"Exact" Algorithm for Random-Bond Ising Models in 2D

We present an efficient algorithm for calculating the properties of Ising models in two dimensions, directly in the spin basis, without the need for mapping to fermion or dimer models. The algorithm gives numerically exact results for the partition function and correlation functions at a single temperature on any planar network of N Ising spins in O(N^{3/2}) time or less. The method can handle continuous or discrete bond disorder and is especially efficient in the case of bond or site dilution, where it executes in O(L^2 ln L) time near the percolation threshold. We demonstrate its feasibility on the ferromagnetic Ising model and the +/- J random-bond Ising model (RBIM) and discuss the regime of applicability in cases of full frustration such as the Ising antiferromagnet on a triangular lattice.Comment: 4.2 pages, 5 figures, accepted for publication in Phys. Rev. Let

Asymmetric Two-component Fermion Systems in Strong Coupling

We study the phase structure of a dilute two-component Fermi system with attractive interactions as a function of the coupling and the polarization or number difference between the two components. In weak coupling, a finite number asymmetry results in phase separation. A mixed phase containing symmetric superfluid matter and an asymmetric normal phase is favored. With increasing coupling strength, we show that the stress on the superfluid phase to accommodate a number asymmetry increases. Near the infinite-scattering length limit, we calculate the single-particle excitation spectrum and the ground-state energy at various polarizations. A picture of weakly-interacting quasi-particles emerges for modest polarizations. In this regime near infinite scattering length, and for modest polarizations, a homogeneous phase with a finite population of excited quasi-particle states characterized by a gapless spectrum should be favored over the phase separated state. These states may be realized in cold atom experiments.Comment: 4 pages, 3 figur

Suppression or enhancement of the Fulde-Ferrell-Larkin-Ovchinnikov order in a one-dimensional optical lattice with particle correlated tunnelling

We study through controlled numerical simulation the ground state properties of spin-polarized strongly interacting fermi gas in an anisotropic optical lattice, which is described by an effective one-dimensional general Hubbard model with particle correlated hopping rate. We show that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) type of state, while enhanced by a negative correlated hopping rate, can be completely suppressed by positive particle correlated hopping, yielding to an unusual magnetic phase even for particles with on-site attractive interaction We also find several different phase separation patterns for these atoms in an inhomogeneous harmonic trap, depending on the correlated hopping rate

Importance of Baryon-Baryon Coupling in Hypernuclei

The $\Lambda N - \Sigma N$ coupling in $\Lambda$--hypernuclei and $\Lambda \Lambda - \Xi N$ coupling in $\Lambda \Lambda$--hypernuclei produce novel physics not observed in the conventional, nonstrange sector. Effects of $\Lambda \leftrightarrow \Sigma$ conversion in $^3_{\Lambda}$H are reviewed. The role of $\Lambda N - \Sigma N$ coupling suppression in the $A=4,5$ $\Lambda$--hypernuclei due to Pauli blocking is highlighted, and the implications for the structure of $^{10}_{\;\, \Lambda}$B are explored. Suppression of $\Lambda \Lambda - \Xi N$ conversion in $^{\;\;\, 6}_{\Lambda \Lambda}$He is hypothesized as the reason that the $$ matrix element is small. Measurement of $^{\;\;\, 4}_{\Lambda \Lambda}$H is proposed to investigate the full $\Lambda \Lambda - \Xi N$ interaction. The implication for $\Lambda \Lambda$ analog states is discussed.Comment: 17 pages LATEX, 1 figure uuencoded postscrip

Inclusive neutrino scattering off deuteron from threshold to GeV energies

Background: Neutrino-nucleus quasi-elastic scattering is crucial to interpret the neutrino oscillation results in long baseline neutrino experiments. There are rather large uncertainties in the cross section, due to insufficient knowledge on the role of two-body weak currents. Purpose: Determine the role of two-body weak currents in neutrino-deuteron quasi-elastic scattering up to GeV energies. Methods: Calculate cross sections for inclusive neutrino scattering off deuteron induced by neutral and charge-changing weak currents, from threshold up to GeV energies, using the Argonne $v_{18}$ potential and consistent nuclear electroweak currents with one- and two-body terms. Results: Two-body contributions are found to be small, and increase the cross sections obtained with one-body currents by less than 10% over the whole range of energies. Total cross sections obtained by describing the final two-nucleon states with plane waves differ negligibly, for neutrino energies $\gtrsim 500$ MeV, from those in which interaction effects in these states are fully accounted for. The sensitivity of the calculated cross sections to different models for the two-nucleon potential and/or two-body terms in the weak current is found to be weak. Comparing cross sections to those obtained in a naive model in which the deuteron is taken to consist of a free proton and neutron at rest, nuclear structure effects are illustrated to be non-negligible. Conclusion: Contributions of two-body currents in neutrino-deuteron quasi-elastic scattering up to GeV are found to be smaller than 10%. Finally, it should be stressed that the results reported in this work do not include pion production channels.Comment: 30 pages, 17 figures; publishe

Normal State Nernst Effect in Electron-doped Pr2-xCexCuO4: Superconducting Fluctuations and Two-band Transport

We report a systematic study of normal state Nernst effect in the electron-doped cuprates Pr$_{2-x}$Ce$_x$CuO$_{4-\delta}$ over a wide range of doping (0.05$\leq x \leq$0.21) and temperature. At low temperatures, we observed a notable vortex Nernst signal above T$_c$ in the underdoped films, but no such normal state vortex Nernst signal is found in the overdoped region. The superconducting fluctuations in the underdoped region are most likely incoherent phase fluctuations as found in hole-doped cuprates. At high temperatures, a large normal state Nernst signal is found at dopings from slightly underdoped to highly overdoped. Combined with normal state thermoelectric power, Hall effect and magnetoresistance measurements, the large Nernst effect is compatible with two-band model. For the highly overdoped films, the large Nernst effect is anomalous and not explainable with a simple hole-like Fermi surface seen in photoemission experiments.Comment: 9 pages, 8 figures, accepted in PR

Lithological maps of selected Apollo 14 Breccia samples

A booklet of mapped surfaces of some Apollo 14 samples was prepared as an intermediate step towards the preparation of a new Apollo 14 sample catalog. It contains recently obtained observations and pictures of some of the largest and less well documented Apollo breccia samples. Some of the samples (14303, 14305, 14306, and 14311) were chosen because they have large sawn surfaces. These were dusted and mapped using a binocular microscope through the window of the nitrogen cabinet

Evaluating matrix elements relevant to some Lorenz violating operators

Carlson, Carone and Lebed have derived the Feynman rules for a consistent formulation of noncommutative QCD. The results they obtained were used to constrain the noncommutativity parameter in Lorentz violating noncommutative field theories. However, their constraint depended upon an estimate of the matrix element of the quark level operator (gamma.p - m) in a nucleon. In this paper we calculate the matrix element of (gamma.p - m), using a variety of confinement potential models. Our results are within an order of magnitude agreement with the estimate made by Carlson et al. The constraints placed on the noncommutativity parameter were very strong, and are still quite severe even if weakened by an order of magnitude.Comment: 4 pages, 3 figures, RevTex, minor change