Hamiltonian Approach to QCD: The effective potential of the Polyakov loop

The effective potential of the order parameter for confinement is calculated within the Hamiltonian approach to Yang--Mills theory. Compactifying one spatial dimension and using a background gauge fixing this potential is obtained by minimizing the energy density for a given background field. Using Gaussian type trial wave functionals I establish an analytic relation between the propagators in the background gauge at finite temperature and the corresponding zero temperature propagators in Coulomb gauge. In the simplest truncation, neglecting the ghost and using the ultraviolet form of the gluon energy one recovers the Weiss potential. From the fully non-perturbative potential (with the ghost included) one extracts a critical temperature of the deconfinement phase transition of 270 MeV for the gauge group SU(2).Comment: 8 pages, 6 eps figures. Talk given by Hugo Reinhardt at Xth Quark Confinement and the Hadron Spectrum, October 8--12, 2012 TUM Campus Garching, Munich, German

The effective potential of the confinement order parameter in the Hamiltonian approach

The effective potential of the order parameter for confinement is calculated for SU(N) Yang--Mills theory in the Hamiltonian approach. Compactifying one spatial dimension and using a background gauge fixing, this potential is obtained within a variational approach by minimizing the energy density for given background field. In this formulation the inverse length of the compactified dimension represents the temperature. Using Gaussian trial wave functionals we establish an analytic relation between the propagators in the background gauge at finite temperature and the corresponding zero-temperature propagators in Coulomb gauge. In the simplest truncation, neglecting the ghost and using the ultraviolet form of the gluon energy, we recover the Weiss potential. We explicitly show that the omission of the ghost drastically increases the transition temperature. From the full non-perturbative potential (with the ghost included) we extract a critical temperature of the deconfinement phase transition of 269 MeV for the gauge group SU(2) and 283 MeV for SU(3).Comment: 26 pages, 17 eps figure

The deconfinement phase transition in the Hamiltonian approach to Yang--Mills theory in Coulomb gauge

The deconfinement phase transition of SU(2) Yang--Mills theory is investigated in the Hamiltonian approach in Coulomb gauge assuming a quasi-particle picture for the grand canonical gluon ensemble. The thermal equilibrium state is found by minimizing the free energy with respect to the quasi-gluon energy. Above the deconfinement phase transition the ghost form factor remains infrared divergent but its infrared exponent is approximately halved, while the gluon energy, being infrared divergent in the confined phase, becomes infrared finite in the deconfined phase. For the effective gluon mass we find a critical exponent of 0.37. Using the lattice results for the gluon propagator to fix the scale, the deconfinement transition temperature is obtained in the range of 275 to 290 MeV.Comment: 20 pages, 13 figures, accepted for publication by Phys. Rev.

Facilitating dental student reflections : using mentor groups to discuss clinical experiences and personal development

Despite the consensus on the importance of reflection for dental professionals, a lack of understanding remains about how students and clinicians should develop their ability to reflect. The aim of this study was to investigate dental students’ and mentors’ perceptions of mentor groups as an instructional method to facilitate students’ reflection in terms of the strategy’s learning potential, role of the mentor, group dynamics, and feasibility. At Ghent University in Belgium, third- and fourth-year dental students were encouraged to reflect on their clinical experiences and personal development in three reflective mentor sessions. No preparation or reports afterwards were required; students needed only to participate in the sessions. Sessions were guided by trained mentors to establish a safe environment, frame clinical discussions, and stimulate reflection. Students’ and mentors’ perceptions of the experience were assessed with a 17-statement questionnaire with response options on a five-point Likert scale (1=totally disagree to 5=totally agree). A total of 50 students and eight mentors completed the questionnaire (response rates 81% and 89%, respectively). Both students and mentors had neutral to positive perceptions concerning the learning potential, role of the mentor, group dynamics, and feasibility. The mean ideal total time for sessions in a year was 99 minutes (third-year students), 111 minutes (fourth-year students), and 147 minutes (mentors). Reported reflective topics related to patient management, frustrations, and practice of dentistry. Overall mean appreciation for the experience ranged from 14.50 to 15.14 on the 20-point scale. These findings about students’ and mentors’ positive perceptions of the experience suggest that mentor groups may be a potentially valuable strategy to promote dental students’ reflection

Color Coulomb Potential in Yang-Mills Theory from Hamiltonian Flows

We consider the Hamiltonian formulation of Yang-Mills theory in the Coulomb gauge and apply the recently developed technique of Hamiltonian flows. We formulate a flow equation for the color Coulomb potential which allows for a scaling solution that results in an almost linearly rising confining potential.Comment: 6 pages, 4 figure

An analysis of the decision-making process for single implant treatment in general practice

Background: There is little information on the decision-making process for single implant treatment in general practice. Aim: To study the incidence of and the factors associated with the decision to perform single implant treatment after tooth extraction by general practitioners in a private, fee-for-service setting. Methods: One hundred practitioners with a general dental practice in Ghent were randomly selected from an official list received by the Belgian Social Security Institute. Clinicians were asked to fill in a study form for every single extraction they performed during an 8-week period. The study form related to the treatment decision as discussed with the patient and a number of patient- and clinician-related factors. The association of these factors with single implant treatment was evaluated using univariate tests and logistic regression. A decision-tree was also constructed with the predictors from the regression analysis as independent variables. Results: Ninety-four general dentists (52 males, 42 females; mean age 49; range 24–68)agreed to participate and extracted 1180 single teeth in an equal number of patients (50% males, 50% females; mean age 53; range 18–90). The main reasons for tooth loss were caries (48%) and periodontal disease (28%). At the time of extraction tooth replacement was deemed necessary in half of the patients and are movable partial denture was chosen in 55% of them. Similar frequencies were found for fixed partial denture (23%) and single implant treatment (21%). Although the vast majority of patient- and clinician-related factors showed a significant association with the latter on the basis of univariate tests, logistic regression only identified seven predictors. These included location of the extracted tooth, number of missing teeth, regular supportive care, bone loss at adjacent teeth, restoration level of adjacent teeth, gender of the clinician and dentists’ experience in implant prosthetics. The decision tree identified bone loss at adjacent teeth and number of missing teeth as the most important predictors for single implant treatment. Conclusions and clinical implications: If tooth replacement was deemed necessary at the time of extraction, a single implant was the treatment of choice in only one-fifth of the patients. Mainly oral factors had an impact on the decision-making process in contrast to patients’ background and medical factors. Dentists’ experience in implant prosthetics also showed a positive association with single implant treatment as opposed to dentists’ experience in implant surgery