6718601
Parton distributions for low Q2.
We extend the MRS(A) set of parton distributions, which provides an up-to-date description of the structure of the proton probed by hard interactions, into the region of ${\mathit{Q}}^{2}$ below 5 ${\mathrm{GeV}}^{2}$. After physically motivated modifications, we obtain a smooth description of the data on the structure function ${\mathit{F}}_{2}$(x,${\mathit{Q}}^{2}$) all the way from ${\mathit{Q}}^{2}$=${10}^{\mathrm{\ensuremath{-}}1}$ to ${10}^{3}$ ${\mathrm{GeV}}^{2}$.
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
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.
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.
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.
10832623
Sparticle spectrum constraints.
The supersymmetric standard model with supergravity-inspired soft breaking terms predicts a rich spectrum of sparticles to be discovered at the SSC, LHC, and NLC. Because there are more supersymmetric particles than unknown parameters, one can write down sum rules relating their masses. We discuss the spectrum of sparticles from this point of view. Some of the sum rules do not depend on the input parameters and can be used to test the consistency of the model, while others are useful in determining the input parameters of the theory. If supersymmetry is discovered but the sum rules turn out to be violated, it will be evidence of new physics beyond the minimal supersymmetric standard model with universal soft supersymmetry-breaking terms.
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.
10342426
Physically meaningful and not so meaningful symmetries in Chern-Simons theory.
We explicitly show that the Landau gauge supersymmetry of Chern-Simons theory does not have any physical significance. In fact, the difference between an effective action that is both Becchi-Rouet-Stora (BRS) invariant and Landau supersymmetric and an effective action that is only BRS invariant is a finite field redefinition. Having established this, we use a BRS-invariant regulator that defines CS theory as the large mass limit of topologically massive Yang-Mills theory to discuss the shift [ital k][r arrow][ital k]+[ital c][sub [ital V]] of the bare Chern-Simons parameter [ital k] in connection with the Landau supersymmetry. Finally, to convince ourselves that the shift above is not an accident of our regularization method, we comment on the fact that all BRS-invariant regulators used as yet yield the same value for the shift.
15021862
Low-energy supersymmetry with D-term contributions to scalar masses.
We investigate how the predictions of the Minimal Supersymmetric Standard Model are modified by D-term contributions to soft scalar masses, which arise whenever the rank of the gauge group at very high energies is greater than four. We give a parameterization of the most general such contributions that can occur when the unbroken gauge symmetry is an arbitrary subgroup of E_6, and show how the D-term contributions leave their imprint on physics at ordinary energies. We impose experimental constraints on the resulting parameter space and discuss some features of the resulting supersymmetric spectrum which differ from the predictions obtained with universal boundary conditions on scalar masses near the Planck scale. These include relations between squark and slepton masses; the behavior of $\sin^2 (\beta-\alpha)$ (which determines the production cross-section for the lightest Higgs scalar boson at an e+e- collider) and the mass of the pseudoscalar Higgs bosons; R_b [the ratio $\Gamma(Z -> b\overline b)/\Gamma(Z -> hadrons)$; and mass differences between charginos and neutralinos.