Benchmark calculation of inclusive electromagnetic responses in the four-body nuclear system

Stetcu, I.; Quaglioni, Sofia; Bacca, Sonia; Barrett, B. R.; Johnson, Calvin W.; Navrátil, Petr; Barnea, Nir; Leidemann, Winfried; Orlandini, Giuseppina

doi:10.1016/j.nuclphysa.2006.12.047

Cited by 21 publications

(18 citation statements)

References 60 publications

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“…The convergence to the exact results with increasing N max is accelerated by the use of an effective interaction derived, in this case, from the adopted NN and NNN χEFT potentials at the three-body cluster level [12]. The reliability of the NCSM approach combined with the LIT method was validated by comparing to the results obtained with the effective-interaction hyper-spherical harmonics (EIHH) technique [29] in a recent benchmark calculation [30]. A complete description of the NCSM approach was presented, e.g., in Refs.…”

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confidence: 99%

“…This choice for the HO frequencies is driven by our final goal of evaluating the 4 He photo-absorption cross section and providing an estimate for its theoretical uncertainty. Indeed, in the particular case of the 4 He nucleus, frequencies in the range 12 ≤ Ω ≤ 28 MeV allow to achieve a good description of both ground state and complex energy continuum, as required in a calculation of response functions with the LIT method [30].…”

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confidence: 99%

“…The actual evaluation of Eq. (5) is performed by applying the Lanczos algorithm to the Hamiltonian of the system, using as starting vector |ϕ 0 = Ψ 0 |D †D |Ψ 0 − 1 2D |Ψ 0 [26,30]. Indeed, the LIT can be written as a continued fraction of the elements of the resulting tridiagonal matrix, the so-called Lanczos coefficients a n and b n :…”

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confidence: 99%

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The 4He total photo-absorption cross section with two- plus three-nucleon interactions from chiral effective field theory

Quaglioni

Navrátil

2007

Physics Letters B

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The total photo-absorption cross section of 4 He is evaluated microscopically using two-(NN) and three-nucleon (NNN) interactions based upon chiral effective field theory (χEFT). The calculation is performed using the Lorentz integral transform method along with the ab initio no-core shell model approach. An important feature of the present study is the consistency of the NN and NNN interactions and also, through the Siegert theorem, of the two-and three-body current operators. This is due to the application of the χEFT framework. The inclusion of the NNN interaction produces a suppression of the low-energy peak and enhancement of the high-energy tail of the cross section. We compare to calculations obtained using other interactions and to representative experiments. The rather confused experimental situation in the giant resonance region prevents discrimination among different interaction models.Key words: PACS: 25.20.Dc, 21.60.Cs, 27.10.+h Interactions among nucleons are governed by quantum chromodynamics (QCD). In the low-energy regime relevant to nuclear structure and reactions, this theory is nonperturbative, and, therefore, hard to solve. Thus, theory has been forced to resort to models for the interaction, which have limited physical basis. New theoretical developments, however, allow us to connect QCD with low-energy nuclear physics. Chiral effective field theory (χEFT) [1,2] provides a promising bridge to the underlying theory, QCD. Beginning with the pionic or the nucleon-pion system [3] one works consistently with systems of increasing number of nucleons [4]. One makes use of spontaneous breaking of chiral symmetry to systematically expand the strong interaction in terms of a generic small momentum and takes the explicit breaking of chiral symmetry into account by expanding in the pion mass. Nuclear interactions are nonperturbative, because diagrams with purely nucleonic intermediate states are enhanced [1,2]. Therefore, the chiral perturbation expansion is performed for the potential. The χEFT predicts, along with the nucleon-nucleon (NN) interaction at the leading order, a three-nucleon (NNN) interaction at the next-to-next-to-leading order or N 2 LO [2,5,6], and even a four-nucleon (NNNN) interaction at the fourth Email addresses: quaglioni1@llnl.gov (Sofia Quaglioni), navratil1@llnl.gov (Petr Navrátil). order (N 3 LO) [7]. The details of QCD dynamics are contained in parameters, low-energy constants (LECs), not fixed by the symmetry, but can be constrained by experiment. At present, high-quality NN potentials have been determined at N 3 LO [8]. A crucial feature of χEFT is the consistency between the NN, NNN and NNNN parts. As a consequence, at N 2 LO and N 3 LO, except for two parameters assigned to two NNN diagrams, the potential is fully constrained by the parameters defining the NN interaction. The full interaction up to N 2 LO was first applied to the analysis of nd scattering [6] and later the N 3 LO NN potential was combined with the available NNN at N 2 LO to study the 7 Li stru...

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The 4He total photo-absorption cross section with two- plus three-nucleon interactions from chiral effective field theory

Quaglioni

Navrátil

2007

Physics Letters B

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“…(4). So far, hyper-spherical harmonics expansions [10], no core shell model [11] and coupled-cluster theory [12] have been used to solve the LIT equation. The response function S O (ω, q) is typically obtained from a numerical inversion of the integral transform [13,14] and is independent on the choice of the width Γ.…”

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confidence: 99%

Electromagnetic Reactions and Few-Nucleon Dynamics

Bacca

2014

EPJ Web of Conferences

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Abstract.We present an update on recent theoretical studies of electromagnetic reactions obtained by using the Lorentz integral transform method. The 4 He nucleus will be the main focus of this report: results for the photo-disintegration and the electro-disintegration processes will be shown, as well as a recent calculation of polarizability effects in muonic atoms. We also discuss the exciting possibility to investigate inelastic reactions for mediummass nuclei in coupled-cluster theory, highlighted by the recent application to the 16 O photo-nuclear cross section.

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“…Unitary transformations of the Hamiltonian have been used to great effect in a range of nuclear physics problems [1][2][3][4][5][6][7][8][9][10][11] to decouple high-and low-momentum components of the interaction and promote numerical convergence in large, but finite model spaces. However, in an A-nucleon system, such beneficial decoupling of momentum scales comes at the price of an effective Hamiltonian containing irreducible three-and higher-body (up to A-body) terms, even when initially absent.…”

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confidence: 99%

Operator evolution forab initioelectric dipole transitions ofHe4

et al. 2015

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A goal of nuclear theory is to make quantitative predictions of low-energy nuclear observables starting from accurate microscopic internucleon forces. A major element of such an effort is applying unitary transformations to soften the nuclear Hamiltonian and hence accelerate the convergence of ab initio calculations as a function of the model space size. The consistent simultaneous transformation of external operators, however, has been overlooked in applications of the theory, particularly for nonscalar transitions. We study the evolution of the electric dipole operator in the framework of the similarity renormalization group method and apply the renormalized matrix elements to the calculation of the 4 He total photoabsorption cross section and electric dipole polarizability. All observables are calculated within the ab initio no-core shell model. We find that, although seemingly small, the effects of evolved operators on the photoabsorption cross section are comparable in magnitude to the correction produced by including the chiral three-nucleon force and cannot be neglected.

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Benchmark calculation of inclusive electromagnetic responses in the four-body nuclear system

Cited by 21 publications

References 60 publications

The 4He total photo-absorption cross section with two- plus three-nucleon interactions from chiral effective field theory

The 4He total photo-absorption cross section with two- plus three-nucleon interactions from chiral effective field theory

Electromagnetic Reactions and Few-Nucleon Dynamics

Operator evolution forab initioelectric dipole transitions ofHe4

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