36563644
Gluon distribution at small x obtained from a unified evolution equation.
We solve a unified integral equation to obtain the x, ${\mathit{Q}}_{\mathit{T}}$, and Q dependence of the gluon distribution of a proton in the small x regime, where x and ${\mathit{Q}}_{\mathit{T}}$ are the longitudinal momentum fraction and the transverse momentum of the gluon probed at a scale Q. The equation generates a gluon with a steep ${\mathit{x}}^{\mathrm{\ensuremath{-}}\ensuremath{\lambda}}$ behavior, with \ensuremath{\lambda}\ensuremath{\sim}0.5, and a ${\mathit{Q}}_{\mathit{T}}$ distribution which broadens as x decreases. We compare our solutions with, on the one hand, those that we obtain using the double-leading-logarithm approximation to Altarelli-Parisi evolution and, on the other hand, to those that we determine from the BFKL equation.
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.
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.
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.
126229857
Structure Function Analysis and psi, Jet, W, Z Production: Pinning Down the Gluon
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.
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.}
16739726
Spacings of quarkonium levels with the same principal quantum number.
The spacings between bound-state levels of the Schr{umlt o}dinger equation with the same principal quantum number {ital N} but orbital angular momenta {ital l} differing by unity are found to be nearly equal for a wide range of power potentials {ital V}={lambda}{ital r}{sup {nu}}, with {ital E}{sub {ital Nl}}{approx_equal}{ital F}({nu},{ital N}){minus}{ital G}({nu},{ital N}){ital l}. Semiclassical approximations are in accord with this behavior. The result is applied to estimates of masses for quarkonium levels which have not yet been observed, including the 2{ital P} {ital c{bar c}} states and the 1{ital D} {ital b{bar b}} states. {copyright} {ital 1996 The American Physical Society.}
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.
17649647
Variational approximation for two-time correlation functions in Phi 4 theory: Optimization of the dynamics.
We apply the time-dependent variational principle of Balian and Veneroni to {Phi}{sup 4} theory. An appropriate parametrization for the variational objects allows us to write coupled dynamical equations from which we derive approximations for the two-time correlation functions involving two, three, or four field operators. {copyright} 1995 The American Physical Society.