11,591 research outputs found
Vector Boson Pair Production and Trilinear Gauge Boson Couplings - Results From the Tevatron
Direct measurements of vector boson pair production processes and trilinear
gauge boson couplings have been conducted by the CDF and DO Collaborations.
Preliminary results from searches for anomalous WW/WZ->muon-neutrino-jet-jet
and WZ->e-e-e-neutrino production are presented. 95% CL anomalous coupling
limits from previously published DO results are -0.20 < lambda < 0.20 (Delta
kappa=0) and -0.30 < Delta kappa < 0.43 (lambda=0) for Lambda=2000 GeV where
the WWgamma couplings are assumed to equal the WWZ couplings. Combined DO + LEP
experiment anomalous coupling limits are presented for the first time. 95% CL
limits are -0.16<lambda(gamma)< 0.10 (Delta kappa=0) and -0.15 < Delta
kappa(gamma) < 0.41 (lambda=0) under the assumption that the couplings are
related by the ``HISZ'' constraints. 95% CL anomalous ZZg and Zgg coupling
limits from DO are |h(30)^Z|<0.36 (h(40)^Z=0) and |h(40)^Z|<0.05 (h(30)^Z=0)
for Lambda=750 GeV. CDF reports the first observation of a ZZ event. Prospects
for Run II are discussed.Comment: Submitted to the proceedings of ICHEP 98 XXIX International
Conference on High Energy Physics, UBC, Vancouver, B.C., Canada, July 23-29,
1998. 6 page
Critical behaviour of three-dimensional Ising ferromagnets at imperfect surfaces: Bounds on the surface critical exponent
The critical behaviour of three-dimensional semi-infinite Ising ferromagnets
at planar surfaces with (i) random surface-bond disorder or (ii) a terrace of
monatomic height and macroscopic size is considered. The
Griffiths-Kelly-Sherman correlation inequalities are shown to impose
constraints on the order-parameter density at the surface, which yield upper
and lower bounds for the surface critical exponent . If the surface
bonds do not exceed the threshold for supercritical enhancement of the pure
system, these bounds force to take the value of the
latter system's ordinary transition. This explains the robustness of
to such surface imperfections observed in recent Monte Carlo
simulations.Comment: Latex, 4 pages, uses Revtex stylefiles, no figures, accepted EPJB
version, only minor additions and cosmetic change
Energy Momentum Tensor in Conformal Field Theories Near a Boundary
The requirements of conformal invariance for the two point function of the
energy momentum tensor in the neighbourhood of a plane boundary are
investigated, restricting the conformal group to those transformations leaving
the boundary invariant. It is shown that the general solution may contain an
arbitrary function of a single conformally invariant variable , except in
dimension 2. The functional dependence on is determined for free scalar and
fermion fields in arbitrary dimension and also to leading order in the
\vep expansion about for the non Gaussian fixed point in
theory. The two point correlation function of the energy momentum tensor and a
scalar field is also shown to have a unique expression in terms of and the
overall coefficient is determined by the operator product expansion. The energy
momentum tensor on a general curved manifold is further discussed by
considering variations of the metric. In the presence of a boundary this
procedure naturally defines extra boundary operators. By considering
diffeomorphisms these are related to components of the energy momentum tensor
on the boundary. The implications of Weyl invariance in this framework are also
derived.Comment: 22 pages, TeX with epsf.tex, DAMTP/93-1. (original uuencoded file was
corrupted enroute - resubmitted version has uuencoded figures pasted to the
ended of the Plain TeX file
Renormalized field theory and particle density profile in driven diffusive systems with open boundaries
We investigate the density profile in a driven diffusive system caused by a
plane particle source perpendicular to the driving force. Focussing on the case
of critical bulk density we use a field theoretic renormalization
group approach to calculate the density as a function of the distance
from the particle source at first order in (: spatial
dimension). For we find reasonable agreement with the exact solution
recently obtained for the asymmetric exclusion model. Logarithmic corrections
to the mean field profile are computed for with the result for .Comment: 32 pages, RevTex, 4 Postscript figures, to appear in Phys. Rev.
Boundary critical behaviour at -axial Lifshitz points: the special transition for the case of a surface plane parallel to the modulation axes
The critical behaviour of -dimensional semi-infinite systems with
-component order parameter is studied at an -axial bulk
Lifshitz point whose wave-vector instability is isotropic in an -dimensional
subspace of . Field-theoretic renormalization group methods are
utilised to examine the special surface transition in the case where the
potential modulation axes, with , are parallel to the surface.
The resulting scaling laws for the surface critical indices are given. The
surface critical exponent , the surface crossover exponent
and related ones are determined to first order in
\epsilon=4+\case{m}{2}-d. Unlike the bulk critical exponents and the surface
critical exponents of the ordinary transition, is -dependent already
at first order in . The \Or(\epsilon) term of is
found to vanish, which implies that the difference of and
the bulk exponent is of order .Comment: 21 pages, one figure included as eps file, uses IOP style file
Dynamic surface scaling behavior of isotropic Heisenberg ferromagnets
The effects of free surfaces on the dynamic critical behavior of isotropic
Heisenberg ferromagnets are studied via phenomenological scaling theory,
field-theoretic renormalization group tools, and high-precision computer
simulations. An appropriate semi-infinite extension of the stochastic model J
is constructed, the boundary terms of the associated dynamic field theory are
identified, its renormalization in d <= 6 dimensions is clarified, and the
boundary conditions it satisfies are given. Scaling laws are derived which
relate the critical indices of the dynamic and static infrared singularities of
surface quantities to familiar static bulk and surface exponents. Accurate
computer-simulation data are presented for the dynamic surface structure
factor; these are in conformity with the predicted scaling behavior and could
be checked by appropriate scattering experiments.Comment: 9 pages, 2 figure
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