204 research outputs found
Nuclear density functional constrained by low-energy QCD
We have developed a relativistic point-coupling model of nuclear many-body
dynamics constrained by the low-energy sector of QCD. The effective Lagrangian
is characterized by density-dependent coupling strengths determined by chiral
one- and two-pion exchange (with single and double delta isobar excitations)
and by large isoscalar background fields that arise through changes of the
quark condensate and the quark density at finite baryon density. The model has
been tested in the analysis of nuclear ground-state properties along different
isotope chains of medium and heavy nuclei. The agreement with experimental data
is comparable with purely phenomenological predictions. The built-in QCD
constraints and the explicit treatment of pion exchange restrict the freedom in
adjusting parameters and functional forms of density-dependent couplings. It is
shown that chiral pionic fluctuations play an important role for nuclear
binding and saturation mechanism, whereas background fields of about equal
magnitude and opposite sign generate the effective spin-orbit potential in
nuclei.Comment: ws-procs9x6.cls, 8 pgs, Talk presented at "X Convegno su Problemi di
Fisica Nucleare Teorica", Cortona (AR), 6-9 october 200
Neutron density distribution and neutron skin thickness of Pb
We present and discuss numerical predictions for the neutron density
distribution of Pb using various non-relativistic and relativistic
mean-field models for the nuclear structure. Our results are compared with the
very recent pion photoproduction data from Mainz. The parity-violating
asymmetry parameter for elastic electron scattering at the kinematics of the
PREX experiment at JLab and the neutron skin thickness are compared with the
available data. We consider also the dependence between the neutron skin and
the parameters of the expansion of the symmetry energy.Comment: 9 pages, 6 figures, latest MAMI data use
Elastic and quasi-elastic electron scattering off nuclei with neutron excess
We present theoretical predictions for electron scattering on oxygen and
calcium isotopic chains. The calculations are done within the framework of the
distorted-wave Born approximation and the proton and neutron density
distributions are evaluated adopting a relativistic Dirac-Hartree model. We
present results for the elastic and quasi-elastic cross sections and for the
parity-violating asymmetry. As a first step, the results of the models are
tested in comparison with some of the data available for elastic and
quasi-elastic scattering on 16O and 40Ca nuclei. Then, the evolution of some
nuclear properties is investigated as a function of the neutron number. We also
present a comparison with the parity-violating asymmetry parameter obtained by
the PREX Collaboration on 208Pb and give a prediction for the future experiment
CREX on 48Ca.Comment: 37 pages, 17 figures. version accepted for publication in the
Physical Review C. arXiv admin note: text overlap with arXiv:0809.4124 by
other author
Proton-Nucleus Elastic Scattering: Comparison between Phenomenological and Microscopic Optical Potentials
Elastic scattering is a very important process to understand nuclear
interactions in finite nuclei. Despite decades of efforts, the goal of reaching
a coherent description of this physical process in terms of microscopic forces
is still far from being completed.
In previous papers (Phys. Rev. C93, 034619 (2016), Phys. Rev. C96, 044001
(2017)) we derived a nonrelativistic theoretical optical potential from
nucleon-nucleon chiral potentials at fourth (N3LO) and fifth order (N4LO). We
checked convergence patterns and established theoretical error bands. With this
work we study the performances of our optical potential in comparison with
those of a successful nonrelativistic phenomenological optical potential in the
description of elastic proton scattering data on several isotopic chains at
energies around and above 200 MeV.
We use the same framework and the same approximations of our previous papers,
where the nonrelativistic optical potential is derived at the first-order term
within the spectator expansion of the multiple scattering theory and adopting
the impulse approximation and the optimum factorization approximation.
The cross sections and analyzing powers for elastic proton scattering off
calcium, nickel, tin, and lead isotopes are presented for several incident
proton energies, exploring the range MeV, where
experimental data are available. In addition, we provide theoretical
predictions for Ni56 at 400 MeV, which is of interest for the future
experiments at EXL.
Our results indicate that microscopic optical potentials derived from
nucleon-nucleon chiral potentials at N4LO can provide reliable predictions for
the cross section and the analyzing power both of stable and exotic nuclei,
even at energies where the reliability of the chiral expansion starts to be
questionable.Comment: 26 pages, 10 figures, submitted to PR
A comparison of CMB Angular Power Spectrum Estimators at Large Scales: the TT case
In the context of cosmic microwave background (CMB) data analysis, we compare
the efficiency at large scale of two angular power spectrum algorithms,
implementing, respectively, the quadratic maximum likelihood (QML) estimator
and the pseudo spectrum (pseudo-Cl) estimator. By exploiting 1000 realistic
Monte Carlo (MC) simulations, we find that the QML approach is markedly
superior in the range l=[2-100]. At the largest angular scales, e.g. l < 10,
the variance of the QML is almost 1/3 (1/2) that of the pseudo-Cl, when we
consider the WMAP kq85 (kq85 enlarged by 8 degrees) mask, making the pseudo
spectrum estimator a very poor option. Even at multipoles l=[20-60], where
pseudo-Cl methods are traditionally used to feed the CMB likelihood algorithms,
we find an efficiency loss of about 20%, when we considered the WMAP kq85 mask,
and of about 15% for the kq85 mask enlarged by 8 degrees. This should be taken
into account when claiming accurate results based on pseudo-Cl methods. Some
examples concerning typical large scale estimators are provided.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
Microscopic optical potentials for medium-mass isotopes derived at the first order of the Watson multiple scattering theory
We perform a first-principle calculation of optical potentials for nucleon
elastic scattering off medium-mass isotopes. Fully based on a saturating chiral
Hamiltonian, the optical potentials are derived by folding nuclear density
distributions computed with ab initio self-consistent Green's function theory
with a nucleon-nucleon matrix computed with a consistent chiral
interaction. The dependence on the folding interaction as well as the
convergence of the target densities are investigated. Numerical results are
presented and discussed for differential cross sections and analyzing powers,
with focus on elastic proton scattering off Calcium and Nickel isotopes. Our
optical potentials generally show a remarkable agreement with the available
experimental data for laboratory energies in the range 65-200 MeV. We study the
evolution of the scattering observables with increasing proton-neutron
asymmetry by computing theoretical predictions of the cross section and
analyzing power over the Calcium and Nickel isotopic chains
Elastic Antiproton-Nucleus Scattering from Chiral Forces
Elastic scattering of antiprotons off He, C, and O is
described for the first time with a totally microscopic approach based on the
calculation of an optical potential (OP) describing the antiproton-target
interaction. The OP is derived using the recent antiproton-nucleon ()
chiral interaction to calculate the matrix, while the target
densities are computed with the ab initio no-core shell model using chiral
interactions as well. Our results are in a good agreement with the existing
experimental data and the results computed at different chiral orders of the
interaction display the convergence pattern expected from the
theory
Self-consistent single-particle approximation to nuclear state densities at high excitation energy
We compute nuclear state densities for a number of magic and semimagic nuclei in the usual saddle point approximation within the framework of the grand-canonical formalism in an energy range where residual two-body interactions and collective effects can reasonably be neglected. The single-particle states used in the calculations are generated in a relativistic self-consistent mean field at finite temperature based on widely adopted effective interactions. Observed limits and
possible improvements of the adopted formalism are discussed
Nuclear Pairing from Chiral Pion-Nucleon Dynamics: Applications to Finite Nuclei
The 1S0 pairing gap in isospin-symmetric nuclear matter and finite nuclei is
investigated using the chiral nucleon-nucleon potential at the N3LO order in
the two-body sector, and the N2LO order in the three-body sector. To include
realistic nuclear forces in RHB (Relativistic Hartree Bolgoliubov) calculations
we rely on a separable form of the pairing interaction adjusted to the bare
nuclear force. The separable pairing force is applied to the analysis of
pairing properties for several isotopic and isotonic chains of spherical
nuclei.Comment: 13 pages, 3 figures, submitted to PR
Young adult obese subjects with and without insulin resistance: what is the role of chronic inflammation and how to weigh it non-invasively?
<p>Abstract</p> <p>Background</p> <p>Obesity is a leading risk factor for metabolic syndrome whose further expression is non-alcoholic fatty liver disease. Metabolic syndrome is associated with a proinflammatory state that contributes to insulin resistance. Finally, a "metabolically benign obesity" that is not accompanied by insulin resistance has recently been postulated to exist.</p> <p>Aim</p> <p>To find whether any inflammation markers were independently associated with the presence of insulin resistance, evaluating specific anthropometric, ultrasonographic and laboratory parameters in a population of young adult obese subjects.</p> <p>Methods</p> <p>Of forty two young individuals, divided into two groups (with or without insulin resistance), were studied serum C-reactive protein and fibrinogen as indexes of chronic pro-inflammatory status. Body mass index, waist circumference and metabolic syndrome presence were assessed as part of the metabolic evaluation. Ultrasonography weighted visceral and subcutaneous abdominal fat thickness, spleen size as longitudinal diameter and liver hyperechogenicity.</p> <p>Results and Discussion</p> <p>Serum C-reactive protein and fibrinogen as well as spleen longitudinal diameter were significantly increased in the obese young with insulin resistance compared to non-insulin resistance group. Insulin resistance was significantly associated with hepatic steatosis score at sonography (r = 0.33, P = 0.03), spleen longitudinal diameter (r = 0.35, P = 0.02) and C-reactive protein (r = 0.38, P = 0.01), but not with body mass index, visceral or subcutaneous abdominal adipose tissue, waist circumference and fibrinogen (P = 0.18, 0.46, 0.33, 0.37 and 0.4, respectively). Steatosis score at sonography was well associated with spleen volume (rho = 0.40, P = 0.01) and C-reactive protein levels (rho = 0.49, P = 0.002). Metabolic syndrome was much more frequent in obese patients with insulin resistance. These findings show that in young adults the only abdominal adiposity without insulin resistance, plays a scarce role in determining hepatic steatosis as well as metabolic syndrome.</p> <p>Conclusion</p> <p>Increases in spleen size and CRP levels represent a reliable tool in diagnosing insulin resistance.</p
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