18,405 research outputs found
Galaxy peculiar velocities and evolution-bias
Galaxy bias can be split into two components: a formation-bias based on the
locations of galaxy creation, and an evolution-bias that details their
subsequent evolution. In this letter we consider evolution-bias in the peaks
model. In this model, galaxy formation takes place at local maxima in the
density field, and we analyse the subsequent peculiar motion of these galaxies
in a linear model of structure formation. The peak restriction yields
differences in the velocity distribution and correlation between the galaxy and
the dark matter fields, which causes the evolution-bias component of the total
bias to evolve in a scale-dependent way. This mechanism naturally gives rise to
a change in shape between galaxy and matter correlation functions that depends
on the mean age of the galaxy population. This model predicts that older
galaxies would be more strongly biased on large scales compared to younger
galaxies. Our arguments are supported by a Monte-Carlo simulation of galaxy
pairs propagated using the Zel'dovich-approximation for describing linear
peculiar galaxy motion.Comment: 5 pages, 4 figures, MNRAS accepte
Thermodynamics of (2+1)-flavor QCD: Confronting Models with Lattice Studies
The Polyakov-quark-meson (PQM) model, which combines chiral as well as
deconfinement aspects of strongly interacting matter is introduced for three
light quark flavors. An analysis of the chiral and deconfinement phase
transition of the model and its thermodynamics at finite temperatures is given.
Three different forms of the effective Polyakov loop potential are considered.
The findings of the (2+1)-flavor model investigations are confronted to
corresponding recent QCD lattice simulations of the RBC-Bielefeld, HotQCD and
Wuppertal-Budapest collaborations. The influence of the heavier quark masses,
which are used in the lattice calculations, is taken into account. In the
transition region the bulk thermodynamics of the PQM model agrees well with the
lattice data.Comment: 13 pages, 7 figures, 3 tables; minor changes, final version to appear
in Phys. Rev.
Vacuum fluctuations and the thermodynamics of chiral models
We consider the thermodynamics of chiral models in the mean-field
approximation and discuss the relevance of the (frequently omitted) fermion
vacuum loop. Within the chiral quark-meson model and its Polyakov loop extended
version, we show that the fermion vacuum fluctuations can change the order of
the phase transition in the chiral limit and strongly influence physical
observables. We compute the temperature-dependent effective potential and
baryon number susceptibilities in these models, with and without the vacuum
term, and explore the cutoff and the pion mass dependence of the
susceptibilities. Finally, in the renormalized model the divergent vacuum
contribution is removed using the dimensional regularization.Comment: 9 pages, 5 figure
Center phase transition from matter propagators in (scalar) QCD
Novel order parameters for the confinement-deconfinement phase transition of
quenched QCD and fundamentally charged scalar QCD are presented. Similar to the
well-known dual condensate, they are defined via generalized matter propagators
with -valued boundary conditions. The order parameters are easily
accessible with functional methods. Their validity and accessibility is
explicitly demonstrated by numerical studies of the Dyson-Schwinger equations
for the matter propagators. Even in the case of heavy scalar matter, where the
propagator does not show a signature of the phase transition, a discontinuity
due to the transition can be extracted in the order parameters, establishing
also fundamentally charged scalar matter as a probe for color confinement.Comment: accepted versio
More poor kids in more poor places: children increasingly live where poverty persists
More poor kids in more poor places: children increasingly live where poverty persist
Deep Convolutional Neural Networks as strong gravitational lens detectors
Future large-scale surveys with high resolution imaging will provide us with
a few new strong galaxy-scale lenses. These strong lensing systems
however will be contained in large data amounts which are beyond the capacity
of human experts to visually classify in a unbiased way. We present a new
strong gravitational lens finder based on convolutional neural networks (CNNs).
The method was applied to the Strong Lensing challenge organised by the Bologna
Lens Factory. It achieved first and third place respectively on the space-based
data-set and the ground-based data-set. The goal was to find a fully automated
lens finder for ground-based and space-based surveys which minimizes human
inspect. We compare the results of our CNN architecture and three new
variations ("invariant" "views" and "residual") on the simulated data of the
challenge. Each method has been trained separately 5 times on 17 000 simulated
images, cross-validated using 3 000 images and then applied to a 100 000 image
test set. We used two different metrics for evaluation, the area under the
receiver operating characteristic curve (AUC) score and the recall with no
false positive (). For ground based data our
best method achieved an AUC score of and a
of . For space-based data our best
method achieved an AUC score of and a
of . On space-based data adding dihedral invariance to the CNN
architecture diminished the overall score but achieved a higher no
contamination recall. We found that using committees of 5 CNNs produce the best
recall at zero contamination and consistenly score better AUC than a single
CNN. We found that for every variation of our CNN lensfinder, we achieve AUC
scores close to within .Comment: 9 pages, accepted to A&
Discovery of the 2010 Eruption and the Pre-Eruption Light Curve for Recurrent Nova U Scorpii
We report the discovery by B. G. Harris and S. Dvorak on JD 2455224.9385
(2010 Jan 28.4385 UT) of the predicted eruption of the recurrent nova U Scorpii
(U Sco). We also report on 815 magnitudes (and 16 useful limits) on the
pre-eruption light curve in the UBVRI and Sloan r' and i' bands from 2000.4 up
to 9 hours before the peak of the January 2010 eruption. We found no
significant long-term variations, though we did find frequent fast variations
(flickering) with amplitudes up to 0.4 mag. We show that U Sco did not have any
rises or dips with amplitude greater than 0.2 mag on timescales from one day to
one year before the eruption. We find that the peak of this eruption occurred
at JD 2455224.69+-0.07 and the start of the rise was at JD 2455224.32+-0.12.
From our analysis of the average B-band flux between eruptions, we find that
the total mass accreted between eruptions is consistent with being a constant,
in agreement with a strong prediction of nova trigger theory. The date of the
next eruption can be anticipated with an accuracy of +-5 months by following
the average B-band magnitudes for the next ~10 years, although at this time we
can only predict that the next eruption will be in the year 2020+-2.Comment: Astronomical Journal submitted, 36 pages, 3 figures, full table
QCD critical region and higher moments for three flavor models
One of the distinctive feature of the QCD phase diagram is the possible
emergence of a critical endpoint. The critical region around the critical point
and the path dependency of the critical exponents is investigated within
effective chiral (2+1)-flavor models with and without Polyakov-loops. Results
obtained in no-sea mean-field approximations where a divergent vacuum part in
the fermion-loop contribution is neglected, are confronted to the renormalized
ones. Furthermore, the modifications caused by the back-reaction of the matter
fluctuations on the pure Yang-Mills system are discussed. Higher order,
non-Gaussian moments of event-by-event distributions of various particle
multiplicities are enhanced near the critical point and could serve as a probe
to determine its location in the phase diagram. By means of a novel derivative
technique higher order generalized quark-number susceptibilities are calculated
and their sign structure in the phase diagram is analyzed.Comment: 12 pages, 11 figures. Final PRD version (references and one more
equation added
Towards finite density QCD with Taylor expansions
Convergence properties of Taylor expansions of observables, which are also
used in lattice QCD calculations at non-zero chemical potential, are analyzed
in an effective N_f = 2+1 flavor Polyakov-quark-meson model. A recently
developed algorithmic technique allows the calculation of higher-order Taylor
expansion coefficients in functional approaches. This novel technique is for
the first time applied to an effective N_f = 2+1 flavor Polyakov-quark-meson
model and the findings are compared with the full model solution at finite
densities. The results are used to discuss prospects for locating the QCD phase
boundary and a possible critical endpoint in the phase diagram.Comment: 11 pages, 6 figures; minor clarifying changes, version to be
published in Phys. Lett.
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