3,506 research outputs found
Instantons in the QCD Vacuum and in Deep Inelastic Scattering
We give a brief status report on our on-going investigation of the prospects
to discover QCD instantons in deep inelastic scattering (DIS) at HERA. A recent
high-quality lattice study of the topological structure of the QCD vacuum is
exploited to provide crucial support of our predictions for DIS, based on
instanton perturbation theory.Comment: 6 pages, 5 figures, talk presented at the 7th International Workshop
on Deep Inelastic Scattering and QCD (DIS 99), Zeuthen/Germany, April 19-23,
1999; to be published in the Proceedings (Nuclear Physics B (Proc. Suppl.)
On the zero of the fermion zero mode
We argue that the fermionic zero mode in non-trivial gauge field backgrounds
must have a zero. We demonstrate this explicitly for calorons where its
location is related to a constituent monopole. Furthermore a topological
reasoning for the existence of the zero is given which therefore will be
present for any non-trivial configuration. We propose the use of this property
in particular for lattice simulations in order to uncover the topological
content of a configuration.Comment: 6 pages, 3 figures in 5 part
Strong to weak coupling transitions of SU(N) gauge theories in 2+1 dimensions
We investigate strong-to-weak coupling transitions in D=2+1 SU(N->oo) gauge
theories, by simulating lattice theories with a Wilson plaquette action. We
find that there is a strong-to-weak coupling cross-over in the lattice theory
that appears to become a third-order phase transition at N=oo, in a manner that
is essentially identical to the Gross-Witten transition in the D=1+1 SU(oo)
lattice gauge theory. There is also evidence for a second order transition at
N=oo at approximately the same coupling, which is connected with centre
monopoles (instantons) and so analogues to the first order bulk transition that
occurs in D=3+1 lattice gauge theories for N>4. We show that as the lattice
spacing is reduced, the N=oo gauge theory on a finite 3-torus suffers a
sequence of (apparently) first-order ZN symmetry breaking transitions
associated with each of the tori (ordered by size). We discuss how these
transitions can be understood in terms of a sequence of deconfining transitions
on ever-more dimensionally reduced gauge theories.We investigate whether the
trace of the Wilson loop has a non-analyticity in the coupling at some critical
area, but find no evidence for this although, just as in D=1+1,the eigenvalue
density of a Wilson loop forms a gap at N=oo for a critical trace. The physical
implications of this are unclear.The gap formation is a special case of a
remarkable similarity between the eigenvalue spectra of Wilson loops in D=1+1
and D=2+1 (and indeed D=3+1): for the same value of the trace, the eigenvalue
spectra are nearly identical.This holds for finite as well as infinite N;
irrespective of the Wilson loop size in lattice units; and for Polyakov as well
as Wilson loops.Comment: 44 pages, 28 figures. Extensive changes and clarifications with new
results on non-analyticities and eigenvalue spectra of Wilson loops. This
version to be submitted for publicatio
Black Hole Evaporation without Information Loss
An approach to black hole quantization is proposed wherein it is assumed that
quantum coherence is preserved. A consequence of this is that the Penrose
diagram describing gravitational collapse will show the same topological
structure as flat Minkowski space. After giving our motivations for such a
quantization procedure we formulate the background field approximation, in
which particles are divided into "hard" particles and "soft" particles. The
background space-time metric depends both on the in-states and on the
out-states. We present some model calculations and extensive discussions. In
particular, we show, in the context of a toy model, that the -matrix
describing soft particles in the hard particle background of a collapsing star
is unitary, nevertheless, the spectrum of particles is shown to be
approximately thermal. We also conclude that there is an important topological
constraint on functional integrals.Comment: 35 pages (including Figures); TEX, 3 figures in postscrip
Chern-Simons term in the 4-dimensional SU(2) Higgs Model
Using Seiberg's definition for the geometric charge in SU(2) lattice gauge
theory, we have managed to apply it also to the Chern-Simons term. We checked
the periodic structure and determined the Chern-Simons density on small
lattices and with L=4,\, 6,\mbox{ and }8 near the
critical region in the SU(2) Higgs model. The data indicate that tunneling is
increased at high temperature.Comment: 7 pages plus 4 PS figure
phi-fourth model on a circle
The four dimensional critical scalar theory at equilibrium with a thermal
bath at temperature is considered. The thermal equilibrium state is labeled
by the winding number of the vacua around the compact imaginary-time
direction which compactification radius is 1/T. The effective action for zero
modes is a three dimensional scalar theory in which the mass of the
the scalar field is proportional to resembling the Kaluza-Klein
dimensional reduction. Similar results are obtained for the theory at zero
temperature but in a one-dimensional potential well. Since parity is violated
by the vacua with odd vacuum number , in such cases there is also a cubic
term in the effective potential. The -term contribution to the vacuum
shift at one-loop is of the same order of the contribution from the
-term in terms of the coupling constant of the four dimensional theory
but becomes negligible as tends to infinity. Finally, the relation between
the scalar classical vacua and the corresponding SU(2) instantons on
in the 't Hooft ansatz is studied.Comment: 9 pages, revtex4, to appear in Phys.Lett.
The scalar glueball spectrum
We discuss scenarios for scalar glueballs using arguments based on sum rules,
spectral decomposition, the approximation, the scales of the
strong interaction and the topology of the flux tubes. We analyze the
phenomenological support of those scenarios and their observational
implications. Our investigations hint a rich low lying glueball spectrum.Comment: 11 pages: New title, figure, table and a more detailed comparison
with experiment
Baryons in QCD_{AS} at Large N_c: A Roundabout Approach
QCD_{AS}, a variant of large N_c QCD in which quarks transform under the
color two-index antisymmetric representation, reduces to standard QCD at N_c =
3 and provides an alternative to the usual large N_c extrapolation that uses
fundamental representation quarks. Previous strong plausibility arguments
assert that the QCD_{AS} baryon mass scales as N_c^2; however, the complicated
combinatoric problem associated with quarks carrying two color indices impeded
a complete demonstration. We develop a diagrammatic technique to solve this
problem. The key ingredient is the introduction of an effective multi-gluon
vertex: a "traffic circle" or "roundabout" diagram. We show that arbitrarily
complicated diagrams can be reduced to simple ones with the same leading N_c
scaling using this device, and that the leading contribution to baryon mass
does, in fact, scale as N_c^2.Comment: 9 pages, 9 pdf figures, ReVTeX with pdflate
Algebraic renormalization of the BF Yang-Mills Theory
We discuss the quantum equivalence, to all orders of perturbation theory,
between the Yang-Mills theory and its first order formulation through a second
rank antisymmetric tensor field. Moreover, the introduction of an additional
nonphysical vector field allows us to interpret the Yang-Mills theory as a kind
of perturbation of the topological BF model.Comment: 14 pages, some references and acknowledgments added, version to
appear in Phys.Lett.
Elaborations on the String Dual to N=1 SQCD
In this paper we make further refinements to the duality proposed between N=1
SQCD and certain string (supergravity plus branes) backgrounds, working in the
regime of comparable large number of colors and flavors. Using the string
theory solutions, we predict different field theory observables and phenomena
like Seiberg duality, gauge coupling and its running, the behavior of Wilson
and 't Hooft loops, anomalous dimensions of the quark superfields, quartic
superpotential coupling and its running, continuous and discrete anomaly
matching. We also give evidence for the smooth interpolation between higgsed
and confining vacua. We provide several matchings between field theory and
string theory computations.Comment: 44 pages, 6 figures. References added, minor rewritings, published
versio
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