19,363 research outputs found
Perturbations of Schwarzschild black holes in Dynamical Chern-Simons modified gravity
Dynamical Chern-Simons (DCS) modified gravity is an attractive, yet
relatively unexplored, candidate to an alternative theory of gravity. The DCS
correction couples a dynamical scalar field to the gravitational field. In this
framework, we analyze the perturbation formalism and stability properties of
spherically symmetric black holes. Assuming that no background scalar field is
present, gravitational perturbations with polar and axial parities decouple. We
find no effect of the Chern-Simons coupling on the polar sector, while axial
perturbations couple to the Chern-Simons scalar field. The axial sector can
develop strong instabilities if the coupling parameter beta, associated to the
dynamical coupling of the scalar field, is small enough; this yields a
constraint on beta which is much stronger than the constraints previously known
in the literature.Comment: 9 pages, 1 figure. Minor changes to match version accepted by Phys.
Rev.
Spin inversion devices with Fano anti-resonances
Analyzing spin transport of quasi-2D electrons gas moving through a
semiconductor wave guide subject to a sectionally homogeneous tilted magnetic
field, we found well-defined selection rules for resonant and antiresonant spin
carrier transmission. Based on these selection rules and the band shift induced
by the magnetic field strength and the tilting angles, we propose an efficient
spin inversion device. For a polarized incoming electron beam, we can determine
from our theoretical approach, physical conditions for spin-inversion
efficiency up to 80%. We visualize this mechanism in terms of conductance and
the spacial behavior of the wave function amplitude along the superlattice.Comment: 3 pages, 3 figures, regular pape
New gravitational solutions via a Riemann-Hilbert approach
We consider the Riemann-Hilbert factorization approach to solving the field
equations of dimensionally reduced gravity theories. First we prove that
functions belonging to a certain class possess a canonical factorization due to
properties of the underlying spectral curve. Then we use this result, together
with appropriate matricial decompositions, to study the canonical factorization
of non-meromorphic monodromy matrices that describe deformations of seed
monodromy matrices associated with known solutions. This results in new
solutions, with unusual features, to the field equations.Comment: 29 pages, 2 figures; v2: reference added, matches published versio
On Quantum Special Kaehler Geometry
We compute the effective black hole potential V of the most general N=2, d=4
(local) special Kaehler geometry with quantum perturbative corrections,
consistent with axion-shift Peccei-Quinn symmetry and with cubic leading order
behavior. We determine the charge configurations supporting axion-free
attractors, and explain the differences among various configurations in
relations to the presence of ``flat'' directions of V at its critical points.
Furthermore, we elucidate the role of the sectional curvature at the
non-supersymmetric critical points of V, and compute the Riemann tensor (and
related quantities), as well as the so-called E-tensor. The latter expresses
the non-symmetricity of the considered quantum perturbative special Kaehler
geometry.Comment: 1+43 pages; v2: typo corrected in the curvature of Jordan symmetric
sequence at page 2
Matched-filtering and parameter estimation of ringdown waveforms
Using recent results from numerical relativity simulations of non-spinning
binary black hole mergers we revisit the problem of detecting ringdown
waveforms and of estimating the source parameters, considering both LISA and
Earth-based interferometers. We find that Advanced LIGO and EGO could detect
intermediate-mass black holes of mass up to about 1000 solar masses out to a
luminosity distance of a few Gpc. For typical multipolar energy distributions,
we show that the single-mode ringdown templates presently used for ringdown
searches in the LIGO data stream can produce a significant event loss (> 10%
for all detectors in a large interval of black hole masses) and very large
parameter estimation errors on the black hole's mass and spin. We estimate that
more than 10^6 templates would be needed for a single-stage multi-mode search.
Therefore, we recommend a "two stage" search to save on computational costs:
single-mode templates can be used for detection, but multi-mode templates or
Prony methods should be used to estimate parameters once a detection has been
made. We update estimates of the critical signal-to-noise ratio required to
test the hypothesis that two or more modes are present in the signal and to
resolve their frequencies, showing that second-generation Earth-based detectors
and LISA have the potential to perform no-hair tests.Comment: 19 pages, 9 figures, matches version in press in PR
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