16441248
Nuclear lattice simulations with chiral effective field theory
We study nuclear and neutron matter by combining chiral effective field theory with nonperturbative lattice methods. In our approach, nucleons and pions are treated as point particles on a lattice. This allows us to probe larger volumes, lower temperatures, and greater nuclear densities than in lattice QCD. The low-energy interactions of these particles are governed by chiral effective theory, and operator coefficients are determined by fitting to zero temperature few-body scattering data. The leading dependence on the lattice spacing can be understood from the renormalization group and absorbed by renormalizing operator coefficients. In this way, we have a realistic simulation of many-body nuclear phenomena with no free parameters, a systematic expansion, and a clear theoretical connection to QCD. We present results for hot neutron matter at temperatures 20-40 MeV and densities below twice the nuclear matter density.
15307965
The role of Monte Carlo within a diagonalization/Monte Carlo scheme
Abstract We review the method of stochastic error correction which eliminates the truncation error associated with any subspace diagonalization. Monte Carlo sampling is used to compute the contribution of the remaining basis vectors not included in the initial diagonalization. The method is part of a new approach to computational quantum physics which combines both diagonalization and Monte Carlo techniques.
118374917
Lattice calculations for A = 3 , 4, 6, 12 nuclei using chiral effective field theory
Abstract.We present lattice calculations for the ground-state energies of tritium, helium-3, helium-4, lithium-6, and carbon-12 nuclei. Our results were previously summarized in a letter publication. This paper provides full details of the calculations. We include isospin-breaking, Coulomb effects, and interactions up to next-to-next-to-leading order in chiral effective field theory.
125749692
Nuclear lattice simulations
We review recent progress on nuclear lattice simulations using chiral effective field theory. We discuss lattice results for dilute neutron matter at next-to-leading order, three-body forces at next-to-next-to- leading order, isospin-breaking and Coulomb effects, and the binding energy of light nuclei.
13972554
A non-perturbative analysis of symmetry breaking in two-dimensional φ4 theory using periodic field methods
Abstract We describe the generalization of spherical field theory to other modal expansion methods. The main approach remains the same, to reduce a d -dimensional field theory into a set of coupled one-dimensional systems. The method we discuss here uses an expansion with respect to periodic-box modes. We apply the method to φ 4 theory in two dimensions and compute the critical coupling and critical exponents. We compare with lattice results and predictions via universality and the two-dimensional Ising model.
119868800
Ab initio lattice results for Fermi polarons in two and three dimensions
We investigate the attractive Fermi polaron problem in two and three dimensions using non-perturbative Monte Carlo simulations. We introduce a new Monte Carlo algorithm called the impurity lattice Monte Carlo method. This algorithm samples the path integral in a computationally efficient manner and has only small sign oscillations for systems with a single impurity. To benchmark the method, we calculate the universal polaron energy in three dimensions in the scale-invariant unitarity limit and find agreement with published results. We then present the first fully non-perturbative calculations of the polaron energy in two dimensions in the limit of zero range interactions. We find evidence for a smooth crossover transition from a fermionic quasiparticle to a molecular state as a function of interaction strength with significant mixing between the two descriptions in the crossover region.
124265140
Low-energy neutron shielding
The attenuation of low-energy neutrons (< 20 MeV) through a 120-cm-thick slab shield of various mixtures of concrete, boron compounds, and water has been investigated. A Monte Carlo code was used to sample the neutron probability distribution and track the neutrons through the shield.
89609083
Evidence for a New Phase of Solid He-3
)Permanent address: Faculte des Sciences, Orsay, France. See, for exaxnple, I. Prigogine, Non Equi/ibrinm Statistica/ Mechanics (Wiley, New York, 1962); P. Resibois, in-Many Pmticle Physics, edited by K. Meeron (Gordon and Breach, New York, 1966). J. Van der Waals, Dissertation, University of Leiden, 1873 (unpublished) . See M. Kac, G. Uhlenbeck, and P. Hemmer, J. Math. Phys. 4, 216, 229 (1963), and 5, 60 (1964); J. Lebowitz, G. Steli, and S. Baer, J. Math. Phys. (N.Y.) 4, 1282 (1965). See K. Kawasaki, Progr. Theor. Phys. 41, 1190 (1969), snd references quoted therein. ~H. Mori, Progr. Theor. Phys. 28, 763 (1962}. P. Resibois, J. Chem. Phys. 41, 2979 (1964). P. Resibois, J. Stat. Phys. 2, 21 (1970). J. Dorfman and E. Cohen, Phys. Rev. Lett. 25, 1257 (1970). L. Kadanoff and J. Swift, Phys. Rev. 166, 89 (1968). M. Ernst, E. Hauge, and J. Van Leeuwen, Phys. Rev. Lett. 25, 1254 (1970), and Phys. Rev. A 4, 2055 (1971). "B.Alder and T. Wainwright, Phys. Rev. A 1, 18 (1970); see also Refs. 8 and 10; and Y. Pomeau, to be published.
121136564
Proportional chambers with monofilar helical cathodes for high spatial resolution
Abstract Multiware proportional chambers with monofilar helical delay line cathodes have been developed. Spatial resolutions better than 0.33 mm fwhm have been achieved. Such chambers are easily constructed and read out and can be adapted to a large variety of geometries. The properties of monofilar helical delay lines are analyzed in detail.
120849057
Design and performance of an 8 cm thick intrinsic germanium detector telescope
Abstract A detector telescope consisting of eight 1 cm thick intrinsic Ge diodes is described. The diodes have thin dead layer Li junctions (∼15 ωm ) and are mounted in interchangeable holders. Designs of the holders and the mounting assembly are presented. The major problem in using stopping detectors at medium energies is the tail of low pulse height events produced by nuclear reactions and scattering out. A technique for rejecting these events is described and the results obtained with deuterons from p-d elastic scattering of 800 MeV protons are presented. Analysis of the nuclear reaction tail for 120, 220, and 250 MeV deutrons yields an average total reaction cross section for deuterons on Ge of σ R = (1490±130) mb.
118608523
MEASURING TRANSVERSE MOTIONS FOR NEARBY GALAXY CLUSTERS
Measuring the full three-dimensional motions of extragalactic objects in the universe presents a seemingly insurmountable challenge. In this Letter, we investigate the application of a technique to measure tangential motion that has previously only been applied nearby within the Local Group of galaxies, to clusters of galaxies far beyond its borders. We show that mapping the mean line-of-sight motion throughout a galaxy cluster could in principle be used to detect the perspective rotation induced by the projection of the cluster's tangential motion into the line of sight. The signal will be most prominent for clusters of the largest angular extent, most symmetric intrinsic velocity distribution and surveyed with the largest number of pointings possible. We investigate the feasibility of detecting this signal using three different approaches: measuring line-of-sight motions of individual cluster members, taking spectra of intracluster gas, and mapping distortions of the cosmic microwave background radiation. We conclude that future spectroscopic surveys of thousands of members of nearby galaxy clusters hold the most promise of measuring cluster tangential motions using this technique.