3,513 research outputs found
Ultralong-range order in the Fermi-Hubbard model with long-range interactions
We use the dual boson approach to reveal the phase diagram of the
Fermi-Hubbard model with long-range dipole-dipole interactions. By using a
large-scale finite-temperature calculation on a square lattice
we demonstrate the existence of a novel phase, possessing an `ultralong-range'
order. The fingerprint of this phase -- the density correlation function --
features a non-trivial behavior on a scale of tens of the lattice sites. We
study the properties and the stability of the ultralong-range ordered phase,
and show that it is accessible in modern experiments with ultracold polar
molecules and magnetic atoms
Ice chemistry in massive Young Stellar Objects: the role of metallicity
We present the comparison of the three most important ice constituents
(water, CO and CO2) in the envelopes of massive Young Stellar Objects (YSOs),
in environments of different metallicities: the Galaxy, the Large Magellanic
Cloud (LMC) and, for the first time, the Small Magellanic Cloud (SMC). We
present observations of water, CO and CO2 ice in 4 SMC and 3 LMC YSOs (obtained
with Spitzer-IRS and VLT/ISAAC). While water and CO2 ice are detected in all
Magellanic YSOs, CO ice is not detected in the SMC objects. Both CO and CO2 ice
abundances are enhanced in the LMC when compared to high-luminosity Galactic
YSOs. Based on the fact that both species appear to be enhanced in a consistent
way, this effect is unlikely to be the result of enhanced CO2 production in
hotter YSO envelopes as previously thought. Instead we propose that this
results from a reduced water column density in the envelopes of LMC YSOs, a
direct consequence of both the stronger UV radiation field and the reduced
dust-to-gas ratio at lower metallicity. In the SMC the environmental conditions
are harsher, and we observe a reduction in CO2 column density. Furthermore, the
low gas-phase CO density and higher dust temperature in YSO envelopes in the
SMC seem to inhibit CO freeze-out. The scenario we propose can be tested with
further observations.Comment: accepted by MNRAS Letters; 5 pages, 3 figures, 1 tabl
The M33 Variable Star Population Revealed by Spitzer
We analyze five epochs of Spitzer Space Telescope/Infrared Array Camera
(IRAC) observations of the nearby spiral galaxy M33. Each epoch covered nearly
a square degree at 3.6, 4.5, and 8.0 microns. The point source catalog from the
full dataset contains 37,650 stars. The stars have luminosities characteristic
of the asymptotic giant branch and can be separated into oxygen-rich and
carbon-rich populations by their [3.6] - [4.5] colors. The [3.6] - [8.0] colors
indicate that over 80% of the stars detected at 8.0 microns have dust shells.
Photometric comparison of epochs using conservative criteria yields a catalog
of 2,923 variable stars. These variables are most likely long-period variables
amidst an evolved stellar population. At least one-third of the identified
carbon stars are variable.Comment: Accepted for publication in ApJ. See published article for full
resolution figures and electronic table
Two-particle correlations and the metal-insulator transition: Iterated Perturbation Theory revisited
Recent advances in many-body physics have made it possible to study
correlated electron systems at the two-particle level. In Dynamical Mean-Field
theory, it has been shown that the metal-insulator phase diagram is closely
related to the eigenstructure of the susceptibility. So far, this situation has
been studied using accurate but numerically expensive solvers. Here, the
Iterated Perturbation Theory (IPT) approximation is used instead. Its
simplicity makes it possible to obtain analytical results for the two-particle
vertex and the DMFT Jacobian. The limited computational cost also enables a
detailed comparison of analytical expressions for the response functions to
results obtained using finite differences. At the same time, the approximate
nature of IPT precludes an interpretation of the metal-insulator transition in
terms of a Landau free energy functional.Comment: Revised versio
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