15,755 research outputs found
Core instability models of giant planet accretion II: forming planetary systems
We develop a simple model for computing planetary formation based on the core
instability model for the gas accretion and the oligarchic growth regime for
the accretion of the solid core. In this model several planets can form
simultaneously in the disc, a fact that has important implications specially
for the changes in the dynamic of the planetesimals and the growth of the cores
since we consider the collision between them as a source of potential growth.
The type I and II migration of the embryos and the migration of the
planetesimals due to the interaction with the disc of gas are also taken into
account. With this model we consider different initial conditions to generate a
variety of planetary systems and analyse them statistically. We explore the
effects of using different type I migration rates on the final number of
planets formed per planetary system such as on the distribution of masses and
semimajor axis of extrasolar planets, where we also analyse the implications of
considering different gas accretion rates. A particularly interesting result is
the generation of a larger population of habitable planets when the gas
accretion rate and type I migration are slower.Comment: 4 figures and 1 table. Accepted for publication in MNRA
Dirac points merging and wandering in a model Chern insulator
We present a model for a Chern insulator on the square lattice with complex
first and second neighbor hoppings and a sublattice potential which displays an
unexpectedly rich physics. Similarly to the celebrated Haldane model, the
proposed Chern insulator has two topologically non-trivial phases with Chern
numbers . As a distinctive feature of the present model, phase
transitions are associated to Dirac points that can move, merge and split in
momentum space, at odds with Haldane's Chern insulator where Dirac points are
bound to the corners of the hexagonal Brillouin zone. Additionally, the
obtained phase diagram reveals a peculiar phase transition line between two
distinct topological phases, in contrast to the Haldane model where such
transition is reduced to a point with zero sublattice potential. The model is
amenable to be simulated in optical lattices, facilitating the study of phase
transitions between two distinct topological phases and the experimental
analysis of Dirac points merging and wandering
On the instability of Reissner-Nordstrom black holes in de Sitter backgrounds
Recent numerical investigations have uncovered a surprising result:
Reissner-Nordstrom-de Sitter black holes are unstable for spacetime dimensions
larger than 6. Here we prove the existence of such instability analytically,
and we compute the timescale in the near-extremal limit. We find very good
agreement with the previous numerical results. Our results may me helpful in
shedding some light on the nature of the instability.Comment: Published in Phys.Rev.
- …