Sakurai’s ${\mathrm{SU}}_F\mathrm{}\left(3\right)\mathrm{}$ universality symmetry is employed to provide a unified description of pseudoscalar meson nonet elastic form factors calculated using a modified vector meson dominance (VMD) formalism. We incorporate excited resonances with modified propagators derived from analyticity and elastic unitarity, employing a single channel $N/D$ approximation to model nonresonant meson exchange contributions. Existing spacelike and timelike data for ${\pi }^{+},$ $K^{+}$, and $K^0$ mesons indicate that finite width corrections to the $\rho$ propagator and couplings are essential for a precise theoretical description in the VMD framework. Our analysis verifies that existing data cannot rule out the possible existence of two unconfirmed resonances (one narrow isoscalar and one broad isovector) just below and above the $p\overline{p}$ threshold previously suggested to explain the anomalous features observed in timelike $G_M^p$ LEAR and $G_E^n$ FENICE data.

The problem of nucleon propagation through the nuclear medium in quasielastic ${A(e,e}^{\prime }p)$ reactions is discussed in the kinematic range $1<~Q^2<~7\hspace{0.5em}(\mathrm{GeV}{/c)}^2.$ Experimental data are available from SLAC, BATES, and, recently, also from TJNAF. The coefficient of nuclear transparency is calculated for each $Q^2$ in the framework of the intranuclear cascade model (INC) and of the eikonal approximation (EA). The former has the capability of directly implementing the detector acceptances giving a very detailed analysis of the different observables. The latter, essentially based on an exclusive mechanism, contains explicit information about the dependence on the target shell structure. The predictions of both models are in good agreement with each other. The INC model reproduces the experimental data quite well in the measured range. The EA gives an explanation of the $Q^2$ behavior of the transparency coefficient as a kinematic effect related to the superposition of contributions from each target shell.

Nucleon electromagnetic form factors are studied in the cloudy bag model (CBM) with center-of-mass and recoil corrections. This is the first presentation of a full set of nucleon form factors using the CBM. The center-of-mass motion is eliminated via several different momentum projection techniques and the results are compared. It is found that the shapes of these form factors are significantly improved with respect to the experimental data if the Lorentz contraction of the internal structure of the baryon is also appropriately taken into account.

The electric and magnetic dipole moments of the ρ meson are calculated using the propagators and vertices derived from the QCD Dyson-Schwinger equations. Results obtained from using the Bethe-Salpeter amplitude studied by Chappell, Mitchell, and Tandy, and Pichowsky and Lee, are compared. The ρ meson electric dipole moment is generated through the inclusion of a quark electric dipole moment, which is left as a free variable. These results are compared to the perturbative results to obtain a measure of the effects of quark interactions and confinement. The two dipole moments are also calculated using the phenomenological MIT bag model to provide a further basis for comparison.

ρ photoproduction on complex nuclei is reexamined using a generalized vector dominance model which succesfully predicts the oberved nuclear shadowing in real photoabsorption and deep inelastic scattering. This model is shown to give a good fit to ρ photoproduction data on both nucleons and complex nuclei, in which the disagreement between the measured γ-ρ coupling and the γ-ρ coupling required by the simple vector dominance model is eliminated. The $\rho N$ total cross sections required are similar to those predicted by the additive quark model, and the magnitude of the correction to simple vector dominance is consistent with that inferred from the analysis of real photoabsorption and deep inelastic scattering.

In the theory of deep inelastic scattering the final state interaction between the struck quark and the remnants of the target is usually assumed to be negligible in the Bjorken limit. This assumption, still awaiting a full validation within nonperturbative QCD, is investigated in a model composed of two relativistic particles, interacting via a relativistic harmonic oscillator potential, within light-cone Hamiltonian dynamics. An electromagnetic current operator whose matrix elements behave properly under Poincaré transformations is adopted. It is shown that (i) the parton model is recovered, once the standard parton model assumptions are adopted, and (ii) when relativistic, interacting eigenfunctions are exactly taken into account for both the initial and final states, the values of the structure functions, averaged over small, but finite intervals of the Bjorken variable $x$, coincide with the results of the parton model in the Bjorken limit.

The long-range part of the weak axial exchange currents (AXC) is considered in the framework of the chiral $\sigma$-$\omega$ model, which preserves basic symmetries of QCD and includes $\sigma$, $\omega$, and $\pi$ mesons. Linear and nonlinear realizations of the model are considered, and it is explicitly demonstrated that the way one splits relativistic many-body effects into AXC contributions and one-body relativistic corrections to the traditional nuclear axial current is model dependent. In the linear realization of the $\sigma$-$\omega$ model spatial two-body AXC are shown to be necessary to preserve the partial conservation of axial-vector current (PCAC) relation to order $O(1/M)\mathrm{}$ in inverse nucleon mass. In the nonlinear realization of the model PCAC is satisfied for the one-body current identically. Indeed, it is shown that there are no AXC of order $O(1/M)\mathrm{}$ in this realization, but one now has to include a new one-body relativistic correction of order $O(1/M)\mathrm{}$ in the analysis to preserve PCAC for a single nucleon. A familiar result for axial exchange charge is reproduced in both models. The obtained correction terms are estimated in a simple unified analysis of electroweak processes with a few light nuclei.

We study inclusive ${\nu }_e$ and ${\nu }_{\mu }$ cross sections in ${}^{12}\mathrm{C}$ in a theory that takes into account significant nuclear renormalization of strengths. Our calculation is in excellent agreement with the measured inclusive muon capture rate and the flux-averaged ${\nu }_e$ cross section, but overestimates the flux-averaged ${\nu }_{\mu }$ inclusive cross section. These reactions are of crucial relevance to the issue of possible ${\nu }_{\mu }$ to ${\nu }_e$ oscillations. We also calculate the flux-averaged cross sections in ${}^{13}\mathrm{C}$ and ${}^{27}\mathrm{Al}$, which are found to be consistent with the available experimental result.

We study the weak production of $\Delta$ (i.e., $e^{-}+\overrightarrow{p}{\Delta }^0+{\nu }_e$ and $e^{+}+\overrightarrow{p}{\Delta }^{++}+{\overline{\nu }}_e)$ in the intermediate energy range corresponding to the Mainz and TJNAF electron accelerators. The differential cross sections $\sigma \left(\theta \right)$ are found to be of the order of ${10}^{-39}$ cm${}^2$/sr, over a range of angles which increases with energy. The possibility of observing these reactions with the high luminosities available at these accelerators, and studying the weak $N$-$\Delta$ transition form factors through these reactions is discussed. The production cross section of $N^{*}\mathrm{}\left(1440\right)\mathrm{}$ in the same kinematic region is also estimated and found to be smaller than the $\Delta$ production cross section.

We report on the results of the ${}^3\mathrm{He}{(}^4\mathrm{He}{,2p)}^4\mathrm{He}$ experiment at the underground accelerator facility LUNA (Gran Sasso). For the first time the lowest projectile energies utilized for the cross section measurement correspond to energies below the center of the solar Gamow peak ${(E}_0=22\mathrm{}\hspace{0.5em}\mathrm{keV})$. The data provide no evidence for the existence of a hypothetical resonance in the energy range investigated. Although no extrapolation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the data must be corrected for the effects of electron screening, clearly observed the first time for the ${}^3\mathrm{He}{(}^3\mathrm{He}{,2p)}^4\mathrm{He}$ reaction. The effects are, however, larger than expected and not understood, leading presently to the largest uncertainty on the quoted $S_b\mathrm{}\left(0\right)\mathrm{}$ value for bare nuclides (=5.40 MeV b).

The population of the ${}^{20}\mathrm{Na}$ resonances at 448, 661, 797, and 887 keV above the proton threshold has been studied in measurements of the ${}^{19}\mathrm{Ne}(p,\gamma {)}^{20}\mathrm{Na}$ reaction with radioactive ${}^{19}\mathrm{Ne}$ beams. The data have been analyzed fully in terms of resonance strengths, enabling a comparison with theoretical estimates and the extraction of upper and lower limits on the resonant part of the ${}^{19}\mathrm{Ne}(p,\gamma {)}^{20}\mathrm{Na}$ astrophysical reaction rate. The total cross section of the ${}^{19}\mathrm{Ne}{\mathrm{}(d,n)\mathrm{}}^{20}\mathrm{Na}$ reaction has been measured from 0.6 to 1.8 MeV (c.m.). On the basis of the results of a subsequent distorted-wave Born approximation analysis the direct component of the ${}^{19}\mathrm{Ne}(p,\gamma {)}^{20}\mathrm{Na}$ astrophysical reaction rate has been calculated in a potential model. The astrophysical implications of the resulting total reaction rate have been investigated: the conditions for the breakout from the hot CNO cycle into the rapid-proton capture process are determined by the preceding ${}^{15}\mathrm{O}(\alpha ,\gamma {)}^{19}\mathrm{Ne}$ reaction and the photodisintegration of the produced ${}^{20}\mathrm{Na}$ nuclei will not impede the breakout.

Discrete γ rays from the neutron capture state of ${}^{13}\mathrm{C}$ to its low-lying bound states have been measured using pulsed neutrons at $E_n=550\mathrm{}\mathrm{keV}.$ The partial capture cross sections have been determined to be $1.7\pm 0.5,$ $24.2\pm 1.0,$ $2.0\pm 0.4,$ and $1.0\pm 0.4\mu \mathrm{b}$ for the ground ${(J}^{\pi }{=1/2\mathrm{}}^{-})$ and first- ${(J}^{\pi }{=1/2\mathrm{}}^{+}),$ second- ${(J}^{\pi }{=3/2\mathrm{}}^{-}),$ and third- ${(J}^{\pi }{=5/2\mathrm{}}^{+})$ excited states, respectively. From a comparison with theoretical predictions based on the nonresonant direct radiative capture mechanism, we could determine the spectroscopic factor for the $J^{\pi }{=1/2\mathrm{}}^{+}$ state to be $0.80\pm 0.04,$ free from neutron-nucleus interaction ambiguities in the continuum. In addition we have detected the contribution of the nonresonant $d$-wave capture component in the partial cross sections for transitions leading to the $J^{\pi }{=1/2\mathrm{}}^{-}$ and $J^{\pi }{=3/2\mathrm{}}^{-}$ states. While the $s$-wave capture dominates at $E_n<~100\mathrm{keV},$ the $d$-wave component turns out to be very important at higher energies. From the present investigation the ${}^{12}\mathrm{C}(n,\gamma {)}^{13}\mathrm{C}$ reaction rate is obtained for temperatures in the range ${10}^7–{10}^{10}\mathrm{K}.$

We have studied the properties of low-lying ${}^{18}\mathrm{F}+p$ resonances as excited states in ${}^{19}\mathrm{Ne}.$ Three new levels have been found in the range $0<~E_{\mathrm{c}.\mathrm{m}.\mathrm{}}<~1\hspace{0.5em}\mathrm{MeV}$ just above the ${}^{18}\mathrm{F}+p$ threshold, and partial decay widths and isospin-mirror connections are suggested to known states in ${}^{19}\mathrm{F}$ for each of the nine states in this energy range. The properties of these resonances have been used to calculate the reaction rate $N_A〈\sigma v〉$ for the ${}^{18}\mathrm{F}(p,\gamma {)}^{19}\mathrm{Ne}$ and ${}^{18}\mathrm{F}(p,\alpha {)}^{15}\mathrm{O}$ reactions in the temperature range ${10}^8<T<\mathrm{}{10}^9.$ A comparison of these rates indicates that in this temperature range, the ${}^{14}\mathrm{O}\left(\alpha {,p)}^{17}\mathrm{F}\right(p,\gamma {)}^{18}\mathrm{Ne}{(e}^{+}\nu {)}^{18}\mathrm{F}(p,\gamma {)}^{19}\mathrm{Ne}$ reaction sequence is not as fast as the ${}^{15}\mathrm{O}(\alpha ,\gamma {)}^{19}\mathrm{Ne}$ reaction.

An expanded level scheme of states in ${}^{208}$Pb populated with the ${}^{207}$Pb$(n,\gamma )$ reaction on an enriched ${}^{207}$Pb target at the new Budapest cold neutron facility has been deduced. An upper limit on the intensity of the 2626-keV transition from the recently suggested 0${}^{+}$ two-phonon octupole state was obtained.

The incomplete fusion, onset of multifragmentation and vaporization is studied in Ca-Ca collisions at bombarding energies between $20–1000A\mathrm{MeV}$ and at impact parameters between $b=0\mathrm{}$ and $b_{\max }.$ The simulations of Ca-Ca are performed using the quantum molecular dynamics (QMD) model. We find incomplete fusion events at $E/A=20\mathrm{}–30\mathrm{MeV}.$ With an increase in the bombarding energy, the multiplicity of fragments first increases to a maximum value and then decreases for central and semi-central collisions. This peak in the multiplicity of fragments shifts towards higher energies for light mass fragments compared to intermediate mass fragments. The peak in the fragment production can be related to a critical point where onset of the fragmentation starts. The light mass fragment production at a given incident energy does not show any rise and fall in the multiplicity with a change in the impact parameter. The IMF production at higher energies $(>~150A$ MeV), however, has a clear rise and fall in their multiplicity.

The excitation region in ${}^{12}\mathrm{C}$ from $7\mathrm{MeV}<E_x<60\mathrm{}\mathrm{MeV}$ was studied with inelastic scattering of 240-MeV α particles at small angles including 0° where $E0\mathrm{}$ strength is enhanced. The strengths of known $0^{+}$ states at $E_x=7.655\mathrm{}\mathrm{MeV}$ and $E_x=10.3\mathrm{}\mathrm{MeV}$ were obtained and $E0\mathrm{}$ strength was observed to be distributed between $E_x=14\mathrm{}\mathrm{MeV}$ and $E_x=30\mathrm{}\mathrm{MeV}$ with a centroid of $21.5\pm 0.4\mathrm{MeV}$ and an rms width of $3.1\pm 0.2\mathrm{MeV}$ containing $14.5\pm 4.0\%$ of the isoscalar $E0\mathrm{}$ energy-weighted sum rule. Angular distributions and strengths of the $E_x$$=4.439\mathrm{}\mathrm{MeV}{2}^{+},$ $9.641\mathrm{MeV}{3}^{-},$ and $10.844\mathrm{MeV}{1}^{-}$ states were also obtained.

The newly discovered proton halo in the first excited ${\mathrm{}(1/2)\mathrm{}}^{+}$ state of ${}^{17}$F [R. Morlock et al., Phys. Rev. Lett. 79, 3837 (1997)] is investigated in the nonlinear relativistic mean-field model. It is shown that this model, without introducing any specifically adjusted parameters, can reproduce well not only the ground state properties of ${}^{17}$F but also the proton halo in the excited ${\mathrm{}(1/2)\mathrm{}}^{+}$ state. The possibility of the existence of a proton halo in the neighboring nucleus ${}^{18}$Ne is also discussed.

We test the Salpeter formalism for the electron screening of the solar proton-proton fusion reaction by solving numerically the relevant Schrödinger equation. We evaluate exactly the square of the overlap integral of the two-proton wave function and the deuteron wave function and compare with the usual analytic approximation. The usual WKB solution agrees with the numerical result to ${O(10\mathrm{}}^{-4})$. The WKB approximation should be even more precise for the other nuclear fusion reactions in the $\mathrm{pp}$ chain and CNO cycles.

It is shown that all the rotational bands in ${}^{44}\mathrm{Ti}$ at low and high excitation energies can be well explained in an $\alpha$-cluster model in which the $\alpha$-like excitation of the core, ${}^{40}\mathrm{Ca}$, is incorporated by employing density-dependent M3Y (DDM3Y) double folding potentials.

In a recent paper [Phys. Rev. C 55, 2521 (1997)] two-photon coincidences were studied for three nuclear reactions. From a correlation analysis, the authors evaluated the size and lifetime of the emitting source. In this Comment we correct some arguments used in the comparison of the extracted and estimated sizes, and show that the parametrization of the relative-momentum correlations leads to values which should not be assigned to the space-time extent of the source.