37,826 research outputs found
Smooth, identifiable supermodels of discrete DAG models with latent variables
We provide a parameterization of the discrete nested Markov model, which is a
supermodel that approximates DAG models (Bayesian network models) with latent
variables. Such models are widely used in causal inference and machine
learning. We explicitly evaluate their dimension, show that they are curved
exponential families of distributions, and fit them to data. The
parameterization avoids the irregularities and unidentifiability of latent
variable models. The parameters used are all fully identifiable and
causally-interpretable quantities.Comment: 30 page
Highly eccentric inspirals into a black hole
We model the inspiral of a compact stellar-mass object into a massive
nonrotating black hole including all dissipative and conservative
first-order-in-the-mass-ratio effects on the orbital motion. The techniques we
develop allow inspirals with initial eccentricities as high as and
initial separations as large as to be evolved through many thousands
of orbits up to the onset of the plunge into the black hole. The inspiral is
computed using an osculating elements scheme driven by a hybridized self-force
model, which combines Lorenz-gauge self-force results with highly accurate flux
data from a Regge-Wheeler-Zerilli code. The high accuracy of our hybrid
self-force model allows the orbital phase of the inspirals to be tracked to
within radians or better. The difference between self-force models
and inspirals computed in the radiative approximation is quantified.Comment: Updated to reflect published versio
Evolution of small-mass-ratio binaries with a spinning secondary
We calculate the evolution and gravitational-wave emission of a spinning
compact object inspiraling into a substantially more massive (non-rotating)
black hole. We extend our previous model for a non-spinning binary [Phys. Rev.
D 93, 064024] to include the Mathisson-Papapetrou-Dixon spin-curvature force.
For spin-aligned binaries we calculate the dephasing of the inspiral and
associated waveforms relative to models that do not include spin-curvature
effects. We find this dephasing can be either positive or negative depending on
the initial separation of the binary. For binaries in which the spin and
orbital angular momentum are not parallel, the orbital plane precesses and we
use a more general osculating element prescription to compute inspirals.Comment: 17 pages, 6 figure
Comptonisation of Cosmic Microwave Background Photons in Dwarf Spheroidal Galaxies
We present theoretical modelling of the electron distribution produced by
annihilating neutralino dark matter in dwarf spheroidal galaxies (dSphs). In
particular, we follow up the idea of Colafrancesco (2004) and find that such
electrons distort the cosmic microwave background (CMB) by the
Sunyaev-Zeldovich effect. For an assumed neutralino mass of 10 GeV and beam
size of 1'', the SZ temperature decrement is of the order of nano-Kelvin for
dSph models with a soft core. By contrast, it is of the order of micro-Kelvin
for the strongly cusped dSph models favoured by some cosmological simulations.
Although this is out of reach of current instruments, it may well be detectable
by future mm telescopes, such as ALMA. We also show that the upscattered CMB
photons have energies within reach of upcoming X-ray observatories, but that
the flux of such photons is too small to be detectable soon. Nonetheless, we
conclude that searching for the dark matter induced Sunyaev-Zeldovich effect is
a promising way of constraining the dark distribution in dSphs, especially if
the particles are light.Comment: 10 pages, 5 figures, MNRAS, in pres
Terrestrial heat flow studies in Eastern Africa and the North Sea
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