6,308 research outputs found
From Super-Yang-Mills Theory to QCD: Planar Equivalence and its Implications
We review and extend our recent work on the planar (large N) equivalence
between gauge theories with varying degree of supersymmetry. The main emphasis
is made on the planar equivalence between N=1 gluodynamics (super-Yang-Mills
theory) and a non-supersymmetric "orientifold field theory." We outline an
"orientifold" large N expansion, analyze its possible phenomenological
consequences in one-flavor massless QCD, and make a first attempt at extending
the correspondence to three massless flavors. An analytic calculation of the
quark condensate in one-flavor QCD starting from the gluino condensate in N=1
gluodynamics is thoroughly discussed. We also comment on a planar equivalence
involving N=2 supersymmetry, on "chiral rings" in non-supersymmetric theories,
and on the origin of planar equivalence from an underlying, non-tachyonic
type-0 string theory. Finally, possible further directions of investigation,
such as the gauge/gravity correspondence in large-N orientifold field theory,
are briefly discussed.Comment: 106 pages, LaTex. 15 figures. v2:minor changes, refs. added. To be
published in the Ian Kogan Memorial Collection "From Fields to Strings:
Circumnavigating Theoretical Physics," World Scientific, 200
Manifestly Invariant Approach to Space-Time Dependent String Vacua
An symmetry of the manifold of string vacua that do not depend on
(out of ) space-time coordinates has been recently identified. Here we
write down, for , the low energy equations of motion and their general
solution in a manifestly -invariant form, pointing out an amusing
similarity with the renormalization group framework. Previously considered
cosmological and black hole solutions are recovered as particular examples.Comment: 9 page
Pre-Big Bang Cosmology and Quantum Fluctuations
The quantum fluctuations of a homogeneous, isotropic, open pre-big bang model
are discussed. By solving exactly the equations for tensor and scalar
perturbations we find that particle production is negligible during the
perturbative Pre-Big Bang phase.Comment: 4 pages, use esprc2.sty. Talk given at the 3rd Meeting on Constrained
Dynamics and Quantum Gravity (QG 99), Villasimius, Sardinia, Italy, 14-18 Sep
199
Exact Results in Non-Supersymmetric Large N Orientifold Field Theories
We consider non-supersymmetric large N orientifold field theories.
Specifically, we discuss a gauge theory with a Dirac fermion in the
anti-symmetric tensor representation. We argue that, at large N and in a large
part of its bosonic sector, this theory is non-perturbatively equivalent to N=1
SYM, so that exact results established in the latter (parent) theory also hold
in the daughter orientifold theory. In particular, the non-supersymmetric
theory has an exactly calculable bifermion condensate, exactly degenerate
parity doublets, and a vanishing cosmological constant (all this to leading
order in 1/N).Comment: 18 pages, Latex. 3 figures. v2,v3: minor changes, refs. added, to
appear in Nucl.Phys.
The Price of an Exact, Gauge-Invariant RG-Flow Equation
We combine old ideas about exact renormalization-group-flow (RGF) equations
with the Vilkovisky-De Witt (VDW) approach to reparametrization invariant
effective actions and arrive at a new, exact, gauge-invariant RGF equation. The
price to be paid for such a result is that both the action and the RGF equation
depend explicitly upon the base point (in field space) needed for the VDW
construction. We briefly discuss the complications originating from this fact
and possible ways to overcome them.Comment: 12 pages. To appear in Phys. Lett.
Quantum Fluctuations in Open Pre-Big Bang Cosmology
We solve exactly the (linear order) equations for tensor and scalar
perturbations over the homogeneous, isotropic, open pre-big bang model recently
discussed by several authors. We find that the parametric amplification of
vacuum fluctuations (i.e. particle production) remains negligible throughout
the perturbative pre-big bang phase.Comment: 12 pages, ReVTeX, Discussion of relation to Ref.[8] modifie
Quantum Inhomogeneities in String Cosmology
Within two specific string cosmology scenarios --differing in the way the
pre- and post-big bang phases are joined-- we compute the size and spectral
slope of various types of cosmologically amplified quantum fluctuations that
arise in generic compactifications of heterotic string theory. By further
imposing that these perturbations become the dominant source of energy at the
onset of the radiation era, we obtain physical bounds on the background's
moduli, and discuss the conditions under which both a (quasi-) scale-invariant
spectrum of axionic perturbations and sufficiently large seeds for the galactic
magnetic fields are generated. We also point out a potential problem with
achieving the exit to the radiation era when the string coupling is near its
present value.Comment: 30 pages, RevteX, epsfig, 5 figure
SUSY Relics in One-Flavor QCD from a New 1/N Expansion
We suggest a new large-N_c limit for multi flavor QCD. Since fundamental and
two-index antisymmetric representations are equivalent in SU(3), we have the
option to define SU(N_c) QCD keeping quarks in the latter. We can then define a
new 1/N_c expansion (at fixed number of flavors N_f) that shares appealing
properties with the topological (fixed N_f/N_c) expansion while being more
suitable for theoretical analysis. In particular, for N_f=1, our large-N_c
limit gives a theory that we recently proved to be equivalent, in the bosonic
sector, to N=1 supersymmetric gluodynamics. Using known properties of the
latter, we derive several qualitative and semi-quantitative predictions for
N_f=1 massless QCD which can be easily tested in lattice simulations. Finally,
we comment on possible applications for pure SU(3) Yang-Mills theory and real
QCD.Comment: 4 pages, RevTex. v2: note added at the end of the paper, ref. added.
To appear in Phys.Rev.Let
EVOLUTION OF A STRING NETWORK IN BACKGROUNDS WITH ROLLING HORIZONS
We discuss the temporal variation of the equation of state of a classical
string network, evolving in a background in which the Hubble radius 1/H shrinks
to a minimum and then re-expands to infinity. We also present a method to look
for self-consistent non-vacuum string backgrounds, correponding to the
simultaneous solution of the gravi-dilaton backgrounds equations and of the
string equations of motion.Comment: 19 pages, plain tex, no figures, to appear in "String gravity and
physics at the Planck energy scale" (World Scientific, Singapore, 1995
Black holes from high-energy beam--beam collisions
Using a recent technique, proposed by Eardley and Giddings, we extend their
results to the high-energy collision of two beams of massless particles, i.e.
of two finite-front shock waves. Closed (marginally) trapped surfaces can be
determined analytically in several cases even for collisions at non-vanishing
impact parameter in D\ge 4 space-time dimensions. We are able to confirm and
extend earlier conjectures by Yurtsever, and to deal with arbitrary
axisymmetric profiles, including an amusing case of ``fractal'' beams. We
finally discuss some implications of our results in high-energy experiments and
in cosmology.Comment: 17 pages Revtex, 1 figure, references adde
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