Proper-time methods in the presence of non-constant background fields

A formalism is developed to enable the construction of the effective action and related quantities in QED for the case of time-varying background electric fields. Some examples are studied and evidence is sought for a possible transition to a phase in which chiral symmetry is spontaneously broken. YCTP-P14-94Comment: 13 pages, YCTP-P14-9

Reality of Complex Affine Toda Solitons

There are infinitely many topological solitons in any given complex affine Toda theories and most of them have complex energy density. When we require the energy density of the solitons to be real, we find that the reality condition is related to a simple ``pairing condition.'' Unfortunately, rather few soliton solutions in these theories survive the reality constraint, especially if one also demands positivity. The resulting implications for the physical applicability of these theories are briefly discussed.Comment: LaTeX, 15 pages, UBTH-049

Large NN Weinberg-Tomozawa interaction and spin-flavor symmetry

The construction of an extended version of the Weinberg-Tomozawa Lagrangian, in which baryons and mesons form spin-flavor multiplets, is reviewed and some of its properties discussed, for an arbitrary number of colors and flavors. The coefficient tables of spin-flavor irreducible representations related by crossing between the $s$-, $t$- and $u$-channels are explicitly constructed.Comment: 3 pages, no figures. Presented at the IVth International Conference on Quarks and Nuclear Physics, Madrid, June 5th-10th 200

The Rho-Meson as a Collective Excitation

A model of the rho-meson as a collective excitation of $q\bar{q}$ pairs in a system that obeys the modified Nambu--Jona-Lasinio Lagrangian is proposed. The rho emerges as a dormant Goldstone boson. The origin of the rho-meson mass is understood as a result of spontaneous chiral symmetry breaking. The low-energy dynamics of rho, pi, omega and gamma is consistently described in this new framework. The model accounts for the origin of the celebrated Kawarabayashi--Suzuki--Riazuddin--Fayyazuddin relation.Comment: 8 pages, plain LaTe

Low-lying even parity meson resonances and spin-flavor symmetry

A study is presented of the $s-$wave meson-meson interactions involving members of the $\rho-$nonet and of the $\pi-$octet. The starting point is an SU(6) spin-flavor extension of the SU(3) flavor Weinberg-Tomozawa Lagrangian. SU(6) symmetry breaking terms are then included to account for the physical meson masses and decay constants, while preserving partial conservation of the axial current in the light pseudoscalar sector. Next, the $T-$matrix amplitudes are obtained by solving the Bethe Salpeter equation in coupled-channel with the kernel built from the above interactions. The poles found on the first and second Riemann sheets of the amplitudes are identified with their possible Particle Data Group (PDG) counterparts. It is shown that most of the low-lying even parity PDG meson resonances, specially in the $J^P=0^+$ and $1^+$ sectors, can be classified according to multiplets of the spin-flavor symmetry group SU(6). The $f_0(1500)$, $f_1(1420)$ and some $0^+(2^{++})$ resonances cannot be accommodated within this SU(6) scheme and thus they would be clear candidates to be glueballs or hybrids. Finally, we predict the existence of five exotic resonances ($I \ge 3/2$ and/or $|Y|=2$) with masses in the range 1.4--1.6 GeV, which would complete the $27_1$, $10_3$, and $10_3^*$ multiplets of SU(3)$\otimes$SU(2).Comment: 43 pages, 2 figures, 61 tables. Improved discussion of Section II. To appear in Physical Review

Dimensional Reduction and Dynamical Chiral Symmetry Breaking by a Magnetic Field in 3+13+1 Dimensions

It is shown that in $3+1$ dimensions, a constant magnetic field is a catalyst of dynamical chiral symmetry breaking, leading to generating a fermion mass even at the weakest attractive interaction between fermions. The essence of this effect is the dimensional reduction $D \rightarrow D-2$ ($3+1 \rightarrow 1+1$) in the dynamics of fermion pairing in a magnetic field. The effect is illustrated in the Nambu-Jona-Lasinio model. Possible applications of this effect are briefly discussed.Comment: 13 pages, LaTeX, no figure

Restricted Quantum Theory of Affine Toda Solitons

We quantise the reduced theory obtained by substituting the soliton solutions of affine Toda theory into its symplectic form. The semi-classical S-matrix is found to involve the classical Euler dilogarithm.Comment: 10pp, LaTe

``GLUELUMP'' SPECTRUM AND ADJOINT SOURCE POTENTIAL IN LATTICE QCD3_3

We calculate the potential between ``quarks'' which are in the adjoint representation of SU(2) color in the three-dimensional lattice theory. We work in the scaling region of the theory and at large quark separations $R$. We also calculate the masses $M_{Qg}$ of color-singlet bound states formed by coupling an adjoint quark to adjoint glue (``gluelumps''). Good scaling behavior is found for the masses of both magnetic (angular momentum $J=0$) and electric ($J=1$) gluelumps, and the magnetic gluelump is found to be the lowest-lying state. It is naively expected that the potential for adjoint quarks should saturate above a separation $R_{\rm scr}$ where it becomes energetically favorable to produce a pair of gluelumps. We obtain a good estimate of the naive screening distance $R_{\rm scr}$. However we find little evidence of saturation in the potential out to separations $R$ of about twice $R_{\rm scr}$.Comment: 8 pages plus 8 figures in 2 postscript files (uuencoded

The Magnetic Moments of the Octet Baryons in Quenched Chiral Perturbation Theory

We compute the magnetic moments of the octet baryons up to two orders in quenched chiral perturbation theory. In addition to the $\sim\sqrt{m_q}$ contributions that arise in QCD, there are lower-order contributions of the form $M_0^2\log m_q$ from loop diagrams involving hairpin interactions.Comment: 18 pages, 3 figures, late

Strong and Electromagnetic Decays of the Baryon Decuplet

We discuss the strong and radiative decays of the decuplet of baryon resonances to the baryon octet in chiral perturbation theory. We comment on the implications for the polarisability of the nucleon.Comment: 16 pages + 5 figures (.ps files) appended to file. Uses tables.tex and harvmac.te