587 research outputs found
A Diffusion Approximation for the Riskless Profit Under Selling of Discrete Time Call Options. Non-identically Distributed Jumps
A discrete time model of financial markets is considered. It is assumed that the relative jumps of the risky security price are independent non-identically distributed random variables. In the focus of attention is the expected non-risky profit of the investor that arises when the jumps of the stock price are bounded while the investor follows the upper hedge. The considered discrete time model is approximated by a continuous time model that generalizes the classical geometrical Brownian motion.Asymptotic uniformity, Local limit theorem, Volatility
A Diffusion Approximation to the Markov Chains Model of the Financial Market and the Expected Riskless Profit Under Selling of Call and Put Options
A discrete time model of financial markets is considered. It is assumed that the stock price evolution is described by a homogeneous Markov chain. In the focus of attention is the expected value of the guaranteed profit of the investor that arises when the jumps of the stock price are bounded. The suggested diffusion approximation for the Markov chain allows establishing a convenient approximate formula for the studied characteristic.Ergodic and irreducible Markov chains, Stationary distribution, Local limit theorem, Upper hedge, Upper rational price
Phase diagram as a function of temperature and magnetic field for magnetic semiconductors
Using an extension of the Nagaev model of phase separation (E.L. Nagaev, and
A.I. Podel'shchikov, Sov. Phys. JETP, 71 (1990) 1108), we calculate the phase
diagram for degenerate antiferromagnetic semiconductors in the T-H plane for
different current carrier densities. Both, wide-band semiconductors and
'double-exchange' materials, are investigated.Comment: 5 pages, 6 figures, RevTex, Accepted for publication in PR
The phase-separated states in antiferromagnetic semiconductors with polarizable lattice
The possibility of the slab or stripe phase separation (alternating
ferromagnetic highly- conductive and insulating antiferromagnetic layers) is
proved for isotropic degenerate antiferromagnetic semiconductors. This type of
phase separation competes with the droplet phase separation (ferromagnetic
droplets in the antiferromagnetic host or vice versa). The interaction of
electrons with optical phonons alone cannot cause phase-separated state with
alternating highly-conductive and insulating regions but it stabilizes the
magnetic phase separation. The magnetostriction deformation of the lattice in
the phase-separated state is investigated.Comment: 17 Pages, 1 EPS Figur
Frequency-Dependent Shot Noise as a Probe of Electron-Electron Interaction in Mesoscopic Diffusive Contacts
The frequency-dependent shot noise in long and narrow mesoscopic diffusive
contacts is numerically calculated. The case of arbitrarily strong
electron-electron scattering and zero temperature of electrodes is considered.
For all voltages, the noise increases with frequency and tends to finite
values. These limiting values are larger than the Poissonian noise and increase
nearly as voltage to power 4/3. This allows one to experimentally determine the
parameters of electron-electron interaction.Comment: 3 pages, RevTeX, 3 eps figure
Semiclassical theory of shot noise in disordered SN contacts
We present a semiclassical theory of shot noise in diffusive superconductor -
normal metal contacts. At subgap voltages, we reproduce the doubling of shot
noise with respect to conventional normal-metal contacts, which is interpreted
in terms of an energy balance of electrons. Above the gap, the voltage
dependence of the noise crosses over to the standard one with a
voltage-independent excess noise. The semiclassical description of noise leads
to correlations between currents at different electrodes of multiterminal SN
contacts which are always of fermionic type, i.e. negative. Using a quantum
extension of the Boltzmann - Langevin method, we reproduce the peculiarity of
noise at the Josephson frequency and obtain an analytical frequency dependence
of noise at above-gap voltages.Comment: 4 pages RevTeX, 1 eps figur
Inhomogeneous Phases in a Double-Exchange Magnet with Long Range Coulomb Interactions
We consider a model with competing double-exchange (ferromagnetic) and
super-exchange (anti-ferromagnetic) interactions in the regime where phase
separation takes place. The presence of a long range Coulomb interaction
frustrates a macroscopic phase separation, and favors microscopically
inhomogeneous configurations. We use the variational Hartree-Fock approach, in
conjunction with Monte-Carlo simulations to study the geometry of such
configurations in a two-dimensional system. We find that an array of diamond
shaped ferromagnetic droplets is the preferred configuration at low electronic
densities, while alternating ferromagnetic and anti-ferromagnetic diagonal
stripes emerge at higher densities. These findings are expected to be relevant
for thin films of colossal magneto-resistive manganates.Comment: 15 pages, 9 figures. Journal Ref. added, errors correcte
Nanoscale phase separation in manganites
We study the possibility of nanoscale phase separation in manganites in the
framework of the double exchange model. The homogeneous canted state of this
model is proved to be unstable toward the formation of small ferromagnetic
droplets inside an antiferromagnetic insulating matrix. For the ferromagnetic
polaronic state we analyze the quantum effects related to the tails of
electronic wave function and a possibility of electron hopping in the
antiferromagnetic background. We find that these effects lead to the formation
of the threshold for the polaronic state.Comment: 10 pages, 2 figures, invited talk on the workshop on Strongly
Correlated Electrons in New Materials (SCENM02), Loughborough (UK). submitted
to Journal of Physics A: Mathematical and Genera
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