25,606 research outputs found
The space of unipotently supported class functions on a finite reductive group
We determine the Lusztig restrictions on the space of class functions with a
unipotent support on a finite reductive group. In particular we give a simple
expression for the Lusztig restrictions of the generalized Green functions and
we describe the Lusztig restrictions of the generalized Gelfand-Graev
representations. We make explicit computations for the Gelfand-Graev
representations associated to the subregular unipotent class. In the case of
SLn we show that the computations can be reduced to the case of GLn' for
various n'.Comment: 21 page
Spin ice thin films: Large-N theory and Monte Carlo simulations
We explore the physics of highly frustrated magnets in confined geometries,
focusing on the Coulomb phase of pyrochlore spin ices. As a specific example,
we investigate thin films of nearest-neighbor spin ice, using a combination of
analytic large-N techniques and Monte Carlo simulations. In the simplest film
geometry, with surfaces perpendicular to the [001] crystallographic direction,
we observe pinch points in the spin-spin correlations characteristic of a
two-dimensional Coulomb phase. We then consider the consequences of crystal
symmetry breaking on the surfaces of the film through the inclusion of orphan
bonds. We find that when these bonds are ferromagnetic, the Coulomb phase is
destroyed by the presence of fluctuating surface magnetic charges, leading to a
classical Z_2 spin liquid. Building on this understanding, we discuss other
film geometries with surfaces perpendicular to the [110] or the [111]
direction. We generically predict the appearance of surface magnetic charges
and discuss their implications for the physics of such films, including the
possibility of an unusual Z_3 classical spin liquid. Finally, we comment on
open questions and promising avenues for future research.Comment: 17 pages, 11 figures. Minor improvements, typos correcte
Ab-initio No-Core Gamow Shell Model calculations with realistic interactions
No-Core Gamow Shell Model (NCGSM) is applied for the first time to study
selected well-bound and unbound states of helium isotopes. This model is
formulated on the complex energy plane and, by using a complete Berggren
ensemble, treats bound, resonant, and scattering states on equal footing. We
use the Density Matrix Renormalization Group method to solve the many-body
Schr\"{o}dinger equation. To test the validity of our approach, we benchmarked
the NCGSM results against Faddeev and Faddeev-Yakubovsky exact calculations for
H and He nuclei. We also performed {\textit ab initio} NCGSM
calculations for the unstable nucleus He and determined the ground state
energy and decay width, starting from a realistic NLO chiral interaction.Comment: 17 pages, 14 figures. Revised version. Discussion on microscopic
overlap functions, SFs and ANCs is added. Added references. Accepted for
publication at PR
Coarse-grained simulation of amphiphilic self-assembly
We present a computer simulation study of amphiphilic self assembly performed using a computationally efficient single-site model based on Gay-Berne and Lennard-Jones particles. Molecular dynamics simulations of these systems show that free self-assembly of micellar, bilayer and inverse micelle arrangements can be readily achieved for a single model parameterisation. This self-assembly is predominantly driven by the anisotropy of the amphiphile-solvent interaction, amphiphile-amphiphile interactions being found to be of secondary importance. While amphiphile concentration is the main determinant of phase stability, molecular parameters such as headgroup size and interaction strength also have measurable affects on system properties. </p
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