A. C. Fonseca, R. Machleidt, G. A. Miller
We show that using parameters consistent with the charge symmetry violating difference between the strong nn and pp scattering lengths provides significant constraints on the amplitude for the dd -> alpha pi0 reaction.
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Using the new set of dd --> eta alpha near threshold experimental data, the estimate of the importance of the nucleon-nucleon correlations for the eta alpha S-wave scattering length in the multiple scattering theory is obtained using the low-energy scattering length model. The contribution turns out to be much bigger then previously believed. The pi-eta mixing angle is extracted using the experimental data on the dd --> eta alpha and dd --> pi alpha processes. The model is dominated by the subthreshold extrapolation recipe for the eta alpha scattering amplitudes. When the recipe is chosen the …
In this project, we have investigated the 5-nucleon model system in the picture of the specific alpha-state structure, by extending the Yakubovsky scheme with the inclusion of the spin and isospin degrees of freedom. The Yakubovsky formalism for the 5-nucleon system in the effective alpha-neutron attractive model leads to a set of two coupled equations, based on two relevant alpha-nucleon sub-cluster components. To this regard, by switching off the fifth nucleon interactions, the 5-nucleon Yakubovsky equations can be reduced to a typical 4-nucleon problem. To calculate the 5- and 4-nucleon bou…
The properties of warm dilute alpha-nucleon matter are studied in a variational approach in the Thomas-Fermi approximation starting from an effective two-body nucleon-nucleon interaction. The equation of state, symmetry energy, incompressibility of the said matter as well as the alpha fraction are in consonance with those evaluated from the virial approach that sets a bench-mark for such calculations at low densities.
The equation of state and phase diagram of isospin-symmetric chemically equilibrated mixture of alpha particles and nucleons are studied in the mean-field approximation. The model takes into account the effects of Fermi and Bose statistics for nucleons and alphas, respectively. We use Skyrme-like parametrization of the mean-field potentials as functions of partial densities, which contain both attractive and repulsive terms. Parameters of these potentials are chosen by fitting known properties of pure nucleon- and pure alpha matter at zero temperature. The sensitivity of results to the choice …
An extended pairing plus QQ force model, which has been shown to successfully explain the nuclear binding energy and related quantities such as the symmetry energy, is applied to study the alpha-like four-nucleon correlations in 1f_{7/2} shell nuclei. The double difference of binding energies, which displays a characteristic behavior at $N \approx Z$, is interpreted in terms of the alpha-like correlations. Important roles of proton-neutron interactions forming the alpha-like correlated structure are discussed.
We study the competition between alpha-type and conventional pair condensation in the ground state of nuclei with neutrons and protons interacting via a charge-independent pairing interaction. The ground state is described by a product of two condensates, one of alpha-like quartets and the other one of pairs in excess relative to the isotope with N=Z. It is shown that this ansatz for the ground state gives very accurate pairing correlation energies for nuclei with the valence nucleons above the closed cores 16O, 40Ca and 100Sn. These results indicate that alpha-type correlations are important …
We report variational Monte Carlo calculations of single-nucleon momentum distributions for A <= 12 nuclei and nucleon-pair and nucleon-cluster momentum distributions for A <= 8. The wave functions have been generated for a Hamiltonian containing the Argonne v18 two-nucleon and Urbana X three-nucleon potentials. The single-nucleon and nucleon-pair momentum distributions exhibit universal features attributable to the one-pion-exchange tensor interaction. The single-nucleon distributions are broken down into proton and neutron components and spin-up and spin-down components where appropriate. Th…
We discuss charge symmetry and charge independence breaking in an effective field theory approach for few-nucleon systems. We systematically introduce strong isospin-violating and electromagnetic operators in the theory. The charge dependence observed in the nucleon-nucleon scattering lengths is due to one-pion exchange and one electromagnetic four-nucleon contact term. This gives a parameter free expression for the charge dependence of the corresponding effective ranges, which is in agreement with the rather small and uncertain empirical determinations. We also compare the low energy phase sh…
The phase diagram of isospin-symmetric chemically equilibrated mixture of alpha particles and nucleons is studied in the mean-field approximation. Skyrme-like parametrization is used for the mean-field potentials as functions of partial densities of nucleons and alphas. We find that there is a threshold value a* of the parameter a(N-alpha) which describes the attractive interaction between alpha-particles and nucleons. At a(N-alpha)<a* the ground state of nuclear matter at zero temperature behaves as a pure system of interacting nucleons, whereas at a(N-alpha)>a* the nuclear ground state inclu…
In this paper, we have solved a simple specific model of the five-body problem in the framework of the Yakubovsky equations, restricted to the configurations of the alpha-nucleon types only, to investigate the effective interaction between an inert alpha-particle and a neutron. In general case, the Yakubovsky scheme for the solution of the five-body system leads to a set of four coupled equations related to four independent configurations, which can be restricted to two coupled ones, to describe the effective alpha-nucleon structure model, namely an inert four-body alpha-core and a nucleon. He…
The effects of charge independence breaking of nucleon-nucleon interaction on the bulk properties of nuclear matter are investigated. Our results indicate that at high densities, the inclusion of charge dependence in the nucleon-nucleon potential affects the bulk properties of nuclear matter. However, at low densities, this effect is not considerable. It is seen that the change of our results for the nuclear matter calculations due to the breaking of the charge independence increases by increasing density. It is shown that the energy contribution of the $^1S_0$ channel is sensitive to consider…
Charge-independence breaking due to the pion-mass difference in the (chiral) two-pion-exchange nucleon-nucleon force is investigated. A general argument based on symmetries is presented that relates the charge-symmetric part of that force to the proton-proton case. The static potential linear in that mass difference is worked out as an explicit example by means of Feynman diagrams, and this confirms the general argument.
We study the leading isospin-breaking contributions to the two-nucleon two-pion exchange potential due to explicit Delta degrees of freedom in chiral effective field theory. In particular, we find important contributions due to the delta mass splittings to the charge symmetry breaking potential that act opposite to the effects induced by the nucleon mass splitting.
We use the method of QCD sum rules in the presence of an external pion field to investigate isospin symmetry breakings in pion-nucleon couplings. Possible manifestations of such isospin symmetry breaking are examined in the context of low-energy nucleon-nucleon ($NN$) scattering. We discuss numerical results in relation to both the existing data and other theoretical predictions.
Modern nucleon-nucleon (NN) potentials, which accurately fit the nucleon-nucleon scattering phase shifts, contain terms which break isospin symmetry. The effects of these symmetry violating terms on the bulk properties of nuclear matter are investigated. The predictions of the charge symmetry breaking (CSB) terms are compared with the Nolen-Schiffer (NS) anomaly regarding the energies of neighboring mirror nuclei. We find that, for a quantitative explanation of the NS anomaly, it is crucial to include CSB in partial waves with $L>0$ (besides $^1S_0$) as derived from a microscopic model for CSB…
Leading-order three-nucleon forces that violate isospin symmetry are calculated in Chiral Perturbation Theory. The effect of the charge-symmetry-breaking three-nucleon force is investigated in the trinucleon systems using Faddeev calculations. We find that the contribution of this force to the 3He - 3H binding-energy difference is approximately 5 keV.
Charge-symmetry breaking in the nucleon-nucleon force is investigated within an effective field theory, using a classification of isospin-violating interactions based on power-counting arguments. The relevant charge-symmetry-breaking interactions corresponding to the first two orders in the power counting are discussed, including their effects on the 3He-3H binding-energy difference. The static charge-symmetry-breaking potential linear in the nucleon-mass difference is constructed using chiral perturbation theory. Explicit formulae in momentum and configuration spaces are presented. The presen…
We present new calculations of the $α$-particle which are based on the most modern nucleon-nucleon interactions alone and combined with the Tucson-Melbourne or the Urbana IX three-nucleon interaction. Results for the binding energies and some properties of the wavefunction are given. On that phenomenological level little room is left for the action of a possible four-nucleon force.
Coulomb displacement energies, i.e., the differences between the energies of corresponding nuclear states in mirror nuclei, are evaluated using recent models for the nucleon-nucleon (NN) interaction. These modern NN potentials account for breaking of isospin symmetry and reproduce $pp$ and $pn$ phase shifts accurately. The predictions by these new potentials for the binding of $^{16}O$ are calculated. A particular focus of our study are effects due to nuclear correlations and charge-symmetry breaking (CSB). We find that the CSB terms in the modern NN interactions substantially reduce the discr…
Parity-even time reversal violation (TRV) in the nucleon-nucleon interaction is reconsidered. The TRV $ρ$-exchange interaction on which recent analyses of measurements are based is necessarily also charge-symmetry breaking (CSB). Limits on its strength $\bar{g}_ρ$ relative to regular $ρ$-exchange are extracted from recent CSB experiments in neutron-proton scattering. The result $\bar{g}_ρ\le 6.7\times 10^{-3}$ (95% CL) is considerably lower than limits inferred from direct TRV tests in nuclear processes. Properties of $a_1$-exchange and limit imposed by the neutron EDM are briefly discussed.
Background: Modern ab initio theory combined with high-quality nucleon-nucleon (NN) and three-nucleon (3N) interactions from chiral effective field theory (EFT) can provide a predictive description of low-energy light-nuclei reactions relevant for astrophysics and fusion-energy applications. However, the high cost of computations has so far impeded a complete analysis of the uncertainty budget of such calculations. Purpose: Starting from NN potentials up to fifth order (N4LO) combined with leading-order 3N forces, we study how the order-by-order convergence of the chiral expansion and confiden…
The role of the off-shell dependence of $ρ-ω$ mixing in the charge symmetry breaking nucleon-nucleon potential is discussed. It is shown that models describing the off-shell dependence of $ρ-ω$ mixing are not sufficient to determine the charge symmetry breaking nucleon-nucleon potential.
We report the first calculations of cross sections for the radiative capture reactions t(alpha,gamma)^7Li and ^3He(alpha,gamma)^7Be below 2 MeV which use wave functions derived from realistic nucleon-nucleon interactions by the variational Monte Carlo technique. After examining several small corrections to the dominant E1 operator, we find energy dependences for the low-energy S-factors which agree reasonably with experimental measurements. There is no contradiction with the previous theoretical understanding of these processes, but the zero-energy derivative of the t(alpha,gamma)^7Li S-factor…
We focus upon the raison d'etre of the alpha-chain states on the basis of the fully microscopic framework, where the Pauli principle among all the nucleons is fully taken into account. Our purpose is to find out the limiting number of alpha clusters, on which the linear alpha-cluster state can stably exist. How many alpha-clusters can stably make an alpha-chain state? We examine the properties of equally separated alpha clusters on a straight line and compare its stability with that on a circle. We also confirm its stability in terms of break-up and binary disintegrations including alpha-decay…
The present paper is written in response to the comment of M. R. Hadizadeh et. al on our original paper "Solution of the Specific Model of Five-body Problem to Investigate the Effective Alpha-Nucleon Interaction in a Partial-Wave analysis" [Acta Physica Polonica B, 48, 1279 (2017)]. In this paper we present our clarifications and statements on the authors of the comment arguments about of the accuracy of the procedure in solution of simple five- and four-body problems. In this regard our arguments turn out to be very efficient mainly discussed from the authors misunderstanding of the issues di…
The neutron and proton scattering with either deuteron or stable alpha particle can be modeled as a two particle system. In this paper, using Morse function as reference potential, inverse potentials have been computationally constructed directly from scattering phase shifts (SPS) data for light nucleon-nucleus systems. The phase equation for various l-channels has been numerically solved using 5th order Runge-Kutta (RK-5) method in each iteration within the optimization procedure to obtain best model parameters of Morse function that minimize mean absolute percentage error (MAPE). The inverse…
We present a new high-quality nucleon-nucleon potential with explicit charge dependence and charge asymmetry, which we designate Argonne $v_{18}$. The model has a charge-independent part with fourteen operator components that is an updated version of the Argonne $v_{14}$ potential. Three additional charge-dependent and one charge-asymmetric operators are added, along with a complete electromagnetic interaction. The potential has been fit directly to the Nijmegen $pp$ and $np$ scattering data base, low-energy $nn$ scattering parameters, and deuteron binding energy. With 40 adjustable parameters…
We suggest that the emergence of a large deformation in the magnesium, Mg, nuclides, especially at the Z = 12, N = 12, should be associated with an octahedral deformed shape. Within the framework of molecular geometrical symmetry, we find a possibility that the Z = 12, N = 12 system would form an octahedral structure consisting of six points of alpha(4He) particles, yielding the ground collectivity. With this point of view, we draw the following serial molecular structures; the Z = 10, N = 10, 20Ne, corresponds to a hexahedral, the Z = 8, N = 8, 16O, does to a tetrahedral, and the Z = 6, N = 6…
Elastic nucleon scattering from the 3He and 3H mirror nuclei is examined as a test of charge symmetry violation. The differential cross-sections are calculated at 500 MeV using a microsopic, momentum-space optical potential including the full coupling of two spin 1/2 particles and an exact treatment of the Coulomb force. The charge-symmetry-breaking effects investigated arise from a violation within the nuclear structure, from the p-nucleus Coulomb force, and from the mass-differences of the charge symmetric states. Measurements likely to reveal reliable information are noted.
The status of the theoretical effort to calculate charge-symmetry-breaking pion production reactions will be presented. The main emphasis will be on the d d -> alpha pi0 reaction, especially in relation to the recent IUCF experiment. Suggestions for future theoretical and experimental work will be made.
We describe a new method to treat low-energy scattering problems in few-nucleon systems, and we apply it to the five-body case of neutron-alpha scattering. The method allows precise calculations of low-lying resonances and their widths. We find that a good three-nucleon interaction is crucial to obtain an accurate description of neutron-alpha scattering.
In this study, the effects of repulsive nucleon-nucleon interactions arising from the Pauli exclusion principle were examined regarding the half-lives of heavy even-even nuclei with $84\leq Z\leq92$. The Pauli exclusion principle is applied to our investigations by renormalizing the nucleon-nucleon interactions according to the Bohr-Sommerfeld quantization condition. It is also applied to the double-folding ($DF$) formalism as a modification term by investigating the kinetic energy variation at the overlapping regions between the densities of the alpha and daughter nuclei. The standard deviati…
In order to study the bound-state structure of the Helium halo nuclei, the 8-nucleon Yakubovsky formalism has been implemented for 8He in a 5-body sub-cluster model, i.e. alpha+n+n+n+n. In this case, the 8-nucleon Yakubovsky equations has been obtained in the form of two coupled equations, based on the two independent components. In addition, by removing the contribution interactions of the 8 and 7s bound nucleons in the formalism, the obtained equations explicitly reduce to the 6-nucleon Yakubovsky equations for 6He, in the case of effective 3-body model, i.e. alpha+n+n. In view of the expect…
We have studied the influences of isospin symmetry breaking of nucleon-nucleon interaction on the various properties of asymmetrical nuclear matter and $β$-stable matter. For asymmetrical nuclear matter, it is found that by including this isospin symmetry breaking, the changes of bulk properties increase by increasing both density and asymmetry parameter. However, these effects on the total energy and equation of state of $β$-stable matter are ignorable. For asymmetrical nuclear matter, the validity of the empirical parabolic law in the isospin symmetry breaking case is shown. It is observed t…
The problem of calculating the four--nucleon bound state properties for the case of realistic two- and three-body nuclear potentials is studied using the hyperspherical harmonic (HH) approach. A careful analysis of the convergence of different classes of HH functions has been performed. A restricted basis is chosen to allow for accurate estimates of the binding energy and other properties of the 4He ground state. Results for various modern two-nucleon and two- plus three-nucleon interactions are presented. The 4He asymptotic normalization constants for separation in 2+2 and 1+3 clusters are al…
We study the effect of one-loop corrections from nucleon together with those from boson in the massless chiral sigma model, where we perform the Coleman-Weinberg renormalization procedure. This renormalization procedure has a mechanism of spontaneous symmetry breaking due to radiative corrections in $ϕ^4$ theory. We apply it to the system of nucleon and bosons with chiral symmetry where the negative-mass term of bosons does not exist. Spontaneous chiral symmetry breaking is derived from the contribution of nucleon and boson loops which generates the masses of nucleon, scalar meson, and vector …
Estimates are made of the d d -> alpha gamma gamma production cross sections in a model where each neutron-proton pair in the beam and target initiates an n p -> d gamma reaction. This approach, which successfully reproduces observables in two-pion production at intermediate energies, suggests that direct two-photon production could provide a very significant background to the measurement of the charge-symmetry-breaking (CSB) reaction d d -> alpha pi0. A non-vanishing CSB cross section has been reported which might be confused with such two-photon production under the given experimental condit…
We treat ${}^6$Li as an effective three-body ($n$-$p$-$α$) system and compute the $d$-$α$ $S-$wave scattering length and three-body separation energy of ${}^6$Li for a wide variety of nucleon-nucleon and $α$-nucleon potentials which have the same (or nearly the same) phase shifts. The Coulomb interaction in the $p$-$α$ subsystem is omitted. The results of all calculations lie on a one-parameter curve in the plane defined by the $d$-$α$ $S-$wave scattering length and the amount by which ${}^6$Li is bound with respect to the $n$-$p$-$α$ threshold. We argue that these aspects of the $n$-$p$-$α$ s…
The 4He total photoabsorption cross section is calculated with the realistic nucleon-nucleon potential Argonne V18 and the three-nucleon force (3NF) Urbana IX. Final state interaction is included rigorously via the Lorentz Integral Transform method. A rather pronounced giant resonance with peak cross sections of 3 (3.2) mb is obtained with (without) 3NF. Above 50 MeV strong 3NF effects, up to 35%, are present. Good agreement with experiment is found close to threshold. A comparison in the giant resonance region is inconclusive, since present data do not show a unique picture.
We analyze isospin breaking through quark mass differences and virtual photons in the pion-nucleon scattering lengths in all physical channels in the framework of covariant baryon chiral perturbation theory.
The de-excitation of alpha-conjugate nuclei produced in reactions of 35 MeV/nucleon 40Ca with 40Ca has been investigated. Particular emphasis is placed on examining the dynamics of collisions leading to projectile-like fragment exit channels. A general exploration of the reaction systematics reveals the binary dissipative character of the collisions and a hierarchy effect similar to that seen for heavier systems. Investigation of the subset of events characterized by a total alpha-conjugate mass (alpha particles plus alpha-conjugate fragments) equal to 40 and atomic number equal to 20 reveals …
The value of the alpha spectroscopic factor (S_alpha) of the 6.356 MeV 1/2+ state of 17O is believed to have significant astrophysical implications due to the importance of the 13C(alpha,n)16O reaction as a possible source of neutron production for the s process. To further study this effect, an accurate measurement of the 13C(6Li,d)17O reaction at E_lab = 60 MeV has been performed recently by Kubono et al., who found a new value for the spectroscopic factor of the 6.356 MeV 1/2+ state of 17O based on a distorted wave Born approximation (DWBA) analysis of these data. This new value, S_alpha ap…
Phenomenological Lagrangians that exhibit (broken) chiral symmetry as well as isospin violation suggest short-range charge symmetry breaking (CSB) nucleon-nucleon potentials with a $\mbox{\boldmath $σ$}_1 \!\cdot\!\mbox{\boldmath $σ$}_2$ structure. This structure could be realized by the mixing of axial-vector ($1^+$) mesons in a single-meson exchange picture. The Coleman-Glashow scheme for $ΔI_{z}=1$ charge symmetry breaking applied to meson and baryon $SU(2)$ mass splittings suggests a universal scale. This scale can be extended to $ΔI=1$ nonstrange CSB transitions $\langle a_1^\circ|H_{em}|…
We consider the correlation between the binding energies of the triton and the alpha-particle which is empirically observed in calculations employing different phenomenological nucleon-nucleon interactions. Using an effective quantum mechanics approach for short-range interactions with large scattering length |a| >> l, where l is the natural low-energy length scale, we construct the effective interaction potential at leading order in l/|a|. In order to renormalize the four-nucleon system, it is sufficient to include a SU(4)-symmetric one-parameter three-nucleon interaction in addition to the S…
We calculate at two-loop order in chiral perturbation theory the electromagnetic corrections to the two-pion exchange nucleon-nucleon interaction that is generated by the isovector spin-flip $ππNN$ contact-vertex proportional to the large low-energy constant $c_4\simeq 3.4 $GeV$^{-1}$. We find that the respective $2πγ$-exchange potentials contain sizeable isospin-breaking components which reach up to -4% of corresponding isovector $2π$-exchange potentials. The typical values of these novel charge-independence breaking spin-spin and tensor potentials are $-0.11 $MeV and $0.09 $MeV, at a nucleon…
We study the interplay between charge symmetry breaking and renormalization in the NN system for s-waves. We find a set of universality relations which disentangle explicitly the known long distance dynamics from low energy parameters and extend them to the Coulomb case. We analyze within such an approach the One-Boson-Exchange potential and the theoretical conditions which allow to relate the proton-neutron, proton-proton and neutron-neutron scattering observables without the introduction of extra new parameters and providing good phenomenological success.
We revisit the charge symmetry breaking $(CSB)$ in nucleon-nucleon $(NN)$ interaction caused by $π$-$η$ mixing in nuclear matter $(NM)$ employing one boson exchange $(OBE)$ model. The medium effect on $CSB$ is incorporated through the in-medium $π$ and $η$ propagators. In addition, the medium modification to the nucleon mass is also taken into account to construct the $CSB$ class $III$ potential considering off-shell $π$-$η$ mixing amplitude and large contribution of in-medium meson propagators to $CSB$ potential is found for the pseudoscalar $(PS)$ interaction compared to that of pseudovector…
Studying the possible breaking of various parton model symmetries by the parton distribution functions of the nucleon can provide important information for the non-perturbative structure of hadrons and the strong interaction. We review theoretical calculations for the breaking of flavor symmetry, quark-antiquark symmetry and charge symmetry in the unpolarized and polarized nucleons using the meson cloud model. We report an estimation for the total distribution of strange and antistrange quarks in the nucleon by combining theoretical calculations of SU(3) flavor symmetry breaking with light ant…
The Faddeev-Yakubovsky equations for the alpha-particle are solved. Accurate results are obtained for several modern NN interaction models, which include charge-symmetry breaking effects in the NN force, nucleon mass dependences as well as the Coulomb interaction. These models are augmented by three-nucleon forces of different types and adjusted to the 3N binding energy. Our results are close to the experimental binding energy with a slight overbinding. Thus there is only little room left for the contribution of possible 4N interactions to the alpha-particle binding energy. We also discuss mod…
An abrupt change in $α$ decay systematics around the N=126 neutron shell closure is discussed. It is explained as a sudden hindrance of the clustering of the nucleons that eventually form the $α$ particle. This is because the clustering induced by the pairing mode acting upon the four nucleons is inhibited if the configuration space does not allow a proper manifestation of the pairing collectivity.
With both three-nucleon force and continuum coupling included, we have developed a self-consistent {\it ab initio} Gamow shell model within the Gamow Hartree-Fock (GHF) basis obtained by the realistic interaction itself. With the chiral two-nucleon N$^3$LO and three-nucleon N$^2$LO interactions, the Gamow shell model has been applied to the mirror systems of $Z=8$ neutron-rich isotopes and $N=8$ proton-rich isotones, giving good agreements with data in binding energies, dripline positions and excitation spectra. The GHF calculated that the $0d_{3/2}$, $1s_{1/2}$ and $1p_{3/2}$ orbitals are res…
We discuss the role of the three-nucleon isospin T=3/2 amplitude in elastic neutron-deuteron scattering and in the deuteron breakup reaction. The contribution of this amplitude originates from charge-independence breaking of the nucleon-nucleon potential and is driven by the difference between neutron-neutron (proton-proton) and neutron-proton forces. We study the magnitude of that contribution to the elastic scattering and breakup observables, taking the locally regularized chiral N4LO nucleon-nucleon potential supplemented by the chiral N2LO three-nucleon force. For comparison we employ also…
We analyze isospin breaking through quark mass differences and virtual photons in the pion-nucleon scattering lengths in all physical channels in the framework of covariant baryon chiral perturbation theory. The so-called triangle relation is found to be violated by about 1.5 %. We encounter a substantial isospin-breaking correction to neutral-pion-nucleon scattering beyond Weinberg's prediction due to a cusp effect. Finally, the application to hadronic atoms is briefly discussed.
Alpha-cluster Formation and Decay: Four-Body Correlation and Configuration Mixing
本研究通过粒子数投影BCS方法改进四重态波函数方法，纳入配对诱导的组态混合，发现配对增强开壳层核的α团簇形成，闭壳层则抑制该过程。
The breaking of rotational symmetry on the lattice for bound eigenstates of the two lightest alpha conjugate nuclei is explored. Moreover, a macroscopic alpha-cluster model is used for investigating the general problems associated with the representation of a physical many-body problem on a cubic lattice. In view of the descent from the 3D rotation group to the cubic group symmetry, the role of the squared total angular momentum operator in the classification of the lattice eigenstates in terms of SO(3) irreps is discussed. In particular, the behaviour of the average values of the latter opera…
A quantitative understanding of charge-symmetry breaking is an increasingly important ingredient for the extraction of the nucleon's strange vector form factors. We review the theoretical understanding of the charge-symmetry-breaking form factors, both for single nucleons and for Helium-4.
We suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave--functions while the charge operators have no (or only small) explicit symmetry breaking components. We utilize the collective coordinate approach to chiral soliton models to support this picture. In particular we compute the $g_A/g_V$ ratios for hyperon beta--decay and the strangeness contribution to the nucleon axial current matrix elements and analyze their variation with increasing flavor symmetry breaking.
The charge-symmetry-breaking amplitudes for the recently observed d d -> alpha pi0 reaction are investigated. Chiral perturbation theory is used to classify and identify the leading-order terms. Specific forms of the related one- and two-body tree level diagrams are derived. As a first step toward a full calculation, a few tree-level two-body diagrams are evaluated at each considered order, using a simplified set of d and alpha wave functions and a plane-wave approximation for the initial dd state. The leading-order pion-exchange term is shown to be suppressed in this model because of poor ove…
The effects of charge symmetry breaking in nucleon electromagnetic form factors on parity- violating elastic electron-12C scattering is studied, and found to be much smaller than other known effects. The analysis of a planned experiment is discussed.
We calculate at two-loop order in chiral perturbation theory the electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon interaction that is generated by the isoscalar $πN$ contact-vertex proportional to the large low-energy constant $c_3$. We find that the respective $2πγ$-exchange potential contains sizeable isospin-breaking components which amount to about -1% of the strongly attractive isoscalar central $2π$-exchange potential. The typical value of these novel charge-independence and charge-symmetry breaking central potentials is $0.3 $MeV at a nucleon distance of $r=…
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