The Bogomol'nyi Bound of Lee-Weinberg Magnetic Monopoles

The Lee-Weinberg $U(1)$ magnetic monopoles, which have been reinterpreted as topological solitons of a certain non-Abelian gauged Higgs model recently, are considered for some specific choice of Higgs couplings. The model under consideration is shown to admit a Bogomol'nyi-type bound which is saturated by the configurations satisfying the generalized BPS equations. We consider the spherically symmetric monopole solutions in some detail.Comment: RevTex, 11page

Exact Solution of Noncommutative U(1) Gauge Theory in 4-Dimensions

Noncommutative U(1) gauge theory on the Moyal-Weyl space ${\bf R}^2{\times}{\bf R}^2_{\theta}$ is regularized by approximating the noncommutative spatial slice ${\bf R}^2_{\theta}$ by a fuzzy sphere of matrix size $L$ and radius $R$ . Classically we observe that the field theory on the fuzzy space ${\bf R}^2{\times}{\bf S}^2_L$ reduces to the field theory on the Moyal-Weyl plane ${\bf R}^2{\times}{\bf R}^2_{\theta}$ in the flattening continuum planar limits $R,L{\longrightarrow}{\infty}$ where $R^2/L^{2q}{\simeq}{\theta}^2/4^q$ and $q>{3/2}$ . The effective noncommutativity parameter is found to be given by ${\theta}_{eff}^2{\sim}2{\theta}^2(\frac{L}{2})^{2q-1}$ and thus it corresponds to a strongly noncommuting space. In the quantum theory it turns out that this prescription is also equivalent to a dimensional reduction of the model where the noncommutative U(1) gauge theory in 4 dimensions is shown to be equivalent in the large $L$ limit to an ordinary $O(M)$ non-linear sigma model in 2 dimensions where $M{\sim}3L^2$ . The Moyal-Weyl model defined this way is also seen to be an ordinary renormalizable theory which can be solved exactly using the method of steepest descents . More precisely we find for a fixed renormalization scale $\mu$ and a fixed renormalized coupling constant $g_r^2$ an $O(M)-$symmetric mass, for the different components of the sigma field, which is non-zero for all values of $g_r^2$ and hence the $O(M)$ symmetry is never broken in this solution . We obtain also an exact representation of the beta function of the theory which agrees with the known one-loop perturbative result .Comment: 14 pages, two references added, Nucl.Phys.B.690:230-24

Meanfield Approximation For Field Theories On The Worldsheet Revisited

This work is the continuation of the earlier efforts to apply the mean field approximation to the world sheet formulation of planar phi^3 theory. The previous attempts were either simple but without solid foundation or well founded but excessively complicated. In this article, we present an approach both simple, and also systematic and well founded. We are able to carry through the leading order mean field calculation analytically, and with a suitable tuning of the coupling constant, we find string formation.Comment: 38 pages, 8 figures, late

Theta Dependence In The Large N Limit Of Four-Dimensional Gauge Theories

The theta dependent of pure gauge theories in four dimensions can be studied using a duality of large N gauge theories with string theory on a certain spacetime. Via this duality, one can argue that for every theta, there are infinitely many vacua that are stable in the large N limit. The true vacuum, found by minimizing the energy in this family, is a smooth function of theta except at theta equal to pi, where it jumps. This jump is associated with spontaneous breaking of CP symmetry. Domain walls separating adjacent vacua are described in terms of wrapped sixbranes.Comment: 8 p

A New Lattice Action for Studying Topological Charge

We propose a new lattice action for non-abelian gauge theories, which will reduce short-range lattice artifacts in the computation of the topological susceptibility. The standard Wilson action is replaced by the Wilson action of a gauge covariant interpolation of the original fields to a finer lattice. If the latter is fine enough, the action of all configurations with non-zero topological charge will satisfy the continuum bound. As a simpler example we consider the $O(3)$ $\sigma$-model in two dimensions, where a numerical analysis of discretized continuum instantons indicates that a finer lattice with half the lattice spacing of the original is enough to satisfy the continuum bound.Comment: 12 pages, LateX, 1 figur

Further Results about Field Theory on the World Sheet and String Formation

The present article is the continuation of the earlier work, which used the world sheet representation and the mean field approximation to sum planar graphs in massless phi^3 field theory. We improve on the previous work in two respects: A prefactor in the world sheet propagator that had been neglected is now taken into account. In addition, we introduce a non-zero bare mass for the field phi. Working with a theory with cutoff, and using the mean field approximation, we find that, depending on the range of values of the mass and coupling constant, the model has two phases: A string forming phase and a perturbative field theory phase. We also find the generation of a new degree of freedom, which was not in the model originally. The new degree of freedom can be thought of as the string slope, which is now promoted into a fluctuating dynamical variable. Finally, we show that the introduction of the bare mass makes it possible to renormalize the model.Comment: 39 pages, 10 figures, typos corrected and one equation simplifie

A new approach to instanton calculations in the O(3) nonlinear sigma model

We construct all instantons in the \nlsig\ on a cylindrical space-time, known not to exist on a finite time interval. The scale parameter, $\rho$, is related to the boundary condition in time. This may cure the $\rho\rightarrow0$ divergent instanton gas, through a proper inclusion of in and out states in the path integral.Comment: References added and corrected. Contribution to Lattice'94, 27 Sep - 1 Oct 1994, Bielefeld, Germany. 3 pages PostScript, uuencoded compresse

Generalized two-dimensional Yang-Mills theory is a matrix string theory

We consider two-dimensional Yang-Mills theories on arbitrary Riemann surfaces. We introduce a generalized Yang-Mills action, which coincides with the ordinary one on flat surfaces but differs from it in its coupling to two-dimensional gravity. The quantization of this theory in the unitary gauge can be consistently performed taking into account all the topological sectors arising from the gauge-fixing procedure. The resulting theory is naturally interpreted as a Matrix String Theory, that is as a theory of covering maps from a two-dimensional world-sheet to the target Riemann surface.Comment: LaTeX, 10 pages, uses espcrc2.sty. Presented by A. D'adda at the Third Meeting on Constrained Dynamics and Quantum Gravity, Villasimius (Sardinia, Italy) September 13-17, 1999; to appear in the proceeding

A peptide found in human serum, derived from the c-terminus of albumin, shows antifungal activity in vitro and in vivo

The growing problem of antimicrobial resistance highlights the need for alternative strategies to combat infections. From this perspective, there is a considerable interest in natural molecules obtained from different sources, which are shown to be active against microorganisms, either alone or in association with conventional drugs. In this paper, peptides with the same sequence of fragments, found in human serum, derived from physiological proteins, were evaluated for their antifungal activity. A 13-residue peptide, representing the 597–609 fragment within the albumin C-terminus, was proved to exert a fungicidal activity in vitro against pathogenic yeasts and a therapeutic effect in vivo in the experimental model of candidal infection in Galleria mellonella. Studies by confocal microscopy and transmission and scanning electron microscopy demonstrated that the peptide penetrates and accumulates in Candida albicans cells, causing gross morphological alterations in cellular structure. These findings add albumin to the group of proteins, which already includes hemoglobin and antibodies, that could give rise to cryptic antimicrobial fragments, and could suggest their role in anti-infective homeostasis. The study of bioactive fragments from serum proteins could open interesting perspectives for the development of new antimicrobial molecules derived by natural sources