1,832 research outputs found
Equilibrium magnetisation structures in ferromagnetic nanorings
The ground state of the ring-shape magnetic nanoparticle is studied.
Depending on the geometrical and magnetic parameters of the nanoring, there
exist different magnetisation configurations (magnetic phases): two phases with
homogeneous magnetisation (easy-axis and easy-plane phases) and two
inhomogeneous (planar vortex phase and out-of-plane one). The existence of a
new intermediate out-of-plane vortex phase, where the inner magnetisation is
not strongly parallel to the easy axis, is predicted. Possible transitions
between different phases are analysed using the combination of analytical
calculations and micromagnetic simulations.Comment: LaTeX, 19 pages, 11 figure
Einstein-Podolsky-Rosen correlations in a hybrid system
We calculate the relativistic correlation function for a hybrid system of a
photon and a Dirac-particle. Such a system can be produced in decay of another
spin-1/2 fermion. We show, that the relativistic correlation function, which
depends on particle momenta, may have local extrema for fermion velocity of
order 0.5 c. This influences the degree of violation of CHSH inequality.Comment: 9 pages, 6 figure
On Effective Action of Multiple M5-branes and ABJM Action
We calculate the fluctuations from the classical multiple M5-brane solution
of ABJM action which we found in the previous paper. We obtain D4-brane-like
action but the gauge coupling constant depends on the spacetime coordinate.
This is consistent with the expected properties of M5-brane action, although we
will need to take into account the monopole operators in order to fully
understand M5-branes. We also see that the Nambu-Poisson bracket is hidden in
the solution.Comment: 21 pages; v2:version to appear in JHE
Lorentz-covariant reduced spin density matrix and EPR-Bohm correlations
We show that it is possible to define a Lorentz-covariant reduced spin
density matrix for massive particles. Such a matrix allows one to calculate the
mean values of observables connected with spin measurements (average
polarizations). Moreover, it contains not only information about polarization
of the particle but also information about its average kinematical state. We
also use our formalism to calculate the correlation function in the
Einstein--Podolsky--Rosen--Bohm type experiment with massive relativistic
particles.Comment: 7 pages, 1 figur
M5-branes in ABJM theory and Nahm equation
We construct BPS solutions representing M2-M5 bound state in the ABJM action
explicitly. They include the funnel type solutions and 't Hooft Polyakov
monopole solutions. Furthermore, we give a one to one correspondence between
the solutions of the BPS equation and the ones of an extended Nahm equation
which includes the Nahm equation. This enables us to construct infinitely many
conserved quantities from the Lax form of the Nahm equation.Comment: 22 pages, 4 figures, minor corrections, references adde
Ghost D-brane, Supersymmetry and Matrix Model
In this note we study the world volume theory of pairs of D-brane and ghost
D-brane, which is shown to have 16 linear supersymmetries and 16 nonlinear
supersymmetries. In particular we study a matrix model based on the pairs of
D(-1)-brane and ghost D(-1)-brane. Since such pairs are supposed to be
equivalent to the closed string vacuum, we expect all 32 supersymmetries should
be unbroken. We show that the world volume theory of the pairs of D-brane and
ghost D-brane has unbroken 32 supersymmetries even though a half of them are
nonlinearly realized.Comment: 12 pages, references adde
Detection of an X-ray periodicity in the Seyfert galaxy IRAS18325-5926
We report the detection of a 58 ks (16 hr) periodicity in the 0.5-10 keV
X-ray light curve of the Seyfert galaxy IRAS18325-5926 (Fairall49), obtained
from a 5-day ASCA observation. Nearly 9 cycles of the periodic variation are
seen; it shows no strong energy dependence and has an amplitude of about 15 per
cent. Unlike most other well-studied Seyfert galaxies, there is no evidence for
strong power-law red noise in the X-ray power spectrum of IRAS18325-5926.
Scaling from the QPOs found in Galactic black hole candidates suggests that the
mass of the black hole in IRAS18325-5926 is (6-40) million solar masses.Comment: 5 pages, 4 Postscript figures, to be published in MNRA
Spin decoherence by spacetime curvature
A decoherence mechanism caused by spacetime curvature is discussed. The spin
state of a particle is shown to decohere if only the particle moves in a curved
spacetime. In particular, when a particle is near the event horizon of a black
hole, an extremely rapid spin decoherence occurs for an observer who is static
in a Killing time, however slow the particle's motion is.Comment: 13 pages, 2 figure
Supertubes in Matrix model and DBI action
We show the equivalence between the supertube solutions with an arbitrary
cross section in two different actions, the DBI action for the D2-brane and the
matrix model action for the D0-branes. More precisely, the equivalence between
the supertubes in the D2-brane picture and the D0-brane picture is shown in the
boundary state formalism which is valid for all order in \alpha'. This is an
application of the method using the infinitely many D0-branes and
anti-D0-branes which was used to show other equivalence relations between two
seemingly different D-brane systems, including the D-brane realization of the
ADHM construction of instanton. We also apply this method to the superfunnel
type solutions successfully.Comment: 24 pages, references added, version to appear in JHE
Duals of noncommutative supersymmetric U(1) gauge theory
Parent actions for component fields are utilized to derive the dual of
supersymmetric U(1) gauge theory in 4 dimensions. Generalization of the
Seiberg-Witten map to the component fields of noncommutative supersymmetric
U(1) gauge theory is analyzed. Through this transformation we proposed parent
actions for noncommutative supersymmetric U(1) gauge theory as generalization
of the ordinary case.Duals of noncommutative supersymmetric U(1) gauge theory
are obtained. Duality symmetry under the interchange of fields with duals
accompanied by the replacement of the noncommutativity parameter
\Theta_{\mu\nu} with \tilde{\Theta}_{\mu \nu} =
\epsilon_{\mu\nu\rho\sigma}\Theta^{\rho\sigma} of the non--supersymmetric case
is broken at the level of actions. We proposed a noncommutative parent action
for the component fields which generates actions possessing this duality
symmetry.Comment: Typos corrected. Version which will appear in JHE
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