We consider a chiral baryon-meson model for nucleons and their parity partners in mirror assignment interacting with pions and sigma and omega mesons to describe the liquid-gas transition of nuclear matter together with chiral symmetry restoration in the high density phase. Within the mean-field approximation the model is known to provide a phenomenologically successful description of the nuclear-matter transition. Here, we go beyond this approximation and include mesonic fluctuations by means of the functional renormalization group. While these fluctuations do not lead to major qualitative changes in the phase diagram of the model, beyond the mean-field approximation, one is no longer free to adjust the parameters so as to reproduce the binding energy per nucleon, the nuclear saturation density, and the nucleon sigma term all at the same time. However, the prediction of a clear first-order chiral transition at low temperatures inside the high baryon-density phase appears to be robust.
We investigate twisted $C$-periodic boundary conditions in $\mathrm{SU}(N)$ gauge field theory with an adjoint Higgs field. We show that with a suitable twist for even $N$ one can impose a nonzero magnetic charge relative to residual U(1) gauge groups in the broken phase, thereby creating a 't Hooft-Polyakov magnetic monopole. This makes it possible to use lattice Monte Carlo simulations to study the properties of these monopoles in the quantum theory.
We review aspects of confinement in the covariant and local description of QCD and discuss to what extend our present knowledge of the infrared behavior of QCD Green functions can support this description. In particular, we emphasize: the positivity violations of transverse gluon and quark states, the Kugo-Ojima confinement criterion, and the conditions necessary to avoid the decomposition property for colored clusters. We summarize how these issues relate to the infrared behavior of the propagators in Landau gauge QCD as extracted from solutions to truncated Dyson-Schwinger equations and lattice simulations.
We investigate the effectiveness of using smearing as a means to generate a preconditioning transformation for gauge fields prior to fixing to Maximal Centre Gauge. This still leaves the gauge-fixed field in the original gauge orbit. As expected, we find that this preconditioning leads to higher maxima of the gauge-fixing condition, resulting in lower numbers of P-vortices. We also find that removing vortices appears to give a loss of confinement for all cases but that the string tension as measured from vortex-only configurations drops from about 65% to as low as 26% when using the preconditioning method.
We study the renormalization of the Fermi velocity by the long-range Coulomb interactions between the charge carriers in the Dirac-cone approximation for the effective low-energy description of the electronic excitations in graphene at half-filling. Solving the coupled system of Dyson-Schwinger equations for the dressing functions in the corresponding fermion propagator with various approximations for the particle-hole polarization, we observe that Fermi velocity renormalization effects generally lead to a considerable increase of the critical coupling for dynamical gap generation and charge-density-wave formation at the semimetal-insulator transition.
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