Non-Abelian Superconductors - Lessons from Supersymmetric Gauge Theories for QCD

Much about the confinement and dynamical symmetry breaking in QCD might be learned from models with supersymmetry. In particular, models based on N=2 supersymmetric theories with gauge groups SU(N), SO(N) and $USp(2 N)$ and with various number of flavors, give deep dynamical hints about these phenomena. For instance, the BPS non-abelian monopoles can become the dominant degrees of freedom in the infrared due to quantum effects. Upon condensation (which can be triggered in these class of models by perturbing them with an adjoint scalar mass) they induce confinement with calculable pattern of dynamical symmetry breaking. This may occur either in a weakly interacting regime or in a strongly coupled regime (in the latter, often the low-energy degrees of freedom contain relatively non-local monopoles and dyons simultaneously and the system is near a nontrivial fixed-point). Also, the existence of sytems with BPS {\it non-abelian vortices} has been shown recently. These results point toward the idea that the ground state of QCD is a sort of dual superconductor of non-abelian variety.Comment: Latex file, 11 eps figures, Talk at the "Confinement 2003", Riken, Tokyo, July 200

Confinement, NonAbelian monopoles, and 2D CP(N-1) model on the worldsheet of finite-length strings

Quark confinement is proposed to be a dual Meissner effect of nonAbelian kind. Important hints come from physics of strongly-coupled infrared-fixed-point theories in N=2 supersymmetric QCD, which turn into confining vacua under a small relevant perturbation. The quest for the semiclassical origin of the nonAbelian monopoles, ubiquitous as the infrared degrees of freedom in supersymmetric gauge theories, motivates us to study the quantum dynamics of 2D CP(N-1)model defined on a finite-width worldstrip, with various boundary conditions. The model is found to possess a unique phase ("confinement phase"), independent of the length of the string, showing the quantum persistence of the nonAbelian monopole.Comment: Latex 14 pages 4 figure

Confinement via strongly-coupled non-Abelian monopoles

New types of confinement phase emerge as singular SCFT's appearing as infrared-fixed-points of N=2 supersymmetric QCD (SQCD) are perturbed by an N=1 adjoint mass term. Based on a recent remarkable work on infrared-fixed-point SCFT of highest criticalities by Gaiotto, Seiberg and Tachikawa, we discuss physics of certain confining systems in SU(N), USp(2N) or SO(N) gauge theories. These show features different from a straightforward dual superconductivity picture of confinement a' la 't Hooft and Mandelstam, which might suggest a new venue in exploring the quark confinement mechanism in the real-world QCD.Comment: Latex 17 pages. arXiv admin note: text overlap with arXiv:1301.042

Confinement, Chiral Symmetry Breaking and Faddeev-Niemi Decomposition in QCD

We identify two distinct, complementary gauge field configurations for QCD with SU(2) gauge group, one (instanton-like configurations) having to do with chiral symmetry breaking but not with confinement, the other (regularized Wu-Yang monopoles) very likely responsible for confinement but unrelated to chiral symmetry breaking. Our argument is based on a semiclassical analysis of fermion zero modes in these backgrounds, made by use of a gauge field decomposition recently introduced by Faddeev and Niemi. Our result suggests that the two principal dynamical phenomena in QCD, confinement and chiral symmetry breaking, are distinct effects, caused by two competing classes of gauge field configurations.Comment: 13 pages, Late

Monopole-vortex complex at large distances and nonAbelian duality

We discuss the large-distance approximation of the monopole-vortex complex soliton in a hierarchically broken gauge system, SU(N+1) - > SU(N) x U(1) - > 1, in a color-flavor locked SU(N) symmetric vacuum. The ('t Hooft-Polyakov) monopole of the higher-mass-scale breaking appears as a point and acts as a source of the thin vortex generated by the lower-energy gauge symmetry breaking. The exact color-flavor diagonal symmetry of the bulk system is broken by each individual soliton, leading to nonAbelian orientational CP^{N-1} zeromodes propagating in the vortex worldsheet, well studied in the literature. But since the vortex ends at the monopoles these fluctuating modes endow the monopoles with a local SU(N) charge. This phenomenon is studied by performing the duality transformation in the presence of the CP^{N-1} moduli space. The effective action is a CP^{N-1} model defined on a finite-width worldstrip.Comment: 36 pages, 4 figure

Fermions in Instanton Anti-Instanton Background

We consider the behaviour of fermions in the background of instanton-anti\-instanton type configurations. Several different physics problems, from the high energy electroweak interactions to the study of vacuum structure of QCD and of large orders of perturbation theory are related to this problem. The spectrum of the Dirac operator in such a background is studied in detail. We present an approximation for the fermion correlation function when the instanton-anti\-instanton separation ($R$) is large compared to their sizes ($\rho$). The situation when the instanton-anti\-instanton overlap and melt, is studied through the behaviour of the Chern Simons number as a function of $R/\rho$ and $x_4$. Applying our results to widely discussed cases of fermion-number violation in the electroweak theory, we conclude that there are no theoretical basis for expecting anomalous cross sections to become observable at energies in $10$ TeV region.Comment: 36 PAGES, GEF-Th-8/199

Convergence of Scaled Delta Expansion: Anharmonic Oscillator

We prove that the linear delta expansion for energy eigenvalues of the quantum mechanical anharmonic oscillator converges to the exact answer if the order dependent trial frequency $\Omega$ is chosen to scale with the order as $\Omega=CN^\gamma$; $1/30$ as $N\rightarrow\infty$. It converges also for $\gamma=1/3$, if $C\geq\alpha_c g^{1/3}$, $\alpha_c\simeq 0.570875$, where $g$ is the coupling constant in front of the operator $q^4/4$. The extreme case with $\gamma=1/3$, $C=\alpha_cg^{1/3}$ corresponds to the choice discussed earlier by Seznec and Zinn-Justin and, more recently, by Duncan and Jones.Comment: 37 pages (with 11 figures uuencoded at the end of the file,to be stripped off), GEF-Th-7/199

Quark Number Fractionalization in N=2 Supersymmetric SU(2)×U(1)NfSU(2) \times U(1)^{N_f} Gauge Theories

Physical quark-number charges of dyons are determined, via a formula which generalizes that of Witten for the electric charge, in N=2 supersymmetric theories with $SU(2) \times U(1)^{N_f}$ gauge group. The quark numbers of the massless monopole at a nondegenerate singularity of QMS turn out to vanish in all cases. A puzzle related to CP invariant cases is solved. Generalization of our results to $SU(N_c)\times U(1)^{N_f}$ gauge theories is straightforward.Comment: Latex file, 14 pages, 1 Postscript figur