2,752 research outputs found
Environmental induced renormalization effects in quantum Hall edge states
We propose a general mechanism for renormalization of the tunneling exponents
in edge states of the fractional quantum Hall effect. Mutual effects of the
coupling with out-of-equilibrium 1/f noise and dissipation are considered both
for the Laughlin sequence and for composite co- and counter-propagating edge
states with Abelian or non-Abelian statistics. For states with
counter-propagating modes we demonstrate the robustness of the proposed
mechanism in the so called disorder-dominated phase. Prototypes of these
states, such as \nu=2/3 and \nu=5/2, are discussed in detail and the rich
phenomenology induced by the presence of a noisy environment is presented. The
proposed mechanism justifies the strong renormalizations reported in many
experimental observations carried out at low temperatures. We show how
environmental effects could affect the relevance of the tunneling excitations,
leading to important implications in particular for the \nu=5/2 case.Comment: 14 pages, 4 figure
Massive stellar systems: observational challenges and perspectives in the E-ELT era
We introduce the empirical framework concerning optical and near-infrared (NIR) photometry of crowded stellar fields. In particular, we address the impact that linear detectors and analytical PSF played in improving the accuracy and the precision of multi-band color-magnitude diagrams (CMDs). We focus our attention on recent findings based on deep NIR images collected with Adaptive Optics (AO) systems at the 8-10m class telescopes and discuss pros and cons of the different approaches. We also discuss the estimate of the absolute age of globular clusters using a well defined knee along the lower main sequence. We mention the role which the current AO-assisted instruments will have in addressing longstanding astrophysical problems of the Galactic center. Finally, we outline the role of first generation of E-ELT instruments upon photometry and spectroscopy of crowded stellar fields
The giant, horizontal and asymptotic branches of galactic globular clusters. I. The catalog, photometric observables and features
A catalog including a set of the most recent Color Magnitude Diagrams (CMDs)
is presented for a sample of 61 Galactic Globular Clusters (GGCs). We used this
data-base to perform an homogeneous systematic analysis of the evolved
sequences (namely, Red Giant Branch (RGB), Horizontal Branch (HB) and
Asymptotic Giant Branch (AGB)). Based on this analysis, we present: (1) a new
procedure to measure the level of the ZAHB (V_ZAHB) and an homogeneous set of
distance moduli obtained adopting the HB as standard candle; (2) an independent
estimate for RGB metallicity indicators and new calibrations of these
parameters in terms of both spectroscopic ([Fe/H]_CG97) and global metallicity
([M/H], including also the alpha-elements enhancement). The set of equations
presented can be used to simultaneously derive a photometric estimate of the
metal abundance and the reddening from the morphology and the location of the
RGB in the (V,B-V)-CMD. (3) the location of the RGB-Bump (in 47 GGCs) and the
AGB-Bump (in 9 GGCs). The dependence of these features on the metallicity is
discussed. We find that by using the latest theoretical models and the new
metallicity scales the earlier discrepancy between theory and observations
(~0.4 mag) completely disappears.Comment: 51 pages, 23 figures, AAS Latex, macro rtrpp4.sty included, accepted
by A
Star count density profiles and structural parameters of 26 Galactic globular clusters
We used a proper combination of high-resolution HST observations and
wide-field ground based data to derive the radial star density profile of 26
Galactic globular clusters from resolved star counts (which can be all freely
downloaded on-line). With respect to surface brightness (SB) profiles (which
can be biased by the presence of sparse, bright stars), star counts are
considered to be the most robust and reliable tool to derive cluster structural
parameters. For each system a detailed comparison with both King and Wilson
models has been performed and the most relevant best-fit parameters have been
obtained. This is the largest homogeneous catalog collected so far of star
count profiles and structural parameters derived therefrom. The analysis of the
data of our catalog has shown that: (1) the presence of the central cusps
previously detected in the SB profiles of NGC 1851, M13 and M62 is not
confirmed; (2) the majority of clusters in our sample are fitted equally well
by the King and the Wilson models; (3) we confirm the known relationship
between cluster size (as measured by the effective radius) and galactocentric
distances; (4) the ratio between the core and the effective radii shows a
bimodal distribution, with a peak at ~ 0.3 for about 80% of the clusters, and a
secondary peak at ~ 0.6 for the remaining 20%. Interestingly, the main peak
turns out to be in agreement with what expected from simulations of cluster
dynamical evolution and the ratio between these two radii well correlates with
an empirical dynamical age indicator recently defined from the observed shape
of blue straggler star radial distribution, thus suggesting that no exotic
mechanisms of energy generation are needed in the cores of the analyzed
clusters.Comment: Accepted for publication in The Astrophysical Journal; 19 pages
(emulateapj style), 15 figures, 2 table
Discovery of short-period binary millisecond pulsars in four globular clusters
We report the discovery using the Parkes radio telescope of binary
millisecond pulsars in four clusters for which no associated pulsars were
previously known. The four pulsars have pulse periods lying between 3 and 6 ms.
All are in circular orbits with low-mass companions and have orbital periods of
a few days or less. One is in a 1.7-hour orbit with a companion of planetary
mass. Another is eclipsed by a wind from its companion for 40% of the binary
period despite being in a relatively wide orbit. These discoveries result from
the use of improved technologies and prove that many millisecond pulsars remain
to be found in globular clusters.Comment: 4 pages, 2 figs, 1 table - Accepted by Astrophysical Journal Letter
Neutral modes edge state dynamics through quantum point contacts
Dynamics of neutral modes for fractional quantum Hall states is investigated
for a quantum point contact geometry in the weak-backscattering regime. The
effective field theory introduced by Fradkin-Lopez for edge states in the Jain
sequence is generalized to the case of propagating neutral modes. The dominant
tunnelling processes are identified also in the presence of non-universal
phenomena induced by interactions. The crossover regime in the backscattering
current between tunnelling of single-quasiparticles and of agglomerates of
p-quasiparticles is analysed. We demonstrate that higher order cumulants of the
backscattering current fluctuations are a unique resource to study
quantitatively the competition between different carrier charges. We find that
propagating neutral modes are a necessary ingredient in order to explain this
crossover phenomena.Comment: 28 pages, 5 figure
A Panchromatic Study of the Globular Cluster NGC 1904. I: The Blue Straggler Population
By combining high-resolution (HST-WFPC2) and wide-field ground based (2.2m
ESO-WFI) and space (GALEX) observations, we have collected a multi-wavelength
photometric data base (ranging from the far UV to the near infrared) of the
galactic globular cluster NGC1904 (M79). The sample covers the entire cluster
extension, from the very central regions up to the tidal radius. In the present
paper such a data set is used to study the BSS population and its radial
distribution. A total number of 39 bright () BSS has been
detected, and they have been found to be highly segregated in the cluster core.
No significant upturn in the BSS frequency has been observed in the outskirts
of NGC 1904, in contrast to other clusters (M 3, 47 Tuc, NGC 6752, M 5) studied
with the same technique. Such evidences, coupled with the large radius of
avoidance estimated for NGC 1904 ( core radii), indicate that
the vast majority of the cluster heavy stars (binaries) has already sunk to the
core. Accordingly, extensive dynamical simulations suggest that BSS formed by
mass transfer activity in primordial binaries evolving in isolation in the
cluster outskirts represent only a negligible (0--10%) fraction of the overall
population.Comment: ApJ accepte
Full characterization of Gaussian bipartite entangled states by a single homodyne detector
We present the full experimental reconstruction of Gaussian entangled states
generated by a type--II optical parametric oscillator (OPO) below threshold.
Our scheme provides the entire covariance matrix using a single homodyne
detector and allows for the complete characterization of bipartite Gaussian
states, including the evaluation of purity, entanglement and nonclassical
photon correlations, without a priori assumptions on the state under
investigation. Our results show that single homodyne schemes are convenient and
robust setups for the full characterization of OPO signals and represent a tool
for quantum technology based on continuous variable entanglement.Comment: 4 pages, 3 figures, slightly longer version of published PR
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