6,609 research outputs found
Stellar wobble caused by a nearby binary system: eccentric and inclined orbits
Most extrasolar planets currently known were discovered by means of an
indirect method that measures the stellar wobble caused by the planet. We
previously studied a triple system composed of a star and a nearby binary on
circular coplanar orbits. We showed that although the effect of the binary on
the star can be differentiated from the stellar wobble caused by a planet,
because of observational limitations the two effects may often remain
indistinguishable. Here, we develop a model that applies to eccentric and
inclined orbits. We show that the binary's effect is more likely to be mistaken
by planet(s) in the case of coplanar motion observed equator-on. Moreover, when
the orbits are eccentric, the magnitude of the binary's effect may be larger
than in the circular case. Additionally, an eccentric binary can mimic two
planets with orbital periods in the ratio 2/1. However, when the star's orbit
around the binary's center of mass has a high eccentricity and a reasonably
well-constrained period, it should be easier to distinguish the binary's effect
from a planet.Comment: 10 pages, 9 figures, 2 table
A semi-empirical stability criterion for real planetary systems
We test a crossing orbit stability criterion for eccentric planetary systems,
based on Wisdom's criterion of first order mean motion resonance overlap
(Wisdom, 1980).
We show that this criterion fits the stability regions in real exoplanet
systems quite well. In addition, we show that elliptical orbits can remain
stable even for regions where the apocenter distance of the inner orbit is
larger than the pericenter distance of the outer orbit, as long as the initial
orbits are aligned.
The analytical expressions provided here can be used to put rapid constraints
on the stability zones of multi-planetary systems. As a byproduct of this
research, we further show that the amplitude variations of the eccentricity can
be used as a fast-computing stability indicator.Comment: 11 pages, 11 figures. MNRAS accepte
Possible Reentrance of the Fractional Quantum Hall Effect in the Lowest Landau Level
In the framework of a recently developed model of interacting composite
fermions, we calculate the energy of different solid and Laughlin-type liquid
phases of spin-polarized composite fermions. The liquid phases have a lower
energy than the competing solids around the electronic filling factors
nu=4/11,6/17, and 4/19 and may thus be responsible for the fractional quantum
Hall effect at nu=4/11. The alternation between solid and liquid phases when
varying the magnetic field may lead to reentrance phenomena in analogy with the
observed reentrant integral quantum Hall effect.Comment: 4 pages, 3 figures; revised version accepted for publication in Phys.
Rev. Let
Second Generation of Composite Fermions and the Self-Similarity of the Fractional Quantum Hall Effect
A recently developed model of interacting composite fermions, is used to
investigate different composite-fermion phases. Their interaction potential
allows for the formation of both solid and new quantum-liquid phases, which are
interpreted in terms of second-generation composite fermions and which may be
responsible for the fractional quantum Hall states observed at unusual filling
factors, such as nu=4/11. Projection of the composite-fermion dynamics to a
single level, involved in the derivation of the Hamiltonian of interacting
composite fermions, reveals the underlying self-similarity of the model.Comment: 4 pages, 1 figure; to appear in "Proceedings of the 16th
International Conference on High Magnetic Fields in Semiconductor Physics
(SemiMag-16)", only change with respect to v1: correction in authors line, no
changes in manuscrip
Quantum Phases in Partially Filled Landau Levels
We compare the energies of different electron solids, such as bubble crystals
with triangular and square symmetry and stripe phases, to those of correlated
quantum liquids in partially filled intermediate Landau levels. Multiple
transitions between these phases when varying the filling of the top-most
partially filled Landau level explain the observed reentrance of the integer
quantum Hall effect. The phase transitions are identified as first-order. This
leads to a variety of measurable phenomena such as the phase coexistence
between a Wigner crystal and a two-electron bubble phase in a Landau-level
filling-factor range , which has recently been observed in
transport measurements under micro-wave irradiation.Comment: 6 pages, 2 figures; to appear in "Proceedings of the 16th
International Conference on High Magnetic Fields in Semiconductor Physics
(SemiMag-16)
Fermi-Bose mixture in mixed dimensions
One of the challenging goals in the studies of many-body physics with
ultracold atoms is the creation of a topological superfluid
for identical fermions in two dimensions (2D). The expectations of reaching the
critical temperature through p-wave Feshbach resonance in spin-polarized
fermionic gases have soon faded away because on approaching the resonance, the
system becomes unstable due to inelastic-collision processes. Here, we consider
an alternative scenario in which a single-component degenerate gas of fermions
in 2D is paired via phonon-mediated interactions provided by a 3D BEC
background. Within the weak-coupling regime, we calculate the critical
temperature for the fermionic pair formation, using Bethe-Salpeter
formalism, and show that it is significantly boosted by higher-order
diagramatic terms, such as phonon dressing and vertex corrections. We describe
in detail an experimental scheme to implement our proposal, and show that the
long-sought p-wave superfluid is at reach with state-of-the-art experiments.Comment: 12 pages, 6 figures, 2 tables and supplementary materia
Tidal damping of the mutual inclination in hierachical systems
Hierarchical two-planet systems, in which the inner body's semi-major axis is
between 0.1 and 0.5 AU, usually present high eccentricity values, at least for
one of the orbits. As a result of the formation process, one may expect that
planetary systems with high eccentricities also have high mutual inclinations.
However, here we show that tidal effects combined with gravitational
interactions damp the initial mutual inclination to modest values in timescales
that are shorter than the age of the system. This effect is not a direct
consequence of tides on the orbits, but it results from a secular forcing of
the inner planet's flattening. We then conclude that these hierarchical
planetary systems are unlikely to present very high mutual inclinations, at
least as long as the orbits remain outside the Lidov-Kozai libration areas. The
present study can also be extended to systems of binary stars and to
planet-satellite systems.Comment: 16 pages, 13 figure
Quantum simulation of correlated-hopping models with fermions in optical lattices
By using a modulated magnetic field in a Feshbach resonance for ultracold
fermionic atoms in optical lattices, we show that it is possible to engineer a
class of models usually referred to as correlated-hopping models. These models
differ from the Hubbard model in exhibiting additional density-dependent
interaction terms that affect the hopping processes. In addition to the
spin-SU(2) symmetry, they also possess a charge-SU(2) symmetry, which opens the
possibility of investigating the -pairing mechanism for superconductivity
introduced by Yang for the Hubbard model. We discuss the known solution of the
model in 1D (where states have been found in the degenerate manifold of
the ground state) and show that, away from the integrable point, quantum Monte
Carlo simulations at half filling predict the emergence of a phase with
coexisting incommensurate spin and charge order.Comment: 10 pages, 9 figure
Momentum Space Regularizations and the Indeterminacy in the Schwinger Model
We revisited the problem of the presence of finite indeterminacies that
appear in the calculations of a Quantum Field Theory. We investigate the
occurrence of undetermined mathematical quantities in the evaluation of the
Schwinger model in several regularization scenarios. We show that the
undetermined character of the divergent part of the vacuum polarization tensor
of the model, introduced as an {\it ansatz} in previous works, can be obtained
mathematically if one introduces a set of two parameters in the evaluation of
these quantities. The formal mathematical properties of this tensor and their
violations are discussed. The analysis is carried out in both analytical and
sharp cutoff regularization procedures. We also show how the Pauli Villars
regularization scheme eliminates the indeterminacy, giving a gauge invariant
result in the vector Schwinger model.Comment: 10 pages, no figure
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