34,629 research outputs found
On the trace anomaly and the energy-momentum conservation of quantum fields at D=2 in classical curved backgrounds
We study the conformal symmetry and the energy-momentum conservation of
scalar field interacting with a curved background at D=2. We avoid to
incorporate the metric determinant into the measure of the scalar field to
explain the conformal anomaly and the consequent energy-momentum conservation.
Contrarily, we split the scalar field in two other fields, in such a way that
just one of them can be quantized. We show that the same usual geometric
quantities of the anomaly are obtained, which are accompanied by terms
containing the new field of the theory.Comment: 5 pages, no figure
Time-dependent cosmological constant in the Jackiw-Teitelboim cosmology
We study the obtainment of a time-dependent cosmological constant at D=2 in a
model based on the Jackiw-Teitelboim cosmology. We show that the cosmological
term goes to zero asymptotically and can induce a nonsingular behavior at the
origin.Comment: 4 pages, Revtex4, twocolum
Hipparcos distances of Ophiuchus and Lupus cloud complexes
We combine extinction maps from the Two Micron All Sky Survey (2MASS) with
Hipparcos and Tycho parallaxes to obtain reliable and high-precision estimates
of the distance to the Ophiuchus and Lupus dark complexes. Our analysis, based
on a rigorous maximum-likelihood approach, shows that the rho-Ophiuchi cloud is
located at (119 +/- 6) pc and the Lupus complex is located at (155 +/- 8) pc;
in addition, we are able to put constraints on the thickness of the clouds and
on their orientation on the sky (both these effects are not included in the
error estimate quoted above). For Ophiuchus, we find some evidence that the
streamers are closer to us than the core. The method applied in this paper is
currently limited to nearby molecular clouds, but it will find many natural
applications in the GAIA-era, when it will be possible to pin down the distance
and three-dimensional structure of virtually every molecular cloud in the
Galaxy.Comment: A&A in press - Corrected typo (Lupus distance) in the electronic
abstrac
Fibers in the NGC1333 proto-cluster
Are the initial conditions for clustered star formation the same as for
non-clustered star formation? To investigate the initial gas properties in
young proto-clusters we carried out a comprehensive and high-sensitivity study
of the internal structure, density, temperature, and kinematics of the dense
gas content of the NGC1333 region in Perseus, one of the nearest and best
studied embedded clusters. The analysis of the gas velocities in the
Position-Position-Velocity space reveals an intricate underlying gas
organization both in space and velocity. We identified a total of 14
velocity-coherent, (tran-)sonic structures within NGC1333, with similar
physical and kinematic properties than those quiescent, star-forming (aka
fertile) fibers previously identified in low-mass star-forming clouds. These
fibers are arranged in a complex spatial network, build-up the observed total
column density, and contain the dense cores and protostars in this cloud. Our
results demonstrate that the presence of fibers is not restricted to low-mass
clouds but can be extended to regions of increasing mass and complexity. We
propose that the observational dichotomy between clustered and non-clustered
star-forming regions might be naturally explained by the distinct spatial
density of fertile fibers in these environments.Comment: 25 pages, 17 figures; Accepted for publication in A&
Gravitational collapse of the OMC-1 region
We have investigated the global dynamical state of the Integral Shaped
Filament in the Orion A cloud using new NH (1-0) large-scale, IRAM30m
observations. Our analysis of its internal gas dynamics reveals the presence of
accelerated motions towards the Orion Nebula Cluster, showing a characteristic
blue-shifted profile centred at the position of the OMC-1 South region. The
properties of these observed gas motions (profile, extension, and magnitude)
are consistent with the expected accelerations for the gravitational collapse
of the OMC-1 region and explain both the physical and kinematic structure of
this cloud.Comment: 5 pages, 2 figures; Accepted by A&
Statistical stability and limit laws for Rovella maps
We consider the family of one-dimensional maps arising from the contracting
Lorenz attractors studied by Rovella. Benedicks-Carleson techniques were used
by Rovella to prove that there is a one-parameter family of maps whose
derivatives along their critical orbits increase exponentially fast and the
critical orbits have slow recurrent to the critical point. Metzger proved that
these maps have a unique absolutely continuous ergodic invariant probability
measure (SRB measure).
Here we use the technique developed by Freitas and show that the tail set
(the set of points which at a given time have not achieved either the
exponential growth of derivative or the slow recurrence) decays exponentially
fast as time passes. As a consequence, we obtain the continuous variation of
the densities of the SRB measures and associated metric entropies with the
parameter. Our main result also implies some statistical properties for these
maps.Comment: 1 figur
The Musca cloud: A 6 pc-long velocity-coherent, sonic filament
Filaments play a central role in the molecular clouds' evolution, but their
internal dynamical properties remain poorly characterized. To further explore
the physical state of these structures, we have investigated the kinematic
properties of the Musca cloud. We have sampled the main axis of this
filamentary cloud in CO and CO (2--1) lines using APEX
observations. The different line profiles in Musca shows that this cloud
presents a continuous and quiescent velocity field along its 6.5 pc of
length. With an internal gas kinematics dominated by thermal motions (i.e.,
) and large-scale velocity gradients, these results
reveal Musca as the longest velocity-coherent, sonic-like object identified so
far in the ISM. The transonic properties of Musca present a clear departure
from the predicted supersonic velocity dispersions expected in the Larson's
velocity dispersion-size relationship, and constitute the first observational
evidence of a filament fully decoupled from the turbulent regime over
multi-parsec scales.Comment: 12 pages, 6 figures; Accepted for publication in A&
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