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Nuclear Theory·nucl-th

Thursday·April 13, 2023

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    Building an Equation of State Density Ladder

    Marc Salinas · Jorge Piekarewicz

    The confluence of major theoretical, experimental, and observational advances are providing a unique perspective on the equation of state of dense neutron-rich matter -- particularly its symmetry energy -- and its imprint on the mass-radius relation for neutron stars. In this contribution we organize these developments in an equation of state density ladder. Of particular relevance to this discussion is the impact of the various rungs on the equation of state and the identification of possible discrepancies among the various methods. A preliminary analysis identifies a possible tension between laboratory measurements and gravitational-wave detections that could indicate the emergence of a phase transition in the stellar core.

    nucl-thastro-ph.HEastro-ph.SRnucl-exSymmetry(2023)·5 citations
  2. 02

    Relativistic bulk viscous fluids of Burgers type and their presence in neutron stars

    Lorenzo Gavassino

    It is well known that a mixture of two chemical components undergoing one chemical reaction is a bulk viscous fluid, where the bulk stress evolves according to the Israel-Stewart theory. Here, we show that a mixture of three independent chemical components undergoing two distinct chemical reactions can also be viewed as a bulk viscous fluid, whose bulk stress now is governed by a second-order differential equation which reproduces the Burgers model for viscoelasticity. This is a rigorous and physically motivated example of a fluid model where the viscous stress does not undergo simple Maxwell-Cattaneo relaxation, and can actually overshoot the Navier-Stokes stress. We show that, if one accounts for muons, neutron star matter is indeed a bulk viscous fluid of Burgers type.

    nucl-thgr-qcphysics.flu-dynClass.Quant.Grav.(2023)·20 citations
  3. 03

    Symmetry breaking and restoration on a fermionic quantum ring

    Joshua Cesca · Cédric Simenel

    Background: The Hartree-Fock mean-field approximation is standard in combination with energy density functionals (EDF) that account for some dynamical correlations. Breaking and restoring the symmetries of the system allow for the inclusion of additional static correlations. However, exact solutions to evaluate the effectiveness of these methods are rare. Purpose: To benchmark the Hartree-Fock method with broken and restored rotational symmetry in a system of identical interacting fermions on a one-dimensional quantum ring using model interactions. Method: The ground-state wave function is found using the Hartree-Fock method both with rotational invariance and with the symmetry broken at the mean-field level. Rotational symmetry is then restored with an angular momentum projection method. The ground-state energies are compared to variational Monte Carlo predictions. This is done for a range of different interactions between the particles. Results: Breaking the rotational symmetry in the Hartree-Fock mean-field brings little improvement to the ground-state energy in weakly repulsive systems or attractive systems confined on small rings. Larger improvements are found in strongly repulsive systems and attractive systems on larger rings in which the particles form a self-bound system. Symmetry restoration brought only small improvements in most cases but was able to account for most of the remaining correlation energy (after symmetry breaking) in repulsive systems. Conclusions: The effectiveness of incorporating correlations through rotational symmetry breaking followed by angular momentum projection is demonstrated for one-dimensional quantum rings using model interactions, encouraging generalisations to other symmetries, extensions to higher dimensions, as well as applications in the EDF framework.

    nucl-thcond-mat.otherPRC(2023)·1 citation
  4. 04

    Gravitational form factors of nuclei in the Skyrme model

    Alberto García Martín-Caro🇨🇱 · Yoshitaka Hatta🇨🇱 · Miguel Huidobro🇺🇸

    We compute the gravitational form factor of various nuclei in the generalized Skyrme model where nuclei are described as solitonic field configurations each with a definite baryon number . We separately discuss the cases (nucleons), (deuteron), (helium-3 and tritium) and extrapolate to larger -values. Configurations with are in general not spherically symmetric, and we demonstrate how group theory helps to extract the form factor. Numerical results are presented for the configurations with . We find that the -dependence is consistent with a power-law with . Other gravitational form factors can be calculated in the same framework, and we show the result for the form factor associated with angular momentum for the solution.

    nucl-thhep-phhep-thPRD(2023)·34 citations
  5. 05

    DoBe -- A Python Tool for Neutrinoless Double Beta Decay

    Oliver Scholer🇩🇪 · Jordy de Vries🇳🇱 · Lukáš Gráf🇺🇸

    We present DoBe, a Python tool for the computation of neutrinoless double beta decay () rates in terms of lepton-number-violating operators in the Standard Model Effective Field Theory (SMEFT). The tool can be used for automated calculations of rates, electron spectra and angular correlations for all isotopes of experimental interest, for lepton-number-violating operators up to and including dimension 9. The tool takes care of renormalization-group running to lower energies and provides the matching to the low-energy effective field theory and, at lower scales, to a chiral effective field theory description of rates. The user can specify different sets of nuclear matrix elements from various many-body methods and hadronic low-energy constants. The tool can be used to quickly generate analytical and numerical expressions for rates and to generate a large variety of plots. In this work, we provide examples of possible use along with a detailed code documentation. The code can be accessed through: GitHub: https://github.com/OScholer/nudobe Online User-Interface: https://nudobe.streamlit.app

    ↳ hep-phhep-exnucl-exnucl-thJHEP(2023)·30 citations
  6. 06

    Integrating by parts at finite density

    Juuso Österman🇫🇮 · Philipp Schicho🇫🇮 · Aleksi Vuorinen🇫🇮

    Both nonzero temperature and chemical potentials break the Lorentz symmetry present in vacuum quantum field theory by singling out the rest frame of the heat bath. This leads to complications in the application of thermal perturbation theory, including the appearance of novel infrared divergences in loop integrals and an apparent absence of four-dimensional integration-by-parts (IBP) identities, vital for high-order computations. Here, we propose a new strategy that enables the use of IBP techniques in the evaluation of Feynman integrals, in particular vacuum or bubble diagrams, in the limit of vanishing temperature but nonzero chemical potentials . The central elements of the new setup include a contour representation for the temporal momentum integral, the use of a small but nonzero as an IR regulator, and the systematic application of both temporal and spatial differential operators in the generation of linear relations among the loop integrals of interest. The relations we derive contain novel inhomogeneous terms featuring differentiated Fermi-Dirac distribution functions, which severely complicate calculations at nonzero temperature, but are shown to reduce to solvable lower-dimensional objects as tends to zero. Pedagogical example computations are kept at the one- and two-loop levels, but the application of the new method to higher-order calculations is discussed in some detail.

    ↳ hep-phhep-thnucl-thJHEP(2023)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE