29640694
Parton distributions at small x.
We perform a next-to-leading-order QCD analysis of the recent data for deep-inelastic lepton-nucleon scattering and related processes, in which we pay particular attention to the forms of the parton distributions at very small {ital x}. We discuss in detail, and we incorporate in the analysis, the theoretical QCD results leading to the singular {ital x}{sup {minus}1/2}-type behavior of the gluon and sea-quark distributions, as well as the modifications due to shadowing effects. We find the QCD shadowing corrections are significant for {ital x}{approx lt}10{sup {minus}3} even though the parton distributions are below their saturation limit. We give predictions for the structure functions {ital F}{sub 2} and {ital F}{sub {ital L}} accessible at the DESY {ital ep} collider HERA, and for {ital W} and {ital Z} production up to the energies of the CERN Large Hadron Collider and the Superconducting Super Collider. We discuss the possibility of experiments at these colliders probing the parton distributions in the very-small-{ital x} region.
15108358
Off-diagonal parton distributions and their evolution
We construct off-diagonal parton distributions defined on the interval 0 ≤ X ≤ 1 starting from the off-forward distributions defined by Ji. We emphasize the particular role played by the symmetry relations in the “ERBL-like” region. We find the evolution equations for the off-diagonal distributions which conserve these symmetries. We present numerical results of the evolution, and verify that the analytic asymptotic forms of the parton distributions are reproduced. We also compare the constructed off-diagonal distributions with the non-forward distributions defined by Radyushkin and comment on the singularity structure of the basic amplitude written in terms of the off-diagonal distributions.
117807416
Diffractive deep inelastic scattering
A new approach to the analysis of diffractive deep inelastic data is presented. We show that the collinear factorisation theorem, which holds for diffractive DIS, has important modifications in the sub‐asymptotic HERA regime, which can be quantified by using perturbative QCD. In fact the diffractive parton densities are shown to satisfy an inhomogeneous evolution equation. Moreover it is necessary to include both the gluonic and sea‐quark t‐channel components of the perturbative Pomeron.
126229857
Structure Function Analysis and psi, Jet, W, Z Production: Pinning Down the Gluon
123328618
Proton-proton scattering and the pomeron
Abstract We describe various attempts to fit the data on pp and p p elastic scattering and total cross sections, including the recent ISR data, with a variety of Regge pole and cut models. Only two types of model are able to explain the data over the whole energy range satisfactorily. The simplest of these has no cuts, but a pomeron pole with trajectory α p(0) = 1.06 + 0.25 t , and a non-shrinking “core” term at large | t |. The other has a flat trajectory, α p( t ) = 1.06 for all t , and strong eikonal-model cuts which explain both the shrinkage at low | t |, and the lack of it at larger | t |. We also briefly review various speculations which relate the fact that α p(0) > 1 to the small triple-pomeron coupling.
118665854
Diffraction and correlations at the LHC: definitions and observables
We note that the definition of diffractive events is a matter of convention. We discuss two possible “definitions”: one based on unitarity and the other on Large Rapidity Gaps (LRG) or Pomeron exchange. LRG can also arise from fluctuations and we quantify this effect and some of the related uncertainties. We find care must be taken in extracting the Pomeron contribution from LRG events. We show that long-range correlations in multiplicities can arise from the same multi-Pomeron diagrams that are responsible for LRG events, and we explain how early LHC data can illuminate our understanding of ‘soft’ interactions.
41996012
Stability of systems of three arbitrary charges: General properties.
The stability of systems consisting of a negative charge {minus}{ital q}{sub 1} and two positive charges {ital q}{sub 2} and {ital q}{sub 3} is discussed as a function of the values of the charges {ital q}{sub {ital i}} and of the constituent masses {ital m}{sub {ital i}}. We give general results and list some open questions of interest, which hopefully will stimulate further investigations.
17368592
Raising the unification scale in supersymmetry.
In the minimal supersymmetric standard model, the three gauge couplings appear to unify at a mass scale near 2{times}10{sup 16} GeV. We investigate the possibility that intermediate scale particle thresholds modify the running couplings so as to increase the unification scale. By requiring consistency of this scenario, we derive some constraints on the particle content and locations of the intermediate thresholds. There are remarkably few acceptable solutions with a single cleanly defined intermediate scale far below the unification scale.
33800044
Finite-size and dynamical effects in pair production by an external field.
We evaluate the rate of pair production in a uniform electric field confined to a bounded region in space. Using the Balian-Bloch expansion of Green's functions we obtain explicit expressions for finite-size corrections to Schwinger's formula. The case of a time-dependent boundary, relevant to describe energy deposition by quark-antiquark pair production in ultrarelativistic collisions, is also investigated. We find that finite-size effects are important in nuclear collisions. They decrease when the strength of the chromoelectric field between the nuclei is large. As a result, the rate of energy deposition increases sharply with the mass number {ital A} of the colliding nuclei.
875394
phi4 model near the critical point: The Gaussian variational approximation.
Using the Gaussian variational approximation, we describe the approach to the continuum limit in φ 4 theory in 3+1 space-time dimensions. We study the solutions of the variational equations and their stability and compare our results with those of Monte Carlo calculations on a lattice. The importance of lattice effects is investigated by putting the Gaussian wave functional on a lattice. We find an abrupt decrease of the fourth derivative of the effective potential in the vicinity of the critical point, which is consistent with Monte Carlo calculations. In the continuum limit b→0 + , the renormalized theory shows a broken phase which is found to be asymptotically free, in agreement with the conclusions of Branchina et al
5751474
Implications of supersymmetric models with natural R-parity conservation.
In the minimal supersymmetric standard model, the conservation of {ital R} parity is phenomenologically desirable, but is {ital ad} {ital hoc} in the sense that it is not required for the internal consistency of the theory. However, if {ital B}{minus}{ital L} is gauged at very high energies, {ital R} parity will be conserved automatically and exactly, provided only that all order parameters carry even integer values of 3({ital B}{minus}{ital L}). We propose a minimal extension of the supersymmetric standard model in which {ital R}-parity conservation arises naturally in this way. This approach predicts the existence of a very weakly coupled, neutral chiral supermultiplet of particles with electroweak-scale masses and lifetimes which may be cosmologically interesting. Neutrino masses arise via an intermediate-scale seesaw mechanism, and a solution to the {mu} problem is naturally incorporated. The apparent unification of gauge couplings at high energies is shown to be preserved in this approach. We also discuss a next-to-minimal extension, which predicts a pair of electroweak-scale chiral supermultiplets with electric charge 2. {copyright} {ital 1996 The American Physical Society.}