Charge stripe order from antiphase spin spirals in the spin-Fermion model

We revisit the ground state of the spin-Fermion model within a semiclassical approximation. We demonstrate that antiphase spin spirals, or pi-spirals, whose chirality alternates between consecutive rows (or columns) of local moments, have, for sufficiently high carrier concentration, lower energy than the traditional Shraiman and Siggia spirals. Furthermore, pi-spirals give rise to modulated hopping, anisotropic 1D transport, and charge density wave formation. Finally, we discuss the relevance of pi-spirals to the physics of charge stripe formation in cuprates, such as La(2-x)Sr(x)CuO4.Comment: 4 pages, 3 figure

Currents and Superpotentials in classical gauge theories: II. Global aspects and the example of Affine gravity

The conserved charges associated with gauge symmetries are defined at a boundary component of spacetime because the corresponding Noether current can be rewritten on-shell as the divergence of a superpotential. However, the latter is afflicted by ambiguities. Regge and Teitelboim found a procedure to lift the arbitrariness in the Hamiltonian framework. An alternative covariant formula was proposed by one of us for an arbitrary variation of the superpotential, it depends only on the equations of motion and on the gauge symmetry under consideration. Here we emphasize that in order to compute the charges, it is enough to stay at a boundary of spacetime, without requiring any hypothesis about the bulk or about other boundary components, so one may speak of holographic charges. It is well known that the asymptotic symmetries that lead to conserved charges are really defined at infinity, but the choice of boundary conditions and surface terms in the action and in the charges is usually determined through integration by parts, whereas each component of the boundary should be considered separately. We treat the example of gravity (for any spacetime dimension, with or without cosmological constant), formulated as an affine theory which is a natural generalization of the Palatini and Cartan-Weyl (vielbein) first-order formulations. We then show that the superpotential associated with a Dirichlet boundary condition on the metric (the one needed to treat asymptotically flat or AdS spacetimes) is the one proposed by Katz et al and not that of Komar. We finally discuss the KBL superpotential at null infinity

On the rotation of ONC stars in the Tsallis formalism context

The theoretical distribution function of the projected rotational velocity is derived in the context of the Tsallis formalism. The distribution is used to estimate the average for a stellar sample from the Orion Nebula Cloud (ONC), producing an excellent result when compared with observational data. In addition, the value of the parameter q obtained from the distribution of observed rotations reinforces the idea that there is a relation between this parameter and the age of the cluster.Comment: 6 pages, 2 figure

Gaussian Process Structural Equation Models with Latent Variables

In a variety of disciplines such as social sciences, psychology, medicine and economics, the recorded data are considered to be noisy measurements of latent variables connected by some causal structure. This corresponds to a family of graphical models known as the structural equation model with latent variables. While linear non-Gaussian variants have been well-studied, inference in nonparametric structural equation models is still underdeveloped. We introduce a sparse Gaussian process parameterization that defines a non-linear structure connecting latent variables, unlike common formulations of Gaussian process latent variable models. The sparse parameterization is given a full Bayesian treatment without compromising Markov chain Monte Carlo efficiency. We compare the stability of the sampling procedure and the predictive ability of the model against the current practice.Comment: 12 pages, 6 figure

Characterization of Spherical and Plane Curves Using Rotation Minimizing Frames

In this work, we study plane and spherical curves in Euclidean and Lorentz-Minkowski 3-spaces by employing rotation minimizing (RM) frames. By conveniently writing the curvature and torsion for a curve on a sphere, we show how to find the angle between the principal normal and an RM vector field for spherical curves. Later, we characterize plane and spherical curves as curves whose position vector lies, up to a translation, on a moving plane spanned by their unit tangent and an RM vector field. Finally, as an application, we characterize Bertrand curves as curves whose so-called natural mates are spherical.Comment: 8 pages. This version is an improvement of the previous one. In addition to a study of some properties of plane and spherical curves, it contains a characterization of Bertrand curves in terms of the so-called natural mate

What's [Yet] to Be Seen? Re-Using Qualitative Data

This paper considers current debates about re-using qualitative research data by reflecting on its implications for the nature of social science knowledge created in this process and the ways in which the disclosure of researchers\' practices are linked with the making of professional academic careers. It examines a research project using two different approaches – a \'virtual\' and a \'classic\' ethnography – to argue that issues concerned with re-use of data depend on the methods employed and the overall processes of investigation. The paper argues for an appreciation of the contexts involved in the generation of research material which takes into account both the development of the study and related fieldwork processes as well as the academic context in which knowledge is produced, particularly those involved in the construction of academic selves and professional careers, which are part of a wider situation bearing upon scientific enquiry.Secondary Data Analysis, Ethnography, Visual Methodology, Academic Careers