New Signatures of Squarks

When the gluino is light and long lived, missing energy is a poor signature for both squarks and gluinos. Instead, $S_q S_q^*$ production in $e^+ e^-$ and $p \bar{p}$ collisions characteristically results in events with $\ge 4$ jets. Methods are proposed for deciding whether an observed excess of 4-jet events is due to $S_q S_q^*$ production. The recent report by ALEPH of observation of 14 4-jet events when 7 were expected is discussed.Comment: 12/22/95 version (put on net 1/1/96) elaborates remarks on squarks as possible source of ALEPH 4-jet excess and adds a ref. latex, 10 pages (including 1 figure), uufile

Light, long-lived and secluded: can gluinos be driven out from LEP1 data ?

We briefly report about a possible settlement of the still ongoing dispute concerning the existence of SUSY signals in 4jet events at LEP1. We base our arguments on a simple selection strategy exploiting secondary vertex tagging and kinematical constraints, which could allow one to access or exclude gluino events for a broad range of masses and lifetimes.Comment: 10 pages, LaTeX, 3 PostScript figures embedded with epsfig. Complete ps paper and figures available also at ftp://ftae3.ugr.es/pub/rmt/ugrft70.p

Possible manifestation of heavy stable colored particles in cosmology and cosmic rays

We discuss the cosmological implications as well as possible observability of massive, stable, colored particles which often appear in the discussion of physics beyond the standard model. We argue that if their masses are more than a few hundred GeV and if they saturate the halo density and/or occur with closure density of the universe, they are ruled out by the present WIMP search experiments as well as the searches for anomalous heavy isotopes of ordinary nuclei. We then comment on the possibility that these particles as well as the monopoles could be responsible for the ultra high energy cosmic rays with energy $\geq 10^{20}$ eV and point out that their low inelasticity argues against this.Comment: 9 pages; UMD-PP-98-1

Group independent color decomposition of next-to-leading order matrix elements for e^+ e^- \to four partons

We present the next-to-leading order partonic cross sections involving an electroweak vector boson and four massless partons (quarks, gluons or long living gluinos) in a general gauge theory with a simple Lie Group. The vector boson couples to a massless lepton pair and a quark-antiquark pair. The cross sections are given in terms of group independent kinematical functions multiplying the eigenvalues of the Casimir operators of the Lie group. This kind of color decomposition is required for the calculation of O($\alpha_s^3$) corrections to the group independent kinematical functions in the four-jet production cross sections in electron-positron annihilation. The knowledge of these corrections facilitates the simultaneous precision meaurement of the strong coupling and the color charge factors using the four-jet LEP or SLC data as well as the test whether these data favour or exclude the existence of a light gluino.Comment: 11 pages, elsart styl

A General Approach To Photon Radiation Off Fermions

Soft or collinear photon emission potentially poses numerical problems in the phase-space integration of radiative processes. In this paper, a general subtraction formalism is presented that removes such singularities from the integrand of the numerical integration and adds back the analytically integrated contributions that have been subtracted. The method is a generalization of the dipole formalism of Catani and Seymour, which was formulated for NLO QCD processes with massless unpolarized particles. The presented formalism allows for arbitrary mass and helicity configurations in processes with charged fermions and any other neutral particles. Particular attention is paid to the limit of small fermion masses, in which collinear singularities cause potentially large corrections. The actual application and the efficiency of the formalism are demonstrated by the discussion of photonic corrections to the processes \gamma \gamma --> t \bar t (\gamma), e^- \gamma --> e^- \gamma (\gamma), and \mu^+ \mu^- --> \nu_e \bar\nu_e (\gamma).Comment: 51 pages, latex; two sentences dropped (in Sections 3.2 and 4.2); to appear in Nucl. Phys.

Electroweak baryogenesis and the Higgs and stop masses

In this talk we review the actual situation concerning electroweak phase transition and baryogenesis in the minimal supersymmetric extension of the Standard Model. A strong enough phase transition requires light Higgs and stop eigenstates. For a Higgs mass in the range 110--115 GeV, there is a stop window in the range 105--165 GeV. If the Higgs is heavier than 115 GeV, stronger constrains are imposed on the space of supersymmetric parameters. A baryon-to-entropy ratio is generated by the chargino sector provided that the $\mu$ parameter has a CP-violating phase larger than $\sim$ 0.04.Comment: 10 pages, 6 figures, uses espcrc2.sty. Contribution to the conferences: Strong Electroweak Matter, Centre de Physique Theorique, Universite de Marseille, Marseilles (France), June 14-17, 2000; and, Thirty years of supersymmetry, Theoretical Physics Institute, School of Physics and Astronomy, Minneapolis, Minnesota (USA), October 16-27, 200

Galaxies Correlating with Ultra-high Energy Cosmic Rays

The Pierre Auger Observatory reports that 20 of the 27 highest energy cosmic rays have arrival directions within 3.2 deg of a nearby galaxy in the Veron-Cetty & Veron Catalog of Quasars and Active Galactic Nuclei (12th Ed.), with ~5 of the correlations expected by chance. In this paper we examine the correlated galaxies to gain insight into the possible UHECR sources. We find that 14 of the 21 correlated VCV galaxies are AGNs and we determine their bolometric luminosities. The remaining 7 are primarily star-forming galaxies. The bolometric luminosities of the correlated AGNs are all greater than 5 x 10^{42} erg/s, which may explain the absence of UHECRs from the Virgo region in spite of the large number of VCV galaxies in Virgo, since most of the VCV galaxies in the Virgo region are low luminosity AGNs. Interestingly, the bolometric luminosities of most of the AGNs are significantly lower than required to satisfy the minimum condition for UHECR acceleration in a continuous jet. If a UHECR-AGN correlation is substantiated with further statistics, our results lend support to the recently proposed ``giant AGN flare" mechanism for UHECR acceleration.Comment: 13 pages, 3 figures, to be submitted to Ap

SUSYGEN 2.2 - A Monte Carlo Event Generator for MSSM Sparticle Production at e+ e- Colliders

SUSYGEN is a Monte Carlo program designed for computing distributions and generating events for MSSM sparticle production in e+ e- collisions. The Supersymmetric (SUSY) mass spectrum may either be supplied by the user, or can alternatively be calculated in two different models of SUSY Breaking: gravity mediated supersymmetry breaking (SUGRA), and gauge mediated supersymmetry breaking (GMSB). The program incorporates the most important production processes and decay modes, including the full set of R-parity violating decays, and the decays to the gravitino in GMSB models. Initial state radiation corrections take into account pT/pL effects in the Structure Function formalism, and an optimised hadronisation interface to JETSET 7.4 including final state radiation is also provided.Comment: 68 pages, 8 figures. Submitted to Comp. Phys. Commu

Charm production in antiproton-nucleus collisions at the J/ψJ/\psi and the ψ′\psi' thresholds

We discuss the production of charmonium states in antiproton-nucleus collisions at the $\psi'$ threshold. It is explained that measurements in $\bar p A$ collisions will allow to get new information about the strengths of the inelastic $J/\psi N, \psi'N$ interaction, on the production of $\Lambda_c$ and $\bar{D}$ in charmonium-nucleon interactions and for the first time about nondiagonal transitions $\psi' N\to J/\psi N$. The inelastic $J/\psi$-nucleon cross section is extracted from the comparison of hadron-nucleus collisions with hadron-nucleon collisions. We extract the total $J/\psi$ nucleon cross section from photon-nucleon collisions by accounting for the color transparency phenomenon within the frame of the GVDM (Generalized Vector meson Dominance Model). We evaluate also within the GVDM the inelastic $\psi'$-nucleon cross section as well as the cross section for the nondiagonal transitions. Predictions for the ratio of $J/\psi$ to $\psi'$ yields in antiproton-nucleus scatterings close to the threshold of $\psi'$ production for different nuclear targets are presented.Comment: 13 pages, 10 figures, typos corrected, some discussion adde