3,495 research outputs found
Complex Probabilities on R^N as Real Probabilities on C^N and an Application to Path Integrals
We establish a necessary and sufficient condition for averages over complex
valued weight functions on R^N to be represented as statistical averages over
real, non-negative probability weights on C^N. Using this result, we show that
many path-integrals for time-ordered expectation values of bosonic degrees of
freedom in real-valued time can be expressed as statistical averages over
ensembles of paths with complex-valued coordinates, and then speculate on
possible consequences of this result for the relation between quantum and
classical mechanics.Comment: 4 pages, 0 figure
Complementarity and Chiral Fermions in SU(2) gauge Theories
Complementarity - the absence of a phase boundary separating the Higgs and
confinement phases of a gauge theory - can be violated by the addition of
chiral fermions. We utilize chiral symmetry violating fermion correlators such
as \langle \bps \psi \rangle as order parameters to investigate this issue.
Using inequalities similar to those of Vafa-Witten and Weingarten, we show that
SU(2) gauge theories with Higgs and fermion fields in the fundamental
representation exhibit chiral symmetry breaking in the confined phase and
therefore do {\it not} lead to massless composite fermions. We discuss the
implications for the Abbott-Farhi strongly interacting standard model.Comment: 10 pages, HUTP-92-A047, 2 figures not include
Some New/Old Approaches to QCD
This is a talk delivered at the Meeting on Integrable Quantum Field Theories,
Villa Olmo and at STRINGS 1992, Rome, September 1992. I discuss some recent
attempts to revive two old ideas regarding an analytic approach to QCD-the
development of a string representation of the theory and the large N limit of
QCD.Comment: 20 page
Chiral Symmetry Breaking without Bilinear Condensates, Unbroken Axial Z_N Symmetry, and Exact QCD Inequalities
An alternative pattern of the chiral symmetry breaking, suggested recently by
Stern, is investigated. It could be self-consistent provided that the chiral
symmetry is broken spontaneously down to rather than to . The discrete axial then
would play a custodial role preventing the quark bilinears from condensation.
It is shown that this pattern of the chiral symmetry breaking is ruled out in
QCD by exact inequalities. It is not ruled out, however, in other gauge
theories with scalar quarks and/or Yukawa couplings.Comment: 9 pages, Latex, clarifying comments and several references adde
New Glueball-Meson Mass Relations
Using the ``glueball dominance'' picture of the mixing between q\bar{q}
mesons of different hidden flavors, we establish new glueball-meson mass
relations which serve as a basis for glueball spectral systematics. For the
tensor glueball mass 2.3\pm 0.1 GeV used as an input parameter, these relations
predict the following glueball masses: M(0^{++})\simeq 1.65\pm 0.05 GeV,
M(1^{--})\simeq 3.2\pm 0.2 GeV, M(2^{-+})\simeq 2.95\pm 0.15 GeV,
M(3^{--})\simeq 2.8\pm 0.15 GeV. We briefly discuss the failure of such
relations for the pseudoscalar sector. Our results are consistent with
(quasi)-linear Regge trajectories for glueballs with slope \simeq 0.3\pm 0.1
GeV^{-2}.Comment: Extensive revision including response to comments received, value of
glueball Regge slope, and a consideration of radial excitations. 14 pages,
LaTe
Baryon Structure and the Chiral Symmetry of QCD
Beyond the spontaneous chiral symmetry breaking scale light and strange
baryons should be considered as systems of three constituent quarks with an
effective confining interaction and a chiral interaction that is mediated by
the octet of Goldstone bosons (pseudoscalar mesons) between the constituent
quarks.Comment: Lecture given at the 35. Universit\"atswochen f\"ur Kern- und
Teilchenphysik, Schladming, Austria, March 1996 (Perturbative and
Nonperturbative Aspects of Quantum Field Theory, ed. by H. Latal and W.
Schweiger, Springer 1996). Paper (23 pages) with 2 figures and the required
macro lamuphy
Positive Parity Scalar Mesons in the 1-2 GeV Mass Range
Based on the observation that K_0(1430) is lighter than its SU_3 counterpart,
a_0(1450), we examine the possibility that these particles, together with
f_0(1370), f_0(1500) and f_0(1710), fill a tetraquark recurrence of the sub-GeV
0^{++} nonet mixed with a glueball state. We find the picture to be consistent
with the known data about the three f_0 resonances, more than the q-qbar
hypothesis. Conventional spin-orbit coupling suggests the q-qbar, P-wave, nonet
to lie around 1200 MeV. We review possible experimental indications of a scalar
isovector resonance at 1.29 GeV, first observed by OBELIX in p-pbar
annihilation.Comment: 12 pages, 9 figures. Extended version. References added. Results and
conclusions unchange
Eta' Mass and Chiral Symmetry Breaking at Large Nc and Nf
We propose a method for implementing the large-Nc, large-Nf limit of QCD at
the effective Lagrangian level. Depending on the value of the ratio Nf/Nc,
different patterns of chiral symmetry breaking can arise, leading in particular
to different behaviors of the eta-prime mass in the combined large-N limit.Comment: revtex 12 pages, one postscript figur
Speeding up finite step-size updating of full QCD on the lattice
We propose various improvements of finite step-size updating for full QCD on
the lattice that might turn finite step-size updating into a viable alternative
to the hybrid Monte Carlo algorithm. These improvements are noise reduction of
the noisy estimator of the fermion determinant, unbiased inclusion of the
hopping parameter expansion and a multi-level Metropolis scheme. First
numerical tests are performed for the 2 dimensional Schwinger model with two
flavours of Wilson fermions and for QCD two flavours of Wilson fermions and
Schr"odinger functional boundary conditions.Comment: 22 pages, 1 figur
Masses of the physical mesons from an effective QCD--Hamiltonian
The front form Hamiltonian for quantum chromodynamics, reduced to an
effective Hamiltonian acting only in the space, is solved
approximately. After coordinate transformation to usual momentum space and
Fourier transformation to configuration space a second order differential
equation is derived. This retarded Schr\"odinger equation is solved by
variational methods and semi-analytical expressions for the masses of all 30
pseudoscalar and vector mesons are derived. In view of the direct relation to
quantum chromdynamics without free parameter, the agreement with experiment is
remarkable, but the approximation scheme is not adequate for the mesons with
one up or down quark. The crucial point is the use of a running coupling
constant , in a manner similar but not equal to the one of
Richardson in the equal usual-time quantization. Its value is fixed at the Z
mass and the 5 flavor quark masses are determined by a fit to the vector meson
quarkonia.Comment: 18 pages, 4 Postscript figure
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