326 research outputs found
The Bogomol'nyi Bound of Lee-Weinberg Magnetic Monopoles
The Lee-Weinberg 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 is regularized by approximating the
noncommutative spatial slice by a fuzzy sphere of matrix
size and radius . Classically we observe that the field theory on the
fuzzy space reduces to the field theory on the
Moyal-Weyl plane in the flattening
continuum planar limits where
and . The effective
noncommutativity parameter is found to be given by
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 limit to an ordinary non-linear sigma model in 2
dimensions where . 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 and a fixed renormalized coupling constant
an symmetric mass, for the different components of the sigma field,
which is non-zero for all values of and hence the 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 -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 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
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, , is related
to the boundary condition in time. This may cure the
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
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