Isoscalar off-shell effects in threshold pion production from pd collisions

We test the presence of pion-nucleon isoscalar off-shell effects in the $pd\to \pi^+ t$ reaction around the threshold region. We find that these effects significantly modify the production cross section and that they may provide the missing strength needed to reproduce the data at threshold.Comment: 6 pages, REVTeX, twocolumn, including 3 figures (Postscript), uses psfig, updated and extended versio

Predicting narrow states in the spectrum of a nucleus beyond the proton drip line

Properties of particle-unstable nuclei lying beyond the proton drip line can be ascertained by considering those (usually known) properties of its mirror neutron-rich system. We have used a multi-channel algebraic scattering theory to map the known properties of the neutron-${}^{14}$C system to those of the proton-${}^{14}$O one from which we deduce that the particle-unstable ${}^{15}$F will have a spectrum of two low lying broad resonances of positive parity and, at higher excitation, three narrow negative parity ones. A key feature is to use coupling to Pauli-hindered states in the target.Comment: 5 pages, 3 figure

Complex Conjugate Pairs in Stationary Sturmians

Sturmian eigenstates specified by stationary scattering boundary conditions are particularly useful in contexts such as forming simple separable two nucleon t matrices, and are determined via solution of generalised eigenvalue equation using real and symmetric matrices. In general, the spectrum of such an equation may contain complex eigenvalues. But to each complex eigenvalue there is a corresponding conjugate partner. In studies using realistic nucleon--nucleon potentials, and in certain positive energy intervals, these complex conjugated pairs indeed appear in the Sturmian spectrum. However, as we demonstrate herein, it is possible to recombine the complex conjugate pairs and corresponding states into a new, sign--definite pair of real quantities with which to effect separable expansions of the (real) nucleon--nucleon reactance matrices.Comment: (REVTEX) 8 Pages, Padova DFPD 93/TH/78 and University of Melbourn

Why is the three-nucleon force so odd?

By considering a class of diagrams which has been overlooked also in the most recent literature on three-body forces, we extract a new contribution to the three-nucleon interaction which specifically acts on the triplet odd states of the two nucleon subsystem. In the static approximation, this 3N-force contribution is fixed by the underlying 2N interaction, so in principle there are no free parameters to adjust. The 2N amplitude however enters in the 3NF diagram in a form which cannot be directly accessed or constrained by NN phase-shift analysis. We conclude that this new 3N-force contribution provides a mechanism which implies that the presence of the third nucleon modifies the p-wave (and possibly the f-wave) components of the 2N subsystem in the triplet-isotriplet channels.Comment: 10 Pages, 7 figures, RevTeX, twocolumn, epsf (updated version with minor changes

Electromagnetic nucleon form factors in instant and point form

We present a study of the electromagnetic structure of the nucleons with constituent quark models in the framework of relativistic quantum mechanics. In particular, we address the construction of spectator-model currents in the instant and point forms. Corresponding results for the elastic nucleon electromagnetic form factors as well as charge radii and magnetic moments are presented. We also compare results obtained by different realistic nucleon wave functions stemming from alternative constituent quark models. Finally, we discuss the theoretical uncertainties that reside in the construction of spectator-model transition operators.Comment: 13 pages, 9 figures, updated and extended version for publicatio

Reconstruction of the time-dependent electronic wave packet arising from molecular autoionization

Autoionizing resonances are paradigmatic examples of two-path wave interferences between direct photoionization, which takes a few attoseconds, and ionization via quasi-bound states, which takes much longer. Time-resolving the evolution of these interferences has been a long-standing goal, achieved recently in the helium atom owing to progress in attosecond technologies. However, already for the hydrogen molecule, similar time imaging has remained beyond reach due to the complex interplay between fast nuclear and electronic motions. We show how vibrationally resolved photoelectron spectra of H2 allow one to reconstruct the associated subfemtosecond autoionization dynamics by using the ultrafast nuclear dynamics as an internal clock, thus forgoing ultrashort pulses. Our procedure should be general for autoionization dynamics in molecules containing light nuclei, which are ubiquitous in chemistry and biologyThis work was supported by European Research Council advanced grant 290853-XCHEM within the seventh framework program of the European Union. We also acknowledge the financial support from MINECO projects FIS2013-42002-R and FIS2016-77889-R, and the European COST (Cooperation in Science and Technology) Action XLIC CM1204, and the computer time from the Centro de Computación Científica de la Universidad Autónoma de Madrid and Marenostrum Supercomputer Center. A.P. acknowledges a Ramón y Cajal contract from the Ministerio de Economía y Competitividad (Spain). F.M. acknowledges support from the “Severo Ochoa” Programme for Centres of Excellence in R&D (MINECO, grant SEV-2016-0686) and the “María de Maeztu” Programme for Units of Excellence in R&D (MDM-2014-0377). S.E.C. acknowledges funding from the Helmoltz Recognition Award. The Extreme Light Infrastructure Attosecond Light Pulse Source project (GINOP-2.3.6-15-2015-00001) was financed by the European Union and cofinanced by the European Regional Development Fun

The one-pion-exchange three-nucleon force and the AyA_y puzzle

We consider a new three-nucleon force generated by the exchange of one pion in the presence of a 2N correlation. The underlying irreducible diagram has been recently suggested by the authors as a possible candidate to explain the puzzle of the vector analyzing powers $A_y$ and $iT_{11}$ for nucleon-deuteron scattering. Herein, we have calculated the elastic neutron-deuteron differential cross section, $A_y$, $iT_{11}$, $T_{20}$, $T_{21}$, and $T_{22}$ below break-up threshold by accurately solving the Alt-Grassberger-Sandhas equations with realistic interactions. We have also studied how $A_y$ evolves below 30 MeV. The results indicate that this new 3NF diagram provides one possible additional contribution, with the correct spin-isospin structure, for the explanation of the origin of this puzzle.Comment: revised version: We have also studied how Ay evolves below 30 MeV, 4 Pages (twocolumn), 2 figures, uses psfig, RevTe