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Nuclear Theory·nucl-th

Monday·September 11, 2023

7 papers—3 primary·4 cross-listed

All7Primary3Cross-lists4
  1. 04

    Fine structure of the isoscalar giant monopole resonance in Ni, Zr, Sn and Pb

    A. Bahini🇿🇦 · P. von Neumann-Cosel🇩🇪 · J. Carter🇿🇦 · I. T. Usman🇿🇦 · N. N. Arsenyev🇷🇺 · A. P. Severyukhin🇷🇺 · E. Litvinova🇺🇸 · R. W. Fearick🇿🇦 · R. Neveling🇿🇦 · P. Adsley🇿🇦 · N. Botha🇿🇦 · J. W. Brümmer🇿🇦 and 17 other authors

    Over the past two decades high energy-resolution inelastic proton scattering studies were used to gain an understanding of the origin of fine structure observed in the isoscalar giant quadrupole resonance (ISGQR) and the isovector giant dipole resonance (IVGDR). Recently, the isoscalar giant monopole resonance (ISGMR) in Ni, Zr, Sn and Pb was studied at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) by means of inelastic -particle scattering at very forward scattering angles (including ). The good energy resolution of the measurement revealed significant fine structure of the ISGMR.~To extract scales by means of wavelet analysis characterizing the observed fine structure of the ISGMR in order to investigate the role of different mechanisms contributing to its decay width. Characteristic energy scales are extracted from the fine structure using continuous wavelet transforms. The experimental energy scales are compared to different theoretical approaches performed in the framework of quasiparticle random phase approximation (QRPA) and beyond-QRPA including complex configurations using both non-relativistic and relativistic density functional theory. All models highlight the role of Landau fragmentation for the damping of the ISGMR especially in the medium-mass region. Models which include the coupling between one particle-one hole (1p-1h) and two particle-two hole (2p-2h) configurations modify the strength distributions and wavelet scales indicating the importance of the spreading width. The effect becomes more pronounced with increasing mass number. Wavelet scales remain a sensitive measure of the interplay between Landau fragmentation and the spreading width in the description of the fine structure of giant resonances.

    ↳ nucl-exnucl-thPRC(2024)·10 citations
  2. 05

    Artificial first-order phase transition in a magnetized Nambu--Jona-Lasinio model with a quark anomalous magnetic moment

    William R. Tavares🇧🇷 · Sidney S. Avancini🇧🇷 · Ricardo L. S. Farias🇧🇷 · Rafael P. Cardoso🇧🇷

    Recently, first-order phase transitions have been predicted as an effect of the inclusion of quark anomalous magnetic moment (AMM) in the hot and magnetized Nambu--Jona-Lasinio model (NJL). These transitions appear in the chiral condensate for different combinations of AMM and magnetic fields and could lead to inverse magnetic catalysis. However, in this work, we show that the predicted first-order phase transitions are related to regularization-dependent issues. To show this, we explore, in the context of the vacuum magnetic regularization (VMR) scheme, two different scenarios: when mass-dependent (MD) and mass-independent (MI) terms are present in the subtraction of the divergences. In the MD case, as we increase the AMM value, it is observed the appearance of a nonmassive minimum in the thermodynamical potential, which induces a first-order phase transition from the massive minimum. We argue that the MD terms must be avoided in order to satisfy the predictions of Lattice QCD, and we propose a MI solution that is valid in the limit which the magnetic fields are smaller than the squared of vacuum effective quark mass.

    ↳ hep-phhep-lathep-thnucl-thPRD(2024)·13 citations
  3. 06

    The three channels of many-body perturbation theory: , particle-particle, and electron-hole -matrix self-energies

    Roberto Orlando · Pina Romaniello · Pierre-François Loos

    We derive the explicit expression of the three self-energies that one encounters in many-body perturbation theory: the well-known self-energy, as well as the particle-particle and electron-hole -matrix self-energies. Each of these can be easily computed via the eigenvalues and eigenvectors of a different random-phase approximation (RPA) linear eigenvalue problem that completely defines their corresponding response function. For illustrative and comparative purposes, we report the principal ionization potentials of a set of small molecules computed at each level of theory. The performance of these schemes on strongly correlated systems (\ce{B2} and \ce{C2}) is also discussed.

    ↳ physics.chem-phcond-mat.mtrl-scicond-mat.str-elnucl-thJ.Chem.Phys.(2023)·5 citations
  4. 07

    Small systems and the single-hit approximation in the AMY parton cascade ALPACA

    Robin Törnkvist🇸🇪 · Korinna Zapp🇸🇪

    Understanding how momentum anisotropies arise in small collision systems is important for a quantitative understanding of collectivity in terms of QCD dynamics in small and large collision systems. In this letter we present results for small collision systems from the newly developed parton cascade \textsc{Alpaca}, which faithfully encodes the AMY effective kinetic theory. \textsc{Alpaca} reproduces quantitatively previously know results from a calculation in the single-hit approximation for small values of the coupling. We discuss in detail how such a comparison is to be carried out. Particularly at larger coupling a generic differences between the two approaches becomes apparent, namely that in parton cascades particles interact over a finite distance while in direct integrations of the Boltzmann equation the interactions are local. This leads to quantitative differences in the extracted values for the elliptic flow coefficient. These discrepancies appear in situations where the mean free path is not large compared to the interaction time and the applicability of kinetic theory is thus questionable.

    ↳ hep-phnucl-thPLB(2024)·4 citations

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first authorsco-authorsvia INSPIRE