15,174 research outputs found
Stationary quantum Markov process for the Wigner function
As a stochastic model for quantum mechanics we present a stationary quantum
Markov process for the time evolution of the Wigner function on a lattice phase
space Z_N x Z_N with N odd. By introducing a phase factor extension to the
phase space, each particle can be treated independently. This is an improvement
on earlier methods that require the whole distribution function to determine
the evolution of a constituent particle. The process has branching and
vanishing points, though a finite time interval can be maintained between the
branchings. The procedure to perform a simulation using the process is
presented.Comment: 12 pages, no figures; replaced with version accepted for publication
in J. Phys. A, title changed, an example adde
Vortex-line solitons in a periodically modulated Bose gas
We study the nonlinear excitations of a vortex-line in a Bose-Einstein
condensate trapped in a one-dimensional optical lattice. We find that the
classical Euler dynamics of the vortex results in a description of the vortex
line in terms of a (discrete) one-dimensional Gross-Pitaevskii equation, which
allows for both bright and gray soliton solutions. We discuss these solutions
in detail and predict that it is possible to create vortex-line solitons with
current experimental capabilities.Comment: minor changes, updated/corrected references, 4 pages, 3 figure
A Monte Carlo Approach to Measure the Robustness of Boolean Networks
Emergence of robustness in biological networks is a paramount feature of
evolving organisms, but a study of this property in vivo, for any level of
representation such as Genetic, Metabolic, or Neuronal Networks, is a very hard
challenge. In the case of Genetic Networks, mathematical models have been used
in this context to provide insights on their robustness, but even in relatively
simple formulations, such as Boolean Networks (BN), it might not be feasible to
compute some measures for large system sizes. We describe in this work a Monte
Carlo approach to calculate the size of the largest basin of attraction of a
BN, which is intrinsically associated with its robustness, that can be used
regardless the network size. We show the stability of our method through
finite-size analysis and validate it with a full search on small networks.Comment: on 1st International Workshop on Robustness and Stability of
Biological Systems and Computational Solutions (WRSBS
Vortex-boson duality in four space-time dimensions
A continuum version of the vortex-boson duality in (3+1) dimensions is
formulated and its implications studied in the context of a pair Wigner crystal
in underdoped cuprate superconductors. The dual theory to a phase fluctuating
superconductor (or superfluid) is shown to be a theory of bosonic strings
interacting through a Kalb-Ramond rank-2 tensorial gauge field. String
condensation produces Higgs mass for the gauge field and the expected Wigner
crystal emerges as an interesting space-time analog of the Abrikosov lattice.Comment: 4 pages REVTeX; for related work and info visit
http://www.physics.ubc.ca/~fran
Linear response calculation using the canonical-basis TDHFB with a schematic pairing functional
A canonical-basis formulation of the time-dependent Hartree-Fock-Bogoliubov
(TDHFB) theory is obtained with an approximation that the pair potential is
assumed to be diagonal in the time-dependent canonical basis. The
canonical-basis formulation significantly reduces the computational cost. We
apply the method to linear-response calculations for even-even nuclei. E1
strength distributions for proton-rich Mg isotopes are systematically
calculated. The calculation suggests strong Landau damping of giant dipole
resonance for drip-line nuclei.Comment: 6 pages, 1 figure, INPC 2010 conference proceding
Coupled-channel calculation of bound and resonant spectra of Lambda-9Be and Lambda-13C hypernuclei
A Multi-Channel Algebraic Scattering (MCAS) approach has been used to analyze
the spectra of two hyper-nuclear systems, Lambda-9Be and Lambda-13C. The
splitting of the two odd-parity excited levels (1/2^- and 3/2^-) at 11 MeV
excitation in Lambda-13C is driven mainly by the weak Lambda-nucleus spin-orbit
force, but the splittings of the 3/2^+ and 5/2^+ levels in both Lambda-9Be and
Lambda-13C have a different origin. These cases appear to be dominated by
coupling to the collective 2+ states of the core nuclei. Using simple
phenomenological potentials as input to the MCAS method, the observed splitting
and level ordering in Lambda-9Be is reproduced with the addition of a weak
spin-spin interaction acting between the hyperon and the spin of the excited
target. With no such spin-spin interaction, the level ordering in Lambda-9Be is
inverted with respect to that currently observed. In both hyper-nuclei, our
calculations suggest that there are additional low-lying resonant states in the
Lambda-nucleus continua.Comment: 15 pages, 3 figures, 6 tables. To be published in International
Journal of Modern Physics
Radial Correlations between two quarks
In nuclear many-body problems the short-range correlation between two
nucleons is well described by the corresponding correlation in the {two}-body
problem. Therefore, as a first step in any attempt at an analogous description
of many-quark systems, it is necessary to know the two-quark correlation. With
this in mind, we study the light quark distribution in a heavy-light meson with
a static heavy quark. The charge and matter radial distributions of these
heavy-light mesons are measured on a lattice with a light quark mass about that
of the strange quark. Both distributions can be well fitted upto r approx 0.7
fm with the exponential form w_i^2(r), where w_i(r)=A exp(-r/r_i). For the
charge(c) and matter(m) distributions r_c approx 0.32(2) fm and r_m \approx
0.24(2) fm. We also discuss the normalisation of the total charge (defined to
be unity in the continuum limit) and matter integrated over all space, finding
1.30(5) and 0.4(1) respectively for a lattice spacing approx 0.17 fm.Comment: 8 pages, 3 ps figure
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