5,996 research outputs found
Counting Black Holes: The Cosmic Stellar Remnant Population and Implications for LIGO
We present an empirical approach for interpreting gravitational wave signals
of binary black hole mergers under the assumption that the underlying black
hole population is sourced by remnants of stellar evolution. Using the observed
relationship between galaxy mass and stellar metallicity, we predict the black
hole count as a function of galaxy stellar mass. We show, for example, that a
galaxy like the Milky Way should host millions of black holes
and dwarf satellite galaxies like Draco should host such remnants,
with weak dependence on the assumed IMF and stellar evolution model. Most
low-mass black holes () typically reside within massive
galaxies () while massive black holes () typically reside within dwarf galaxies () today. If roughly of black holes are involved in a binary black
hole merger, then the reported merger rate densities from Advanced LIGO can be
accommodated for a range of merger timescales, and the detection of mergers
with black holes should be expected within the next decade.
Identifying the host galaxy population of the mergers provides a way to
constrain both the binary neutron star or black hole formation efficiencies and
the merger timescale distributions; these events would be primarily localized
in dwarf galaxies if the merger timescale is short compared to the age of the
universe and in massive galaxies otherwise. As more mergers are detected, the
prospect of identifying the host galaxy population, either directly through the
detection of electromagnetic counterparts of binary neutron star mergers or
indirectly through the anisotropy of the events, will become a realistic
possibility.Comment: 10 pages, 8 figures. Accepted by MNRA
Asymptotically Optimal Quantum Circuits for d-level Systems
As a qubit is a two-level quantum system whose state space is spanned by |0>,
|1>, so a qudit is a d-level quantum system whose state space is spanned by
|0>,...,|d-1>. Quantum computation has stimulated much recent interest in
algorithms factoring unitary evolutions of an n-qubit state space into
component two-particle unitary evolutions. In the absence of symmetry, Shende,
Markov and Bullock use Sard's theorem to prove that at least C 4^n two-qubit
unitary evolutions are required, while Vartiainen, Moettoenen, and Salomaa
(VMS) use the QR matrix factorization and Gray codes in an optimal order
construction involving two-particle evolutions. In this work, we note that
Sard's theorem demands C d^{2n} two-qudit unitary evolutions to construct a
generic (symmetry-less) n-qudit evolution. However, the VMS result applied to
virtual-qubits only recovers optimal order in the case that d is a power of
two. We further construct a QR decomposition for d-multi-level quantum logics,
proving a sharp asymptotic of Theta(d^{2n}) two-qudit gates and thus closing
the complexity question for all d-level systems (d finite.) Gray codes are not
required, and the optimal Theta(d^{2n}) asymptotic also applies to gate
libraries where two-qudit interactions are restricted by a choice of certain
architectures.Comment: 18 pages, 5 figures (very detailed.) MatLab files for factoring qudit
unitary into gates in MATLAB directory of source arxiv format. v2: minor
change
Dark Matter from Early Decays
Two leading dark matter candidates from supersymmetry and other theories of
physics beyond the standard model are WIMPs and weak scale gravitinos. If the
lightest stable particle is a gravitino, then a WIMP will decay into it with a
natural lifetime of order a month ~ M_{pl}^2/M_{weak}^3. We show that if the
bulk of dark matter today came from decays of neutral particles with lifetimes
of order a year or smaller, then it could lead to a reduction in the amount of
small scale substructure, less concentrated halos and constant density cores in
the smallest mass halos. Such beneficial effects may therefore be realized
naturally, as discussed by Cembranos, Feng, Rajaraman, and Takayama, in the
case of supersymmetry.Comment: Matches version accepted for publication in PRD. Added a paragraph to
Sec V. 9 pages, 3 figure
An ion probe study of the sulphur isotopic composition of Fe-Ni sulphides in CM carbonaceous chondrites
From the Introduction: The CM chondrites have endured variable degrees of aqueous alteration [1] which has changed their original mineralogy. A detailed study of the petrology and mineralogy of the sulphides in a suite of increasingly aqueously altered CMs, combined with sulphur isotope data measured in situ, can provide clues as to whether differences in the CM group are a result of different degrees of aqueous alteration, or whether they are the result of nebular heterogeneity
The Implications of Galaxy Formation Models for the TeV Observations of Current Detectors
This paper represents a step toward constraining galaxy formation models via
TeV gamm a ray observations. We use semi-analytic models of galaxy formation to
predict a spectral distribution for the intergalactic infrared photon field,
which in turn yields information about the absorption of TeV gamma rays from
extra-galactic sources. By making predictions for integral flux observations at
>200 GeV for several known EGRE T sources, we directly compare our models with
current observational upper limits obtained by Whipple. In addition, our
predictions may offer a guide to the observing programs for the current
population of TeV gamma ray observatories.Comment: 6 pages, 11 figures, to appear in the proceedings of the 6th TeV
Workshop at Snowbird, U
YIELD PREDICTION IN 60ft\u3csup\u3e2\u3c/sup\u3e GRIDS
Large detailed yield databases incorporating GPS makes it possible to predict yield on a small scale. The objective of this study was to determine how closely yield could be predicted in grids of 60-ft2 units. Com and soybean yields were averaged to the 60-ft2 grid. The yields were modeled on previous yields, soil fertility, soil type, and terrain variables. Soil fertility variables were kriged from a I-acre grid to the 60-ft2 grid. Terrain data and soil type data were available at the same scale. Multiple regression models and models with spatial correlation determined from yield semivariograms differed some. Previous yields and wetness were the most significant variables. Soil variables alone were not good predictors
Parallelism for Quantum Computation with Qudits
Robust quantum computation with d-level quantum systems (qudits) poses two
requirements: fast, parallel quantum gates and high fidelity two-qudit gates.
We first describe how to implement parallel single qudit operations. It is by
now well known that any single-qudit unitary can be decomposed into a sequence
of Givens rotations on two-dimensional subspaces of the qudit state space.
Using a coupling graph to represent physically allowed couplings between pairs
of qudit states, we then show that the logical depth of the parallel gate
sequence is equal to the height of an associated tree. The implementation of a
given unitary can then optimize the tradeoff between gate time and resources
used. These ideas are illustrated for qudits encoded in the ground hyperfine
states of the atomic alkalies Rb and Cs. Second, we provide a
protocol for implementing parallelized non-local two-qudit gates using the
assistance of entangled qubit pairs. Because the entangled qubits can be
prepared non-deterministically, this offers the possibility of high fidelity
two-qudit gates.Comment: 9 pages, 3 figure
System analysis approach to deriving design criteria (loads) for Space Shuttle and its payloads. Volume 1: General statement of approach
Space shuttle, the most complex transportation system designed to date, illustrates the requirement for an analysis approach that considers all major disciplines simultaneously. Its unique cross coupling and high sensitivity to aerodynamic uncertainties and high performance requirements dictated a less conservative approach than those taken in programs. Analyses performed for the space shuttle and certain payloads, Space Telescope and Spacelab, are used a examples. These illustrate the requirements for system analysis approaches and criteria, including dynamic modeling requirements, test requirements control requirements and the resulting design verification approaches. A survey of the problem, potential approaches available as solutions, implications for future systems, and projected technology development areas are addressed
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