4,159 research outputs found
Long-range nematic order and anomalous fluctuations in suspensions of swimming filamentous bacteria
We study the collective dynamics of elongated swimmers in a very thin fluid
layer by devising long, filamentous, non-tumbling bacteria. The strong
confinement induces weak nematic alignment upon collision, which, for large
enough density of cells, gives rise to global nematic order. This homogeneous
but fluctuating phase, observed on the largest experimentally-accessible scale
of millimeters, exhibits the properties predicted by standard models for
flocking such as the Vicsek-style model of polar particles with nematic
alignment: true long-range nematic order and non-trivial giant number
fluctuations.Comment: 6 pages, 4 figures. Supplemental Material: 6 pages, 3 figure
Bifurcation analysis in an associative memory model
We previously reported the chaos induced by the frustration of interaction in
a non-monotonic sequential associative memory model, and showed the chaotic
behaviors at absolute zero. We have now analyzed bifurcation in a stochastic
system, namely a finite-temperature model of the non-monotonic sequential
associative memory model. We derived order-parameter equations from the
stochastic microscopic equations. Two-parameter bifurcation diagrams obtained
from those equations show the coexistence of attractors, which do not appear at
absolute zero, and the disappearance of chaos due to the temperature effect.Comment: 19 page
Collision of one-dimensional fermion clusters
We study cluster-cluster collisions in one-dimensional Fermi systems with
particular emphasis on the non-trivial quantum effects of the collision
dynamics. We adopt the Fermi-Hubbard model and the time-dependent density
matrix renormalization group method to simulate collision dynamics between two
fermion clusters of different spin states with contact interaction. It is
elucidated that the quantum effects become extremely strong with the
interaction strength, leading to the transmittance much more enhanced than
expected from semiclassical approximation. We propose a concise model based on
one-to-one collisions, which unveils the origin of the quantum effects and also
explains the overall properties of the simulation results clearly. Our concise
model can quite widely describe the one-dimensional collision dynamics with
contact interaction. Some potential applications, such as repeated collisions,
are addressed.Comment: 5 pages, 5 figure
Density-matrix renormalization group study of pairing when electron-electron and electron-phonon interactions coexist: effect of the electronic band structure
Density-matrix renormalization group is used to study the pairing when both
of electron-electron and electron-phonon interactions are strong in the
Holstein-Hubbard model at half-filling in a region intermediate between the
adiabatic (Migdal's) and antiadiabatic limits. We have found: (i) the pairing
correlation obtained for a one-dimensional system is nearly degenerate with the
CDW correlation in a region where the phonon-induced attraction is comparable
with the electron-electron repulsion, but (ii) pairing becomes dominant when we
destroy the electron-hole symmetry in a trestle lattice. This provides an
instance in which pairing can arise, in a lattice-structure dependent manner,
from coexisting electron-electron and electron-phonon interactions.Comment: 4 pages, 3 figures; to appear in Phys. Rev. Let
Resolving Neutrino Mass Hierarchy and CP Degeneracy by Two Identical Detectors with Different Baselines
We explore the possibility of simultaneous determination of neutrino mass
hierarchy and the CP violating phase by using two identical detectors placed at
different baseline distances. We focus on a possible experimental setup using
neutrino beam from J-PARC facility in Japan with beam power of 4MW and megaton
(Mton)-class water Cherenkov detectors, one placed in Kamioka and the other at
somewhere in Korea. We demonstrate, under reasonable assumptions of systematic
uncertainties, that the two-detector complex with each fiducial volume of 0.27
Mton has potential of resolving neutrino mass hierarchy up to sin^2 2theta_{13}
> 0.03 (0.055) at 2\sigma (3\sigma) CL for any values of delta and at the same
time has the sensitivity to CP violation by 4 + 4 years running of nu_e and
nu_e-bar appearance measurement. The significantly enhanced sensitivity is due
to clean detection of modulation of neutrino energy spectrum, which is enabled
by cancellation of systematic uncertainties between two identical detectors
which receive the neutrino beam with the same energy spectrum in the absence of
oscillations.Comment: 23 pages, 10 figures, version published in PR
The geometric measure of entanglement for a symmetric pure state with positive amplitudes
In this paper for a class of symmetric multiparty pure states we consider a
conjecture related to the geometric measure of entanglement: 'for a symmetric
pure state, the closest product state in terms of the fidelity can be chosen as
a symmetric product state'. We show that this conjecture is true for symmetric
pure states whose amplitudes are all non-negative in a computational basis. The
more general conjecture is still open.Comment: Similar results have been obtained independently and with different
methods by T-C. Wei and S. Severini, see arXiv:0905.0012v
Single-ion anisotropy in Haldane chains and form factor of the O(3) nonlinear sigma model
We consider spin-1 Haldane chains with single-ion anisotropy, which exists in
known Haldane chain materials. We develop a perturbation theory in terms of
anisotropy, where magnon-magnon interaction is important even in the low
temperature limit. The exact two-particle form factor in the O(3) nonlinear
sigma model leads to quantitative predictions on several dynamical properties
including dynamical structure factor and electron spin resonance frequency
shift. These agree very well with numerical results, and with experimental data
on the Haldane chain material Ni(CHN)N(PF)
Theory of Low Temperature Electron Spin Resonance in Half-integer Spin Antiferromagnetic Chains
A theory of low temperature (T) electron spin resonance (ESR) in half-integer
spin antiferromagnetic chains is developed using field theory methods and
avoiding previous approximations. It is compared to experiments on Cu benzoate.
Power laws are predicted for the line-width broadening due to various types of
anisotropy. At T -> 0, zero width absorption peaks occur in some cases. The
second ESR peak in Cu benzoate, observed at T<.76K, is argued not to indicate
Neel order as previously claimed, but to correspond to a sine-Gordon "breather"
excitation.Comment: 4 pages, REVTEX, 3 PostScript figures embedded in tex
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