GPU-based single-cluster algorithm for the simulation of the Ising model

We present the GPU calculation with the common unified device architecture (CUDA) for the Wolff single-cluster algorithm of the Ising model. Proposing an algorithm for a quasi-block synchronization, we realize the Wolff single-cluster Monte Carlo simulation with CUDA. We perform parallel computations for the newly added spins in the growing cluster. As a result, the GPU calculation speed for the two-dimensional Ising model at the critical temperature with the linear size L = 4096 is 5.60 times as fast as the calculation speed on a current CPU core. For the three-dimensional Ising model with the linear size L = 256, the GPU calculation speed is 7.90 times as fast as the CPU calculation speed. The idea of quasi-block synchronization can be used not only in the cluster algorithm but also in many fields where the synchronization of all threads is required.     

Leading log radiative corrections to deep inelastic neutral and charged current scattering at HERA

TheO(α) radiative corrections for neutral and charged current deep inelastic scattering are calculated in the leading log approximation. The numerical results are found to agree within a few per cent with the results of a completeO(α) calculation by Bardin et al. It is demonstrated that both for the leading log and completeO(α) calculation all light quark mass terms can be eliminated from the cross section.     

Exact shell-model and projected Hartree-Fock calculations for Mg

The results of a projected Hartree-Fock calculation are compared with those of an exact shell-model calculation for states of J ? 6 in the nucleus ²⁴Mg. The realistic Kuo interaction is used, and gives reasonable agreement with experiment.     

Extended commutator method for boson mapping in the seniority scheme: Two non-degenerate-j shells with |j1 − j2| = 2

The commutator method of Bonatsos, Klein and Li for approximate boson mapping in the seniority scheme, previously illustrated for the single-j shell-model algebra SO(2(2j + 1)), has been extended in order to be applicable to the case of many non-degenerate-j shells, and the physically interesting case of two shells with |j₁ − j₂| = 2 has been studied in detail. The most important new feature of this work is that bosons corresponding to pairs of two fermions each of which belongs to a different shell have been included in the calculation. (These bosons had been omitted in previous work using the Otsuka-Arima-Iachello method.) The calculation is successively carried out to lowest and to next-higher order, the latter exhibiting the necessity of including f- and g-bosons (both of positive parity) in the calculation in order to reach algebraic consistency.     

Classical and quantum pumping in closed systems

Pumping of charge (Q) in a closed ring geometry is not quantized even in the strict adiabatic limit. The deviation form exact quantization can be related to the Thouless conductance. We use the Kubo formalism as a starting point for the calculation of both the dissipative and the adiabatic contributions to Q. As an application we bring examples for classical dissipative pumping, classical adiabatic pumping, and in particular we make an explicit calculation for quantum pumping in case of the simplest pumping device, which is a three site lattice model. We make a connection with the popular S-matrix formalism which has been used to calculate pumping in open systems.     

Fast convergence of path integrals for many-body systems

We generalize a recently developed method for accelerated Monte Carlo calculation of path integrals to the physically relevant case of generic many-body systems. This is done by developing an analytic procedure for constructing a hierarchy of effective actions leading to improvements in convergence of N-fold discretized many-body path integral expressions from 1/N to 1/Np for generic p. In this Letter we present explicit solutions within this hierarchy up to level p=5. Using this we calculate the low lying energy levels of a two particle model with quartic interactions for several values of coupling and demonstrate agreement with analytical results governing the increase in efficiency of the new method. The applicability of the developed scheme is further extended to the calculation of energy expectation values through the construction of associated energy estimators exhibiting the same speedup in convergence.     

Solubility of noble metals in hcp metals: A test for the validity of pseudo-potentials

In the calculation of the energy-band structureU _BS dependence of hcp metal-noble metal dilute alloys on the axialc/a and electron per atome/a ratios, we have used two different types of the pseudo-potential for the noble metals in the virtual crystal approximation. By comparing the experimental data on noble metal-simple hcp metal solubility limits with theoretical curves forU _BS, we show how this type of calculation can serve as one of the criteria for determining the solubility limits and the validity of a given pseudo-potential in the dilute alloy limit.     

Generator-coordinate study of inelastic α + 12C scattering

A multi-channel calculation performed with the generator coordinate method is presented for α + ¹²C scattering. The inelastic channel α + ¹²C(2⁺) is included. Bound-state and resonance energies are determined for J^π = 0⁺ up to 6⁺. For the negative parity levels, the results are very similar to those obtained with a single-channel calculation. The positive parity resonances are more numerous and in better qualitative agreement with experiment in the multi-channel calculation. However, an incorrect value for the threshold energy α + ¹²C(2⁺) channel prevents one from obtaining a quantitative agreement with experiment.     

Relativistic calculation for the reactions\bar p d → 5πp and\bar p d → 3πp at rest

We present a fully relativistic calculation for ¯pd → 5πp and ¯pd → 3πp that includes angular momentum and spin dynamics. We calculate the inclusive proton distributions from two diagrams: the leading “tree” diagram, and the diagram for pion rescattering. Pion-nucleon rescattering proceeds through the Δ, in the RaritaSchwinger formalism, thus preserving the correct angular dependence. We use realistic parameterizations of the deuteron, keeping both theS andD states. The loop integrations for the rescattering amplitude and the phase space integrations have been done numerically. We find that the combined effects of a correct treatment of the rescattered pion and relativity are small in comparison with a simple non-relativistic calculation.     

Projected Hartree-Fock calculation in intermediate coupling for11B

An intermediate coupling calculation has been carried out for¹¹B using the deformed functions obtained from a Projected Hartree-Fock calculation as a basis. The resulting wave functions give an important improvement for the energy spectrum of the low-lying nonnormal parity levels. TheE2 matrix elements are enhanced with respect to the conventional shell model. Nuclear structure¹¹B; calculated levelsJ, π, B(M1),B(E2). Projected Hartree-Fock method, intermediate coupling.     

β-function approach to the Green-Schwarz superstring

We describe the calculation of one-loop β-functions for the Green-Schwarz heterotic superstring in a supergravity background. The calculation is considerably simplified by the use of a new set of superspace constraints. As expected, the one-loop β-functions vanish, since the constraints impose on the background the classical field equations of supergravity.     

Galvanomagnetic effects in graphite—II: The influence of trigonal warping of the constant energy surfaces on σxx(Bz)

The dispersion relationship for the electrons near the region of band overlap in graphite corresponds to the case where the constant energy surfaces are strongly warped in the k_x?k_y plane with three-fold symmetry (trigonal warping). The effects of this warping on the galvanomagnetic tensor component σ_xx(B_z) are examined. In the present calculation the trigonal warping is treated using a simplified mathematical model. Implications with respect to the calculation of the density of free carriers in graphite are discussed.     

Berechnung des oberflächensenkrechten kritischen Magnetfeldes für supraleitende Filme

On the basis of the BCS theory a simplified system of equations for the calculation of the perpendicular critical magnetic field,H _c⊥, for superconducting films is derived with the help of “the method of the correlation function”, developed by Lüders. In the vicinity ofT=T _c for all film thicknesses and mean free paths the problem becomes mathematically equivalent to the calculation of the residual resistance of the film. The results are in good agreement with the experiments of Harper and Tinkham and of others. Further limiting cases are investigated: on the one hand specular reflection and weakly diffuse surface scattering, on the other hand diffuse reflection and very thin films.     

Particle-hole calculation of the isobaric analog and isovector monopole resonances

The correlated proton-particle—neutron-hole spectrum is calculated for N > Z nuclei using a Skyrme type interaction and the response function method. The basis of the calculation is a complete one-particle—one-hole space with the continuum included. As a result the distribution of the isovector monopole strength in the analog nucleus is obtained. This distribution has a narrow peak which corresponds to the isobaric analog resonance and at higher energies a broad peak which is the isovector monopole resonance. The coupling between these two states is inherent in the calculation.     

Static structure factor and electronic transport properties of liquid rubidium from a first principles pseudopotential calculation

A first principles nonlocal pseudopotential calculation is used to obtain the ion-ion potential for liquid rubidium of 45°C. This is then used in a Monte Carlo simulation to determine the liquid structure S(q) and transport properties. It is found that the accuracy of the S(q), in the low q-region, is crucial to the calculation of electronic transport properties.     

The problem of satellites of spectral lines in the Jabłoński theory

This paper presents a calculation of the intensity distribution of a spectral line perturbed by interactions with foreign atoms. The calculation is based on the statistical version of the Jab?oński theory developed for the Lennard-Jones interaction potential.The calculated line profile shows a distinct satellite on the red wing, at a frequency b and a trace of another band at about 2b, where b is the depth of the difference potential. The positions of these bands are in good agreement with previously reported experimental data for the Hg 2537 Å resonance line broadened by krypton. It is shown that the present method describes both the core of the broadened line and its far red wing with the satellite structure.     

Interpretation of photoemission from Na (1 1 0)

A self-consistent calculation of the electronic structure of the Na (1 1 0) surface, using an embedding method to treat the semi-infinite system, gives a prominent surface resonance peak at 0.75 eV above the Fermi energy. The tail of this resonance extends below E_F at the surface, and it is suggested that surface photoemission from this tail is responsible for the peak in the photocurrent at E_F observed experimentally, A photoemission calculation, with a non-self-consistent surface potential, reproduces the enhancement of the peak as a direct transition moves through it.     

Quantum fluctuations in the vicinity of an instanton in the SU(N) group

A general form of the quadratic Lagrangian in the presence of a self-dual classical field has been obtained. The calculation of the amplitude of the vacuum-vacuum transition in the SU(N) group has been reduced to calculation of similar amplitudes in the SU(2) group for scalar particles with different isospins. The value of the amplitude for one instanton has been obtained.     

A method of moments for the optical Jahn-Teller problem

A Method of moments is presented for optical transitions to Jahn-Teller states. The Condon and a modified Born-Oppenheimer approximation have been adopted. On the basis of these 2 principles, the method is exact. Specific orthonormality and closure properties are derived for Jahn-Teller states, which are essential for performing the calculation. As illustrative examples the pure Jahn-Teller casesE-e andT-t have been calculated in the strong coupling limit. Each of these cases leads to specific combinatorial problems and to an application of Wick's theorem. The latter is common to both cases. Comparison with the semi-classical calculation reveals the identity of the results for theE- e system.     

Second Coulomb energy differences of isospin triplets in the 2s-1d shell

Second Coulomb energy differences, which in the present case are proportional to the tensor Coulomb energy, are calculated for 0⁺, T = 1 ground states in the region 18 ≦ A ≦ 42 using a shell model that includes a pairing interaction. The calculation is done with a mathematical formalism that includes p-n pairs as well as p-p and n-n pairs. Besides an enhancement of proton-pair Coulomb energies, the pairing interaction is responsible for lowering the Coulomb energy of N = Z members of isospin triplets and also gives rise to an important term in the second energy difference. Using pairing strengths derived from fitting energy levels for mass-18 and mass-42 nuclei, results of the calculation reproduce experimental second energy differences extremely well.