Strong Correlations and Magnetic Frustration in the High Tc Iron Pnictides

We consider the iron pnictides in terms of a proximity to a Mott insulator. The superexchange interactions contain competing nearest-neighbor and next-nearest-neighbor components. In the undoped parent compound, these frustrated interactions lead to a two-sublattice collinear antiferromagnet (each sublattice forming a Neel ordering), with a reduced magnitude for the ordered moment. Electron or hole doping, together with the frustration effect, suppresses the magnetic ordering and allows a superconducting state. The exchange interactions favor a d-wave superconducting order parameter; in the notation appropriate for the Fe square lattice, its orbital symmetry is $d_{xy}$. A number of existing and future experiments are discussed in light of the theoretical considerations.Comment: (v2) 4+ pages, 4 figures, discussions on several points expanded; references added. To appear in Phys. Rev. Let

Mixed QCD and Weak Corrections to ttˉt\bar{t} Production by Quark-Antiquark Annihilation

We report on our computation of the mixed QCD and weak corrections to $q {\bar q} \to t\bar{t}$ including $t, \bar t$ spin effects, in particular on single top spin asymmetries.Comment: Talk given at "International Conference on QCD and Hadronic Physics", Beijing, China, 16-20 Jun 200

Spin properties of top quark pairs produced at hadron colliders

We discuss the spin properties of top quark pairs produced at hadron colliders at next-to-leading order in the coupling constant alpha_s of the strong interaction. Specifically we present, for some decay channels, results for differential angular distributions that are sensitive to t tbar spin correlations.Comment: Invited talk given by A. Brandenburg at the Cracow epiphany conference on heavy flavours, 3 - 6 January 2003, Cracow, Polan

Investigation of Top quark spin correlations at hadron collider

We report on our results about hadronic $t\bar t$ production at NLO QCD including $t, \bar t$ spin effects, especially on $t\bar t$ spin correlations.Comment: talk given at the 32nd International Conference on High Energy Physics (ICHEP'04), Beijing, China, 16-22 Aug. 200

Production rates for hadrons, pentaquarks Θ+\Theta ^+ and Θ∗++\Theta ^{*++}, and di-baryon (ΩΩ)0+(\Omega\Omega)_{0^{+}} in relativistic heavy ion collisions by a quark combination model

The hadron production in relativistic heavy ion collisions is well described by the quark combination model. The mixed ratios for various hadrons and the transverse momentum spectra for long-life hadrons are predicted and agree with recent RHIC data. The production rates for the pentaquarks $\Theta ^+$, $\Theta ^{*++}$ and the di-baryon $(\Omega\Omega)_{0^{+}}$ are estimated, neglecting the effect from the transition amplitude for constituent quarks to form an exotic state.Comment: The difference between our model and other combination models is clarified. The scaled transverse momentum spectra for pions, kaons and protoms at both 130 AGeV and 200 AGeV are given, replacing the previous results in transverse momentum spectr