The gluon self-coupling in QCD implies the existence of bound states of pure gauge fields known as glueballs. Numerous technical difficulties have so far been present in our understanding of their properties in experiments, largely because glueball states can mix strongly with nearby qq̄ resonances. However recent experimental and lattice studies of 0, 2 and 0−+ glueballs seem to be convergent. ...

where the field strength F a μν = ∂μA a ν − ∂νA a μ + gfAμA c ν , z = y− x and P denotes path ordering of the exponential. In general, the gauge invariant field strength correlator could be defined with an arbitrary gauge string connecting the end points x and y, but in this work we shall restrict ourselves to a straight line. It is the basic ingredient in the stochastic model of the QCD vacuum...

The simplest renormalizable effective field theories with asymmetric dark matter bound states contain two additional gauge singlet fields one being the dark matter and the other a mediator particle that the dark matter annihilates into. We examine the physics of one such model with a Dirac fermion as the dark matter. For a range of parameters the Yukawa coupling of the dark matter to the mediat...

We consider systems of static nuclei and electrons {atoms and molecules{ coupled to the quantized radiation eld. The interactions between electrons and the soft modes of the quantized electromagnetic eld are described by minimal coupling, ~ p ! ~ p?e ~ A(~ x), where ~ A(~ x) is the electromagnetic vector potential with an ultraviolet cutoo. If the interactions between the electrons and the quan...

The scattering off a potential of finite rank (a sum of a finite number of separable potentials) is studied thoroughly in the neighborhood of infinity of potential strength; for this purpose we introduce the "strong coupling representation" by means of a canonical transformation. The same K matrix as for the infinitely strong repulsion is derived for the infinitely strong attraction. The differ...

We report on our recent evaluation of the s-channel cut contribution to J/ψ hadroproduction. We show that it is likely significantly larger than the usual cut contribution of the colour-singlet model (CSM), which is known to underestimate the experimental measurements. Here the s-channel cut develops for configurations with off-shell quarks in the bound state. A correct treatment of its contrib...

The boundary effects in the open Hubbard chain with boundary fields are studied. The boundary string solutions of the Bethe ansatz equations that give rise to a wave functions localized at the boundary and exponentially decreasing away from the boundary are provided. In particular, it is shown that the correct ground state of the model at half-filling contains the boundary 1-string.

Recent experiments on Sr2RuO4 have indicated the presence of linear nodes in the superconducting order parameter. Among the possible spin triplet states, 2D p-wave superconductivity with Eu symmetry appears to be inconsistent with the experiments, whereas the 2D f-wave order parameter with B1g × Eu symmetry turns out to be a more likely candidate. Here it is shown how the quasi-particle bound s...

This colloquium addresses the issue of the shape of hadrons and in particular that of the proton. The concept of shape in the microcosm is critically examined. Special attention is devoted to properly define the meaning of shape for bound-state systems of near massless quarks. The ideas that lead to the expectation of non-sphericity in the shape of hadrons, the calculations that predict it, and...

The polynomial solution of the N -dimensional space Schrödinger equation for a special case of Mie potential is obtained for any arbitrary l-state. The exact bound-state energy eigenvalues and the corresponding eigenfunctions are calculated for diatomic molecular systems in the Mie-type potential.