150 research outputs found
Domain walls in supersymmetric QCD: from weak to strong coupling
We consider domain walls that appear in supersymmetric QCD with Nf < Nc
massive flavours. In particular, for 2 Nf < Nc we explicitly construct the
domain walls that interpolate between vacua labeled by i and (i+ N_f). We show
that these solutions are Bogomol'nyi-Prasad-Sommerfield (BPS) saturated for any
value of the mass of the matter fields. This fact allows us to evaluate the
large mass limit of these domain walls. We comment on the relevance of these
solutions for supersymmetric gluodynamics.Comment: 4 pages, 4 figures, LaTex, uses psfig.st
BPS Saturated Vacua Interpolation along One Compact Dimension
A class of generalized Wess-Zumino models with distinct vacua is
investigated. These models allow for BPS saturated vacua interpolation along
one compact spatial dimension. The properties of these interpolations are
studied.Comment: 8 pages, 4 figure
Exact Results in Gauge Theories: Putting Supersymmetry to Work. The 1999 Sakurai Prize Lecture
Powerful methods based on supersymmetry allow one to find exact solutions to
certain problems in strong coupling gauge theories. The inception of some of
these methods (holomorphy in the gauge coupling and other chiral parameters, in
conjunction with instanton calculations) dates back to the 1980's. I describe
the early exact results -- the calculation of the beta function and the gluino
condensate -- and their impact on the subsequent developments. A brief
discussion of the recent breakthrough discoveries where these results play a
role is given.Comment: Based on the talk at the Centennial Meeting of The American Physical
Society, March 20-26, Atlanta, GA. LaTex (uses sprocl.sty), 36 pages, 5 eps
figures include
Functional Approach to Stochastic Inflation
We propose functional approach to the stochastic inflationary universe
dynamics. It is based on path integral representation of the solution to the
differential equation for the scalar field probability distribution. In the
saddle-point approximation scalar field probability distributions of various
type are derived and the statistics of the inflationary-history-dependent
functionals is developed.Comment: 20 pages, Preprint BROWN-HET-960, uses phyzz
Analytical Heavy Quark Expansion in the 't Hooft Model
We present a number of exact relations for the heavy quark limit and develop
an analytical 1/m_Q expansion for heavy mesons in the 't Hooft model. Among the
new results are relation 3\mu_\pi^2=\bar\Lambda^2 - m_{sp}^2+\beta^2, 1/m_Q
corrections to the decay constants, to the kinetic expectation values and
1/m_Q^2 nonperturbative corrections to the B->D amplitude at zero recoil. The
properties of the IW functions are addressed and the small velocity sum rules
are verified.Comment: 22 pages, plain LaTeX (no figures
Precision Studies of Duality in the 't Hooft Model
We address numerical aspects of local quark-hadron duality using the example
of the exactly solvable 't Hooft model, two-dimensional QCD with N_c -->
infinity. The primary focus of these studies is total semileptonic decay widths
relevant for extracting |V_{cb}| and |V_{ub}|. We compare the exact
channel-by-channel sum of exclusive modes to the corresponding rates obtained
in the standard 1/m_Q expansion arising from the Operator Product Expansion. An
impressive agreement sets in unexpectedly early, immediately after the
threshold for the first hadronic excitation in the final state. Yet even at
higher energy release it is possible to discern the seeds of duality-violating
oscillations. We find the ``Small Velocity'' sum rules to be exceptionally well
saturated already by the first excited state. We also obtain a convincing
degree of duality in the differential distributions and in an analogue of
R_{e^+e^-}(s). Finally, we discuss possible lessons for semileptonic decays of
actual heavy quarks in QCD.Comment: 45 pages, 16 eps figures include
Hanbury Brown-Twiss interferometry and second-order correlations of inflaton quanta
The quantum theory of optical coherence is applied to the scrutiny of the
statistical properties of the relic inflaton quanta. After adapting the
description of the quantized scalar and tensor modes of the geometry to the
analysis of intensity correlations, the normalized degrees of first-order and
second-order coherence are computed in the concordance paradigm and are shown
to encode faithfully the statistical properties of the initial quantum state.
The strongly bunched curvature phonons are not only super-Poissonian but also
super-chaotic. Testable inequalities are derived in the limit of large angular
scales and can be physically interpreted in the light of the tenets of Hanbury
Brown-Twiss interferometry. The quantum mechanical results are compared and
contrasted with different situations including the one where intensity
correlations are the result of a classical stochastic process. The survival of
second-order correlations (not necessarily related to the purity of the initial
quantum state) is addressed by defining a generalized ensemble where
super-Poissonian statistics is an intrinsic property of the density matrix and
turns out to be associated with finite volume effects which are expected to
vanish in the thermodynamic limit.Comment: 42 pages, 3 included figures; corrected typos; to appear in Physical
Review
Domain Walls and Decay Rate of the Excited Vacua in the Large N Yang-Mills Theory
In the (non-supersymmetric) Yang-Mills theory in the large N limit there
exists an infinite set of non-degenerate vacua. The distinct vacua are
separated by domain walls whose tension determines the decay rate of the false
vacua. I discuss the phenomenon from a field-theoretic point of view, starting
from supersymmetric gluodynamics and then breaking supersymmetry, by
introducing a gluino mass. By combining previously known results, the decay
rate of the excited vacua is estimated, \Gamma \sim \exp (-const \times N^4).
The fourth power of N in the exponent is a consequence of the fact that the
wall tension is proportional to N.Comment: Plain Latex, 6 pages, no figure
Conformal Invariance and Cosmic Background Radiation
The spectrum and statistics of the cosmic microwave background radiation
(CMBR) are investigated under the hypothesis that scale invariance of the
primordial density fluctuations should be promoted to full conformal
invariance. As in the theory of critical phenomena, this hypothesis leads in
general to deviations from naive scaling. The spectral index of the two-point
function of density fluctuations is given in terms of the quantum trace anomaly
and is greater than one, leading to less power at large distance scales than a
strict Harrison-Zel'dovich spectrum. Conformal invariance also implies
non-gaussian statistics for the higher point correlations and in particular, it
completely determines the large angular dependence of the three-point
correlations of the CMBR.Comment: 4 pages, Revtex file, uuencoded with one figur
Lessons from : Vacuum structure, Asymptotic Series, Instantons and all that
We discuss two dimensional with fermions in the
fundamental as well as adjoint representation. We find factorial growth in the coefficients of
the large order perturbative expansion. We argue that this behavior is related
to classical solutions of the theory, instantons, thus it has nonperturbative
origin. Phenomenologically such a growth is related to highly excited states in
the spectrum. We also analyze the heavy-light quark system within
operator product expansion (which it turns out to be an asymptotic series).
Some vacuum condensates \la\bar{q}(x_{\mu}D_{\mu})^{2n}q\ra\sim (x^2)^n\cdot
n! which are responsible for this factorial growth are also discussed. We
formulate some general puzzles which are not specific for 2D physics, but are
inevitable features of any asymptotic expansion. We resolve these apparent
puzzles within and we speculate that analogous puzzles might occur in
real 4-dimensional QCD as well.Comment: latex, 26 pages. A final version to appear in Phys. Rev.
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