6,894 research outputs found
A Theory for the Radius of the Transiting Giant Planet HD 209458b
Using a full frequency-dependent atmosphere code that can incorporate
irradiation by a central primary star, we calculate self-consistent boundary
conditions for the evolution of the radius of the transiting planet HD 209458b.
Using a well-tested extrasolar giant planet evolutionary code, we then
calculate the behavior of this planet's radius with age. The measured radius is
in fact a transit radius that resides high in HD 209458b's inflated atmosphere.
Using our derived atmospheric and interior structures, we find that irradiation
plus the proper interpretation of the transit radius can yield a theoretical
radius that is within the measured error bars. We conclude that if HD 209458b's
true transit radius is at the lower end of the measured range, an extra source
of core heating power is not necessary to explain the transit observations.Comment: 6 pages in emulateapj format, plus 2 figures (one color), accepted to
the Astrophysical Journa
Effect of Particle-Hole Asymmetry on the Mott-Hubbard Metal-Insulator Transition
The Mott-Hubbard metal-insulator transition is one of the most important
problems in correlated electron systems. In the past decade, much progress has
been made on examining a particle-hole symmetric form of the transition in the
Hubbard model with dynamical mean field theory where it was found that the
electronic self energy develops a pole at the transition. We examine the
particle-hole asymmetric metal-insulator transition in the Falicov-Kimball
model, and find that a number of features change when the noninteracting
density of states has a finite bandwidth. Since, generically particle-hole
symmetry is broken in real materials, our results have an impact on
understanding the metal-insulator transition in real materials.Comment: 5 pages, 3 figure
Compressibility of the Two-Dimensional infinite-U Hubbard Model
We study the interactions between the coherent quasiparticles and the
incoherent Mott-Hubbard excitations and their effects on the low energy
properties in the Hubbard model. Within the framework of a
systematic large-N expansion, these effects first occur in the next to leading
order in 1/N. We calculate the scattering phase shift and the free energy, and
determine the quasiparticle weight Z, mass renormalization, and the
compressibility. It is found that the compressibility is strongly renormalized
and diverges at a critical doping . We discuss the nature
of this zero-temperature phase transition and its connection to phase
separation and superconductivity.Comment: 4 pages, 3 eps figures, final version to appear in Phys. Rev. Let
Fractional Aharonov-Bohm effect in mesoscopic rings
We study the effects of correlations on a one dimensional ring threaded by a
uniform magnetic flux. In order to describe the interaction between particles,
we work in the framework of the U Hubbard and - models. We focus
on the dilute limit. Our results suggest the posibility that the persistent
current has an anomalous periodicity , where is an integer in
the range ( is the number of particles in the ring
and is the flux quantum). We found that this result depends neither
on disorder nor on the detailed form of the interaction, while remains the on
site infinite repulsion.Comment: 14 pages (Revtex), 5 postscript figures. Send e-mail to:
[email protected]
On Quantum Groups in the Hubbard Model with Phonons
The correct Hamiltonian for an extended Hubbard model with quantum group
symmetry as introduced by A. Montorsi and M. Rasetti is derived for a
D-dimensional lattice. It is shown that the superconducting SUq(2) holds as a
true quantum symmetry only for D = 1 and that terms of higher order in the
fermionic operators in addition to phonons are required for a quantum symmetric
hamiltonian. The condition for quantum symmetry is "half filling" and there is
no local electron-phonon coupling. A discussion of Quantum symmetries in
general is given in a formalism that should be readily accessible to non
Hopf-algebraists.Comment: latex, 17 page
Theoretical Radii of Transiting Giant Planets: The Case of OGLE-TR-56b
We calculate radius versus age trajectories for the photometrically-selected
transiting extrasolar giant planet, OGLE-TR-56b, and find agreement between
theory and observation, without introducing an ad hoc extra source of heat in
its core. The fact that the radius of HD209458b seems larger than the radii of
the recently discovered OGLE family of extremely close-in transiting planets
suggests that HD209458b is anomalous. Nevertheless, our good fit to OGLE-TR-56b
bolsters the notion that the generic dependence of transit radii on stellar
irradiation, mass, and age is, to within error bars, now quantitatively
understood.Comment: 11 pages, 1 figure, submitted to the Astrophysical Journa
A Machine-Learning Algorithm for Estimating and Ranking the Impact of Environmental Risk Factors in Exploratory Epidemiological Studies
Atmosphere, Interior, and Evolution of the Metal-Rich Transiting Planet HD 149026b
We investigate the atmosphere and interior of the new transiting planet HD
149026b, which appears to be very rich in heavy elements. We first compute
model atmospheres at metallicities ranging from solar to ten times solar, and
show how for cases with high metallicity or inefficient redistribution of
energy from the day side, the planet may develop a hot stratosphere due to
absorption of stellar flux by TiO and VO. The spectra predicted by these models
are very different than cooler atmosphere models without stratospheres. The
spectral effects are potentially detectable with the Spitzer Space Telescope.
In addition the models with hot stratospheres lead to a large limb brightening,
rather than darkening. We compare the atmosphere of HD 149026b to other
well-known transiting planets, including the recently discovered HD 189733b,
which we show have planet-to-star flux ratios twice that of HD 209458 and
TrES-1. The methane abundance in the atmosphere of HD 189733b is a sensitive
indicator of atmospheric temperature and metallicity and can be constrained
with Spitzer IRAC observations. We then turn to interior studies of HD 149026b
and use a grid of self-consistent model atmospheres and high-pressure equations
of state for all components to compute thermal evolution models of the planet.
We estimate that the mass of heavy elements within the planet is in the range
of 60 to 93 M_earth. Finally, we discuss trends in the radii of transiting
planets with metallicity in light of this new member of the class.Comment: Accepted to the Astrophysical Journal. 18 pages, including 10
figures. New section on the atmosphere of planet HD 189733b. Enhanced
discussion of atmospheric Ti chemistry and core mass for HD 149026
Cluster coherent potential approximation for electronic structure of disordered alloys
We extend the single-site coherent potential approximation (CPA) to include
the effects of non-local disorder correlations (alloy short-range order) on the
electronic structure of random alloy systems. This is achieved by mapping the
original Anderson disorder problem to that of a selfconsistently embedded
cluster. This cluster problem is then solved using the equations of motion
technique. The CPA is recovered for cluster size , and the disorder
averaged density-of-states (DOS) is always positive definite. Various new
features, compared to those observed in CPA, and related to repeated scattering
on pairs of sites, reflecting the effect of SRO are clearly visible in the DOS.
It is explicitly shown that the cluster-CPA method always yields
positive-definite DOS. Anderson localization effects have been investigated
within this approach. In general, we find that Anderson localization sets in
before band splitting occurs, and that increasing partial order drives a
continuous transition from an Anderson insulator to an incoherent metal.Comment: 7 pages, 6 figures. submitted to PR
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