Toponium as Nonabelian Positronium ?

We report on recent improvements to our non-perturbative calculation of the positronium spectrum. Our Hamiltonian is a two-body effective interaction which incorporates one-photon exchange terms, but neglects fermion self-energy effects. This effective Hamiltonian is diagonalized numerically in a harmonic oscillator basis at strong coupling ($\alpha=0.3$) to obtain the mass eigenvalues. We find that the mass spectrum compares favorably to the Bohr spectrum of non-relativistic...

We present the next-to-next-to-next-to-leading ${\cal O}(\alpha_s^5m_q)$ result for the ground state energy of a heavy quarkonium system. On the basis of this result we determine the bottom quark mass from $\Upsilon(1S)$ resonance and provide an explicit formula relating the top quark mass to the resonance energy in $t\bar t$ threshold production.

I briefly review standard top quark physics at hadron colliders and summarize the contributions to this conference. The possibility of new mechanisms for $t\bar{t}$ production are also discussed.

In this presentation I will primarily focus on top quark physics but I will include a discussion of the W-boson mass and the possibility of discovering a light Higgs boson via associated production at the Tevatron.

I compare the anticipated properties of the top quark with what is known experimentally about the heaviest fermion. I review the scientific opportunities that will be presented in the near future by copious samples of top. These include refined tests of electroweak radiative corrections, studies of the nature of top itself, and exploration of electroweak symmetry breaking. I conclude by illustrating top's influence in the everyday world.

I present the two-loop QCD corrections to the production of a massive quark-anti-quark pair in the massless quark-anti-quark annihilation channel. The result is obtained as a combination of a deep expansion in the mass around the high energy limit and of a numerical integration of a system of differential equations. The primary application of the outcome and developed methods is top quark pair production at the Large Hadron Collider.

In this contribution I review the physics of top quarks at a future Linear Collider. Main emphasis is put on the process e+ e- to ttbar close to threshold. Different physical observables, their sensitivity to the basic parameters and their theoretical prediction are discussed. Recent higher order calculations are shown to have a considerable impact on a precise determination of the top quark mass. It is pointed out how the use of mass definitions different from the pole mass ...

We provide a detailed account of the methods and calculations for the third-order corrections to the S-wave Green function from heavy-quark potentials other than the Coulomb potential. The results of this paper are relevant to the top-antitop threshold production process in next-to-next-to-next-to-leading (NNNLO) order and to the determination of the bottom-quark mass from high-moment sum rules, and have been employed in corresponding previous publications. Further to the thi...

The top quark is the heaviest elementary particle in the Standard Model (SM). For this reason, a precise determination of its mass $m_t$ is part of the LHC physics program. The most accurate determinations of $m_t$ rely on the kinematic reconstruction of the top decay products and on the use of Monte Carlo event generators. In these proceedings I discuss the impact of different theoretical descriptions for the process of top pair production at the LHC on the extraction of $m_...

Quantum field theory near thresholds of ultra-heavy particles is considered. We focus especially on the top-antitop and the stop-antistop systems. The question of the possible large corrections due to a running width of the top quark could be solved in this work. It was shown that a previously not considered contribution gives rise to large cancellations and leads especially to a gauge independent result. With the help of a new zero order equation and a Ward identity it was f...