arXiv subjects

S. Pastore

Publications and source records attributed to S. Pastore.

43 records · Page 3Linked to original sources

arXiv2010

Relativity constraints on the two-nucleon contact interaction

We construct the most general, relativistically invariant, contact Lagrangian at order Q^2 in the power counting, Q denoting the low momentum scale. A complete, but non-minimal, set of (contact) interaction terms is identified, which upon non-relativistic reduction generate 2 leading independent operator combinations of order Q^0 and 7 sub-leading ones of order Q^2 - a result derived previously in the heavy-baryon formulation of effective field theories (EFT's). We show that Poincare covariance of the theory requires that additional terms with fixed coefficients be included, in order to describe the two-nucleon potential in reference frames other than the center-of-mass frame. These terms will contribute in systems with mass number A>2, and their impact on EFT calculations of binding energies and scattering observables in these systems should be studied.

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arXiv2009

Electromagnetic Structure and Reactions of Few-Nucleon Systems in $χ$EFT

We summarize our recent work dealing with the construction of the nucleon-nucleon potential and associated electromagnetic currents up to one loop in chiral effective field theory ($χ$EFT). The magnetic dipole operators derived from these currents are then used in hybrid calculations of static properties and low-energy radiative capture processes in few-body nuclei. A preliminary set of results are presented for the magnetic moments of the deuteron and trinucleons and thermal neutron captures on $p$, $d$, and $^3$He.

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arXiv2009

Electromagnetic processes in a $χ$EFT framework

Recently, we have derived a two--nucleon potential and consistent nuclear electromagnetic currents in chiral effective field theory with pions and nucleons as explicit degrees of freedom. The calculation of the currents has been carried out to include N$^3$LO corrections, consisting of two--pion exchange and contact contributions. The latter involve unknown low-energy constants (LECs), some of which have been fixed by fitting the $np$ S- and P-wave phase shifts up to 100 MeV lab energies. The remaining LECs entering the current operator are determined so as to reproduce the experimental deuteron and trinucleon magnetic moments, as well as the $np$ cross section. This electromagnetic current operator is utilized to study the $nd$ and $n^3$He radiative captures at thermal neutron energies. Here we discuss our results stressing on the important role played by the LECs in reproducing the experimental data.

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arXiv2009

Electromagnetic Currents and Magnetic Moments in $χ$EFT

A two-nucleon potential and consistent electromagnetic currents are derived in chiral effective field theory ($χ$EFT) at, respectively, $Q^{2}$ (or N$^2$LO) and $e Q$ (or N$^3$LO), where $Q$ generically denotes the low-momentum scale and $e$ is the electric charge. Dimensional regularization is used to renormalize the pion-loop corrections. A simple expression is derived for the magnetic dipole ($M1$) operator associated with pion loops, consisting of two terms, one of which is determined, uniquely, by the isospin-dependent part of the two-pion-exchange potential. This decomposition is also carried out for the $M1$ operator arising from contact currents, in which the unique term is determined by the contact potential. Finally, the low-energy constants (LEC's) entering the N$^2$LO potential are fixed by fits to the $np$ S- and P-wave phase shifts up to 100 MeV lab energies.

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arXiv2008

Electromagnetic two-body currents of one- and two-pion range

Nuclear electromagnetic currents are derived in time-ordered perturbation theory within an effective-field-theory framework including explicit nucleons, $Δ$ isobars, and pions up to one loop, or N$^3$LO. The currents obtained at N$^2$LO, {\it i.e.} ignoring loop corrections, are used in a study of neutron radiative captures on protons and deuterons at thermal energies, and of $A$=2 and 3 nuclei magnetic moments. The wave functions for $A$=2 are derived from solutions of the Schrödinger equation with the Argonne $v_{18}$ (AV18) or CD-Bonn (CDB) potentials, while those for $A$=3 are obtained with the hyperspherical-harmonics-expansion method from a realistic Hamiltonian including, in addition to the AV18 or CDB two-nucleon, also a three-nucleon potential. With the strengths of the $Δ$-excitation currents occurring at N$^2$LO determined to reproduce the $n$-$p$ cross section and isovector combination of the trinucleon magnetic moments, we find that the cross section and photon circular polarization parameter, measured in $n$-$d$ and $\vec{n}$-$d$ processes, are underpredicted by theory, for example the cross section by (11--38)% as the cutoff is increased from 500 to 800 MeV. A complete analysis of the results, in particular their large cutoff dependence, is presented.

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arXiv2008

Electromagnetic Processes in $χ$EFT

Nuclear electromagnetic currents derived in a chiral-effective-field-theory framework including explicit nucleons, $Δ$ isobars, and pions up to N$^2$LO, {\it i.e.} ignoring loop corrections, are used in a study of neutron radiative captures on protons and deuterons at thermal energies, and of $A$=2 and 3 nuclei magnetic moments. With the strengths of the $Δ$-excitation currents determined to reproduce the $n$-$p$ cross section and isovector combination of the trinucleon magnetic moments, we find that the cross section and photon circular polarization parameter, measured respectively in $n$-$d$ and $\vec{n}$-$d$ processes, are significantly underpredicted by theory.

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arXiv2006

Bridging the Virtual Observatory and the GRID with the query element

The current generation of Grid infrastructures designed for production activity is strongly computing oriented and tuned on the needs of applications that requires intensive computations. Problems arise when trying to use such Grids to satisfy the sharing of data-oriented and service-oriented resources as happens in the IVOA community. We have designed, developed and implemented a Grid query element to access data source from an existing production Grid environment. We also enhanced the Grid middleware model (collective resources and sites) to manage Data Sources extending the Grid semantic. The query element and the modified grid Information System are able to connect the Grid environment to Virtual Observatory resources. A specialized query element is designed to work as Virtual Observatory resource in the Grid so than an Astronomer can access Virtual Observatory data using the IVOA standards.

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