Nuclear Physics Approach Research Articles

Effect of Nucleon Dressing on Triton Binding Energy

The effect of nucleon dressing by pions, on the binding energy of three nucleons interacting via two-body forces, is calculated for the first time within a conventional nuclear physics approach. It is found that the dressing increases the binding energy of the triton by an amount approximately in the range from 0.3 MeV to 0.9 MeV, depending on the model used for dressing. This suggests that nucleon dressing may help explain the underestimation of the triton binding energy in previous calculations using only two-nucleon forces.

Block-diagonal similarity renormalization group and effective nucleon-nucleon interactions

We apply the block-diagonal similarity renormalization group to a simple toy-model for the nucleon-nucleon (NN) interaction in the 1S0 channel, aiming to analyze the complementarity between the explicit and the implicit renormalization approaches in nuclear physics. By explicit renormalization we mean the methods based on the wilsonian renormalization group in which high-energy modes above a given cutoff scale are integrated out while their effects are replaced by scale dependent effective interactions consistently generated in the process. We call implicit renormalization the usual procedure of cutoff effective theories in which the high-energy modes above the cutoff scale are simply removed and their effects are included through parametrized cutoff dependent counterterms whose strengths are fixed by fitting low-energy data. We compare the effective interactions obtained in both schemes and find a wide range of cutoff scales where they overlap. We further analyze the role played by the one-pion exchange (OPE) considering a δ-shell plus OPE representation for the NN interaction.

NEUTRINO EMISSIVITIES FROM DEUTERON BREAKUP AND FORMATION IN SUPERNOVAE

Neutrino emissions from electron/positron capture on the deuteron and the nucleon-nucleon fusion processes in the surface region of a supernova core are studied. These weak processes are evaluated in the standard nuclear physics approach, which consists of one-nucleon and two-nucleon-exchange currents and nuclear wave functions generated by a high precision nucleon-nucleon potential. In addition to the cross sections for these processes involving the deuteron, we present neutrino emissivities due to these processes calculated for typical profiles of core-collapsed supernovae. These novel neutrino emissivities are compared with the standard neutrino emission mechanisms. We find that the neutrino emissivity due to the electron capture on the deuteron is comparable to that on the proton in the deuteron abundant region. The implications of the new channels involving deuterons for the supernova mechanism are discussed.

Quantum Monte Carlo calculations of electromagnetic moments and transitions inA≤9nuclei with meson-exchange currents derived from chiral effective field theory

Quantum Monte Carlo calculations of electromagnetic moments and transitions are reported for $A\ensuremath{\le}9$ nuclei. The realistic Argonne ${v}_{18}$ two-nucleon and Illinois-7 three-nucleon potentials are used to generate the nuclear wave functions. Contributions of two-body meson-exchange current (MEC) operators are included for magnetic moments and $M1$ transitions. The MEC operators have been derived in both a standard nuclear physics approach and a chiral effective field theory formulation with pions and nucleons including up to one-loop corrections. The two-body MEC contributions provide significant corrections and lead to very good agreement with experiment. Their effect is particularly pronounced in the $A=9$, $T=3/2$ systems, in which they provide up to $\ensuremath{\sim}20%$ ($\ensuremath{\sim}40%$) of the total predicted value for the ${}^{9}$Li (${}^{9}$C) magnetic moment.

Spin Observables in the Two-Nucleon Capture and Dissociation Processes at Low Energies

Spin observables in radiative neutron capture on a proton and its inverse process, photodisintegration of the deuteron are calculated using a pionless effective field theory with di-baryon fields. Good agreement with the results of existing standard nuclear physics approach is obtained at very low energies. As energy increases, however, the discrepancy between the effective field theory and the standard nuclear physics approach becomes substantial. We discuss the origin of the difference.

He6 β-decay rate and the suppression of the axial constant in nuclear matter

We present a microscopic calculation of the $^{6}\mathrm{He} \ensuremath{\beta}$-decay into the ground state of $^{6}\mathrm{Li}$. To this end, we use chiral perturbation theory at next-to-next-to-next-to-leading order to describe the nuclear weak-currents. The nuclear wave functions are derived from the $J$-matrix inverse scattering nucleon-nucleon potential (JISP), and the Schr\"odinger equation is solved using the hyperspherical-harmonics expansion. Our calculation brings the theoretical decay-rate within $3%$ of the measured one. This success is attributed to the use of chiral perturbation theory based mesonic currents, whose contribution is qualitatively different compared to the standard nuclear physics approach, where the use of meson exchange currents worsens the comparison to experiment. The inherent inconsistency in the use of the JISP potential together with chiral perturbation theory based is argued not to affect this conclusion, though a more detailed investigation is called for. We conclude that any suppression of the axial constant in nuclear matter is included in this description of the weak interaction in the nucleus.

EFFECTIVE FIELD THEORY PREDICTIONS FOR THE SOLAR PROTON AND 3He BURNING PROCESSES

A modern effective field theory is exploited to pin down accurately the flux S factors for the pp and hep processes in the Sun. The technique used is to combine the high accuracy established in few-nucleon systems of the "standard nuclear physics approach" (SNPA) and the systematic power counting of chiral perturbation theory (ChPT) into a consistent effective field theory framework. Using highly accurate wave functions obtained in the SNPA and working to N 3 LO in the chiral counting for the current, we make totally parameter-free and error-controlled predictions for the pp and hep processes in the Sun. We also discuss the convergence with respect to chiral expansion.

THE SOLARhepPROCESS

▪ Abstract The hep process is a weak-interaction reaction, [Formula: see text], which occurs in the sun. There is renewed interest in hep owing to current experimental efforts to extract from the observed solar neutrino spectrum information on nonstandard physics in the neutrino sector. hep produces highest-energy solar neutrinos, although their flux is quite modest. This implies that the hep neutrinos can at some level influence the solar neutrino spectrum near its upper end. Therefore, a precise interpretation of the observed solar neutrino spectrum requires an accurate estimate of the hep rate. This is an interesting but challenging task. We describe the difficulties involved and how the recent theoretical developments in nuclear physics have enabled us to largely overcome these difficulties. A historical survey of hep calculations is followed by an overview of the latest developments. We compare the results obtained in the conventional nuclear physics approach and those obtained in a newly developed effective field theory approach. We also discuss the current status of the experiments relevant to hep.

Neutrino magnetic moment contribution to the neutrino–deuteron reaction

We study the effect of the neutrino magnetic moment on the neutrino–deuteron breakup reaction, using a method called the standard nuclear physics approach, which has already been well tested for several electroweak processes involving the deuteron.

EFT for electroweak processes of light nuclei

Recently we succeeded to make a reliable EFT prediction in a totally parameter-free manner for the S factors for the solar pp and hep processes, p + p → d + e + + ν e and 3 He + p → 4 He + e + + ν e [1]. The strategy used in there is to embed a highly sophisticated standard nuclear physics approach (SNPA) exploiting realistic potentials[2,3] into an EFT framework, that we refer to as EFT∗. Up to next-next-to-leading order in chiral expansion, it turnes out that there is effectively only one counter-term relevant to this process, the coefficient of which − ( d ̂ R ) − has been renormalized to reproduce the experimental value of the tritium-beta decay. Our study has also led to very accurate EFT calculations on two-body weak processes that also receive contributions from the d ̂ R term, μ − d capture rate[4], and ν − d scattering cross section[5].

EFT for electroweak processes of light nuclei

Recently we succeeded to make a reliable EFT prediction in a totally parameter-free manner for the S factors for the solar pp and hep processes, p + p → d + e + + ν e and 3 He + p → 4 He + e + + ν e [1]. The strategy used in there is to embed a highly sophisticated standard nuclear physics approach (SNPA) exploiting realistic potentials[2,3] into an EFT framework, that we refer to as EFT∗. Up to next-next-to-leading order in chiral expansion, it turnes out that there is effectively only one counter-term relevant to this process, the coefficient of which − ( d ̂ R ) − has been renormalized to reproduce the experimental value of the tritium-beta decay. Our study has also led to very accurate EFT calculations on two-body weak processes that also receive contributions from the d ̂ R term, μ − d capture rate[4], and ν − d scattering cross section[5].

Solar neutrinos, SNO and neutrino–deuteron reactions

The standard nuclear physics approach and effective field theory approach for calculations of neutrino–deuteron cross sections for the solar neutrino energies are considered. Their main features, the level of accuracy and problems to be addressed for further developments are discussed.

Effective field theory for nuclei: Confronting fundamental questions in astrophysics

Fundamental issues involving nuclei in the celebrated solar neutrino problem are discussed in terms of an effective field theory adapted to nuclear few-body systems, with a focus on the proton fusion process and the hep process. Our strategy in addressing these questions is to combine chiral perturbation theory -- an effective field theory of QCD -- with an accurate nuclear physics approach to arrive at a more effective effective field theory that reveals and exploits a subtle role of the chiral-symmetry scale in short-distance effects encoded in short-range nuclear correlations. Our key argument is drawn from the close analogy of the principal weak matrix element figuring in the hep process to the suppressed matrix elements in the polarized neutron-proton capture at threshold currently being measured in the laboratories.

Algebraic approaches in nuclear physics

In these lectures I discuss algebraic approaches in nuclear physics. The emphasis is on aspects that can not be found in the same form in other publications of the subject. We discuss the relation between bosons and fermions, as well as some of the standard formalism underlying all algebraic models in nuclear physics. We then contrast fermionic and bosonic models. We end with a case study on supersymmetry in superdeformed nuclei.

Application of the Lindblad axiomatic approach to non-equilibrium nuclear processes

In the framework of the Lindblad axiomatic approach for open quantum systems various models for heavy-ion reactions are considered. Assuming the existence of a stationary solution for the Lindblad equation in Gibbs form, the relations between the friction and diffusion coefficients are derived. In this case the evolution operator depends on temperature. Models and Lindblad's evolution operators, which are constructed with the generators of SO(3) and SO(4) algebras, are considered. A master equation for the density operator is derived for the case of a general potential and its connection with similar approaches in nuclear physics is discussed.

Yukawa theories as effective theories of quantum chromodynamics for a large number of colors

An effective theory for low-energy nuclear interactions is proposed, based on results obtained from the 1/${N}_{c}$ expansion of quantum chromodynamics. The Lagrangian is local in the meson sector, but in the baryon sector it is nonlocal both in the meson-baryon Yukawa coupling and in the baryon propagators. It satisfies an important consequence of the 1/${N}_{c}$ expansion, the suppression of baryon loops. Our findings are then shown to support the traditional approaches in nuclear physics and, more especially, the relativistic nuclear many-body theories at baryon-tree level.

Multiquark physics-the great challenge for future directions in the interplays between particle and nuclear physics

Four-, five- and six-body systems are considered as the bridge between particle and nuclear physics. A nuclear physics approach based on an updated Sakharov-Zeldovich model is used to investigate multiquark states. The H dibaryon and a new anticharmed strange baryon are discussed in detail as well as several four-quark states for whichn preliminary experimental evidence has been reported.

On the interpretation of the Coulomb sum rule in electron scattering by nuclei

Abstract The validity of the assumptions underlying the interpretation of the integrated longitudinal response of (e, e′) processes in terms of proton-proton correlation function is analysed. The results of realistic many-body calculations of the Coulomb sum in nuclear matter and complex nuclei indicate that, even within a conventional nuclear physics approach, a highly accurate description of the free nucleon form factors is required to extract quantitative information on dynamical correlation effects.

High angular momentum NN bound-state production in the reaction pp→π-X+

Using a nuclear physics approach, the authors investigate the orbital angular momentum dependence in the baryonium JP=1- production in the reaction pp pi -X+. Although the calculated cross section for l=0 states is larger than the experimental upper limit, they show that the existence of l=2 'nuclear type' baryonium states cannot be discarded.

The role of single-particle density in chemistry

The definition, properties, and applications of the single-particle (electron) density $\ensuremath{\rho}(\mathrm{r})$ are discussed in this review. Since the discovery of Hohenberg-Kohn theorem, which gave a theoretical justification for considering $\ensuremath{\rho}(\mathrm{r})$, rather than the wave function, for studying both nondegenerate and degenerate ground states of many-electron systems, $\ensuremath{\rho}(\mathrm{r})$ has been acquiring increasing attention. The quantum subspace concept of Bader et al. has further highlighted $\ensuremath{\rho}(\mathrm{r})$ since a rigorous decomposition of the three-dimensional (3D) space of a molecule into quantum subspaces or virial fragments is possible, the boundaries of such subspaces being defined solely in terms of $\ensuremath{\rho}(\mathrm{r})$. Further, $\ensuremath{\rho}(\mathrm{r})$ is a very useful tool for studying various chemical phenomena. The successes and drawbacks of earlier models, such as Thomas-Fermi-Dirac, incorporating $\ensuremath{\rho}(\mathrm{r})$ are examined. The applications of $\ensuremath{\rho}(\mathrm{r})$ to a host of properties---such as chemical binding, molecular geometry, chemical reactivity, transferability, and correlation energy---are reviewed. There has been a recent trend in attempting to bypass the Schr\"odinger equation and directly consider single-particle densities and reduced density matrices, since most information of physical and chemical interest are encoded in these quantities. This approach, although beset with problems such as $N$-representability, and although unsuccessful at present, is likely to yield fresh concepts as well as shed new light on earlier ideas. Since charge density in 3D space is a fundamental quantum-mechanical observable, directly obtainable from experiment, and since its use in conjunction with density-functional theory and quantum fluid dynamics would provide broadly similar approaches in nuclear physics, atomic-molecular physics, and solid-state physics, it is not unduly optimistic to say that $\ensuremath{\rho}(\mathrm{r})$ may be the unifying link between the microscopic world and our perception of it.