Single Leptoquark Production at e+e−e^+e^- and γγ\gamma\gamma Colliders

We consider single production of leptoquarks (LQ's) at $e^+e^-$ and $\gamma\gamma$ colliders, for two values of the centre-of-mass energy, $\sqrt{s}=500$ GeV and 1 TeV. We find that LQ's which couple within the first generation are observable for LQ masses almost up to the kinematic limit, both at $e^+e^-$ and $\gamma\gamma$ colliders, for the LQ coupling strength equal to $\alpha_{em}$. The cross sections for single production of $2^{nd}$- and $3^{rd}$-generation LQ's at $e^+e^-$ colliders are too small to be observable. In $\gamma\gamma$ collisions, on the other hand, $2^{nd}$-generation LQ's with masses much larger than $\sqrt{s}/2$ can be detected. However, $3^{rd}$-generation LQ's can be seen at $\gamma\gamma$ colliders only for masses at most $\sim\sqrt{s}/2$, making their observation more probable via the pair production mechanism.Comment: plain TeX, 14 pages, 6 figures (not included but available on request), some minor changes to the text, one reference added, figures and conclusions unchanged, UdeM-LPN-TH-93-152, McGill-93/2

Anatomy of a microearthquake sequence on an active normal fault

The analysis of similar earthquakes, such as events in a seismic sequence, is an effective tool with which to monitor and study source processes and to understand the mechanical and dynamic states of active fault systems. We are observing seismicity that is primarily concentrated in very limited regions along the 1980 Irpinia earthquake fault zone in Southern Italy, which is a complex system characterised by extensional stress regime. These zones of weakness produce repeated earthquakes and swarm-like microearthquake sequences, which are concentrated in a few specific zones of the fault system. In this study, we focused on a sequence that occurred along the main fault segment of the 1980 Irpinia earthquake to understand its characteristics and its relation to the loading-unloading mechanisms of the fault system

An Optical Time-Delay for the Lensed BAL Quasar HE2149-2745

We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE2149-2745. The data, obtained with the 1.5m Danish Telescope (ESO-La Silla) between October 1998 and December 2000, are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere. A time delay of 103+/-12 days is determined from the light curves. In addition, VLT/FORS1 spectra of HE2149-2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy, free of any contamination by the bright nearby two quasar images. By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z=0.495+/-0.01. Adopting this redshift, a Omega=0.3, Lambda=0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H_0=66+/-8 km/s/Mpc with an estimated systematic error of +/-3 km/s/Mpc. Using non-parametric models yields H_0=65+/-8 km/s/Mpc and confirms that the lens exhibits a very dense/concentrated mass profile.Comment: 11 pages, accepted for publication in Astronomy & Astrophysic

A Survey of Volunteered Open Geo-Knowledge Bases in the Semantic Web

Over the past decade, rapid advances in web technologies, coupled with innovative models of spatial data collection and consumption, have generated a robust growth in geo-referenced information, resulting in spatial information overload. Increasing 'geographic intelligence' in traditional text-based information retrieval has become a prominent approach to respond to this issue and to fulfill users' spatial information needs. Numerous efforts in the Semantic Geospatial Web, Volunteered Geographic Information (VGI), and the Linking Open Data initiative have converged in a constellation of open knowledge bases, freely available online. In this article, we survey these open knowledge bases, focusing on their geospatial dimension. Particular attention is devoted to the crucial issue of the quality of geo-knowledge bases, as well as of crowdsourced data. A new knowledge base, the OpenStreetMap Semantic Network, is outlined as our contribution to this area. Research directions in information integration and Geographic Information Retrieval (GIR) are then reviewed, with a critical discussion of their current limitations and future prospects

Bounds on Vector Leptoquarks

We derive bounds on vector leptoquarks coupling to the first generation, using data from low energy experiments as well as from high energy accelerators. Similarly to the case of scalar leptoquarks, we find that the strongest indirect bounds arise from atomic parity violation and universality in leptonic pi decays. These bounds are considerably stronger than the first direct bounds of HERA, restricting vector leptoquarks that couple with electromagnetic strength to right-handed quarks to lie above 430 GeV or 460 GeV, and leptoquarks that couple with electromagnetic strength to left-handed quarks to lie above 1.3 TeV, 1.2 TeV and 1.5 TeV for the SU(2)_W singlet, doublet and triplet respectively.Comment: 14 Pages (LaTeX), including 1 uufiled postscript figure. WIS-93/119/Dec-P

Signal and Backgrounds for the Single Production of Scalar and Vector Leptoquarks at the LHC

We perform a detailed analysis of the potentiality of the CERN Large Hadron Collider to study the single production of leptoquarks via $pp \to e^\pm q\to$ leptoquark $\to e^\pm q$, with $e^\pm$ generated by the splitting of photons radiated by the protons. Working with the most general $SU(2)_L \otimes U(1)_Y$ invariant effective lagrangian for scalar and vector leptoquarks, we analyze in detail the leptoquark signals and backgrounds that lead to a final state containing an $e^\pm$ and a hard jet with approximately balanced transverse momenta. Our results indicate that the LHC will be able to discover leptoquarks with masses up to 2--3 TeV, depending on their type, for Yukawa couplings of the order of the electromagnetic one.Comment: Revtex, 23 pages, 11 postscript files. Uses axodraw.sty (included) and epsfig.sty. Typos corrected. To be published in Phys. Rev.

Signals for Vector Leptoquarks in Hadronic Collisions

We analyze systematically the signatures of vector leptoquarks in hadronic collisions. We examine their single and pair productions, as well as their effects on the production of lepton pairs. Our results indicate that a machine like the CERN Large Hadron Collider (LHC) will be able to unravel the existence of vector leptoquarks with masses up to the range of $2$--$3$ TeV.Comment: 15 pages and 5 figures (available upon request or through anonymous ftp), revtex3, IFUSP-P 108

Much Ado About Leptoquarks: A Comprehensive Analysis

We examine the phenomenological implications of a 200 GeV leptoquark in light of the recent excess of events at HERA. Given the relative predictions of events rates in e^+p versus e^-p, we demonstrate that classes of leptoquarks may be excluded, including those contained in E_6 GUT models. It is shown that future studies with polarized beams at HERA could reveal the chirality of the leptoquark fermionic coupling and that given sufficient luminosity in each e^\pm_{L,R} channel the leptoquark quantum numbers could be determined. The implications of 200-220 GeV leptoquarks at the Tevatron are examined. While present Tevatron data most likely excludes vector leptoquarks and leptogluons in this mass region, it does allow for scalar leptoquarks. We find that while leptoquarks have little influence on Drell-Yan production, further studies at the Main Injector are possible in the single production channel. We investigate precision electroweak measurements as well as the process e^+e^-\to q\bar q at LEP II and find they provide no further restrictions on these leptoquark models. We then ascertain that cross section and polarization asymmetry measurements at the NLC provide the only direct mechanism to determine the leptoquark's electroweak quantum numbers. The single production of leptoquarks in \gamma e collisions by both the backscattered laser and Weisacker-Williams techniques at the NLC is also discussed. Finally, we demonstrate that we can obtain successful coupling constant unification in models with leptoquarks, both with or without supersymmetry. The supersymmetric case requires the GUT group to be larger than SU(5) such as flipped SU(5)\times U(1)_X.Comment: Corrected single production cross section at Tevatron, updated atomic parity violation constraints, 55 page

A Comprehensive Study of Leptoquark Bounds

We make a comprehensive study of indirect bounds on scalar leptoquarks that couple chirally and diagonally to the first generation by examining available data from low energy experiments as well as from high energy e+ e- and p pbar accelerators. The strongest bounds turn out to arise from low energy data: For leptoquarks that couple to right--handed quarks, the most stringent bound comes from atomic parity violation. For leptoquarks that couple to left--handed quarks, there are two mass regions: At low masses the bounds arise from atomic parity violation or from universality in leptonic pi decays. At masses above a few hundred GeV's, the dominant bounds come from the FCNC processes that are unavoidable in these leptoquarks: The FCNC bound of the up sector, that arises from D-Dbar mixing, combines with the FCNC bounds from the down sector, that arise from rare K decays and K-Kbar mixing, to a bound on the flavour CONSERVING coupling to the first generation. The bounds restrict leptoquarks that couple with electromagnetic strength to lie above 600 GeV or 630 GeV for leptoquarks that couple to RH quarks, and above 1040 GeV, 440 GeV, and 750 GeV for the SU(2)_W scalar, doublet and triplet leptoquarks that couple to LH quarks. These bounds are considerably stronger than the first results from the direct searches at HERA. Our bounds also already exclude large regions in the parameter space that could be examined by various methods proposed for indirect leptoquark searches.Comment: 23 Pages (LaTeX), including 3 uufiled postscript figures. WIS--93/90/Sept--PH. To appear in PRD. Changes: updated numbers ---> stronger bound