13,993 research outputs found
Pseudoparticle Multipole Method: A Simple Method to Implement High-Accuracy Treecode
In this letter we describe the pseudoparticle multipole method (P2M2), a new
method to express multipole expansion by a distribution of pseudoparticles. We
can use this distribution of particles to calculate high order terms in both
the Barnes-Hut treecode and FMM. The primary advantage of P2M2 is that it works
on GRAPE. GRAPE is a special-purpose hardware for the calculation of
gravitational force between particles. Although the treecode has been
implemented on GRAPE, we could handle terms only up to dipole, since GRAPE can
calculate forces from point-mass particles only. Thus the calculation cost
grows quickly when high accuracy is required. With P2M2, the multipole
expansion is expressed by particles, and thus GRAPE can calculate high order
terms. Using P2M2, we implemented an arbitrary-order treecode on GRAPE-4.
Timing result shows GRAPE-4 accelerates the calculation by a factor between 10
(for low accuracy) to 150 (for high accuracy). Even on general-purpose
programmable computers, our method offers the advantage that the mathematical
formulae and therefore the actual program is much simpler than that of the
direct implementation of multipole expansion.Comment: 6 pages, 4 figures, latex, submitted to ApJ Letter
String Field Theory from IIB Matrix Model
We derive Schwinger-Dyson equations for the Wilson loops of a type IIB matrix
model. Superstring coordinates are introduced through the construction of the
loop space. We show that the continuum limit of the loop equation reproduces
the light-cone superstring field theory of type IIB superstring in the large-N
limit. We find that the interacting string theory can be obtained in the double
scaling limit as it is expected.Comment: 21 pages, Latex, 1 figur
Towards a Non-Perturbative Renormalization of Euclidean Quantum Gravity
A real space renormalization group technique, based on the hierarchical
baby-universe structure of a typical dynamically triangulated manifold, is used
to study scaling properties of 2d and 4d lattice quantum gravity. In 4d, the
-function is defined and calculated numerically. An evidence for the
existence of an ultraviolet stable fixed point of the theory is presentedComment: 12 pages Latex + 1 PS fi
Fractional S-branes on a Spacetime Orbifold
Unstable D-branes are central objects in string theory, and exist also in
time-dependent backgrounds. In this paper we take first steps to studying brane
decay in spacetime orbifolds. As a concrete model we focus on the R^{1,d}/Z_2
orbifold. We point out that on a spacetime orbifold there exist two kinds of
S-branes, fractional S-branes in addition to the usual ones. We investigate
their construction in the open string and closed string boundary state
approach. As an application of these constructions, we consider a scenario
where an unstable brane nucleates at the origin of time of a spacetime, its
initial energy then converting into energy flux in the form of closed strings.
The dual open string description allows for a well-defined description of this
process even if it originates at a singular origin of the spacetime.Comment: 22 pages, 6 eps figure
The 144 second periodic flux variations during x ray turn-on of Hercules X-1
Hercules X-1 is a well known bright binary X ray pulsator. It has a 1.70 day orbital period, a pulsation period of 1.24 second, and a 35 day semiperiodic variability. The discovery is reported of a new 144 second periodicity in the X ray emission from Her X-1. The periodicity is seen in X ray observations of Her X-1 by the LAC instrument onboard the Ginga satellite during Aug. to Sep. 1988. The periodic flux variations occur during the time of X ray turnon at the beginning of a high state of Her X-1, in the same time that a pre-eclipse dip also occurs. An analysis of the LAC spectra of Her X-1 during this period is also presented. Large changes in spectral shape occur associated with the dip
Spin Dependence of D0-brane Interactions
The long-range, spin-dependent forces between D0-branes are related to
long-range fundamental string interactions using duality. These interactions
can then be computed by taking the long distance non-relativistic expansion of
string four-point amplitudes. The results are in accord with the general
constraints of Matrix Theory.Comment: 6 pages, latex, no figures, talk presented at STRINGS97, substantial
revisions in results and conclusion
Ground state energy fluctuations in nuclear matter II
Improvements are performed on a recently proposed statistical theory of the
mean field of a many-fermion system. The dependence of the predictions of the
theory upon its two basic ingredients, namely the Hartree-Fock energy and the
average energy of the two particle-two hole excitations, is explored.Comment: 16 pages, 1 figure, revte
Josephson effect in a multi-orbital model for SrRuO
We study Josephson current between s-wave/spin-triplet superconductor
junctions by taking into account details of band structures in
SrRuO such as three conduction bands, spin-orbit interaction in the
bulk and that at the interface. We assume five superconducting order parameters
in SrRuO: a chiral p-wave symmetry and four helical p-wave
symmetries. We calculate current-phase relationship in these
junctions, where is the macroscopic phase difference between two
superconductors. The results for a chiral p-wave pairing symmetry show that
term appears in the current-phase relation due to time-reversal
symmetry (TRS) breaking. On the other hand, term is absent in
the helical pairing states which preserve the TRS. We also study the dependence
of maximum Josephson current on an external magnetic flux in a
corner junction. The calculated results of show a relation
in a chiral state and
in a helical state. We calculate in a
corner and a symmetric SQUIDs geometry. In a symmetric SQUID geometry, the
relation is satisfied for all the pairing states and
it is impossible to distinguish chiral state from helical one. On the other
hand, results for a corner SQUID always show
and for a chiral and a helical states, respectively.
Experimental tests of these relations in a corner junctions and SQUIDs may
serve as a tool for unambiguous determination of the pairing symmetry in
SrRuO
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