X(1835): A Possible Baryonium?

We point out that (1) the large $p\bar p$ coupling and suppressed mesonic coupling of X(1835) and (2) the suppression of the three-body strange final states strongly indicate that X(1835) may be a $p\bar p$ baryonium. We also point out that the branching ratio of $X(1835)\to\eta \pi\pi$ should be bigger than that of $X(1835)\to\eta^\prime \pi\pi$. If BES further confirms the non-observation of X(1835) in the $\eta\pi\pi$ channel, that will be very puzzling. Finally, X(1835) may be used a tetraquark generator if X(1835) is really established as a baryonium state.Comment: Comments and suggestions welcom

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.

Top-Quark Decay at Next-to-Next-to-Leading Order in QCD

We present the complete calculation of the top-quark decay width at next-to-next-to-leading order in QCD, including next-to-leading electroweak corrections as well as finite bottom quark mass and $W$ boson width effects. In particular, we also show the first results of the fully differential decay rates for top-quark semileptonic decay $t\to W^+(l^+\nu)b$ at next-to-next-to-leading order in QCD. Our method is based on the understanding of the invariant mass distribution of the final-state jet in the singular limit from effective field theory. Our result can be used to study arbitrary infrared-safe observables of top-quark decay with the highest perturbative accuracy.Comment: 5 pages, 6 figures; version accepted for publication in Physical Review Letter

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