Closing the Low-mass Axigluon Window

In this report, I will present the current status of the low-mass axigluon. The axigluon is a massive, color octet, axial vector boson, predicted in, e.g., chiral color models and some technicolor models, with a mass of order the electroweak scale. Axigluons with a mass larger than about 125 GeV to nearly 1 TeV can be eliminated by di-jet production at hadron colliders like the TEVATRON, but a low-mass window exists that the di-jet search can not probe. Upsilon decays can rule out axigluons with a mass up to 25 GeV, and low energy e^+ e^- (PEP and PETRA) can rule out axigluons with a mass up to 50 GeV using a measurement of R. Top production at the TEVATRON disfavors a light axigluon. A measurement of R at LEP strongly disfavors a light axigluon, and rules out an axigluon with mass < 365 GeV.Comment: 8 pages, LaTeX, 4 .eps figures, uses aipproc.sty and psfi

Leptoquark Production and Identification at High Energy Lepton Colliders

Leptoquarks can be produced in substantial numbers for masses very close to the collider centre of mass energy in $e^+e^-$, $e\gamma$, and $\mu^+\mu^-$ collisions due to the quark content of the photon resulting in equivalently high discovery limits. Using polarization asymmetries in an $e\gamma$ collider the ten different types of leptoquarks listed by Buchm\"uller, R\"uckl and Wyler can be distinquished from one another for leptoquark masses essentially up to the kinematic limit. Thus, if a leptoquark were discovered, an $e\gamma$ collider could play a crucial role in determining its origins.Comment: LaTex file uses aipproc.sty, epsfig, and rotating. 9 pages with 8 postscript figures. Talk given at 20th Annual MRST (Montreal-Rochester-Syracuse-Toronto) Meeting on High-Energy Physics: MRST 98: Toward the Theory of Everything, Montreal, Canada, 13-15 May 199

What Can We Learn About Leptoquarks At LEP200?

We investigate the discovery potential for first generation leptoquarks at the LEP200 $e^+e^-$ collider. We consider direct leptoquark searches using single leptoquark production via resolved photon contributions which offers a much higher kinematic limit than the more commonly considered leptoquark pair production process. Depending on the coupling strength of the leptoquark, search limits can be obtained to within a few GeV of $\sqrt{s}$. We also consider LQ limits that can be obtained from t-channel interferences effects in $e^+e^- \to hadrons$.Comment: Latex file uses revtex version 3, epsfig, and rotate, 5 postscript figures are attache

Recoil Corrections of Order (Zα)6(m/M)m(Z\alpha)^6(m/M)m to the Hydrogen Energy Levels Revisited

The recoil correction of order $(Z\alpha)^6(m/M)m$ to the hydrogen energy levels is recalculated and a discrepancy existing in the literature on this correction for the 1S energy level, is resolved. An analytic expression for the correction to the S-levels with arbitrary principal quantum number is obtained.Comment: 17 pages, ReVTe

Fragmentation production of doubly heavy baryons

Baryons with a single heavy quark are being studied experimentally at present. Baryons with two units of heavy flavor will be abundantly produced not only at future colliders, but also at existing facilities. In this paper we study the production via heavy quark fragmentation of baryons containing two heavy quarks at the Tevatron, the LHC, HERA, and the NLC. The production rate is woefully small at HERA and at the NLC, but significant at $pp$ and $p\bar{p}$ machines. We present distributions in various kinematical variables in addition to the integrated cross sections at hadron colliders.Comment: 13 pages, macro package epsfig needed, 6 .eps figure files in a separate uuencoded, compressed and tarred file; complete paper available at http://www.physics.carleton.ca/~mad/papers/paper.p

Photon-Photon and Electron-Photon Colliders with Energies Below a TeV

We investigate the potential for detecting and studying Higgs bosons in $\gamma\gamma$ and $e\gamma$ collisions at future linear colliders with energies below a TeV. Our study incorporates realistic $\gamma\gamma$ spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: a) a SM-like Higgs boson based on a devoted low energy machine with $\sqrt{s_{ee}}\le 200$ GeV; b) the heavy MSSM Higgs bosons; and c) charged Higgs bosons in $e\gamma$ collisions.We investigate the potential for detecting and studying Higgs bosons in $\gamma\gamma$ and $e\gamma$ collisions at future linear colliders with energies below a TeV. Our study incorporates realistic $\gamma\gamma$ spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: a) a SM-like Higgs boson based on a devoted low energy machine with $\sqrt{s_{ee}}\le 200$ GeV; b) the heavy MSSM Higgs bosons; and c) charged Higgs bosons in $e\gamma$ collisions