29,995 research outputs found
Staggered Ladder Spectra
We exactly solve a Fokker-Planck equation by determining its eigenvalues and
eigenfunctions: we construct nonlinear second-order differential operators
which act as raising and lowering operators, generating ladder spectra for the
odd and even parity states. These are staggered: the odd-even separation
differs from even-odd. The Fokker-Planck equation describes, in the limit of
weak damping, a generalised Ornstein-Uhlenbeck process where the random force
depends upon position as well as time. Our exact solution exhibits anomalous
diffusion at short times and a stationary non-Maxwellian momentum distribution.Comment: 4 pages, 2 figure
M87 black hole mass and spin estimate through the position of the jet boundary shape break
We propose a new method of estimating a mass of a super massive black hole
residing in the center of an active galaxy. The active galaxy M87 offers a
convenient test case for the method due to the existence of a large amount of
observational data on the jet and ambient environment properties in the central
area of the object. We suggest that the observed transition of a jet boundary
shape from a parabolic to a conical form is associated with the flow transiting
from the magnetically dominated regime to the energy equipartition between
plasma bulk motion and magnetic field. By coupling the unique set of
observations available for the jet kinematics, environment and boundary profile
with our MHD modelling under assumption on the presence of a dynamically
important magnetic field in the M87 jet, we estimate the central black hole
mass and spin. The method leads us to believe that the M87 super massive black
hole has a mass somewhat larger than typically accepted so far.Comment: 10 pages, 1 figure, 3 tables, accepted for publication by MNRA
Localization length of a soliton from a non-magnetic impurity in a general double-spin-chain model
A localization length of a free-spin soliton from a non-magnetic impurity is
deduced in a general double-spin-chain model ( model). We have
solved a variational problem which employs the nearest-neighbor singlet-dimer
basis. The wave function of a soliton is expressed by the Airy function, and
the localization length is found to obey a power law of the
dimerization with an exponent -1/3; .
This explains why NaV_2O_5 does not show the antiferromagnetic order, while
CuGeO_3 does by impurity doping. When the gap exists by the bond-dimerization,
a soliton is localized and no order is expected. Contrary, there is a
possibility of the order when the gap is mainly due to frustration.Comment: 4 pages, REVTeX, Figures are in eps-file
On the Energetics of Advection-Dominated Accretion Flows
Using mean field MHD, we discuss the energetics of optically thin, two
temperature, advection-dominated accretion flows (ADAFs). If the magnetic field
is tangled and roughly isotropic, flux freezing is insufficient to maintain the
field in equipartition with the gas. In this case, we expect a fraction of the
energy generated by shear in the flow to be used to build up the magnetic field
strength as the gas flows in; the remaining energy heats the particles. We
argue that strictly equipartition magnetic fields are incompatible with a
priori reasonable levels of particle heating; instead, the plasma in
ADAFs (defined to be the gas pressure divided by magnetic/turbulent pressure)
is likely to be \gsim 5; correspondingly, the viscosity parameter is
likely to be \lsim 0.2Comment: 24 pages, ApJ submitte
Accretion flows: the Role of the Outer Boundary Condition
We investigate the influences of the outer boundary conditions(OBCs) on the
structure of an optically thin accretion flow. We find that OBC plays an
important role in determining the topological structure and the profiles of the
surface density and temperature of the solution, therefore it should be
regarded as a new parameter in the accretion disk model.Comment: 9 pages, 2 figures, to appear in ApJ Letters, Vol. 521, L5
Vanishing of the negative-sign problem of quantum Monte Carlo simulations in one-dimensional frustrated spin systems
The negative-sign problem in one-dimensional frustrated quantum spin systems
is solved. We can remove negative signs of the local Boltzmann weights by using
a dimer basis that has the spin-reversal symmetry. Validity of this new basis
is checked in a general frustrated double-spin-chain system, namely the
J_0-J_1-J_2-J_3 model. The negative sign vanishes perfectly for .Comment: 4 pages, REVTeX, 4 figures in eps-file
Mass Hierarchy Determination via future Atmospheric Neutrino Detectors
We study the problem of determination of the sign of Delta m^2_{31}, or the
neutrino mass hierarchy, through observations of atmospheric neutrinos in
future detectors. We consider two proposed detector types :
(a) Megaton sized water Cerenkov detectors, which can measure the survival
rates of nu_\mu + \bar{\nu}_\mu and nu_e + \bar{\nu}_e and (b) 100 kton sized
magnetized iron detectors, which can measure the survival rates of \nu_\mu and
\bar{\nu}_\mu. For energies and path-lengths relevant to atmospheric neutrinos,
these rates obtain significant matter contributions from P_{\mu e}, P_{\mu \mu}
and P_{ee}, leading to an appreciable sensitivity to the hierarchy. We do a
binned \chi^2 analysis of simulated data in these two types of detectors which
includes the effect of smearing in neutrino energy and direction and
incorporates detector efficiencies and relevant statistical, theoretical and
systematic errors. We also marginalize the \chi^2 over the allowed ranges of
neutrino parameters in order to accurately account for their uncertainties.
Finally, we compare the performance of both types of detectors vis a vis the
hierarchy determination.Comment: 36 pages, 13 figures, revised version accepted in Physical Review
Effect of magnetic field on the phase transition in a dusty plasma
The formation of self-consistent crystalline structure is a well-known
phenomenon in complex plasmas. In most experiments the pressure and rf power
are the main controlling parameters in determining the phase of the system. We
have studied the effect of externally applied magnetic field on the
configuration of plasma crystals, suspended in the sheath of a radio-frequency
discharge using the Magnetized Dusty Plasma Experiment (MDPX) device.
Experiments are performed at a fixed pressure and rf power where a crystalline
structure is formed within a confining ring. The magnetic field is then
increased from 0 to 1.28 T. We report on the breakdown of the crystalline
structure with increasing magnetic field. The magnetic field affects the
dynamics of the plasma particles and first leads to a rotation of the crystal.
At higher magnetic field, there is a radial variation (shear) in the angular
velocity of the moving particles which we believe leads to the melting of the
crystal. This melting is confirmed by evaluating the variation of the pair
correlation function as a function of magnetic field.Comment: 9 pages, 5 figure
Mechanism of CDW-SDW Transition in One Dimension
The phase transition between charge- and spin-density-wave (CDW, SDW) phases
is studied in the one-dimensional extended Hubbard model at half-filling. We
discuss whether the transition can be described by the Gaussian and the
spin-gap transitions under charge-spin separation, or by a direct CDW-SDW
transition. We determine these phase boundaries by level crossings of
excitation spectra which are identified according to discrete symmetries of
wave functions. We conclude that the Gaussian and the spin-gap transitions take
place separately from weak- to intermediate-coupling region. This means that
the third phase exists between the CDW and the SDW states. Our results are also
consistent with those of the strong-coupling perturbative expansion and of the
direct evaluation of order parameters.Comment: 5 pages(REVTeX), 5 figures(EPS), 1 table, also available from
http://wwwsoc.nacsis.ac.jp/jps/jpsj/1999/p68a/p68a42/p68a42h/p68a42h.htm
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