+e^-)p$, estimate corrections and backgrounds, and propose suitable kinematical regions to perform the experiment. Our investigation shows that photoproduction of $e^+e^-$-pairs off the proton and light nuclei may serve as a rather sensitive test of the validity of the Gerasimov-Drell-Hearn sum rule.Comment: 22 pages; revtex; 5 postscript figures included in submission; submitted to Phys. Rev.