Nuclear Theory

The three-dimensional tilted axis cranking covariant density functional theory (3D-TAC CDFT) is used to study the chiral modes in 135 Nd. By modeling the motion of the nucleus in rotating mean field as the interplay between the single-particle motions of several valence particle(s) and hole(s) and the collective motion of a core-like part, a classical Routhian is extracted. This classical Routhian gives qualitative agreement with the 3D-TAC CDFT result for the critical frequency corresponding to the transition from planar to aplanar rotation. Based on this investigation a possible understanding of tilted rotation appearing in a microscopic theory is provided.

The critical properties for the transition to warm, asymmetric, non-homogeneous nuclear matter are analysed within a thermodynamical spinodal approach for a set of well calibrated equations of state. It is shown that even though different equations of state are constrained by the same experimental, theoretical and observational data, and the properties of symmetric nuclear matter are similar within the models, the properties of very asymmetric nuclear matter, such as the one found inside of neutron stars, differ a lot for various models. Some models predict larger transition densities to homogeneous matter for beta-equilibrated matter than for symmetric nuclear matter. Since one expects that such properties have a noticeable impact on the the evolution of either a supernova or neutron star merger, this different behavior should be understood in more detail.

The geometry of fireballs in relativistic heavy ion collisions is approximated by a static box, which is infinite in two directions while finite in the other direction. The critical temperature of deconfinement phase transition is calculated explicitly in the MIT bag model at vanishing baryon density. It is found that the critical temperature shifts to a value higher than that in an unconstrained space.

Modeling nuclear reaction networks for nuclear science applications and for simulations of astrophysical environments relies on cross section data for a vast number of reactions, many of which have never been measured. In this paper we examine the validity of the Weisskopf-Ewing approximation for determining unknown (n,n') and (n, 2n) cross sections from surrogate data. Using statistical reaction calculations with realistic parameterizations, we investigate first whether the assumptions underlying the Weisskopf-Ewing approximation are valid for (n,n') and (n, 2n) reactions on representative target nuclei. We then produce simulated surrogate reaction data and assess the impact of applying the Weisskopf-Ewing approximation when extracting (n,n') and (n, 2n) cross sections in situations where the approximation is not strictly justified. We find that peak cross sections can be estimated using the Weisskopf-Ewing approximation, but the shape of the (n,n') and (n,2n) cross sections, especially for low neutron energies, cannot be reliably determined without accounting for the angular-momentum differences between the neutron-induced and the surrogate reaction.

The nuclear symmetry energy plays an important role in the description of the properties of finite nuclei as well as neutron stars. Especially, for low values of baryon density, the accurate description of the crust-core interface strongly depends on the symmetry energy. Usually, the well known parabolic approximation is employed for the definition of the symmetry energy without avoiding some drawbacks. In the present work, a class of nuclear models, suitable for the description of the inner and outer core of neutron stars, is applied in studying the effect of higher orders of the expansion of the energy on the location of the crust-core transition. The thermodynamical and dynamical methods are used for the determination of the transition density n t and pressure P t . The corresponding energy density functional is applied for the study of some relevant properties of both non-rotating and slow rotating neutron stars. We found that the larger the value of the slope parameter L , the slower the convergence of the expansion. In addition, a universal relation is presented between n t and L , by employing the full expression and dynamical approach. The crustal moment of inertia is very sensitive on the location of the transition while the effects are moderated concerning the critical angular velocity of the r-mode instability and minimum mass configuration. The effect on the tidal deformability is less but not negligible. In any case, the use of the parabolic approximation leads to the overestimation of n t and P t and consequently, on inaccurate predictions.

The high-order cumulants and factorial cumulants of conserved charges are suggested to study the critical dynamics in heavy ion collisions. In this paper, using parametric representation of the 3-dimensional Ising model, the sign distribution on the phase diagram and temperature dependence of the cumulants and factorial cumulants is studied and compared. In the vicinity of the critical point, the cumulants and factorial cumulants can not be distinguished. Far away from the critical point, sign changes occur in the factorial cumulants comparing with the same order cumulants. The cause of these sign changes is analysed. They may be used to measure the distance to the critical point.

It is shown how high-order cumulants of net-charge distribution in hadronic collisions at LHC energies can be expressed via lower-order terms under the assumption that particle-antiparticle pairs are produced in independent local processes. It is argued and tested with HIJING model that this assumption is typically valid for net-proton fluctuations in the case when no critical behaviour is present in the system. Values estimated in such a way can be considered as baselines for direct measurements of high-order net-charge fluctuations in real data.

Background: The nuclear symmetry energy E sym (ρ) encodes information about the energy necessary to make nuclear systems more neutron-rich. While its slope parameter L at the saturation density ρ 0 of nuclear matter has been relatively well constrained by recent astrophysical observations and terrestrial nuclear experiments, its curvature K sym characterizing the E sym (ρ) around 2 ρ 0 remains largely unconstrained. Over 520 calculations for E sym (ρ) using various nuclear theories and interactions in the literature have predicted several significantly different K sym −L correlations. Purpose: If a unique K sym −L correlation of E sym (ρ) can be firmly established, it will enable us to progressively better constrain the high-density behavior of E sym (ρ) using the available constraints on its slope parameter L. We investigate if and by how much the different K sym −L correlations may affect neutron star observables. Method: A meta-model of nuclear Equation of States (EOSs) with three representative K sym −L correlation functions is used to generate multiple EOSs for neutron stars. We then examine effects of the K sym −L correlation on the crust-core transition density and pressure as well as the radius and tidal deformation of canonical neutron stars. Results:The K sym −L correlation affects significantly both the crust-core transition density and pressure. It also has strong imprints on the radius and tidal deformability of canonical neutron stars especially at small L values. The available data from LIGO/VIRGO and NICER set some useful limits for the slope L but can not distinguish the three representative K sym −L correlations considered.

Three-nucleon forces are an essential ingredient for an accurate description of nuclear few- and many-body systems. However, implementing them directly in many-body calculations is technically very challenging. Thus, there is a need for an efficient approximation method. By closing one nucleon line to a loop, it is possible to derive effective in-medium nucleon-nucleon interactions that represent the underlying three-nucleon forces, as constructed in Chiral Effective Field Theory. Since three-neutron forces are equally as important for the computation of the equation of state for pure neutron matter, this work applies the aforementioned approach to the subleading chiral three-neutron forces, in particular the short-range terms and relativistic corrections. It is shown in this work that, while many contributions to the in-medium neutron-neutron interaction are - apart from a constant factor - identical to the terms in isospin-symmetric matter, some differ drastically. Moreover, previously vanishing terms yield now non-zero contributions. As a result of this work, density-dependent in-medium neutron-neutron potentials are now available for the implementation in nuclear many-body calculations, either in closed analytical form, or requiring at most one numerical integration.

We present a critical assessment of the calculation and uncertainty of the 214 Pb → 214 Bi ground state to ground state β decay, the dominant source of background in liquid Xenon dark matter detectors, down to below 1 keV. We consider contributions from atomic exchange effects, nuclear structure and radiative corrections. For each of these, we find changes much larger than previously estimated uncertainties and discuss shortcomings of the original calculation. Specifically, through the use of a self-consistent Dirac-Hartree-Fock-Slater calculation, we find that the atomic exchange effect increases the predicted flux by 10(3)% at 1 keV relative to previous exchange calculations. Further, using a shell model calculation of the nuclear structure contribution to the shape factor, we find a strong disagreement with the allowed shape factor and discuss several sources of uncertainty. In the 1-200 keV window, the predicted flux is up to 20 % lower. Finally, we discuss omissions and detector effects in previously used QED radiative corrections, and find small changes in the slope at the ≳1% MeV −1 level, up to 3% in magnitude due to omissions in O(Z α 2 , Z 2 α 3 ) corrections and 3.5% uncertainty from the neglect of as of yet unavailable higher-order contributions. Combined, these give rise to an increase of at least a factor 2 of the uncertainty in the 1-200 keV window. We comment on possible experimental schemes of measuring this and related transitions.