521 research outputs found
Dynamical Flavour Symmetry Breaking by a Magnetic Field in Lattice QED_3
We perform a lattice study, in the quenched approximation, of dynamical mass
generation in a system of relativistic (Dirac) fermions, coupled to an Abelian
gauge field in (2+1)-dimensions, in the presence of an external (constant)
magnetic field, perpendicular to the spatial planes. It is shown that a strong
magnetic field catalyzes chiral symmetry breaking, in agreement with results in
the continuum. The r\^ole of the higher-Landau poles in inducing a critical
temperature above which the phenomenon disappears is pointed out. We also
discuss the implications of this model on the opening of a gap in doped
antiferromagnetic superconductors.Comment: 18 pages, latex, 9 figures, uses psfig and epsf; minor typos in
eqs.(10) and (17) correcte
Instantons And Baryon Mass Splittings in the MIT Bag Model
The contribution of instanton-induced effective inter-quark interactions to
the baryon mass splittings was considered in the bag model. It is found that
results are different from those obtained in the constituent quark model where
the instanton effects are like those from one-gluon exchange. This is because
in the context of the bag model calculation the one-body instanton-induced
interaction has to be included.Comment: 23 pages, report ZTF-93/10 (to appear in Phys.Rev. D
Instantons in non-Cartesian coordinates
The explicit multi-instanton solutions by 'tHooft and Jackiw, Nohl & Rebbi
are generalized to curvilinear coordinates. The idea is that a gauge
transformation can notably simplify the expressions obtained after the change
of variables. The gauge transform generates a compensating addition to the
gauge potential of pseudoparticles. Singularities of the compensating field are
irrelevant for physics but may affect gauge dependent quantities.Comment: 10 pages, LaTeX, talk given at Quarks-2000 (Pushkin, Russia) and
E.S.Fradkin (Moscow, Russia) conference
Gravitational wave background from neutron star phase transition for a new class of equation of state
We study the generation of a stochastic gravitational wave (GW) background
produced by a population of neutron stars (NSs) which go over a hadron-quark
phase transition in its inner shells. We obtain, for example, that the NS phase
transition, in cold dark matter scenarios, could generate a stochastic GW
background with a maximum amplitude of , in the
frequency band for stars forming at redshifts of up
to We study the possibility of detection of this isotropic GW
background by correlating signals of a pair of `advanced' LIGO observatories.Comment: 7 pages, 1 figur
Path-Integral Formulation of Casimir Effects in Supersymmetric Quantum Electrodynamics
The Casimir effect is an interesting phenomenon in the sense that it provides
us with one of the primitive means of extracting the energy out of the vacuum.
Since the original work of Casimir a number of works have appeared in extending
the result to the case of more general topological and dynamical configurations
of the boundary condition and to the circumstances at finite temperature and
gravity. In the studies of the Casimir effects it is common to assume the free
electromagnetic field in the bounded region. It may be interesting to extend
our arguments for fields other than the electromagnetic field. The Casimir
effect due to the free fermionic fields has been investigated by several
authors and has been found to result in an attractive force under the suitable
physical boundary conditions.Comment: 12 pages, 6 figures, REVTe
Bag Model for a Link in a Closed Gluonic Chain
The large limit of Yang-Mills gauge theory is the dynamics of a closed
gluonic chain, but this fact does not obviate the inherently strong coupling
nature of the dynamical problem. However, we suggest that a single link in such
a chain might be reasonably described in the quasi-perturbative language of
gluons and their interactions. To implement this idea, we use the MIT bag to
model the physics of a nearest neighbor bond.Comment: 10 pages, LaTe
Confined two-dimensional fermions at finite density
We introduce the chemical potential in a system of two-dimensional massless
fermions, confined to a finite region, by imposing twisted boundary conditions
in the Euclidean time direction. We explore in this simple model the
application of functional techniques which could be used in more complicated
situations.Comment: 15 pages, LaTe
Magnetic Z(N) symmetry in 2+1 dimensions
This review describes the role of magnetic symmetry in 2+1 dimensional gauge
theories. In confining theories without matter fields in fundamental
representation the magnetic symmetry is spontaneously broken. Under some mild
assumptions, the low-energy dynamics is determined universally by this
spontaneous breaking phenomenon. The degrees of freedom in the effective theory
are magnetic vortices. Their role in confining dynamics is similar to that
played by pions and sigma in the chiral symmetry breaking dynamics.
I give an explicit derivation of the effective theory in (2+1)-dimensional
weakly coupled confining models and argue that it remains qualitatively the
same in strongly coupled (2+1)-dimensional gluodynamics. Confinement in this
effective theory is a very simple classical statement about the long range
interaction between topological solitons, which follows (as a result of a
simple direct classical calculation) from the structure of the effective
Lagrangian. I show that if fundamentally charged dynamical fields are present
the magnetic symmetry becomes local rather than global. The modifications to
the effective low energy description in the case of heavy dynamical fundamental
matter are discussed. This effective lagrangian naturally yields a bag like
description of baryonic excitations. I also discuss the fate of the magnetic
symmetry in gauge theories with the Chern-Simons term
Bosonic Fields in the String-like Defect Model
We study localization of bosonic bulk fields on a string-like defect with
codimension 2 in a general space-time dimension in detail. We show that in
cases of spin 0 scalar and spin 1 vector fields there are an infinite number of
massless Kaluza-Klein (KK) states which are degenerate with respect to the
radial quantum number, but only the massless zero mode state among them is
coupled to fermion on the string-like defect. It is also commented on
interesting extensions of the model at hand to various directions such as
'little' superstring theory, conformal field theory and a supersymmetric
construction.Comment: 17 pages, LaTex 2e, revised version (to appear in Phys. Rev. D
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