Nuclear Theory·nucl-th

Thursday·July 22, 2021

11 papers—8 primary·3 cross-listed

01
[Submitted on 20 Jul 2021]
Nambu-Covariant Many-Body Theory I: Perturbative Approximations
M. Drissi · A. Rios · C. Barbieri
Symmetry-breaking considerations play an important role in allowing reliable and accurate predictions of complex systems in quantum many-body simulations. The general theory of perturbations in symmetry-breaking phases is nonetheless intrinsically more involved than in the unbroken phase due to non-vanishing anomalous Green's functions or anomalous quasiparticle interactions. In the present paper, we develop a formulation of many-body theory at non-zero temperature which is explicitly covariant with respect to a group containing Bogoliubov transformations. Based on the concept of Nambu tensors, we derive a factorisation of standard Feynman diagrams that is valid for a general Hamiltonian. The resulting factorised amplitudes are indexed over the set of un-oriented Feynman diagrams with fully antisymmetric vertices. We argue that, within this framework, the design of symmetry-breaking many-body approximations is simplified.
Comments:
29 pages, 11 figures, accepted version
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
arXiv:
2107.09759 [pdf]
Annals Phys.(2024)·8 citations
02
[Submitted on 20 Jul 2021]
Nambu-Covariant Many-Body Theory II: Self-Consistent Approximations
M. Drissi · A. Rios · C. Barbieri
The theory of Self-Consistent Green's Function (SCGF) is reformulated in an explicit Nambu-covariant fashion for applications to many-body systems at non-zero temperature in symmetry-broken phases. This is achieved by extending the Nambu-covariant formulation of perturbation theory, presented in the first part of this work, to non-perturbative schemes based on self-consistently dressed propagators and vertices. We work out in detail the self-consistent ladder approximation, motivated by a trade-off between numerical complexity and many-body phenomenology. Taking a complex general Hartree-Fock-Bogoliubov (HFB) propagator as a starting point, we also formulate and prove a sufficient condition on the stability of the HFB self-energy to ensure the convergence of the initial series of ladders at any energy. The self-consistent ladder approximation is written purely in terms of spectral functions and the resulting set of equations, when expressed in terms of Nambu tensors, are remarkably similar to those in the symmetry-conserving case. This puts the application of the self-consistent ladder approximation to symmetry-broken phases of infinite nuclear matter within reach.
Comments:
33 pages, 12 figures and one table; accepted version
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)
arXiv:
2107.09763 [pdf]
Annals Phys.(2024)·6 citations
03
[Submitted on 21 Jul 2021]
Elastic and inelastic alpha transfer in the $^{16}$ O+ $^{12}$ C scattering
Nguyen Tri Toan Phuc · Nguyen Hoang Phuc · Dao. T. Khoa
The elastic scattering cross section measured at energies $E ≲ 10$ MeV/nucleon for some light heavy-ion systems having two identical cores like $^{16}$ O+ $^{12}$ C exhibits an enhanced oscillatory pattern at the backward angles. Such a pattern is known to be due to the transfer of the valence nucleon or cluster between the two identical cores. In particular, the elastic $α$ transfer has been shown to originate directly from the core-exchange symmetry in the elastic $^{16}$ O+ $^{12}$ C scattering. Given the strong transition strength of the $2_{1}^{+}$ state of $^{12}$ C and its large overlap with the $^{16}$ O ground state, it is natural to expect a similar $α$ transfer process (or inelastic $α$ transfer) to take place in the inelastic $^{16}$ O+ $^{12}$ C scattering. The present work provides a realistic coupled channel description of the $α$ transfer in the inelastic $^{16}$ O+ $^{12}$ C scattering at low energies. Based on the results of the 4 coupled reaction-channels calculation, we show a significant contribution of the $α$ transfer to the inelastic $^{16}$ O+ $^{12}$ C scattering cross section at the backward angles. These results suggest that the explicit coupling to the $α$ transfer channels is crucial in the studies of the elastic and inelastic scattering of a nucleus-nucleus system with the core-exchange symmetry.
Comments:
14 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2107.09873 [pdf]
Commun.in Phys.(2021)·2 citations
04
[Submitted on 21 Jul 2021]
Tensor force and deformation in even-even nuclei
G. Co · M. Anguiano · A. M. Lallena
The variational principle is used to build a model which describes open shell nuclei with ground state deformations. Hartree-Fock equations are solved by using single particle wave functions whose radial parts depend on the projection of the angular momentum on the quantization axis. Pairing effects are taken into account by solving Bardeen-Cooper-Schrieffer equations in each step of the minimisation procedure. The Gogny D1S finite-range interaction and an extension of it that includes tensor terms are consistently used in both parts of our calculations. The model is applied to study a set of isotopes with 34 protons and of isotones with 34 neutrons. Total energies, density distributions, their radii and single particle energies are analysed and the results of our calculations are compared with the available experimental data. We focused our attention on the effects of the deformation and of the tensor force on these observables. Our model describes open shell nuclei from a peculiar perspective and opens the possibility of future theoretical developments.
Comments:
23 pages, 15 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2107.09938 [pdf]
PRC(2021)·7 citations
05
[Submitted on 21 Jul 2021]
Potential energy surfaces and fission fragment mass yields of even-even superheavy nuclei
P. V. Kostryukov · A. Dobrowolski · B. Nerlo-Pomorska · M. Warda · Z. G. Xiao · Y. J. Chen · L. L. Liu · J. L. Tian · K. Pomorski
Potential energy surfaces and fission barriers of superheavy nuclei are analyzed in the macroscopic-microscopic model. The Lublin-Strasbourg Drop (LSD) is used to obtain the macroscopic part of the energy, whereas the shell and pairing energy corrections are evaluated using the Yukawa-folded potential. A standard flooding technique has been used to determine the barrier heights. It was shown the Fourier shape parametrization containing only three deformation parameters reproduces well the nuclear shapes of nuclei on their way to fission. In addition, the non-axial degree of freedom is taken into account to describe better the form of nuclei around the ground state and in the saddles region. Apart from the symmetric fission valley, a new very asymmetric fission mode is predicted in most superheavy nuclei. The fission fragment mass distributions of considered nuclei are obtained by solving the 3D Langevin equations.
Comments:
20 pages, 17 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2107.09981 [pdf]
CPC(2021)·25 citations
06
[Submitted on 21 Jul 2021]
Light-Front Transverse Momentum Distributions for $J$ =1/2 Hadronic Systems in Valence Approximation
Rocco Alessandro🇮🇹 · Alessio Del Dotto🇮🇹 · Emanuele Pace🇮🇹 · Gabriele Perna🇮🇹 · Giovanni Salmè🇮🇹 · Sergio Scopetta🇮🇹
The semi-inclusive correlator for a $J$ =1/2 bound-system, composed by A spin-1/2 fermions, is linearly expressed in terms of the light-front Poincaré covariant spin-dependent spectral function, in valence approximation. The light-front spin-dependent spectral function is fully determined by six scalar functions that allow for a complete description of the six T-even transverse-momentum distributions, suitable for a detailed investigation of the dynamics inside the bound system. The application of the developed formalism to a case with a sophisticated dynamical content, like $^{3}$ He, reaches two goals: (i) to illustrate a prototype of an investigation path for gathering a rich wealth of information on the dynamics and also finding valuable constraints to be exploited from the phenomenological standpoint; (ii) to support for the three-nucleon system a dedicated experimental effort for obtaining a detailed 3D picture in momentum space. In particular, the orbital-angular momentum decomposition of the bound state can be studied through the assessment of relations among the transverse-momentum distributions, as well as the relevance of the relativistic effect generated by the implementation of macrocausality. A fresh evaluation of the longitudinal and transverse polarizations of the neutron and proton is also provided, confirming essentially the values used in the standard procedure for extracting the neutron structure functions from both deep-inelastic scattering and semi-inclusive reactions, in the same kinematical regime.
Comments:
26 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
2107.10187 [pdf]
PRC(2021)·9 citations
07
[Submitted on 21 Jul 2021]
Nuclear ab initio calculations of 6He $β$ -decay for beyond the Standard Model studies
Ayala Glick-Magid🇮🇱 · Christian Forssén🇸🇪 · Daniel Gazda🇨🇿 · Doron Gazit🇮🇱 · Peter Gysbers🇨🇦 · Petr Navrátil🇨🇦
Precision measurements of $β$ -decay observables offer the possibility to search for deviations from the Standard Model. A possible discovery of such deviations requires accompanying first-principles calculations. Here we compute the nuclear structure corrections for the $β$ -decay of $^{6}$ He which is of central interest in several experimental efforts. We employ the impulse approximation together with wave functions calculated using the ab initio no-core shell model with potentials based on chiral effective field theory. We use these state-of-the-art calculations to give a novel and comprehensive analysis of theoretical uncertainties. We find that nuclear corrections, which we compute within the sensitivity of future experiments, create significant deviation from the naive Gamow-Teller predictions, making their accurate assessment essential in searches for physics beyond the Standard Model.
Comments:
Published version
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
2107.10212 [pdf]
PLB(2022)·41 citations
08
[Submitted on 21 Jul 2021]
A method to remove lower order contributions in multi-particle femtoscopic correlation functions
Raffaele Del Grande🇩🇪 · Laura Šerkšnytė🇩🇪 · Laura Fabbietti🇩🇪 · Valentina Mantovani Sarti🇩🇪 · Dimitar Mihaylov🇩🇪
In recent years the femtoscopy technique has been used by the ALICE Collaboration in small colliding systems at the LHC to investigate the strong-interaction of hadron pairs in the low-energy regime. The extension of this technique to the study of many-body correlations aims to deliver in the next years the first experimental measurements of the genuine many-hadron interactions, provided that the contributions due to the lower order terms are properly accounted for. In this paper we present a method that allows to determine the residual lower order contributions to the three-body correlation functions, based on the cumulant decomposition approach and on kinematic transformations. A procedure to simulate genuine three-body correlations in three-baryon correlation functions is also developed. A qualitative study of the produced correlation signal is performed by varying the strength of the adopted three-body interaction model and comparisons with the expectations for the lower order contributions to the correlation function are shown. The method can be also applied to evaluate the combinatorial background in the two-body correlation functions, providing an improved statistical accuracy with respect to the standard techniques. The example of the contribution by the pK $^{+}$ K $^{-}$ channel to the recently measured p $ϕ$ correlation is discussed.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
2107.10227 [pdf]
EPJC(2022)·23 citations

Affiliations

first authorsco-authorsvia INSPIRE