Deriving exact results for Ising-like models from the cluster variation method

The cluster variation method (CVM) is an approximation technique which generalizes the mean field approximation and has been widely applied in the last decades, mainly for finding accurate phase diagrams of Ising-like lattice models. Here we discuss in which cases the CVM can yield exact results, considering: (i) one-dimensional systems and strips (in which case the method reduces to the transfer matrix method), (ii) tree-like lattices and (iii) the so-called disorder points of euclidean lattice models with competitive interactions in more than one dimension.Comment: 3 pages, presented at Lattice '9

Motivation and demotivation over two years: A case study of English language learners in Japan

This paper is about four Japanese university students majoring in international studies, who participated in a two-year study examining changes in their motivation. Using monthly interviews and a 29-item questionnaire on Dörnyei’s (2005) L2 motivational self system that was administered alongside each interview, the trajectories of learner motivation were investigated, based on both quantitative and qualitative data. First, changes in the participants’ motivation were identified using quantitative data. Next, a variety of motivators and demotivators that learners experienced both inside and outside of their classrooms were analyzed using the qualitative data. With the data obtained, this study focuses on how four learners’ language learning motivation and contexts adapt to each other, and how the dynamics of the four learners’ motivation changes due to their learning experiences. Each learner was different in their trajectory of motivation and the kinds of motivators and demotivators that they experienced in their particular contexts. The four learners underwent unique motivators and demotivators, and reacted differently. While participants identified their ideal L2 selves, or ought-to L2 selves, these self-guides were not strengthened by their L2 experiences over time. Based on these findings, the importance of studying the rich experiences of language learners in motivation research is discussed

Poincare invariance in temporal gauge canonical quantization and θ\theta-vacua

The Poincare invariance in the temporal gauge canonical quantization of QCD is shown manifestly by verifying the energy-momentum-vector and angular-momentum-tensor satisfy the Poincare algebra in the physical Hilbert space. Two different values of $\theta$ for the $\theta$-term in QCD lagrangian lead to different representations of the Poincare group, which are, however, connected by an unitary transformation. Thus the parameter $\theta$ becomes physically irrelevant unless we can further restrict the physical Hilbert space.Comment: 18 pages, UCRHEP-T10

Flavor-Changing Magnetic Dipole Moment and Oscillation of a Neutrino in a Degenerate Electron Plasma

The standard model prediction for a magnetic dipole moment of a neutrino is proportional to the neutrino mass and extremely small. It also generates a flavor-changing process, but the GIM mechanism reduces the corresponding amplitude. These properties of a neutrino magnetic moment change drastically in a degenerate electron plasma. We have shown that an electron-hole excitation gives a contribution proportional to the electrons' Fermi momentum. Since this effect is absent in $\mu$ and $\tau$ sector, the GIM cancellation does not work. The magnetic moment induces a neutrino oscillation if a strong enough magnetic field exists in the plasma. The required magnitude of the field strength that affects the \nue\ burst from a supernova is estimated to be the order of $10^8$ Gauss.Comment: 10 pages, Latex, Misleading terminology and typographical errors are correcte