3,995 research outputs found
Large-Scale Model of the Milky Way: Stellar Kinematics and Microlensing Event Timescale Distribution in the Galactic Bulge
We build a stellar-dynamical model of the Milky Way barred bulge and disk,
using a newly implemented adaptive particle method. The underlying mass model
has been previously shown to match the Galactic near-infrared surface
brightness as well as gas-kinematic observations. Here we show that the new
stellar-dynamical model also matches the observed stellar kinematics in several
bulge fields, and that its distribution of microlensing event timescales
reproduces the observed timescale distribution of the {\it MACHO} experiment
with a reasonable stellar mass function. The model is therefore an excellent
basis for further studies of the Milky Way. We also predict the observational
consequences of this mass function for parallax shifted events.Comment: 13 pages, 3 figures. Accepted to ApJ
Gradient Representations and Affine Structures in AE(n)
We study the indefinite Kac-Moody algebras AE(n), arising in the reduction of
Einstein's theory from (n+1) space-time dimensions to one (time) dimension, and
their distinguished maximal regular subalgebras sl(n) and affine A_{n-2}^{(1)}.
The interplay between these two subalgebras is used, for n=3, to determine the
commutation relations of the `gradient generators' within AE(3). The low level
truncation of the geodesic sigma-model over the coset space AE(n)/K(AE(n)) is
shown to map to a suitably truncated version of the SL(n)/SO(n) non-linear
sigma-model resulting from the reduction Einstein's equations in (n+1)
dimensions to (1+1) dimensions. A further truncation to diagonal solutions can
be exploited to define a one-to-one correspondence between such solutions, and
null geodesic trajectories on the infinite-dimensional coset space H/K(H),
where H is the (extended) Heisenberg group, and K(H) its maximal compact
subgroup. We clarify the relation between H and the corresponding subgroup of
the Geroch group.Comment: 43 page
Harmonic entanglement with second-order non-linearity
We investigate the second-order non-linear interaction as a means to generate
entanglement between fields of differing wavelengths. And show that perfect
entanglement can, in principle, be produced between the fundamental and second
harmonic fields in these processes. Neither pure second harmonic generation,
nor parametric oscillation optimally produce entanglement, such optimal
entanglement is rather produced by an intermediate process. An experimental
demonstration of these predictions should be imminently feasible.Comment: 4 pages, 4 figure
Vacua of N=10 three dimensional gauged supergravity
We study scalar potentials and the corresponding vacua of N=10 three
dimensional gauged supergravity. The theory contains 32 scalar fields
parametrizing the exceptional coset space . The admissible gauge groups considered in this work involve both
compact and non-compact gauge groups which are maximal subgroups of
and , respectively. These gauge groups are
given by for , , , and . We
find many AdS critical points with various unbroken gauge symmetries. The
relevant background isometries associated to the maximally supersymmetric
critical points at which all scalars vanish are also given. These correspond to
the superconformal symmetries of the dual conformal field theories in two
dimensions.Comment: 37 pages no figures, typos corrected and a little change in the
forma
An improved estimate of black hole entropy in the quantum geometry approach
A proper counting of states for black holes in the quantum geometry approach
shows that the dominant configuration for spins are distributions that include
spins exceeding one-half at the punctures. This raises the value of the Immirzi
parameter and the black hole entropy. However, the coefficient of the
logarithmic correction remains -1/2 as before.Comment: 5 pages, LaTeX; references and remarks adde
The influence of bond-rigidity and cluster diffusion on the self-diffusion of hard spheres with square-well interaction
Hard spheres interacting through a square-well potential were simulated using
two different methods: Brownian Cluster Dynamics (BCD) and Event Driven
Brownian Dynamics (EDBD). The structure of the equilibrium states obtained by
both methods were compared and found to be almost the identical. Self diffusion
coefficients () were determined as a function of the interaction strength.
The same values were found using BCD or EDBD. Contrary the EDBD, BCD allows one
to study the effect of bond rigidity and hydrodynamic interaction within the
clusters. When the bonds are flexible the effect of attraction on is
relatively weak compared to systems with rigid bonds. increases first with
increasing attraction strength, and then decreases for stronger interaction.
Introducing intra-cluster hydrodynamic interaction weakly increases for a
given interaction strength. Introducing bond rigidity causes a strong decrease
of which no longer shows a maximum as function of the attraction strength
P-values for high-dimensional regression
Assigning significance in high-dimensional regression is challenging. Most
computationally efficient selection algorithms cannot guard against inclusion
of noise variables. Asymptotically valid p-values are not available. An
exception is a recent proposal by Wasserman and Roeder (2008) which splits the
data into two parts. The number of variables is then reduced to a manageable
size using the first split, while classical variable selection techniques can
be applied to the remaining variables, using the data from the second split.
This yields asymptotic error control under minimal conditions. It involves,
however, a one-time random split of the data. Results are sensitive to this
arbitrary choice: it amounts to a `p-value lottery' and makes it difficult to
reproduce results. Here, we show that inference across multiple random splits
can be aggregated, while keeping asymptotic control over the inclusion of noise
variables. We show that the resulting p-values can be used for control of both
family-wise error (FWER) and false discovery rate (FDR). In addition, the
proposed aggregation is shown to improve power while reducing the number of
falsely selected variables substantially.Comment: 25 pages, 4 figure
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