11,168 research outputs found
Rigorous QCD Predictions for Decays of P-Wave Quarkonia
Rigorous QCD predictions for decay rates of the P-wave states of heavy
quarkonia are presented. They are based on a new factorization theorem which is
valid to leading order in the heavy quark velocity and to all orders in the
running coupling constant of QCD. The decay rates for all four P states into
light hadronic or electromagnetic final states are expressed in terms of two
phenomenological parameters, whose coefficients are perturbatively calculable.
Logarithms of the binding energy encountered in previous perturbative
calculations of P-wave decays are factored into a phenomenological parameter
that is related to the probability for the heavy quark-antiquark pair to be in
a color-octet S-wave state. Applying these predictions to charmonium, we use
measured decay rates for the \chione and \chitwo to predict the decay rates
of the \chizero and .Comment: 13 page
Ab initio optical potentials and nucleon scattering on medium mass nuclei
We show the first results for the elastic scattering of neutrons off oxygen
and calcium isotopes obtained from ab initio optical potentials. The potential
is derived using self consistent Green's function theory (SCGF) with the
saturating chiral interaction NNLO. Our calculations are
compared to available scattering data and show that it is possible to reproduce
low energy scattering observables in medium mass nuclei from first principles.Comment: 6 pages, 4 figures, Zakopane conference on nuclear physic
Chiral three-nucleon forces and the evolution of correlations along the oxygen isotopic chain
The impact of three-nucleon forces (3NFs) along the oxygen chain is
investigated for the spectral distribution for attachment and removal of a
nucleon, spectroscopic factors and matter radii. We employ self-consistent
Green's function (SCGF) theory which allows a comprehensive calculation of the
single particle spectral function. For the closed subshell isotopes, O,
O, O, O and O, we perform calculations with the
Dyson-ADC(3) method. The remaining open shell isotopes are studied using the
newly developed Gorkov-SCGF formalism up to second order. We produce plots for
the full-fledged spectral distributions. The spectroscopic factors for the
dominant quasiparticle peaks are found to depend very little on the leading
order (NNLO) chiral 3NFs. The latters have small impact on the calculated
matter radii, which, however are consistently obtained smaller than experiment.
Similarly, single particle spectra tend to be diluted with respect to
experiment. This effect might hinder, to some extent, the onset of correlations
and screen the quenching of calculated spectroscopic factors. The most
important effects of 3NFs is thus the fine tuning of the energies for the
dominant quasiparticle states, which govern the shell evolution and the
position of driplines. Although present chiral NNLO 3NFs interactions do
reproduce the binding energies correctly in this mass region, the details of
the nuclear wave function remain at odd with the experiment showing too small
radii and a too dilute single particle spectrum, similar to what already
pointed out for larger masses. This suggests a lack of repulsion in the present
model of NN+3N interactions which is mildly apparent already for masses in the
A=14--28 range.Comment: 13 pages, accepted for publication on Phys. Rev.
Oceanographic applications of the Kalman filter
The Kalman filter is a data-processing algorithm with a distinguished history in systems theory. Its application to oceanographic problems is in the embryo stage. The behavior of the filter is demonstrated in the context of an internal equatorial Rossby wave propagation problem
Pre-MS depletion, accretion and primordial 7Li
We reconsider the role of pre-main sequence (pre-MS) Li depletion on the
basis of new observational and theoretical evidence: i) new observations of
Halpha emissions in young clusters show that mass accretion could be continuing
till the first stages of the MS, ii) theoretical implications from
helioseismology suggest large overshooting values below the bottom of the
convective envelopes. We argue here that a significant pre-MS 7Li destruction,
caused by efficient overshoot mixing, could be followed by a matter accretion
after 7Li depletion has ceased on MS thus restoring Li almost to the pristine
value. As a test case we show that a halo dwarf of 0.85 Msun with an extended
overshooting envelope starting with an initial abundance of A(Li) = 2.74 would
burn Li completely, but an accretion rate of the type 1e-8xe^{-t/3e6} Msun
yr would restore Li to end with an A(Li) = 2.31. A self-regulating
process is required to produce similar final values in a range of different
stellar masses to explain the PopII Spite plateau. However, this framework
could explain why open cluster stars have lower Li abundances than the
pre-solar nebula, the absence of Li in the most metal poor dwarfs and a number
of other features which lack of a satisfactory explanation.Comment: To be published in Memorie della Societ\`a Astronomica Italiana
Supplementi Vol. 22, Proceedings of Lithium in the cosmos, Iocco F.,
Bonifacio P., Vangioni E., ed
The Neron-Severi group of a proper seminormal complex variety
We prove a Lefschetz (1,1)-Theorem for proper seminormal varieties over the
complex numbers. The proof is a non-trivial geometric argument applied to the
isogeny class of the Lefschetz 1-motive associated to the mixed Hodge structure
on H^2.Comment: 16 pages; Mathematische Zeitschrift (2008
Generation of polarization entangled photon pairs by a single crystal interferometric source pumped by femtosecond laser pulses
Photon pairs, highly entangled in polarization have been generated under
femtosecond laser pulse excitation by a type I crystal source, operating in a
single arm interferometric scheme. The relevant effects of temporal walk-off
existing in these conditions between the ordinary and extraordinary photons
were experimentally investigated. By introducing a suitable temporal
compensation between the two orthogonal polarization components highly
entangled pulsed states were obtained
Optical phase coherent timing of the Crab nebula pulsar with Iqueye at the ESO New Technology Telescope
The Crab nebula pulsar was observed in 2009 January and December with a novel
very fast optical photon counter, Iqueye, mounted at the ESO 3.5 m New
Technology Telescope. Thanks to the exquisite quality of the Iqueye data, we
computed accurate phase coherent timing solutions for the two observing runs
and over the entire year 2009. Our statistical uncertainty on the determination
of the phase of the main pulse and the rotational period of the pulsar for
short (a few days) time intervals are s and ~0.5 ps,
respectively. Comparison with the Jodrell Bank radio ephemerides shows that the
optical pulse leads the radio one by ~240 s in January and ~160 s in
December, in agreement with a number of other measurements performed after
1996. A third-order polynomial fit adequately describes the spin-down for the
2009 January plus December optical observations. The phase noise is consistent
with being Gaussian distributed with a dispersion of s in most observations, in agreement with theoretical expectations for
photon noise-induced phase variability.Comment: 10 pages, 5 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
- …