9,201 research outputs found
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.
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
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
Supersymmetry phenomenology beyond the MSSM after 5/fb of LHC data
We briefly review the status of motivated beyond-the-MSSM phenomenology in
the light of the LHC searches to date. In particular, we discuss the conceptual
consequences of the exclusion bounds, of the hint for a Higgs boson at about
125 GeV, and of interpreting the excess of direct CP violation in the charm
sector as a signal of New Physics. We try to go into the various topics in a
compact way while providing a relatively rich list of references, with
particular attention to the most recent developments.Comment: 20 pages + refs. v2: minor modifications, published versio
Toward the Ab-initio Description of Medium Mass Nuclei
As ab-initio calculations of atomic nuclei enter the A=40-100 mass range, a
great challenge is how to approach the vast majority of open-shell (degenerate)
isotopes. We add realistic three-nucleon interactions to the state of the art
many-body Green's function theory of closed-shells, and find that physics of
neutron driplines is reproduced with very good quality. Further, we introduce
the Gorkov formalism to extend ab-initio theory to semi-magic, fully
open-shell, isotopes. Proof-of-principle calculations for Ca-44 and Ni-74
confirm that this approach is indeed feasible. Combining these two advances
(open-shells and three-nucleon interactions) requires longer, technical, work
but it is otherwise within reach.Comment: Contribution to Summary Report of EURISOL Topical and Town Meetings,
15-19 October 2012; missing affiliations added and corrected errors in Tab
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
The exact eigenstates of the neutrino mass matrix without CP-phase violation
In this paper we obtain the exact mass-eigenstates of the Majorana physical
neutrinos. We start by taking into account a general mass matrix
without any CP-phase violation. It is then diagonalized by exactly solving an
appropriate set of equations. The solution supplies straightforwardly the mass
eigenvalues depending on the diagonal entries and mixing angles. Finally, the
consequences of these analytical expressions are discussed assuming various
phenomenological restrictions such as conserving the global lepton number
and the interchange symmetry. The minimal
absolute mass in the neutrino sector is also obtained since the two plausible
scenarios invoked above are employed.Comment: 9 pages, no figure
Aqueye+: a new ultrafast single photon counter for optical high time resolution astrophysics
Aqueye+ is a new ultrafast optical single photon counter, based on single
photon avalanche photodiodes (SPAD) and a 4-fold split-pupil concept. It is a
completely revisited version of its predecessor, Aqueye, successfully mounted
at the 182 cm Copernicus telescope in Asiago. Here we will present the new
technological features implemented on Aqueye+, namely a state of the art timing
system, a dedicated and optimized optical train, a high sensitivity and high
frame rate field camera and remote control, which will give Aqueye plus much
superior performances with respect to its predecessor, unparalleled by any
other existing fast photometer. The instrument will host also an optical
vorticity module to achieve high performance astronomical coronography and a
real time acquisition of atmospheric seeing unit. The present paper describes
the instrument and its first performances.Comment: Proceedings of the SPIE, Volume 9504, id. 95040C 14 pp. (2015
Experimental quantum computing without entanglement
Entanglement is widely believed to lie at the heart of the advantages offered
by a quantum computer. This belief is supported by the discovery that a
noiseless (pure) state quantum computer must generate a large amount of
entanglement in order to offer any speed up over a classical computer. However,
deterministic quantum computation with one pure qubit (DQC1), which employs
noisy (mixed) states, is an efficient model that generates at most a marginal
amount of entanglement. Although this model cannot implement any arbitrary
algorithm it can efficiently solve a range of problems of significant
importance to the scientific community. Here we experimentally implement a
first-order case of a key DQC1 algorithm and explicitly characterise the
non-classical correlations generated. Our results show that while there is no
entanglement the algorithm does give rise to other non-classical correlations,
which we quantify using the quantum discord - a stronger measure of
non-classical correlations that includes entanglement as a subset. Our results
suggest that discord could replace entanglement as a necessary resource for a
quantum computational speed-up. Furthermore, DQC1 is far less resource
intensive than universal quantum computing and our implementation in a scalable
architecture highlights the model as a practical short-term goal.Comment: 5 pages, 4 figure
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