Small quarkonium states in an anisotropic QCD plasma

We determine the hard-loop resummed propagator in an anisotropic QCD plasma in general covariant gauges and define a potential between heavy quarks from the Fourier transform of its static limit. We find that the potential exhibits angular dependence and that binding of very small quarkonium states is stronger than in an isotropic plasma.     

Exotic states in long-range spin glasses

We consider Ising spin glasses onZ ^d with couplingsJ _xy =c _y–x Z _xy , where thec _y 's are nonrandom real coefficients and theZ _xy 's are independent, identically distributed random variables withE[Z _xy ]=0 andE[Z _xy ² ]=1. We prove that if _y |c _y |= while _y |c _y |²=, then (with probability one) there are uncountably many (infinite volume) ground states , each of which has the following property: forany temperatureT<, there is a Gibbs state supported entirely on (infinite volume) spin configurations which differ from only atfinitely many sites. This and related results are examples of the bizarre effects that can occur in disordered systems with coupling-dependent boundary conditions.Research supported in part by NSF Grants DMS-9196086 and 9209053Research supported in part by U.S. Department of Energy Grant No. DE-FG03-93ER25155     

Majorana flipping of quarkonium spin states in transient magnetic field

We demonstrate that spin flipping transitions occur between various quarkonium spin states due to transient magnetic field produced in non central heavy ion collisions (HICs). The inhomogeneous nature of the magnetic field results in non adiabatic evolution of (spin)states of quarkonia moving inside the transient magnetic environment. Our calculations explicitly show that the consideration of azimuthal inhomogeneity gives rise to dynamical mixing between different spin states owing to Majorana spin flipping. Notably, this effect of non-adiabaticity is novel and distinct from previously predicted mixing of the singlet and one of the triplet states of quarkonia in the presence of a static and homogeneous magnetic field.     

Exotic baryon states in topological soliton models

The novel observation of an exotic strangeness S=+1 baryon state at 1.54 GeV is to trigger an intensified search for this and other baryons with exotic quantum numbers. This state was predicted long ago in topological soliton models. We use this approach together with the new datum in order to investigate its implications for the baryon spectrum. In particular, we estimate the positions of other pentaquark and septuquark states with exotic and with nonexotic quantum numbers.     

Exotic states in the dynamical Casimir effect

Inhibited decoherence has been recently observed in a dissipative two-level system by increasing the strength of the coupling with the reservoir. The system is described by the spin-boson model under a perturbation approach in the delocalized phase regime occurring in weak-coupling limit at zero temperature. Within this scenario, persistence of coherence is found over long times for various low frequency structures of the bosonic environment near a band gap. Special resonances provoke transitions in the long time dynamics if the transition amplitude of the two-level system is greater than the band gap frequency or in absence of any band gap. These transitions may hinder the the loss of coherence in the spin-boson model. Limitations of the approximations are also discussed.     

Search for promptly produced heavy quarkonium states in hadronic Z decays

A search has been made for direct production of heavy quarkonium states in more than 3 million hadronic Z ⁰ decays in the 1991–1994 DELPHI data. Prompt J/ψ, ψ(2S) and Υ candidates have been searched for through their leptonic decay modes using criteria based on the kinematics and decay vertex positions. New upperlimits are set at the 90% confidence level for Br(Z⁰ → (QQ) X)/Br (Z⁰ → hadrons) for various strong production mechanisms of J/ψ and Υ these range down to 0.9 × 10^?4. The limits are set in the presence of a small excess (～ 1% statistical probability of a background fluctuation) in the sum of candidates from prompt J/ψ, ψ(2S), Υ(1S),Υ(2S) and Υ(3S) relative to the estimated background.     

Higher Fock states and power counting in exclusive P-wave quarkonium decays

Exclusive processes at large momentum transfer factor into perturbatively calculable short-distance parts and long-distance hadronic wave functions. Usually, only contributions from the leading Fock states have to be included to leading order in . We show that for exclusive decays of -wave quarkonia the contribution from the next-higher Fock state contributes at the same order in . We investigate how the constituent gluon attaches to the hard process in order to form colour-singlet final-state hadrons and argue that a single additional long-distance factor is sufficient to parametrize the size of its contribution. Incorporating transverse degrees of freedom and Sudakov factors, our results are perturbatively stable in the sense that soft phase-space contributions are largely suppressed. Explicit calculations yield good agreement with data on decays into pairs of pions, kaons, and etas. We also comment on decays into two pions. Received: 25 April 1997 / Published online: 20 February 1998     

Exotic superfluid states of lattice fermions in elongated traps

We present real-space dynamical mean-field theory calculations for attractively interacting fermions in three-dimensional lattices with elongated traps. The critical polarization is found to be 0.8, regardless of the trap elongation. Below the critical polarization, we find unconventional superfluid structures where the polarized superfluid and Fulde-Ferrell-Larkin-Ovchinnikov-type states emerge across the entire core region.     

Gluonic corrections to the decay rate of heavy quarkonium states into lepton pairs

We calculate one-gluon corrections to the decay rate of heavy quarkonium states into lepton pairs. We find that the correction due to one-gluon exchange is not very significant for charmonium, and for practical purposes only the relativistic kinematical effects need to be taken into account. For theY family the gluonic corrections are, relatively, of greater importance.     

Gluons in quarkonium decay

We discuss what can be learned from the ³S₁ quarkonium decay $\text{Q}\text{Q}\text{→ 3}\text{gluons}$, $\text{Q}\text{Q}\text{→ γ + 2}\text{gluons}$. The former is a way to find gluon jets and test QCD. The latter also allows us to measure gluon + gluon → hadrons, and look for pure gluonic resonances (glueballs).