55 research outputs found
Dynamical chiral symmetry breaking and confinement with an infrared-vanishing gluon propagator?
We study a model Dyson-Schwinger equation for the quark propagator closed
using an {\it Ansatz} for the gluon propagator of the form \mbox{} and two {\it Ans\"{a}tze} for the quark-gluon vertex: the
minimal Ball-Chiu and the modified form suggested by Curtis and Pennington.
Using the quark condensate as an order parameter, we find that there is a
critical value of such that the model does not support dynamical chiral
symmetry breaking for . We discuss and apply a confinement test which
suggests that, for all values of , the quark propagator in the model {\bf is
not} confining. Together these results suggest that this Ansatz for the gluon
propagator is inadequate as a model since it does not yield the expected
behaviour of QCD.Comment: 21 Pages including 4 PostScript figures uuencoded at the end of the
file. Replacement: slight changes of wording and emphasis. ADP-93-215/T133,
ANL-PHY-7599-TH-93, FSU-SCRI-93-108, REVTEX 3.
Asymptotic Scaling and Infrared Behavior of the Gluon Propagator
The Landau gauge gluon propagator for the pure gauge theory is evaluated on a
32^3x64 lattice with a physical volume of (3.35^3x6.7)fm^4. Comparison with two
smaller lattices at different lattice spacings allows an assessment of finite
volume and finite lattice spacing errors. Cuts on the data are imposed to
minimize these errors. Scaling of the gluon propagator is verified between
beta=6.0 and beta=6.2. The tensor structure is evaluated and found to be in
good agreement with the Landau gauge form, except at very small momentum
values, where some small finite volume errors persist. A number of functional
forms for the momentum dependence of the propagator are investigated. The form
D(q^2)=D_ir+D_uv, where D_ir(q^2) ~ (q^2+M^2)^-\eta and D_uv is an infrared
regulated one-loop asymptotic form, is found to provide an adequate description
of the data over the entire momentum region studied - thereby bridging the gap
between the infrared confinement region and the ultraviolet asymptotic region.
The best estimate for the exponent \eta is 3.2(+0.1/-0.2)(+0.2/-0.3), where the
first set of errors represents the uncertainty associated with varying the
fitting range, while the second set of errors reflects the variation arising
from different choices of infrared regulator in D_uv. Fixing the form of D_uv,
we find that the mass parameter M is (1020+/-100)MeV.Comment: 37 pages, RevTeX, 16 postscript figures, 7 gif figures. Revised
version accepted for publication in Phys. Rev. D. Model functions and
discussion of asymptotic behaviour modified; all model fits have been redone.
This paper, including postscript version of all figures, can be found at
http://www.physics.adelaide.edu.au/~jskuller/papers
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Letter of intent: a muon to electron conversion experiment at Fermilab
We are writing this letter to express our interest in pursuing an experiment at Fermilab to search for neutrinoless conversion of muons into electrons in the field of a nucleus, which is a lepton flavor-violating (LFV) reaction. The sensitivity goal of this experiment represents an improvement of more than a factor of 10,000 over existing limits. It would provide the most sensitive test of LFV, a unique and essential window on new physics unavailable at the high energy frontier. We present a conceptual scheme that would exploit the existing Fermilab Accumulator and Debuncher rings to generate the required characteristics of the primary proton beam. The proposal requires only modest modifications to the accelerator complex beyond those already planned for the NOvA experiment, with which this experiment would be fully compatible; however, it could also benefit significantly from possible upgrades such as the 'Project X' linac. We include the conceptual design of the muon beam and the experimental apparatus, which use the previously proposed MECO experiment as a starting point
Closing the Light Gluino Window in Supersymmetric Grand Unified Models
We study the light gluino scenario giving special attention to constraints
from the masses of the light CP-even neutral Higgs , the lightest chargino
, and the second lightest neutralino , and from
the decay. We find that minimal supergravity, with
a radiatively broken electroweak symmetry group and universality of scalar and
gaugino masses at the unification scale, is incompatible with the existence of
a light gluino.Comment: 12 pages (plain tex), 1 figure not included, VAND-TH-94-7-R. An error
is corrected. Modifications to the text and the figure are mad
The Standard Model Prediction of the Muon Anomalous Magnetic Moment
This article reviews and updates the Standard Model prediction of the muon
g-2. QED, electroweak and hadronic contributions are presented, and open
questions discussed. The theoretical prediction deviates from the present
experimental value by 2-3 standard deviations, if e+e- annihilation data are
used to evaluate the leading hadronic term.Comment: 30 pages, 8 figures. v2: Updated version to appear in J.Phys.G.
Comments and references added, typo corrected in eq.(17
The Physics of Hadronic Tau Decays
Hadronic tau decays represent a clean laboratory for the precise study of
quantum chromodynamics (QCD). Observables (sum rules) based on the spectral
functions of hadronic tau decays can be related to QCD quark-level calculations
to determine fundamental quantities like the strong coupling constant,
parameters of the chiral Lagrangian, |V_us|, the mass of the strange quark, and
to simultaneously test the concept of quark-hadron duality. Using the best
available measurements and a revisited analysis of the theoretical framework,
the value alpha_s(m_tau) = 0.345 +- 0.004[exp] +- 0.009[theo] is obtained.
Taken together with the determination of alpha_s(m_Z) from the global
electroweak fit, this result leads to the most accurate test of asymptotic
freedom: the value of the logarithmic slope of 1/alpha_s(s) is found to agree
with QCD at a precision of 4%. In another approach, the tau spectral functions
can be used to determine hadronic quantities that, due to the nonperturbative
nature of long-distance QCD, cannot be computed from first principles. An
example for this is the contribution from hadronic vacuum polarization to
loop-dominated processes like the anomalous magnetic moment of the muon. This
article reviews the measurements of nonstrange and strange tau spectral
functions and their phenomenological applications.Comment: 89 pages, 32 figures; final version accepted for publication by
Reviews of Modern Physic
Search for Baryon and Lepton Number Violating Decays of the Lepton
We have searched for five decay modes of the tau lepton that simultaneously
violate lepton and baryon number: tau -> anti-proton gamma, tau -> anti-proton
pi0, tau -> anti-proton eta, tau -> anti-proton 2pi0, and tau -> anti-proton
pi0eta. The data used in the search were collected with the CLEO II detector at
the Cornell Electron Storage Ring (CESR). The integrated luminosity of the data
sample is 4.7 fb^{-1}, corresponding to the production of 4.3 x 10^6 tau+tau-
events. No evidence is found for any of the decays, resulting in much improved
upper limits on the branching fractions for the two-body decays and first upper
limits for the three-body decays.Comment: 8 pages, postscript file also available through
http://w4.lns.cornell.edu/public/CLN
The Muon Magnetic Moment and Supersymmetry
The present review is devoted to the muon magnetic moment and its role in
supersymmetry phenomenology. Analytical results for the leading supersymmetric
one- and two-loop contributions are provided, numerical examples are given and
the dominant tan(beta)sign(mu)/M_SUSY^2 behaviour is qualitatively explained.
The consequences of the Brookhaven measurement are discussed. The 2 sigma
deviation from the Standard Model prediction implies preferred ranges for
supersymmetry parameters, in particular upper and lower mass bounds.
Correlations with other observables from collider physics and cosmology are
reviewed. We give, wherever possible, an intuitive understanding of each result
before providing a detailed discussion.Comment: Topical Review; 54 pages, 18 figure
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