Spin Correlations in top quark pair production near threshold at the e−e+ e^- e^+ Linear Collider

We investigate the spin correlations in top quark pair production near threshold at the $e^- e^+$ linear collider. Comparing with the results above the threshold region, we find that near the threshold region the off-diagonal basis, the optimized decomposition of the top quark spins above the threshold region, does not exist, and the beamline basis is the optimal basis, in which there are the dominant spin components: the up-down (UD) component for $e_L^- e^+$ scattering and the down-up (DU) component for $e_R^- e^+$ scattering can make up more than 50% of the total cross section, respectively.Comment: 12 pages, 3 figures, minor modification

Next-to-leading order QCD predictions for associated production of top squarks and charginos at the CERN LHC

We present the calculations of the complete next-to-leading order (NLO) inclusive total cross sections for the associated production processes $pp\to \tilde{t}_i\tilde{\chi}_k^-+X$ in the Minimal Supersymmetric Standard Model at the CERN Large Hadron Collider. Our calculations show that the total cross sections for the $\tilde{t}_1\tilde{\chi}_1^-$ production for the lighter top squark masses in the region 100 GeV $< m_{\tilde{t}_1}<$ 160 GeV can reach 1 pb in the favorable parameter space allowed by the current precise experiments, and in other cases the total cross sections generally vary from 10 fb to several hundred fb except both $m_{\tilde{t}_1}>$ 500 GeV and the $\tilde{t}_2\tilde{\chi}_2^-$ production channel. Moreover, we find that the NLO QCD corrections in general enhance the leading order total cross sections significantly, and vastly reduce the dependence of the total cross sections on the renormalization/factorization scale, which leads to increased confidence in predictions based on these results.Comment: 42 pages, 13 figures, RevTex4. Journal-ref adde

Higgs Boson Production via Gluon Fusion in the Standard Model with four Generations

Higgs bosons can be produced copiously at the LHC via gluon fusion induced by top and bottom quark loops, and can be enhanced strongly if extra heavy quarks exist. We present results for Higgs +zero-, one- and two-jet production at the LHC, in both the Standard Model and the 4th generation model, by evaluating the corresponding heavy quark triangle, box and pentagon Feynman diagrams. We compare the results by using the effective Higgs-gluon interactions in the limit of heavy quarks with the cross sections including the full mass dependences. NLO effects with full mass dependence are included in the inclusive Higgs boson production rate. Our results improve the theoretical basis for fourth generation effects on the Higgs boson search at the LHC.Comment: Published version in PR

Next-to-leading order QCD corrections to the single top quark production via model-independent t-q-g flavor-changing neutral-current couplings at hadron colliders

We present the calculations of the complete next-to-leading order (NLO) QCD effects on the single top productions induced by model-independent $tqg$ flavor-changing neutral-current couplings at hadron colliders. Our results show that, for the $tcg$ coupling the NLO QCD corrections can enhance the total cross sections by about 60% and 30%, and for the $tug$ coupling by about 50% and 20% at the Tevatron and LHC, respectively, which means that the NLO corrections can increase the experimental sensitivity to the FCNC couplings by about 10%$-$30%. Moreover, the NLO corrections reduce the dependence of the total cross sections on the renormalization or factorization scale significantly, which lead to increased confidence on the theoretical predictions. Besides, we also evaluate the NLO corrections to several important kinematic distributions, and find that for most of them the NLO corrections are almost the same and do not change the shape of the distributions.Comment: minor changes, version published in PR

Transverse momentum resummation in soft-collinear effective theory

We present a universal formalism for transverse momentum resummation in the view of soft-collinear effective theory (SCET), and establish the relation between our SCET formula and the well known Collins-Soper-Sterman's pQCD formula at the next-to-leading logarithmic order (NLLO). We also briefly discuss the reformulation of joint resummation in SCET.Comment: 23 pages, 7 figures; version to appear in Phys. Rev.