2,451 research outputs found
Charmonium-Nucleon Dissociation Cross Sections in the Quark Model
Charmonium dissociation cross sections due to flavor-exchange
charmonium-baryon scattering are computed in the constituent quark model. We
present results for inelastic and scattering amplitudes
and cross sections into 46 final channels, including final states composed of
various combinations of , , , and . These results
are relevant to experimental searches for the deconfined phase of quark matter,
and may be useful in identifying the contribution of initial
production to the open-charm final states observed at RHIC through the
characteristic flavor ratios of certain channels. These results are also of
interest to possible charmonium-nucleon bound states.Comment: 10 pages, 5 eps figures, revte
Cosmology with the lights off: Standard sirens in the Einstein Telescope era
We explore the prospects for constraining cosmology using gravitational-wave
(GW) observations of neutron-star binaries by the proposed Einstein Telescope
(ET), exploiting the narrowness of the neutron-star mass function. Double
neutron-star (DNS) binaries are expected to be one of the first sources
detected after "first-light" of Advanced LIGO and are expected to be detected
at a rate of a few tens per year in the advanced era. However the proposed ET
could catalog tens of thousands per year. Combining the measured source
redshift distributions with GW-network distance determinations will permit not
only the precision measurement of background cosmological parameters, but will
provide an insight into the astrophysical properties of these DNS systems. Of
particular interest will be to probe the distribution of delay times between
DNS-binary creation and subsequent merger, as well as the evolution of the
star-formation rate density within ET's detection horizon. Keeping H_0,
\Omega_{m,0} and \Omega_{\Lambda,0} fixed and investigating the precision with
which the dark-energy equation-of-state parameters could be recovered, we found
that with 10^5 detected DNS binaries we could constrain these parameters to an
accuracy similar to forecasted constraints from future CMB+BAO+SNIa
measurements. Furthermore, modeling the merger delay-time distribution as a
power-law, and the star-formation rate (SFR) density as a parametrized version
of the Porciani and Madau SF2 model, we find that the associated astrophysical
parameters are constrained to within ~ 10%. All parameter precisions scaled as
1/sqrt(N), where N is the number of cataloged detections. We also investigated
how precisions varied with the intrinsic underlying properties of the Universe
and with the distance reach of the network (which may be affected by the
low-frequency cutoff of the detector).Comment: 24 pages, 11 figures, 6 tables. Minor changes to reflect published
version. References updated and correcte
Imaging the Cosmic Matter Distribution using Gravitational Lensing of Pregalactic HI
21-cm emission from neutral hydrogen during and before the epoch of cosmic
reionisation is gravitationally lensed by material at all lower redshifts.
Low-frequency radio observations of this emission can be used to reconstruct
the projected mass distribution of foreground material, both light and dark. We
compare the potential imaging capabilities of such 21-cm lensing with those of
future galaxy lensing surveys. We use the Millennium Simulation to simulate
large-area maps of the lensing convergence with the noise, resolution and
redshift-weighting achievable with a variety of idealised observation
programmes. We find that the signal-to-noise of 21-cm lens maps can far exceed
that of any map made using galaxy lensing. If the irreducible noise limit can
be reached with a sufficiently large radio telescope, the projected convergence
map provides a high-fidelity image of the true matter distribution, allowing
the dark matter halos of individual galaxies to be viewed directly, and giving
a wealth of statistical and morphological information about the relative
distributions of mass and light. For instrumental designs like that planned for
the Square Kilometer Array (SKA), high-fidelity mass imaging may be possible
near the resolution limit of the core array of the telescope.Comment: version accepted for publication in MNRAS (reduced-resolution
figures
A comparison of the excess mass around CFHTLenS galaxy-pairs to predictions from a semi-analytic model using galaxy-galaxy-galaxy lensing
The matter environment of galaxies is connected to the physics of galaxy
formation and evolution. Utilising galaxy-galaxy-galaxy lensing as a direct
probe, we map out the distribution of correlated surface mass-density around
galaxy pairs for different lens separations in the Canada-France-Hawaii
Telescope Lensing Survey (CFHTLenS). We compare, for the first time, these
so-called excess mass maps to predictions provided by a recent semi-analytic
model, which is implanted within the dark-matter Millennium Simulation. We
analyse galaxies with stellar masses between in
two photometric redshift bins, for lens redshifts , focusing on
pairs inside groups and clusters. To allow us a better interpretation of the
maps, we discuss the impact of chance pairs, i.e., galaxy pairs that appear
close to each other in projection only. Our tests with synthetic data
demonstrate that the patterns observed in the maps are essentially produced by
correlated pairs that are close in redshift ().
We also verify the excellent accuracy of the map estimators. In an application
to the galaxy samples in the CFHTLenS, we obtain a
significant detection of the excess mass and an overall good agreement with the
galaxy model predictions. There are, however, a few localised spots in the maps
where the observational data disagrees with the model predictions on a
confidence level. Although we have no strong indications for
systematic errors in the maps, this disagreement may be related to the residual
B-mode pattern observed in the average of all maps. Alternatively, misaligned
galaxy pairs inside dark matter halos or lensing by a misaligned distribution
of the intra-cluster gas might also cause the unanticipated bulge in the
distribution of the excess mass between lens pairs.Comment: 21 pages, 12 figures; abridged abstract; revised version for A&A
after addressing all comments by the refere
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Large anisotropic uniaxial pressure dependencies of Tc in single crystalline Ba(Fe0.92Co0.08)2As2
Using high-resolution dilatometry, we study the thermodynamic response of the
lattice parameters to superconducting order in a self-flux grown
Ba(Fe0.92Co0.08)2As2 single crystal. The uniaxial pressure dependencies of the
critical temperature of Tc, calculated using our thermal expansion and specific
heat data via the Ehrenfest relation, are found to be quite large and very
anisotropic (dTc/dpa = 3.1(1) K/GPa and dTc/dpc = - 7.0(2) K/GPa). Our results
show that there is a strong coupling of the c/a ratio to superconducting order,
which demonstrates that Tc is far from the optimal value. A surprising
similarity with the uniaxial pressure effects in several other layered
superconductors is discussed.Comment: 11 pages, 4 Figure
Intrinsic galaxy shapes and alignments II: Modelling the intrinsic alignment contamination of weak lensing surveys
Intrinsic galaxy alignments constitute the major astrophysical systematic of
forthcoming weak gravitational lensing surveys but also yield unique insights
into galaxy formation and evolution. We build analytic models for the
distribution of galaxy shapes based on halo properties extracted from the
Millennium Simulation, differentiating between early- and late-type galaxies as
well as central galaxies and satellites. The resulting ellipticity correlations
are investigated for their physical properties and compared to a suite of
current observations. The best-faring model is then used to predict the
intrinsic alignment contamination of planned weak lensing surveys. We find that
late-type galaxy models generally have weak intrinsic ellipticity correlations,
marginally increasing towards smaller galaxy separation and higher redshift.
The signal for early-type models at fixed halo mass strongly increases by three
orders of magnitude over two decades in galaxy separation, and by one order of
magnitude from z=0 to z=2. The intrinsic alignment strength also depends
strongly on halo mass, but not on galaxy luminosity at fixed mass, or galaxy
number density in the environment. We identify models that are in good
agreement with all observational data, except that all models over-predict
alignments of faint early-type galaxies. The best model yields an intrinsic
alignment contamination of a Euclid-like survey between 0.5-10% at z>0.6 and on
angular scales larger than a few arcminutes. Cutting 20% of red foreground
galaxies using observer-frame colours can suppress this contamination by up to
a factor of two.Comment: 23 pages, 14 figures; minor changes to match version published in
MNRA
A linear theory for control of non-linear stochastic systems
We address the role of noise and the issue of efficient computation in
stochastic optimal control problems. We consider a class of non-linear control
problems that can be formulated as a path integral and where the noise plays
the role of temperature. The path integral displays symmetry breaking and there
exist a critical noise value that separates regimes where optimal control
yields qualitatively different solutions. The path integral can be computed
efficiently by Monte Carlo integration or by Laplace approximation, and can
therefore be used to solve high dimensional stochastic control problems.Comment: 5 pages, 3 figures. Accepted to PR
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