9,799 research outputs found
Theory of Orbital Ordering, Fluctuation and Resonant X-ray Scattering in Manganites
A theory of resonant x-ray scattering in perovskite manganites is developed
by applying the group theory to the correlation functions of the pseudospin
operators for the orbital degree of freedom. It is shown that static and
dynamical informations of the orbital state are directly obtained from the
elastic, diffuse and inelastic scatterings due to the tensor character of the
scattering factor. We propose that the interaction and its anisotropy between
orbitals are directly identified by the intensity contour of the diffuse
scattering in the momentum space.Comment: 4 pages, 1 figur
Entangled-photon generation in nano-to-bulk crossover regime
We have theoretically investigated a generation of entangled photons from
biexcitons in a semiconductor film with thickness in nano-to-bulk crossover
regime. In contrast to the cases of quantum dots and bulk materials, we can
highly control the generated state of entangled photons by the design of
peculiar energy structure of exciton-photon coupled modes in the thickness
range between nanometers and micrometers. Owing to the enhancement of radiative
decay rate of excitons at this thickness range, the statistical accuracy of
generated photon pairs can be increased beyond the trade-off problem with the
signal intensity. Implementing an optical cavity structure, the generation
efficiency can be enhanced with keeping the high statistical accuracy.Comment: 9 pages, 3 figure
Parametric resonance at the critical temperature in high energy heavy ion collisions
Parametric resonance in soft modes at the critical temperature () in
high energy heavy ion collisions is studied in the case when the temperature
() of the system is almost constant for a long time. By deviding the fields
into three parts, zero mode (condensate), soft modes and hard modes and
assuming that the hard modes are in thermal equilibrium, we derive the equation
of motion for soft modes at . Enhanced modes are extracted by
comparing with the Mathieu equation for the condensate oscillating along the
sigma axis at . It is found that the soft mode of fields at
about 174 MeV is enhanced.Comment: 8 pages, 1 figure Some statements and equations are modified to
clarif
Topology Change of Coalescing Black Holes on Eguchi-Hanson Space
We construct multi-black hole solutions in the five-dimensional
Einstein-Maxwell theory with a positive cosmological constant on the
Eguchi-Hanson space, which is an asymptotically locally Euclidean space. The
solutions describe the physical process such that two black holes with the
topology of S^3 coalesce into a single black hole with the topology of the lens
space L(2;1)=S^3/Z_2. We discuss how the area of the single black hole after
the coalescence depends on the topology of the horizon.Comment: 10 pages, Some comments are added. to be published as a letter in
Classical and Quantum Gravit
D3/D7 holographic Gauge theory and Chemical potential
N=2 supersymmetric Yang-Mills theory with flavor hypermultiplets at finite
temperature and in the dS are studied for finite quark number density
() by a dual supergravity background with non-trivial dilaton and axion.
The quarks and its number density are introduced by embedding a probe D7
brane. We find a critical value of the chemical potential at the limit of
, and it coincides with the effective quark mass given in each theory
for . At this point, a transition of the D7 embedding configurations
occurs between their two typical ones. The phase diagrams of this transition
are shown in the plane of chemical potential versus temperature and
cosmological constant for YM theory at finite temperature and in dS
respectively. In this phase transition, the order parameter is considered as
. % and the critical value of the chemical potential This result seems to
be reasonable since both theories are in the quark deconfinement phase.Comment: 17 pages, 8 figure
Magnetic Ordering, Orbital Ordering and Resonant X-ray Scattering in Perovskite Titanates
The effective Hamiltonian for perovskite titanates is derived by taking into
account the three-fold degeneracy of orbitals and the strong
electron-electron interactions. The magnetic and orbital ordered phases are
studied in the mean-field approximation applied to the effective Hamiltonian. A
large degeneracy of the orbital states in the ferromagnetic phase is found in
contrast to the case of the doubly degenerate orbitals. Lifting of this
orbital degeneracy due to lattice distortions and spin-orbit coupling is
examined. A general form for the scattering cross section of the resonant x-ray
scattering is derived and is applied to the recent experimental results in
YTiO. The spin wave dispersion relation in the orbital ordered YTiO is
also studied.Comment: 10 pages, 6 figure
Parametric amplification with a friction in heavy ion collisions
We study the effects of the expansion of the system and the friction on the
parametric amplification of mesonic fields in high energy heavy ion collisions
within the linear model . The equation of motion which is similar to
Mathieu equation is derived to describe the time development of classical
fields in the last stage of a heavy ion collision after the freezeout time. The
enhanced mode is extracted analytically by comparison with Mathieu equation and
the equation of motion is solved numerically to examine whether soft modes will
be enhanced or not. It is found that the strong peak appears around 267 MeV in
the pion transverse momentum distribution in cases with weak friction and high
maximum temperature. This enhancement can be extracted by taking the ratio
between different modes in the pion transverse momentum distribution.Comment: 10 pages, 9 figures LaTeX: appendix adde
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