Effects of QCD Resummation on W+hW^+h and tbˉt\bar b Production at the Tevatron

The resummation of multiple soft gluon emission affects the production rate and kinematic distributions of $W^+h$ (where h is a Higgs boson) and $t \bar b$ pairs at the Tevatron with $\sqrt{s}=2$ TeV. Using the Collins-Soper-Sterman resummation formalism, the production rate is enhanced over the next-to-leading-order (NLO) prediction by 2-3% for the $W^+h$ process, for Higgs boson masses between 80-120 GeV, and over 3% for the $t\bar b$ process for $m_t=175$ GeV. After resummation, the $t\bar b$ rate changes by 12-13% when $m_t$ is varied by $\pm 5$ GeV. Various kinematic distributions are presented for the individual final state particles and for the pair. The explicit radiation of hard gluons in NLO QCD is included also for the $t\bar b$ final state.Comment: 9 pages, 12 Postscript figures, in RevTeX format, uses epsf.te

Doping dependence of the electron-doped cuprate superconductors from the antiferromagnetic properties of the Hubbard model

Within the Kotliar-Ruckenstein slave-boson approach, we have studied the antiferromagnetic (AF) properties for the $t$-$t'$-$t''$-$U$ model applied to electron-doped cuprate superconductors. Due to inclusion of spin fluctuations the AF order decreases with doping much faster than obtained in the Hartree-Fock theory. Under an intermediate {\it constant} $U$ the calculated doping evolution of the spectral intensity has satisfactorily reproduced the experimental results, without need of a strongly doping-dependent $U$ as argued earlier. This may reconcile a discrepancy suggested in recent studies on photoemission and optical conductivity.Comment: 5 pages, 4 eps figures, minor improvement, references added, to appear in Phys. Rev.

Study of gossamer superconductivity and antiferromagnetism in the t-J-U model

The d-wave superconductivity (dSC) and antiferromagnetism are analytically studied in a renormalized mean field theory for a two dimensional t-J model plus an on-site repulsive Hubbard interaction $U$. The purpose of introducing the $U$ term is to partially impose the no double occupancy constraint by employing the Gutzwiller approximation. The phase diagrams as functions of doping $\delta$ and $U$ are studied. Using the standard value of $t/J=3.0$ and in the large $U$ limit, we show that the antiferromagnetic (AF) order emerges and coexists with the dSC in the underdoped region below the doping $\delta\sim0.1$. The dSC order parameter increases from zero as the doping increases and reaches a maximum near the optimal doping $\delta\sim0.15$. In the small $U$ limit, only the dSC order survives while the AF order disappears. As $U$ increased to a critical value, the AF order shows up and coexists with the dSC in the underdoped regime. At half filing, the system is in the dSC state for small $U$ and becomes an AF insulator for large $U$. Within the present mean field approach, We show that the ground state energy of the coexistent state is always lower than that of the pure dSC state.Comment: 7 pages, 8 figure

Theory of antiferromagnetism in the electron-doped cuprate superconductors

On the basis of the Hubbard model, we present the formulation of antiferromagnetism in electron-doped cuprates using the fluctuation-exchange approach. Taking into account the spin fluctuations in combination with the impurity scattering effect due to the randomly distributed dopant-atoms, we investigate the magnetic properties of the system. It is shown that the antiferromagnetic transition temperature, the onset temperature of the pseudogap formation, the single particle spectral density, and the staggered magnetization obtained by the present approach are in very good agreement with the experimental results. The distribution function in momentum space at very low temperature is observed to differ significantly from that of the Fermi liquid. Also, we find zero-energy peak in the density of states (DOS) of the antiferromagnetic phase. This DOS peak is sharp in the low doping regime, and disappears near the optimal doping where the AF order becomes weak.Comment: 12 pages, 19 figure

Fermi surface evolution in the antiferromagnetic state for the electron-doped t-t'-t''-J model

By use of the slave-boson mean-field approach, we have studied the electron-doped t-t'-t''-J model in the antiferromagnetic (AF) state. It is found that at low doping the Fermi surface (FS) pockets appear around $(\pm\pi,0)$ and $(0,\pm\pi)$, and upon increasing doping the other ones will form around $(\pm{\pi\over 2},\pm{\pi\over 2})$. The evolution of the FS with doping as well as the calculated spectral weight are consistent with the experimental results.Comment: Fig. 4 is updated, to appear in Phys. Rev.