39,269 research outputs found
Flow Representation of the Bose-Hubbard Hamiltonian : General Case
In this paper the explicit flow representation to the Bose-Hubbard
Hamiltonian is given in the general case. This representation may be useful in
creating cat states for the system of atoms trapped in the optical ring.Comment: Latex ; 8 pages ; 1 figure ; minor change
Time resolution below 100 ps for the SciTil detector of PANDA employing SiPM
The barrel time-of-flight (TOF) detector for the PANDA experiment at FAIR in
Darmstadt is planned as a scintillator tile hodoscope (SciTil) using 8000 small
scintillator tiles. It will provide fast event timing for a software trigger in
the otherwise trigger-less data acquisition scheme of PANDA, relative timing in
a multiple track event topology as well as additional particle identification
in the low momentum region. The goal is to achieve a time resolution of sigma ~
100 ps. We have conducted measurements using organic scintillators coupled to
Silicon Photomultipliers (SiPM). The results are encouraging such that we are
confident to reach the required time resolution.Comment: 10 pages, 7 figure
Exact results for quench dynamics and defect production in a two-dimensional model
We show that for a d-dimensional model in which a quench with a rate
\tau^{-1} takes the system across a d-m dimensional critical surface, the
defect density scales as n \sim 1/\tau^{m\nu/(z\nu +1)}, where \nu and z are
the correlation length and dynamical critical exponents characterizing the
critical surface. We explicitly demonstrate that the Kitaev model provides an
example of such a scaling with d=2 and m=\nu=z=1. We also provide the first
example of an exact calculation of some multispin correlation functions for a
two-dimensional model which can be used to determine the correlation between
the defects. We suggest possible experiments to test our theory.Comment: 4 pages including 4 figures; generalized the discussion of the defect
density scaling to the case of arbitrary critical exponents, and added some
references; this version will appear in Physical Review Letter
Shell-model calculations for the three-nucleon system
We use Faddeev's decomposition to solve the shell-model problem for three
nucleons. The dependence on harmonic-oscillator excitations allowed in the
model space, up to in the present calculations, and on the
harmonic-oscillator frequency is studied. Effective interactions derived from
Nijmegen II and Reid93 potentials are used in the calculations. The binding
energies obtained are close to those calculated by other methods. The structure
of the Faddeev equations is discussed and a simple formula for matrix elements
of the permutation operators in a harmonic-oscillator basis is given. The Pauli
principle is properly treated in the calculations.Comment: 11 pages. REVTEX. 6 PostScript figure
Analyzing powers in inclusive pion production at high energy and the nucleon spin structure
Analyzing powers in inclusive pion production in high energy transversely
polarized proton-proton collisions are studied theoretically in the framework
of the quark recombination model. Calculations by assuming the SU(6)
spin-flavor symmetry for the nucleon structure disagree with the experiments.
We solve this difficulty by taking into account the %We overcome this
difficulty by taking into account the realistic spin distribution functions of
the nucleon, which differs from the SU(6) expectation at large , %but
coincides with a perturbative QCD constraint on the ratio of the unpolarized
valence distributions, as . We also discuss the kaon spin
asymmetry and find in the polarized proton-proton
collisions at large .Comment: 13 pages, 4 figures, late
Aging dynamics in reentrant ferromagnet: CuCoCl-FeCl graphite bi-intercalation compound
Aging dynamics of a reentrant ferromagnet
CuCoCl-FeCl graphite bi-intercalation compound has
been studied using AC and DC magnetic susceptibility. This compound undergoes
successive transitions at the transition temperatures ( K) and
( K). The relaxation rate exhibits a characteristic
peak at close to a wait time below , indicating that
the aging phenomena occur in both the reentrant spin glass (RSG) phase below
and the ferromagnetic (FM) phase between and . The
relaxation rate () in the FM phase
exhibits two peaks around and a time much shorter than under
the positive -shift aging, indicating a partial rejuvenation of domains. The
aging state in the FM phase is fragile against a weak magnetic-field
perturbation. The time () dependence of around is well approximated by a stretched exponential relaxation:
. The exponent depends on
, , and . The relaxation time () exhibits a
local maximum around 5 K, reflecting a chaotic nature of the FM phase. It
drastically increases with decreasing temperature below .Comment: 16 pages,16 figures, submitted to Physical Review
Non-Universal Critical Behaviour of Two-Dimensional Ising Systems
Two conditions are derived for Ising models to show non-universal critical
behaviour, namely conditions concerning 1) logarithmic singularity of the
specific heat and 2) degeneracy of the ground state. These conditions are
satisfied with the eight-vertex model, the Ashkin-Teller model, some Ising
models with short- or long-range interactions and even Ising systems without
the translational or the rotational invariance.Comment: 17 page
Spikes and diffusion waves in one-dimensional model of chemotaxis
We consider the one-dimensional initial value problem for the viscous
transport equation with nonlocal velocity with a given kernel . We show the existence
of global-in-time nonnegative solutions and we study their large time
asymptotics. Depending on , we obtain either linear diffusion waves ({\it
i.e.}~the fundamental solution of the heat equation) or nonlinear diffusion
waves (the fundamental solution of the viscous Burgers equation) in asymptotic
expansions of solutions as . Moreover, for certain aggregation
kernels, we show a concentration of solution on an initial time interval, which
resemble a phenomenon of the spike creation, typical in chemotaxis models
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