Magnetic multipole analysis of kagome and artificial ice dipolar arrays

We analyse an array of linearly extended monodomain dipoles forming square and kagome lattices. We find that its phase diagram contains two (distinct) finite-entropy kagome ice regimes - one disordered, one algebraic - as well as a low-temperature ordered phase. In the limit of the islands almost touching, we find a staircase of corresponding entropy plateaux, which is analytically captured by a theory based on magnetic charges. For the case of a modified square ice array, we show that the charges ('monopoles') are excitations experiencing two distinct Coulomb interactions: a magnetic 'three-dimensional' one as well as a logarithmic `two dimensional' one of entropic origin.Comment: 4 pages, 2 figures; v2: minor changes as in final published versio

Paired composite fermion wavefunctions

We construct a family of BCS paired composite fermion wavefunctions that generalize, but remain in the same topological phase as, the Moore-Read Pfaffian state for the half-filled Landau level. It is shown that for a wide range of experimentally relevant inter-electron interactions the groundstate can be very accurately represented in this form.Comment: 4 pages, 2 figure

Paired composite fermion phase of quantum Hall bilayers at \nu = 1/2 + 1/2

We provide numerical evidence for composite fermion pairing in quantum Hall bilayer systems at filling $\nu=1/2 + 1/2$ for intermediate spacing between the layers. We identify the phase as $p_x + i p_y$ pairing, and construct high accuracy trial wavefunctions to describe the groundstate on the sphere. For large distances between the layers, and for finite systems, a competing "Hund's rule" state, or composite fermion liquid, prevails for certain system sizes. We argue that for larger systems, the pairing phase will persist to larger layer spacing.Comment: 4 pages, 2 figures; v2: final version, as published in journa

Dependence of direct neutron capture on nuclear-structure models

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We calculate direct neutron capture on the even-even isotopes $^{124-145}$Sn and $^{208-238}$Pb with energy levels, masses, and nuclear density distributions taken from different nuclear-structure models. The utilized structure models are a Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a macroscopic-microscopic model based on the finite-range droplet model and a folded-Yukawa single-particle potential. Due to the differences in the resulting neutron separation and level energies, the investigated models yield capture cross sections sometimes differing by orders of magnitude. This may also lead to differences in the predicted astrophysical r-process paths. Astrophysical implications are discussed.Comment: 25 pages including 12 figures, RevTeX, to appear in Phys. Rev.

Fractional Quantum Hall Effect of Lattice Bosons Near Commensurate Flux

We study interacting bosons on a lattice in a magnetic field. When the number of flux quanta per plaquette is close to a rational fraction, the low energy physics is mapped to a multi-species continuum model: bosons in the lowest Landau level where each boson is given an internal degree of freedom, or \emph{pseudospin}. We find that the interaction potential between the bosons involves terms that do not conserve pseudospin, corresponding to umklapp processes, which in some cases can also be seen as BCS-type pairing terms. We argue that in experimentally realistic regimes for bosonic atoms in optical lattices with synthetic magnetic fields, these terms are crucial for determining the nature of allowed ground states. In particular, we show numerically that certain paired wave functions related to the Moore-Read Pfaffian state are stabilized by these terms, whereas certain other wave functions can be destabilized when umklapp processes become strong

First decay study of the very neutron-rich isotope Br-93

The decay of the mass-separated, very neutron-rich isotope Br-93 has been studied by gamma-spectroscopy. A level scheme of its daughter Kr-93 has been constructed. Level energies, gamma-ray branching ratios and multipolarities suggest spins and parities which are in accord with a smooth systematics of the N=57 isotones for Z less-equal 40, suggesting the N=56 shell closure still to be effective in Kr isotopes. So far, there is no indication of a progressive onset of deformation in neutron-rich Kr isotopes.Comment: 17 pages, 3 figures, Phys. Rev. C, in prin

RPA approach to rotational symmetry restoration in a three-level Lipkin model

We study an extended Lipkin-Meshkov-Glick model that permits a transition to a deformed phase with a broken continuous symmetry. Unlike simpler models, one sees a persistent zero-frequency Goldstone mode past the transition point into the deformed phase. We found that the RPA formula for the correlation energy provides a useful correction to the Hartree-Fock energy when the number of particle N satisfies N > 3, and becomes accurate for large N. We conclude that the RPA correlation energy formula offers a promising way to improve the Hartree-Fock energy in a systematic theory of nuclear binding energies.Comment: RevTex, 11 pages, 3 postscript figure

A Factorization Algorithm for G-Algebras and Applications

It has been recently discovered by Bell, Heinle and Levandovskyy that a large class of algebras, including the ubiquitous $G$-algebras, are finite factorization domains (FFD for short). Utilizing this result, we contribute an algorithm to find all distinct factorizations of a given element $f \in \mathcal{G}$, where $\mathcal{G}$ is any $G$-algebra, with minor assumptions on the underlying field. Moreover, the property of being an FFD, in combination with the factorization algorithm, enables us to propose an analogous description of the factorized Gr\"obner basis algorithm for $G$-algebras. This algorithm is useful for various applications, e.g. in analysis of solution spaces of systems of linear partial functional equations with polynomial coefficients, coming from $\mathcal{G}$. Additionally, it is possible to include inequality constraints for ideals in the input