36 research outputs found
On the analytical approximation to the GLAP evolution at small x and moderate Q^2
Comparing the numerically evaluated solution to the leading order GLAP
equations with its analytical small-x approximation we have found that in the
domain covered by a large fraction of the HERA data the analytic approximation
has to be augmented by the formally non-leading term which has been usually
neglected. The corrected formula fits the data much better and provides a
natural explanation of some of the deviations from the scaling
observed in the HERA kinematical range.Comment: LaTeX, 13 pages including 6 figures, figure 5 replaced, to appear in
Phys. Lett.
Quark spin coupling in baryons - revisited
A direct connection can be made between mixing angles in negative parity
baryons and the spin coupling of constituent quarks. The mixing angles do not
depend on spectral data. These angles are recalculated for gluon exchange and
pion exchange between quarks. For pion exchange the results of Glozman and
Riska are corrected. The experimental data on mixing are very similar to those
derived from gluon exchange but substantially different from the values
obtained for pion exchange.Comment: 10 pages, RevTex; a sign error is corrected, spin-orbit results are
include
The QCD Coupling Constant
This paper presents a summary of the current status of determinations of the
strong coupling constant alpha_s. A detailed description of the definition,
scale dependence and inherent theoretical ambiguities is given. The various
physical processes that can be used to determine alpha_s are reviewed and
attention is given to the uncertainties, both theoretical and experimental.Comment: 56 page
Moments of the Proton F2 Structure Function at Low Q2
The Q^2 dependence of inclusive electron-proton scattering F_2 structure
function data in both the nucleon resonance region and the deep inelastic
region, at momentum transfers below 5 (GeV/c)^2, is investigated. Moments of
F_2 are constructed, down to momentum transfers of Q^2 ~ 0.1 (GeV/c)^2. The
second moment is only slowly varying with Q^2 down to Q^2 ~ 1 (GeV/c)^2, which
is a reflection of duality. Below Q^2 of 1 (GeV/c)^2, the Q^2 dependence of the
moments is predominantly governed by the elastic contribution, whereas the
inelastic channels still seem governed by local duality.Comment: 11 page paper, 1 LaTeX file, 10 postscript figure file
Cartography with Accelerators: Locating Fermions in Extra Dimensions at Future Lepton Colliders
In the model of Arkani-Hamed and Schmaltz the various chiral fermions of the
Standard Model(SM) are localized at different points on a thick wall which
forms an extra dimension. Such a scenario provides a way of understanding the
absence of proton decay and the fermion mass hierarchy in models with extra
dimensions. In this paper we explore the capability of future lepton colliders
to determine the location of these fermions in the extra dimension through
precision measurements of conventional scattering processes both below and on
top of the lowest lying Kaluza-Klein gauge boson resonance. We show that for
some classes of models the locations of these fermions can be very precisely
determined while in others only their relative positions can be well measured.Comment: 32 pages, 10 figs, LaTe
Radiative decays of decuplet hyperons
We calculate the radiative decay widths of decuplet hyperons in a chiral
constituent quark model including electromagnetic exchange currents between
quarks. Exchange currents contribute significantly to the E2 transition
amplitude, while they largely cancel for the M1 transition amplitude.
Strangeness suppression of the radiative hyperon decays is found to be weakened
by exchange currents. Differences and similarities between our results and
other recent model predictions are discussed.Comment: 11 pages, 1 eps figure, revtex, accepted for publication in Phys.
Rev.
Moduli in Exceptional SUSY Gauge Theories
The low energy structures of N=1 supersymmetric models with E_6, F_4 and E_7
gauge groups and fundamental irrep matter contents are studied herein. We
identify sets of gauge invariant composites which label all flat directions in
the confining/Higgs phases of these theories. The impossibility of mapping
several of these primary operators rules out previously conjectured exceptional
self duals reported in the literature.Comment: 20 pages, harvmac and tables macro
Gravity and Matter in Extra Dimensions
In this paper, we derive from the viewpoint of the effective 4D theory the
interaction terms between linearized gravity propagating in N>= 2 large extra
dimensions and matter propagating into one extra dimension. This generalizes
known results for the interactions between gravity and 4D matter in ADD-type
models. Although we assume that matter is described by an Universal Extra
Dimensions (UED) scenario (with all fields propagating into the fifth
dimension), we present our results in a general form that can be easily adapted
to various other scenarios of matter distribution. We then apply our results to
the UED model on a fat brane and consider some phenomenological applications.
Among these are the computation of the gravitational decay widths of the matter
KK excitations and the effect the width of the brane has on the interactions of
gravity with Standard Model particles. We also estimate the cross-section for
producing single KK excitations at colliders through KK number-violating
gravitational interaction.Comment: 21 pages, 6 figures, Late
Quark-hadron duality in a relativistic, confining model
Quark-hadron duality is an interesting and potentially very useful
phenomenon, as it relates the properly averaged hadronic data to a perturbative
QCD result in some kinematic regions. While duality is well established
experimentally, our current theoretical understanding is still incomplete. We
employ a simple model to qualitatively reproduce all the features of
Bloom-Gilman duality as seen in electron scattering. In particular, we address
the role of relativity, give an explicit analytic proof of the equality of the
hadronic and partonic scaling curves, and show how the transition from coherent
to incoherent scattering takes place.Comment: This paper is dedicated to the memory of our collaborator Nathan
Isgur. (34 pages, 13 figures
Non-perturbative Gluons and Pseudoscalar Mesons in Baryon Spectroscopy
We study baryon spectroscopy including the effects of pseudoscalar meson
exchange and one gluon exchange potentials between quarks, governed by
. The non-perturbative, hyperspherical method calculations show that
one can obtain a good description of the data by using a quark-meson coupling
constant that is compatible with the measured pion-nucleon coupling constant,
and a reasonably small value of .Comment: 12 pages; Submitted to Phys. Rev. C. Rapid Communication