2,316 research outputs found
Charge tunneling in fractional edge channels
We explain recent experimental observations on effective charge of edge
states tunneling through a quantum point contact in the weak backscattering
regime. We focus on the behavior of the excess noise and on the effective
tunneling charge as a function of temperature and voltage. By introducing a
minimal hierarchical model different filling factors, \nu=p/(2p+1), in the Jain
sequence are treated on equal footing, in presence also of non-universal
interactions. The agreement found with the experiments for \nu=2/3 and \nu=2/5
reinforces the description of tunneling of bunching of quasiparticles at low
energies and quantitatively defines the condition under which one expects to
measure the fundamental quasiparticle charge. We propose high-order current
cumulant measurement to cross-check the validity of the above scenario and to
better clarify the peculiar temperature behavior of the effective charges
measured in the experiments.Comment: 6 pages, 3 figure
The optical companion to the binary millisecond pulsar J1824-2452H in the globular cluster M28
We report on the optical identification of the companion star to the
eclipsing millisecond pulsar PSR J1824-2452H in the galactic globular cluster
M28 (NGC 6626). This star is at only 0.2" from the nominal position of the
pulsar and it shows optical variability (~ 0.25 mag) that nicely correlates
with the pulsar orbital period. It is located on the blue side of the cluster
main sequence, ~1.5 mag fainter than the turn-off point. The observed light
curve shows two distinct and asymmetric minima, suggesting that the companion
star is suffering tidal distortion from the pulsar. This discovery increases
the number of non-degenerate MSP companions optically identified so far in
globular clusters (4 out of 7), suggesting that these systems could be a common
outcome of the pulsar recycling process, at least in dense environments where
they can be originated by exchange interactions.Comment: accepted for publication on ApJ, 17 pages, 5 figure
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
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
Dynamical age differences among coeval star clusters as revealed by blue stragglers
Globular star clusters that formed at the same cosmic time may have evolved
rather differently from a dynamical point of view (because that evolution
depends on the internal environment) through a variety of processes that tend
progressively to segregate stars more massive than the average towards the
cluster centre. Therefore clusters with the same chronological age may have
reached quite different stages of their dynamical history (that is, they may
have different dynamical ages). Blue straggler stars have masses greater than
those at the turn-off point on the main sequence and therefore must be the
result of either a collision or a mass-transfer event. Because they are among
the most massive and luminous objects in old clusters, they can be used as test
particles with which to probe dynamical evolution. Here we report that globular
clusters can be grouped into a few distinct families on the basis of the radial
distribution of blue stragglers. This grouping corresponds well to an effective
ranking of the dynamical stage reached by stellar systems, thereby permitting a
direct measure of the cluster dynamical age purely from observed properties.Comment: Published on the 20 December 2012 issue of Natur
Discovery of Carbon/Oxygen depleted Blue Straggler Stars in 47 Tucanae: the chemical signature of a mass-transfer formation process
We use high-resolution spectra obtained with the ESO Very Large Telescope to
measure surface abundance patterns of 43 Blue Stragglers stars (BSS) in 47 Tuc.
We discovered that a sub-population of BSS shows a significant depletion of
Carbon and Oxygen with respect to the dominant population. This evidence would
suggest the presence of CNO burning products on the BSS surface coming from a
deeply peeled parent star, as expected in the case of mass-transfer process.
This is the first detection of a chemical signature clearly pointing to a
specific BSS formation process in a globular cluster.Comment: Published on 2006, August 10, in ApJ 647, L5
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
Blue Straggler Stars in Globular Clusters: a powerful tool to probe the internal dynamical evolution of stellar systems
This chapter presents an overview of the main observational results obtained
to date about Blue Straggler Stars (BSSs) in Galactic Globular Clusters (GCs).
The BSS specific frequency, radial distribution, chemical composition and
rotational properties are presented and discussed in the framework of using
this stellar population as probe of GC internal dynamics. In particular, the
shape of the BSS radial distribution has been found to be a powerful tracer of
the dynamical age of stellar systems, thus allowing the definition of the first
empirical "dynamical clock".Comment: Chapter 5, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
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