12,727 research outputs found
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.
Update rules and interevent time distributions: Slow ordering vs. no ordering in the Voter Model
We introduce a general methodology of update rules accounting for arbitrary
interevent time distributions in simulations of interacting agents. In
particular we consider update rules that depend on the state of the agent, so
that the update becomes part of the dynamical model. As an illustration we
consider the voter model in fully-connected, random and scale free networks
with an update probability inversely proportional to the persistence, that is,
the time since the last event. We find that in the thermodynamic limit, at
variance with standard updates, the system orders slowly. The approach to the
absorbing state is characterized by a power law decay of the density of
interfaces, observing that the mean time to reach the absorbing state might be
not well defined.Comment: 5pages, 4 figure
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