8,972 research outputs found
Survival Rates of Planets in Open Clusters: the Pleiades, Hyades, and Praesepe clusters
In clustered environments, stellar encounters can liberate planets from their
host stars via close encounters. Although the detection probability of planets
suggests that the planet population in open clusters resembles that in the
field, only a few dozen planet-hosting stars have been discovered in open
clusters. We explore the survival rates of planets against stellar encounters
in open clusters similar to the Pleiades, Hyades, and Praesepe and embedded
clusters. We performed a series of N-body simulations of high-density and
low-density open clusters, open clusters that grow via mergers of subclusters,
and embedded clusters. We semi-analytically calculated the survival rate of
planets in star clusters up to 1Gyr using relative velocities, masses, and
impact parameters of intruding stars. Less than 1.5% of close-in planets within
1 AU and at most 7% of planets with 1-10 AU are ejected by stellar encounters
in clustered environments after the dynamical evolution of star clusters. If a
planet population from 0.01-100 AU in an open cluster initially follows the
probability distribution function of exoplanets with semi-major axis ()
between 0.03-3 AU in the field discovered by RV surveys, the PDF of surviving
planets beyond ~10 AU in open clusters can be slightly modified to . The production rate of free-floating planets (FFPs) per star is
0.0096-0.18, where we have assumed that all the stars initially have one giant
planet with a mass of 1--13 MJ in a circular orbit. The expected frequency of
FFPs is compatible with the upper limit on that of FFPs indicated by recent
microlensing surveys. Our survival rates of planets in open clusters suggest
that planets within 10 AU around FGKM-type stars are rich in relatively-young
(<~10-100 Myr for open clusters and ~1-10 Myr for embedded clusters), less
massive open clusters, which are promising targets for planet searches.Comment: 23 pages, 15 figures, A&A accepte
Dipole trap model for the metallic state in gated silicon-inversion layers
In order to investigate the metallic state in high-mobility Si-MOS
structures, we have further developed and precised the dipole trap model which
was originally proposed by B.L. Altshuler and D.L. Maslov [Phys. Rev. Lett.\
82, 145 (1999)]. Our additional numerical treatment enables us to drop several
approximations and to introduce a limited spatial depth of the trap states
inside the oxide as well as to include a distribution of trap energies. It
turns out that a pronounced metallic state can be caused by such trap states at
appropriate energies whose behavior is in good agreement with experimental
observations.Comment: 16 pages, 10 figures, submitte
Orientifolds and Mirror Symmetry
We study parity symmetries and crosscap states in classes of N=2
supersymmetric quantum field theories in 1+1 dimensions, including non-linear
sigma models, gauged WZW models, Landau-Ginzburg models, and linear sigma
models. The parity anomaly and its cancellation play important roles in many of
them. The case of the N=2 minimal model are studied in complete detail, from
all three realizations -- gauged WZW model, abstract RCFT, and LG models. We
also identify mirror pairs of orientifolds, extending the correspondence
between symplectic geometry and algebraic geometry by including unorientable
worldsheets. Through the analysis in various models and comparison in the
overlapping regimes, we obtain a global picture of orientifolds and D-branes.Comment: 137 page
N=2 Supersymmetric Sigma Models and D-branes
We study D-branes of N=2 supersymmetric sigma models. Supersymmetric
nonlinear sigma models with 2-dimensional target space have D0,D1,D2-branes,
which are realized as A-,B-type supersymmetric boundary conditions on the
worldsheet. When we embed the models in the string theory, the Kahler potential
is restricted and leads to a 2-dim black hole metric with a dilaton background.
The D-branes in this model are susy cycles and consistent with the analysis of
conjugacy classes. The generalized metrics with U(n) isometry is proposed and
dynamics on them are realized by linear sigma models. We investigate D-branes
of the linear sigma models and compare the results with those in the nonlinear
sigma models.Comment: 23 pages, 5 figure
Strings in Twistor Superspace and Mirror Symmetry
We obtain the super-Landau-Ginzburg mirror of the A-twisted topological sigma
model on a twistor superspace -- the quadric in CP^{3|3} x CP^{3|3} which is a
Calabi-Yau supermanifold. We show that the B-model mirror has a geometric
interpretation. In a particular limit for one of the Kaehler parameters of the
quadric, we show that the mirror can be interpreted as the twistor superspace
CP^{3|4}. This agrees with the recent conjecture of Neitzke and Vafa proposing
a mirror equivalence between the two twistor superspaces.Comment: 12 pages, uses harvma
A Bilocal Field Theory in Four Dimensions
A bilocal field theory having M\"{o}bius gauge invariance is proposed. In
four dimensions there exists a zero momentum state of the first quantized
model, which belongs to a non-trivial BRS cohomology class. A field theory
lagrangian having a gauge invariance only in four dimensions is constructed.Comment: 13 pages, TEP-9R, LaTe
Evidence for Carrier-Induced High-Tc Ferromagnetism in Mn-doped GaN film
A GaN film doped with 8.2 % Mn was grown by the molecular-beam-epitaxy
technique. Magnetization measurements show that this highly Mn-doped GaN film
exhibits ferromagnetism above room temperature. It is also revealed that the
high-temperature ferromagnetic state is significantly suppressed below 10 K,
accompanied by an increase of the electrical resistivity with decreasing
temperature. This observation clearly demonstrates a close relation between the
ferromagnetism with extremely high-Tc and the carrier transport in the Mn-doped
GaN film.Comment: 9 pages, 3 figure
Orientifolds of Gepner Models
We systematically construct and study Type II Orientifolds based on Gepner
models which have N=1 supersymmetry in 3+1 dimensions. We classify the parity
symmetries and construct the crosscap states. We write down the conditions that
a configuration of rational branes must satisfy for consistency (tadpole
cancellation and rank constraints) and spacetime supersymmetry. For certain
cases, including Type IIB orientifolds of the quintic and a two parameter
model, one can find all solutions in this class. Depending on the parity, the
number of vacua can be large, of the order of 10^{10}-10^{13}. For other
models, it is hard to find all solutions but special solutions can be found --
some of them are chiral. We also make comparison with the large volume regime
and obtain a perfect match. Through this study, we find a number of new
features of Type II orientifolds, including the structure of moduli space and
the change in the type of O-planes under navigation through non-geometric
phases.Comment: 142 page
N=2 Liouville Theory with Boundary
We study N=2 Liouville theory with arbitrary central charge in the presence
of boundaries. After reviewing the theory on the sphere and deriving some
important structure constants, we investigate the boundary states of the theory
from two approaches, one using the modular transformation property of annulus
amplitudes and the other using the bootstrap of disc two-point functions
containing degenerate bulk operators. The boundary interactions describing the
boundary states are also proposed, based on which the precise correspondence
between boundary states and boundary interactions is obtained. The open string
spectrum between D-branes is studied from the modular bootstrap approach and
also from the reflection relation of boundary operators, providing a
consistency check for the proposal.Comment: 1+48 pages, no figure. typos corrected and references added. the
version to appear in JHE
- …