2,488 research outputs found
Thermal Equilibria of Optically Thin, Magnetically Supported, Two-Temperature, Black Hole Accretion Disks
We obtained thermal equilibrium solutions for optically thin, two-temperature
black hole accretion disks incorporating magnetic fields. The main objective of
this study is to explain the bright/hard state observed during the bright/slow
transition of galactic black hole candidates. We assume that the energy
transfer from ions to electrons occurs via Coulomb collisions. Bremsstrahlung,
synchrotron, and inverse Compton scattering are considered as the radiative
cooling processes. In order to complete the set of basic equations, we specify
the magnetic flux advection rate. We find magnetically supported (low-beta),
thermally stable solutions. In these solutions, the total amount of the heating
via the dissipation of turbulent magnetic fields goes into electrons and
balances the radiative cooling. The low- solutions extend to high mass
accretion rates and the electron temperature is moderately cool. High
luminosities and moderately high energy cutoffs in the X-ray spectrum observed
in the bright/hard state can be explained by the low-beta solutions.Comment: 24 pages, 10 figures,accepted for publication in Astrophysical
Journa
Stability of half quantum vortex in rotating superfluid 3He-A between parallel plates
We have found the precise stability region of the half quantum vortex (HQV)
for superfluid He A phase confined in parallel plates with a narrow gap
under rotation. Standard Ginzburg-Landau free energy, which is well
established, is solved to locate the stability region spanned by temperature
and rotation speed (). This - stability region is wide
enough to check it experimentally in available experimental setup. The detailed
order parameter structure of HQV characterized by A core is given to
facilitate the physical reasons of its stability over other vortices or
textures.Comment: 5 pages, 4 figure
Majorana surface states of superfluid 3He A- and B-phases in a slab
Motivated by experiments on the superfluid 3He confined in a thin slab, we
design a concrete experimental setup for observing the Majorana surface states.
We solve the quasi-classical Eilenberger equation, which is quantitatively
reliable, to evaluate several quantities, such as local density of states
(LDOS), mass current for the A-phase, and spin current for the B-phase. In
connection with realistic slab samples, we consider the upper and lower
surfaces and the side edges including the corners with several thicknesses.
Consequently the influence on the Majorana zero modes from the spatial
variation of l-vector for the A-phase in thick slabs and the energy splitting
of the zero-energy quasi-particles for the B-phase confined in thin slabs are
demonstrated. The corner of slabs in the B-phase is accompanied by the unique
zero-energy LDOS of corner modes. On the basis of the quantitative calculation,
we propose several feasible and verifiable experiments to check the existence
of the Majorana surface states, such as the measurement of specific heat, edge
current, and anisotropic spin susceptibility.Comment: 13 pages, 10 figures, published versio
Global Structure of Optically Thin, Magnetically Supported, Two-Temperature, Black Hole Accretion Disks
We present global solutions of optically thin, two-temperature black hole
accretion disks incorporating magnetic fields. We assume that the
{\pi}{\phi}-component of the Maxwell stress is proportional to the total
pressure, and prescribe the radial dependence of the magnetic flux advection
rate in order to complete the set of basic equations. We obtained magnetically
supported (low-{\beta}) disk solutions, whose luminosity exceeds the maximum
luminosity for an advection-dominated accretion flow (ADAF), L > 0.4 {\alpha}^2
L_Edd, where L_Edd is the Eddington luminosity. The accretion flow is composed
of the outer ADAF, a luminous hot accretion flow (LHAF) inside the transition
layer from the outer ADAF to the low-{\beta} disk, the low-{\beta} disk, and
the inner ADAF. The low-{\beta} disk region becomes wider as the mass-accretion
rate increases further. In the low-{\beta} disk, the magnetic heating balances
the radiative cooling, and the electron temperature decreases from ~ 10^9.5 K
to ~ 10^8 K as the luminosity increases. These results are consistent with the
anti-correlation between the energy cutoff in X-ray spectra (hence the electron
temperature) and the luminosity when L > 0.1 L_Edd, observed in the bright/hard
state during the bright hard-to-soft transitions of transient outbursts in
galactic black hole candidates.Comment: 27 pages, 15 figures, accepted for Publications of Astronomical
Society of Japa
Vortex structures and zero energy states in the BCS-to-BEC evolution of p-wave resonant Fermi gases
Multiply quantized vortices in the BCS-to-BEC evolution of p-wave resonant
Fermi gases are investigated theoretically. The vortex structure and the
low-energy quasiparticle states are discussed, based on the self-consistent
calculations of the Bogoliubov-de Gennes and gap equations. We reveal the
direct relation between the macroscopic structure of vortices, such as particle
densities, and the low-lying quasiparticle state. In addition, the net angular
momentum for multiply quantized vortices with a vorticity is found to
be expressed by a simple equation, which reflects the chirality of the Cooper
pairing. Hence, the observation of the particle density depletion and the
measurement of the angular momentum will provide the information on the
core-bound state and -wave superfluidity. Moreover, the details on the zero
energy Majorana state are discussed in the vicinity of the BCS-to-BEC
evolution. It is demonstrated numerically that the zero energy Majorana state
appears in the weak coupling BCS limit only when the vortex winding number is
odd. There exist the branches of the core bound states for a vortex
state with vorticity , whereas only one of them can be the zero energy.
This zero energy state vanishes at the BCS-BEC topological phase transition,
because of interference between the core-bound and edge-bound states.Comment: 15 pages, 9 figures, published versio
Spontaneous mass current and textures of p-wave superfluids of trapped Fermionic atom gases at rest and under rotation
It is found theoretically based on the Ginzburg-Landau framework that p-wave
superfluids of neutral atom gases in three dimension harmonic traps exhibit
spontaneous mass current at rest, whose direction depends on trap geometry.
Under rotation various types of the order parameter textures are stabilized,
including Mermin-Ho and Anderson-Toulouse-Chechetkin vortices. In a cigar shape
trap spontaneous current flows longitudial to the rotation axis and thus
perpendicular to the ordinary rotational current. These features, spontaneous
mass current at rest and texture formation, can be used as diagnoses for p-wave
superfluidity.Comment: 5 pages, 5 figure
Vortex states in superconductors with strong Pauli-paramagnetic effect
Using the quasiclassical theory, we analyze the vortex structure of
strong-paramagnetic superconductors.There, induced paramagnetic moments are
accumulated exclusively around the vortex core. We quantitatively evaluate the
significant paramagnetic effect in the H-dependence of various quantities, such
as low temperature specific heat, Knight shift, magnetization and the flux line
lattice (FLL) form factor. The anomalous H-dependence of the FLL form factor
observed by the small angle neutron scattering in CeCoIn_5 is attributable to
the large paramagnetic contribution.Comment: 7 pages, 5 figure
The early history of protostellar disks, outflows, and binary stars
In star formation, magnetic fields act as a cosmic angular momentum extractor
that increases mass accretion rates onto protostars and in the process, creates
spectacular outflows. However, recently it has been argued that this magnetic
brake is so strong that early protostellar disks -- the cradles of planet
formation -- cannot form. Our three-dimensional numerical simulations of the
early stages of collapse (\lesssim 10^5 yr) of overdense star--forming clouds
form early outflows and have magnetically regulated and rotationally dominated
disks (inside 10 AU) with high accretion rates, despite the slip of the field
through the mostly neutral gas. We find that in three dimensions, magnetic
fields suppress gravitationally driven instabilities which would otherwise
prevent young, well ordered disks from forming. Our simulations have surprising
consequences for the early formation of disks, their density and temperature
structure, the mechanism and structure of early outflows, the flash heating of
dust grains through ambipolar diffusion, and the origin of planets and binary
stars.Comment: 12 pages, 3 figures, accepted by ApJ Letters; corrected text to match
journal version; movies can be found at
http://www.physics.mcmaster.ca/~duffindf/movies.htm
Quantum Hall line junction with impurities as a multi-slit Luttinger liquid interferometer
We report on quantum interference between a pair of counterpropagating
quantum Hall edge states that are separated by a high quality tunnel barrier.
Observed Aharonov-Bohm oscillations are analyzed in terms of resonant tunneling
between coupled Luttinger liquids that creates bound electronic states between
pairs of tunnel centers that act like interference slits. We place a lower
bound in the range of 20-40 m for the phase coherence length and directly
confirm the extended phase coherence of quantum Hall edge states.Comment: 4 pages, 3 figures, 1 tabl
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