548 research outputs found
Deep inelastic lepton-hadron scattering as a test of perturbative QCD
Exploration of the small kinematic region by the HERA experiments led to
a revival of some models which existed before the advent of Quantum Chromo
Dynamics (QCD) as the theory of the strong interactions. Predictions of these
models for the deep inelastic structure functions are compared with those given
by QCD. Future experiments will concentrate on the large -region and we will
discuss some issues which are important for the test of QCD. In particular we
emphasize the next-to-next-to-leading (NNLO) order analysis of the structure
functions and the determination of the strong coupling constant . We
also make some critical remarks about the relevance of so called large
corrections in the small and large -region.Comment: 15 pages, LaTeX. To appear in the proceedings of the workshop DIS99,
DESY-Zeuthen, Germany, April 19-23, 1999. To be published in Nucl. Phys.
Proc. Suppl.
Equidistribution of zeros of holomorphic sections in the non compact setting
We consider N-tensor powers of a positive Hermitian line bundle L over a
non-compact complex manifold X. In the compact case, B. Shiffman and S.
Zelditch proved that the zeros of random sections become asymptotically
uniformly distributed with respect to the natural measure coming from the
curvature of L, as N tends to infinity. Under certain boundedness assumptions
on the curvature of the canonical line bundle of X and on the Chern form of L
we prove a non-compact version of this result. We give various applications,
including the limiting distribution of zeros of cusp forms with respect to the
principal congruence subgroups of SL2(Z) and to the hyperbolic measure, the
higher dimensional case of arithmetic quotients and the case of orthogonal
polynomials with weights at infinity. We also give estimates for the speed of
convergence of the currents of integration on the zero-divisors.Comment: 25 pages; v.2 is a final update to agree with the published pape
Theory of Coexistence of Superconductivity and Ferroelectricity : A Dynamical Symmetry Model
We propose and investigate a model for the coexistence of Superconductivity
(SC) and Ferroelectricity (FE) based on the dynamical symmetries for
the pseudo-spin SC sector, for the displaced oscillator FE sector, and
for the composite system. We assume a minimal
symmetry-allowed coupling, and simplify the hamiltonian using a double mean
field approximation (DMFA). A variational coherent state (VCS) trial
wave-function is used for the ground state: the energy, and the relevant order
parameters for SC and FE are obtained. For positive sign of the SC-FE coupling
coefficient, a non-zero value of either order parameter can suppress the other
(FE polarization suppresses SC and vice versa). This gives some support to
"Matthias' Conjecture" [1964], that SC and FE tend to be mutually exclusive.
For such a Ferroelectric Superconductor we predict: a) the SC gap
(and ) will increase with increasing applied pressure when pressure
quenches FE as in many ferroelectrics, and b) the FE polarization will increase
with increaesing magnetic field up to . The last result is equivalent to
the prediction of a new type of Magneto-Electric Effect in a coexistent SC-FE
material. Some discussion will be given of the relation of these results to the
cuprate superconductors.Comment: 46 page
Search for the standard model Higgs boson in tau final states
We present a search for the standard model Higgs boson using hadronically
decaying tau leptons, in 1 inverse femtobarn of data collected with the D0
detector at the Fermilab Tevatron ppbar collider. We select two final states:
tau plus missing transverse energy and b jets, and tau+ tau- plus jets. These
final states are sensitive to a combination of associated W/Z boson plus Higgs
boson, vector boson fusion and gluon-gluon fusion production processes. The
observed ratio of the combined limit on the Higgs production cross section at
the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of
115 GeV.Comment: publication versio
Search for W' bosons decaying to an electron and a neutrino with the D0 detector
This Letter describes the search for a new heavy charged gauge boson W'
decaying into an electron and a neutrino. The data were collected with the D0
detector at the Fermilab Tevatron proton-antiproton Collider at a
center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity
of about 1 inverse femtobarn. Lacking any significant excess in the data in
comparison with known processes, an upper limit is set on the production cross
section times branching fraction, and a W' boson with mass below 1.00 TeV can
be excluded at the 95% C.L., assuming standard-model-like couplings to
fermions. This result significantly improves upon previous limits, and is the
most stringent to date.Comment: submitted to Phys. Rev. Let
Search for a scalar or vector particle decaying into Zgamma in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for a narrow scalar or vector resonance decaying into
Zgamma with a subsequent Z decay into a pair of electrons or muons. The data
for this search were collected with the D0 detector at the Fermilab Tevatron
ppbar collider at a center of mass energy sqrt(s) = 1.96 TeV. Using 1.1 (1.0)
fb-1 of data, we observe 49 (50) candidate events in the electron (muon)
channel, in good agreement with the standard model prediction. From the
combination of both channels, we derive 95% C.L. upper limits on the cross
section times branching fraction (sigma x B) into Zgamma. These limits range
from 0.19 (0.20) pb for a scalar (vector) resonance mass of 600 GeV/c^2 to 2.5
(3.1) pb for a mass of 140 GeV/c^2.Comment: Published by Phys. Lett.
Measurement of the ratios of the Z/G* + >= n jet production cross sections to the total inclusive Z/G* cross section in ppbar collisions at sqrt(s) = 1.96 TeV
We present a study of events with Z bosons and jets produced at the Fermilab
Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV.
The data sample consists of nearly 14,000 Z/G* -> e+e- candidates corresponding
to the integrated luminosity of 0.4 fb-1 collected using the D0 detector.
Ratios of the Z/G* + >= n jet cross sections to the total inclusive Z/G* cross
section have been measured for n = 1 to 4 jet events. Our measurements are
found to be in good agreement with a next-to-leading order QCD calculation and
with a tree-level QCD prediction with parton shower simulation and
hadronization.Comment: 7 pages, 2 figures, slightly modified, submitted to Phys. Lett.
On the Drell-Levy-Yan Relation to
We study the validity of a relation by Drell, Levy and Yan (DLY) connecting
the deep inelastic structure (DIS) functions and the single-particle
fragmentation functions in e^+e^- annihilation which are defined in the
spacelike (q^20) regions respectively. Here q denotes the
momentum of the virtual photon exchanged in the deep inelastic scattering
process or the annihilation process. An extension of the DLY-relation, which
originally was only derived in the scaling parton model, to all orders in QCD
leads to a connection between the two evolution kernels determining the
q^2-dependence of the DIS structure functions and the fragmentation functions
respectively. In relation to this we derive the transformation relations
between the space-and time-like splitting functions up to next-to-leading order
(NLO) and the coefficient functions up to NNLO both for unpolarized and
polarized scattering. It is shown that the evolution kernels describing the
combined singlet evolution for the structure functions F_2(x,Q^2), F_L(x,Q^2)
where Q^2=|q^2| or and the
corresponding fragmentation functions satisfy the DLY relation up to
next-to-leading order. We also comment on a relation proposed by Gribov and
Lipatov.Comment: 33 pages LATEX, 1 style fil
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