QCD at high baryon density in a random matrix model

A high density diquark phase seems to be a generic feature of QCD. If so it should also be reproduced by random matrix models. We discuss a specific one in which the random matrix elements of the Dirac operator are supplemented by a finite chemical potential and by non-random elements which model the formation of instanton-anti-instanton molecules. Comparing our results to those found in a previous investigation by Vanderheyden and Jackson we find additional support for our starting assumption, namely that the existence of a high density diquark phase is common to all QCD-like models.Comment: 16 pages, 4 figures, final version to appear in Eur.Phys.J.

The Nucleon-Nucleon Potential in the Chromo-Dielectric Soliton Model: Statics

We study the N-N interaction in the framework of the chromo-dielectric soliton model. Here, the long-range parts of the nonabelian gluon self-interactions are assumed to give rise to a color-dielectric function which is parameterized in terms of an effective scalar background field. The six-quark system is confined in a deformed mean field through an effective non-linear interaction between the quarks and the scalar field. The CDM is covariant, respects chiral invariance, leads to absolute color confinement and is free of the spurious long range Van der Waals forces which trouble non-relativistic investigations employing a confining potential. Six-quark molecular-type configurations are generated as a function of deformation and their energies are evaluated in a coupled channel analysis. By using molecular states instead of cluster model wave functions, all important six-quark configurations are properly taken into account. The corresponding Hamiltonian includes the effective interaction between the quarks and the scalar background field and quark-quark interactions generated through one gluon exchange treated in Coulomb gauge. When evaluating the gluonic propagators, the inhomogeneity and deformation of the dielectric medium are taken into account. Results for the adiabatic nucleon-nucleon potential are presented, and the various contributions are discussed. Finally, an outlook is given on how, in the next stage of our investigation, the dynamical effects will be incorporated by employing the generator coordinate method.Comment: 43 pages, REVTeX file followed by 11 uuencoded PostScript figures, DOE/ER/40427-02-N9

Quantum Phase Transitions

We give a general introduction to quantum phase transitions in strongly-correlated electron systems. These transitions which occur at zero temperature when a non-thermal parameter $g$ like pressure, chemical composition or magnetic field is tuned to a critical value are characterized by a dynamic exponent $z$ related to the energy and length scales $\Delta$ and $\xi$. Simple arguments based on an expansion to first order in the effective interaction allow to define an upper-critical dimension $D_{C}=4$ (where $D=d+z$ and $d$ is the spatial dimension) below which mean-field description is no longer valid. We emphasize the role of pertubative renormalization group (RG) approaches and self-consistent renormalized spin fluctuation (SCR-SF) theories to understand the quantum-classical crossover in the vicinity of the quantum critical point with generalization to the Kondo effect in heavy-fermion systems. Finally we quote some recent inelastic neutron scattering experiments performed on heavy-fermions which lead to unusual scaling law in $\omega /T$ for the dynamical spin susceptibility revealing critical local modes beyond the itinerant magnetism scheme and mention new attempts to describe this local quantum critical point.Comment: 13 pages, 4 figure

Multiquark Systems in a Constituent Quark Model with Chiral Dynamics

We discuss the stability of multiquark systems within the recent model of Glozman et al. where the chromomagnetic hyperfine interaction is replaced by pseudoscalar-meson exchange. We find that such an interaction binds a heavy tetraquark system $QQ\bar q\bar q$ ($Q=c, b$ and $q=u, d)$ by $0.2-0.4$ GeV. This is at variance with results of previous models where $cc\bar q\bar q$ is unstable.Comment: 6 pages, Plain Latex, Contribution to the Workshop''Quark Confinement and the Hadron Spectrum II'', Como, Italy, June 26--29, 1996, to appear in the Proceedings, ed. Nora Brambilla, World Scientifi

Heavy-Flavour Pentaquarks in a Chiral Constituent Quark Model

Within the chiral constituent quark model of Glozman and Riska, we discuss the stability of heavy pentaquarks, i.e. hadrons containing four light quarks and a heavy antiquark. The spin-dependent part of the Hamiltonian is dominated by the short-range part of the Goldstone-boson-exchange interaction. We find that these systems are not bound, having an energy above the lowest dissociation threshold into a baryon and a meson.Comment: 10 pages + table

New approach to 4^4He charge distribution

We present a study of the $^4$He charge distribution based on realistic nucleonic wave functions and incorporation of the nucleon's quark substructure. The central depression of the proton point density seen in modern four-body calculations is too small by itself to lead to a correct description of the charge distribution. We utilize six-quark structures calculated in the Chromodielectric Model for N-N interactions, and we find a swelling of the proton charge distribution as the internucleon distance decreases. These charge distributions are combined with the $^4$He wave function using the Independent Pair Approximation and two-body distributions generated from Green's Function Monte Carlo calculations. We obtain a reasonably good fit to the experimental charge distribution without including meson exchange currents.Comment: 9 pages, LaTeX, 4 figures (Figures 1 and 2 doesn't exist as postscript files : they are only available on request

BOARD INVITED REVIEW: Prospects for improving management of animal disease introductions using disease-dynamic models

Management and policy decisions are continually made to mitigate disease introductions in animal populations despite often limited surveillance data or knowledge of disease transmission processes. Science-based management is broadly recognized as leading to more effective decisions yet application of models to actively guide disease surveillance and mitigate risks remains limited. Disease-dynamic models are an efficient method of providing information for management decisions because of their ability to integrate and evaluate multiple, complex processes simultaneously while accounting for uncertainty common in animal diseases. Here we review disease introduction pathways and transmission processes crucial for informing disease management and models at the interface of domestic animals and wildlife. We describe how disease transmission models can improve disease management and present a conceptual framework for integrating disease models into the decision process using adaptive management principles. We apply our framework to a case study of African swine fever virus in wild and domestic swine to demonstrate how disease-dynamic models can improve mitigation of introduction risk. We also identify opportunities to improve the application of disease models to support decision-making to manage disease at the interface of domestic and wild animals. First, scientists must focus on objective-driven models providing practical predictions that are useful to those managing disease. In order for practical model predictions to be incorporated into disease management a recognition that modeling is a means to improve management and outcomes is important. This will be most successful when done in a cross-disciplinary environment that includes scientists and decisionmakers representing wildlife and domestic animal health. Lastly, including economic principles of value-of-information and cost-benefit analysis in disease-dynamic models can facilitate more efficient management decisions and improve communication of model forecasts. Integration of disease-dynamic models into management and decision-making processes is expected to improve surveillance systems, risk mitigations, outbreak preparedness, and outbreak response activities

Timing of maternal exposure and fetal sex determine the effects of low-level chemical mixture exposure on the fetal neuroendocrine system in sheep

We have shown that continuous maternal exposure to the complex mixture of environmental chemicals (ECs) found in human biosolids (sewage sludge), disrupts mRNA expression of genes crucial for development and long-term regulation of hypothalamo-pituitary gonadal (HPG) function in sheep. This study investigated whether exposure to ECs only during preconceptional period or only during pregnancy perturbed key regulatory genes within the hypothalamus and pituitary gland and whether these effects were different from chronic (life-long) exposure to biosolid ECs. The findings demonstrate that the timing and duration of maternal EC exposure influences the subsequent effects on the fetal neuroendocrine system in a sex-specific manner. Maternal exposure prior to conception or during pregnancy only, altered the expression of key fetal neuroendocrine regulatory systems such as GnRH and kisspeptin to a greater extent than when maternal exposure was ‘life-long’. Furthermore, hypothalamic gene expression was affected to a greater extent in males than in females, and following EC exposure, male fetuses expressed more “female-like” mRNA levels for some key neuroendocrine genes. This is the first study to show that “real-life” maternal exposure to low levels of a complex cocktail of chemicals prior to conception can subsequently affect the developing fetal neuroendocrine system. These findings demonstrate that the developing neuroendocrine system is sensitive to EC mixtures in a sex-dimorphic manner likely to predispose to reproductive dysfunction in later life