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.
120869890
Conformal field theory representation and background-independent action for superstring field theory
Abstract The two-dimensional conformal field theory representation of Witten's open superstring field theory is discussed. We argue that the previously suggested cubic action for the superstring is actually dependent on the spacetime background, and suggest a modification which formally removes this dependence. The transformation from the new version of the superstring cubic action to Witten's action for open string states is discussed. A class of linearized solutions to the equations of motion of the open superstring cubic action are exhibited. These solutions are in one-to-one correspondence with the physical excitations (both massless and massive) of the open and closed type I superstrings.
118973381
A Supersymmetry Primer
I provide a pedagogical introduction to supersymmetry. The level of discussion is aimed at readers who are familiar with the Standard Model and quantum field theory, but who have had little or no prior exposure to supersymmetry. Topics covered include: motivations for supersymmetry, the construction of supersymmetric Lagrangians, supersymmetry-breaking interactions, the Minimal Supersymmetric Standard Model (MSSM), R-parity and its consequences, the origins of supersymmetry breaking, the mass spectrum of the MSSM, decays of supersymmetric particles, experimental signals for supersymmetry, and some extensions of the minimal framework.
44961063
Two-loop scalar self-energies in a general renormalizable theory at leading order in gauge couplings
I present results for the two-loop self-energy functions for scalars in a general renormalizable field theory, using mass-independent renormalization schemes based on dimensional regularization and dimensional reduction. The results are given in terms of a minimal set of loop-integral basis functions, which are readily evaluated numerically by computers. This paper contains the contributions corresponding to the Feynman diagrams with zero or one vector propagator lines. These are the ones needed to obtain the pole masses of the neutral and charged Higgs scalar bosons in supersymmetry, neglecting only the purely electroweak parts at two-loop order. A subsequent paper will present the results for the remaining diagrams, which involve two or more vector lines. I also include an illustrative example, featuring several nontrivial consistency checks.
122018065
BRST current algebra anomalies in string theory
Abstract We have calculated the operator product of the BRST current with itself in the cases of bosonic and fermionic strings. Despite some confusion in the recent literature, these operator products cannot vanish. In fact they are equal to total derivatives only if the total derivative part of the (super) BRST current is chosen correctly. Thus the BRST current algebra has anomalous Schwinger terms.
43631942
Refined gluino and squark pole masses beyond leading order
The physical pole and running masses of squarks and gluinos have recently been related at two-loop order in a mass-independent renormalization scheme. I propose a general method for improvement of such formulas, and argue that better accuracy results. The improved version gives an imaginary part of the pole mass that agrees exactly with the direct calculation of the physical width at next-to-leading order. I also find the leading three-loop contributions to the gluino pole mass in the case that squarks are heavier, using effective field theory and renormalization group methods. The efficacy of these improvements for the gluino and squarks is illustrated with numerical examples. Some necessary three-loop results for gauge coupling and fermion mass beta functions and pole masses in theories with more than one type of fermion representation, which are not directly accessible from the published literature, are presented in an Appendix.
23673028
New information on parton distributions.
New data on structure functions from deep-inelastic scattering provide new information on parton distributions, particularly in the 0.01[lt][ital x][lt]0.1 interval. This has important implications for predictions for the DESY [ital ep] collider HERA and for present and future high-energy hadron colliders. We present the results of updated fits to all available precision structure function and related data. We focus in particular on two issues: (a) the increase in the sea-quark distribution at small [ital x] implied by new [ital F][sub 2] data from the New Muon Collaboration, and its implications for other processes, and (b) the evidence for SU(2)-symmetry breaking in the light-quark sea. We show that although good fits can be obtained with or without this symmetry breaking, more physically reasonable parton distributions are obtained if we allow [ital [bar d]][gt][ital [bar u]] at small [ital x]. With the inclusion of the latest deep-inelastic data we find [alpha][sub [ital s]]([ital M][sub [ital Z]])=0.111[sub [minus]0.005][sup +0.004]. We also show how [ital W], [ital Z], and Drell-Yan production at [ital [bar p]p] colliders can give information on parton 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
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.
14833247
Deep inelastic events containing a forward photon as a probe of small x dynamics.
We calculate the rate of producing deep inelastic events containing an energetic isolated forward photon at DESY HERA. We quantify the enhancement arising from the leading log1/{ital x} gluon emissions with a view to using such events to identify the underlying dynamics. {copyright} {ital 1996 The American Physical Society.}
17028127
Coulomb effects in W+W- production.
We calculate the Coulomb effects on the cross section for e+ e- --> W+ W- taking into account the instability of the W bosons. We carefully explain the consequences of instability throughout the energy range which will be accessible at LEP2. We present a formula which allows these effects to be easily implemented.