We describe a calculation of the spectrum of strange and nonstrange hadrons that simultaneously correlates the dressed-quark-core masses of meson and baryon ground-and excited-states within a single framework. The foundation for this analysis is a symmetry-preserving Dyson-Schwinger equation treatment of a vector×vector contact interaction. Our results exemplify and highlight the deep impact of dynamical chiral symmetry breaking on the hadron spectrum: an accurate description of the meson spectrum entails a similarly successful prediction of the spectrum of baryons, including those with strangeness. The analysis also provides numerous insights into baryon structure. For example, that baryon structure is largely flavour-blind, the first radial excitation of ground-state baryons is constituted almost entirely from axial-vector diquark correlations, and DCSB is the foundation for the ordering of low-lying baryon levels; viz., (1/2) + , (1/2) + , (1/2) − .

We describe expressions for pion and kaon dressed-quark distribution functions that incorporate contributions from gluons which bind quarks into these mesons and hence overcome a flaw of the commonly used handbag approximation. The distributions therewith obtained are purely valence in character, ensuring that dressed-quarks carry all a meson's momentum at a characteristic hadronic scale and vanishing as $(1-x)^2$ when Bjorken-$x\to 1$. Comparing such distributions within the pion and kaon, it is apparent that the size of SU(3)-flavour symmetry breaking in meson parton distribution functions is modulated by the flavour dependence of dynamical chiral symmetry breaking. Corrections to these leading-order formulae may be divided into two classes, responsible for shifting dressed-quark momentum into glue and sea-quarks. Working with available empirical information, we build an algebraic framework that is capable of expressing the principal impact of both classes of corrections. This enables a realistic comparison with experiment which allows us to identify and highlight basic features of measurable pion and kaon valence-quark distributions. We find that whereas roughly two-thirds of the pion's light-front momentum is carried by valence dressed-quarks at a characteristic hadronic scale, this fraction rises to 95% in the kaon; evolving distributions with these features to a scale typical of available Drell-Yan data produces a kaon-to-pion ratio of u-quark distributions that is in agreement with the single existing data set; and predict a u-quark distribution within the pion that agrees with a modern reappraisal of $\pi N$ Drell-Yan data. Precise new data are essential in order to validate this reappraisal and because a single modest-quality measurement of the kaon-to-pion ratio cannot be considered definitive.Comment: 10 pages, 3 figures. arXiv admin note: text overlap with arXiv:1406.545

In the Mott insulating phase of the transition metal oxides, the effective orbital-orbital interaction is directional both in the orbital space and in the real space. We discuss a classical realization of directional coupling in two dimensions. Despite extensive degeneracy of the ground state, the model exhibits partial orbital ordering in the form of directional ordering of fluctuations at low temperatures stabilized by an entropy gap. Transition to the disordered phase is shown to be in the Ising universality class through exact mapping and multicanonical Monte Carlo simulations.PACS numbers: 64.60. Cn,05.10.Ln,75.30.Et,75.40.Cx Recently, there has been growing interest in the effects of orbital degeneracy in the physics of transition metal oxide insulators [1,2]. In these systems, the dominating energy scales for d-electrons on transition metal (TM) ions are the on-site Coulomb repulsion (which freezes out the charge degrees of freedom), the Hund's rule coupling, and the crystal field due to the surrounding oxygen ions. The latter two together determine the degeneracies and degrees of freedom of spin and orbital on each transition metal ions. Spins and orbitals on neighboring TM ions can then be coupled through the superexchange mechanism. In the case of orbitals, they are also coupled through the phonon-mediated cooperative JahnTeller mechanism [1]. These couplings determine the low temperature properties of these systems.Because orbital coupling is intrinsically directional[3], orbital ordering brings up some unusual questions. Especially interesting is when the coupling along a given bond direction is Ising like, but with different Ising axes along different bond directions [4]. The Hamiltonian for orbitals is then given bywhere τ is an isospin operator representing the orbital degree of freedom, and n ij is a unit vector giving the Ising axis for the bond ij . For example, for e g orbitals in Perovskite structures, n ij for the three different bond directions are coplanar and oriented relative to each other by 120• , giving rise to the so-called 120• Model [4,5,6]. This model is also applicable to t 2g orbitals on the three bonds of a honeycomb lattice as in planes of V 2 O 3 [7,8]. On the other hand, for t 2g orbitals on Perovskite structures, the relevant model is the Compass Model [1,4,10] with n ij = x, y, z for the three bond directions. The Compass Model may also feature as part of the spinspin coupling of t 2g orbitals when spin-orbit interaction is taken into account [11]. A common feature of both the Compass Model and the 120• Model is the competition between bonds in different directions, with the resulting frustration leading to macroscopic degeneracy of the classical ground state.In this Letter, we report analytical and numerical results on a classical version of (1) in 2D. The highly anisotropic coupling gives rise to interesting interplay between one-and two-dimensional ordering, between continuous and discrete spin physics, and between slow and fast modes. Our main result is that at low ...

We investigate the ground state of a uniform two-dimensional polarized Fermi gas with Rashba spin-orbit coupling at zero temperature. We construct the phase diagram by comparing the thermodynamic potential of superfluid and phase-separated states in detail. Due to the competition between polarization and spin-orbit coupling, we find that phase-separated states in the phase diagram can be topologically trivial and nontrivial. These two topologically distinct phase-separated states can not be connected without topological phase transition. The spin-orbit coupling reduces the effect of the population imbalance. Therefore, the phase-separated states are unstable to the superfluid phases for a large spin-orbit coupling.