Inequivalent representations of commutator or anticommutator rings of field operators and their applications

Hamiltonian of a system in quantum field theory can give rise to infinitely many partition functions which correspond to infinitely many inequivalent representations of the canonical commutator or anticommutator rings of field operators. This implies that the system can theoretically exist in infinitely many Gibbs states. The system resides in the Gibbs state which corresponds to its minimal Helmholtz free energy at a given range of the thermodynamic variables. Individual inequivalent representations are associated with different thermodynamic phases of the system. The BCS Hamiltonian of superconductivity is chosen to be an explicit example for the demonstration of the important role of inequivalent representations in practical applications. Its analysis from the inequivalent representations' point of view has led to a recognition of a novel type of the superconducting phase transition.Comment: 25 pages, 6 figure

From the Feynman-Schwinger representation to the non-perturbative relativistic bound state interaction

We write the 4-point Green function in QCD in the Feynman-Schwinger representation and show that all the dynamical information are contained in the Wilson loop average. We work out the QED case in order to obtain the usual Bethe-Salpeter kernel. Finally we discuss the QCD case in the non-perturbative regime giving some insight in the nature of the interaction kernel.Comment: 25 pages, RevTex, 3 figures included, typos corrected, to appear in Phys. Rev. D 5

QCD Sum Rules for Σ\Sigma Hyperons in Nuclear Matter

Within finite-density QCD sum-rule approach we investigate the self-energies of $\Sigma$ hyperons propagating in nuclear matter from a correlator of $\Sigma$ interpolating fields evaluated in the nuclear matter ground state. We find that the Lorentz vector self-energy of the $\Sigma$ is similar to the nucleon vector self-energy. The magnitude of Lorentz scalar self-energy of the $\Sigma$ is also close to the corresponding value for nucleon; however, this prediction is sensitive to the strangeness content of the nucleon and to the assumed density dependence of certain four-quark condensate. The scalar and vector self-energies tend to cancel, but not completely. The implications for the couplings of $\Sigma$ to the scalar and vector mesons in nuclear matter and for the $\Sigma$ spin-orbit force in a finite nucleus are discussed.Comment: 20 pages in revtex, 6 figures available under request as ps files, UMD preprint #94--11

In-medium operator product expansion for heavy-light-quark pseudoscalar mesons

The operator product expansion (OPE) for heavy-light-quark pseudoscalar mesons (D-mesons and B-mesons) in medium is determined, both for a moving meson with respect to the surrounding medium as well as for a meson at rest. First of all, the OPE is given in terms of normal-ordered operators up to mass dimension 5, and the mass of the heavy-quark and the mass of the light-quark are kept finite. The Wilson coefficients of such an expansion are infrared (IR) divergent in the limit of a vanishing light-quark mass. A consistent separation of scales necessitates an OPE in terms of non-normal-ordered operators, which implies operator mixing, where the IR-divergences are absorbed into the operators. It is shown that the Wilson coefficients of such an expansion are IR-stable, and the limit of a vanishing light-quark mass is perfomed. Details of the major steps for the calculation of the Wilson coefficients are presented. By a comparison with previous results obtained by other theoretical groups we have found serious disagreements.Comment: 51 pages, 3 figure

The theory and phenomenology of polarized deep inelastic scattering

Comprehensive review paper on the theory and phenomenology of polarized deep inelastic scattering, to appear in Physics ReportsComment: 113 pages, latex, 40 figures not included (hard copies available via mail upon request to [email protected]

Association between sensory function and hop performance and self-reported outcomes in patients with anterior cruciate ligament injury

Anna Cronström,1 Ewa M Roos,2 Eva Ageberg1 1Department of Health Sciences, Lund University, Lund, Sweden; 2Research Unit for Musculoskeletal Function and Physiotherapy, Department of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark Background: In patients with anterior cruciate ligament (ACL) deficiency (ACLD) or reconstruction (ACLR), sensory deficits are commonly assessed as knee kinesthesia using time-consuming laboratory equipment. Portable equipment such as that used for evaluation of vibration sense would be preferable. In contrast to kinesthesia, vibration sense is not well studied in these patients. Objectives: 1) To study the association between kinesthesia and vibration sense to investigate if one sensory measurement can replace the other; and 2) to determine the clinical relevance by investigating associations between the sensory measurements and functional performance and patient-reported outcomes in patients with ACLD or ACLR. Methods: Twenty patients with ACLD and 33 patients with ACLR were assessed with knee kinesthesia, vibration sense, the one-leg hop test for distance, as well as the Knee injury and Osteoarthritis Outcome Score (KOOS) and the Tegner Activity Scale. Results: There were no significant correlations between kinesthesia and vibration sense (r= –0.267, p>0.269) or between the sensory measures and hop performance (r= –0.351, p>0.199). In patients with ACLD, worse knee kinesthesia was associated with worse scores on KOOS subscales pain (r= –0.464, p=0.046) and activities of daily living (r= –0.491, p=0.033), and worse vibration sense was associated with worse scores on KOOS subscale quality of life (r= –0.469, p=0.037) and worse knee confidence (item Q3 from subscale quality of life) (rs=0.436, p=0.054). In patients with ACLR, worse vibration sense was associated with worse scores on KOOS subscales pain (r= –0.402, p=0.020) and activities of daily living (r= –0.385, p=0.027). Conclusion: Kinesthesia and vibration sense cannot be used interchangeably as measures of sensory function in patients with ACLD or ACLR. Both sensory measurements were weakly related to hop performance. Adequate sensory function appears to have importance for perceived function in patients with ACLD or ACLR and may therefore be a factor that needs to be addressed in rehabilitation programs for these patients. Keywords: knee injury, proprioception, sensory function, functional performance, patient reported outcome