Excited nucleon electromagnetic form factors from broken spin-flavor symmetry

A group theoretical derivation of a relation between the N --> Delta charge quadrupole transition and neutron charge form factors is presented.Comment: 4 pages, Proc. of the 12 th Int'l. Workshop on the Physics of Excited Nucleons, NSTAR 2009, Beijing, April 19-22, 200

Relativistic Hamiltonians in many-body theories

We discuss the description of a many-body nuclear system using Hamiltonians that contain the nucleon relativistic kinetic energy and potentials with relativistic corrections. Through the Foldy-Wouthuysen transformation, the field theoretical problem of interacting nucleons and mesons is mapped to an equivalent one in terms of relativistic potentials, which are then expanded at some order in 1/m_N. The formalism is applied to the Hartree problem in nuclear matter, showing how the results of the relativistic mean field theory can be recovered over a wide range of densities.Comment: 14 pages, uses REVTeX and epsfig, 3 postscript figures; a postscript version of the paper is available by anonymous ftp at ftp://carmen.to.infn.it/pub/depace/papers/951

Structure of solar coronal loops: from miniature to large-scale

We will use new data from the High-resolution Coronal Imager (Hi-C) with unprecedented spatial resolution of the solar corona to investigate the structure of coronal loops down to 0.2 arcsec. During a rocket flight Hi-C provided images of the solar corona in a wavelength band around 193 A that is dominated by emission from Fe XII showing plasma at temperatures around 1.5 MK. We analyze part of the Hi-C field-of-view to study the smallest coronal loops observed so far and search for the a possible sub-structuring of larger loops. We find tiny 1.5 MK loop-like structures that we interpret as miniature coronal loops. These have length of the coronal segment above the chromosphere of only about 1 Mm and a thickness of less than 200 km. They could be interpreted as the coronal signature of small flux tubes breaking through the photosphere with a footpoint distance corresponding to the diameter of a cell of granulation. We find loops that are longer than 50 Mm to have a diameter of about 2 arcsec or 1.5 Mm, consistent with previous observations. However, Hi-C really resolves these loops with some 20 pixels across the loop. Even at this greatly improved spatial resolution the large loops seem to have no visible sub-structure. Instead they show a smooth variation in cross-section. The fact that the large coronal loops do not show a sub-structure at the spatial scale of 0.1 arcsec per pixel implies that either the densities and temperatures are smoothly varying across these loops or poses an upper limit on the diameter of strands the loops might be composed of. We estimate that strands that compose the 2 arcsec thick loop would have to be thinner than 15 km. The miniature loops we find for the first time pose a challenge to be properly understood in terms of modeling.Comment: Accepted for publication in A&A (Jun 19, 2013), 11 pages, 10 figure

Scaling in many-body systems and proton structure function

The observation of scaling in processes in which a weakly interacting probe delivers large momentum ${\bf q}$ to a many-body system simply reflects the dominance of incoherent scattering off target constituents. While a suitably defined scaling function may provide rich information on the internal dynamics of the target, in general its extraction from the measured cross section requires careful consideration of the nature of the interaction driving the scattering process. The analysis of deep inelastic electron-proton scattering in the target rest frame within standard many-body theory naturally leads to the emergence of a scaling function that, unlike the commonly used structure functions $F_1$ and $F_2$, can be directly identified with the intrinsic proton response.Comment: 11 pages, 4 figures. Proceedings of the 11th Conference on Recent Progress in Many-Body Theories, Manchester, UK, July 9-13 200

Inelastic electron-nucleus scattering and scaling at high inelasticity

Highly inelastic electron scattering is analyzed within the context of the unified relativistic approach previously considered in the case of quasielastic kinematics. Inelastic relativistic Fermi gas modeling that includes the complete inelastic spectrum - resonant, non-resonant and Deep Inelastic Scattering - is elaborated and compared with experimental data. A phenomenological extension of the model based on direct fits to data is also introduced. Within both models, cross sections and response functions are evaluated and binding energy effects are analyzed. Finally, an investigation of the second-kind scaling behavior is also presented.Comment: 39 pages, 13 figures; formalism extended and slightly reorganized, conclusions extended; to appear in Phys. Rev.

Effect of kinematics on final state interactions in (e,e'p) reactions

Recent data from experiment E97-006 at TJNAF using the 12C(e,e'p) reaction at very large missing energies and momenta are compared to a calculation of two-step rescattering. A comparison between parallel and perpendicular kinematics suggests that the effects of final state interactions can be strongly reduced in the former case.Comment: 10 pages, 3 figures, submitted to LP

Comment on "Hara's theorem in the constituent quark model"

It is pointed out that current conservation alone does not suffice to prove Hara's theorem as it was claimed recently. By explicit calculation we show that the additional implicit assumption made in such "proofs" is that of a sufficiently localized current.Comment: 8 pages, Late

Nuclear structure studies with the 7Li(e,e'p) reaction

Experimental momentum distributions for the transitions to the ground state and first excited state of 6He have been measured via the reaction 7Li(e,e'p)6He, in the missing momentum range from -70 to 260 MeV/c. They are compared to theoretical distributions calculated with mean-field wave functions and with variational Monte Carlo (VMC) wave functions which include strong state-dependent correlations in both 7Li and 6He. These VMC calculations provide a parameter-free prediction of the momentum distribution that reproduces the measured data, including its normalization. The deduced summed spectroscopic factor for the two transitions is 0.58 +/- 0.05, in perfect agreement with the VMC value of 0.60. This is the first successful comparison of experiment and ab initio theory for spectroscopic factors in p-shell nuclei.Comment: 4 pages, 3 figure