Nuclear Theory·nucl-th

Monday·August 27, 2018

8 papers—4 primary·4 cross-listed

01
Delineating Effects of Nuclear Symmetry Energy on the Radii and Tidal Polarizabilities of Neutron Stars
Nai-Bo Zhang · Bao-An Li
What can we learn about the density dependence of nuclear symmetry energy $E_{sym} (ρ)$ from precise measurements of the radius ( $R_{1.4}$ ) and/or tidal polarizability ( $Λ_{1.4}$ ) of canonical neutron stars (NSs) with a mass of 1.4 M $_{⊙}$ ? With the $E_{sym} (ρ)$ parameterized using three parameters $L$ , $K_{sym}$ , and $J_{sym}$ which have the asymptotic meaning of being respectively the slope, curvature, and skewness of symmetry energy at saturation density, we found that, while both the $R_{1.4}$ and $Λ_{1.4}$ depend strongly on the slope $L$ , the $K_{sym}$ and $J_{sym}$ parameters characterizing the high-density behavior of $E_{sym} (ρ)$ also play appreciable roles. Thus, there is not a simple relation between the $Λ_{1.4}$ / $R_{1.4}$ and $L$ alone. Precise measurements of just the $Λ_{1.4}$ and $R_{1.4}$ can not completely determine the $E_{sym} (ρ)$ but limit combinations of its parameters. In particular, stringent constraints approximately independent of the $J_{sym}$ on the $L$ - $K_{sym}$ correlations can be obtained. However, infinite combinations of the larger (smaller) $L$ and smaller (larger) $K_{sym}$ can lead to the same $Λ_{1.4}$ and $R_{1.4}$ . Additional observables including those from terrestrial nuclear experiments are thus necessary to break this degeneracy in order to completely determine the density dependence of nuclear symmetry energy $E_{sym} (ρ)$ .
nucl-thastro-ph.HEastro-ph.SRgr-qc+1J.Phys.G(2019)·60 citations
02
Adiabatic approach to large-amplitude collective motion with the higher-order collective-coordinate operator
Koichi Sato🇯🇵
We propose a new set of equations to determine the collective Hamiltonian including the second-order collective-coordinate operator on the basis of the adiabatic self-consistent collective-coordinate (ASCC) theory. We illustrate, with the two-level Lipkin model, that the collective operators including the second-order one are self-consistently determined. We compare the results of the calculations with and without the second-order operator and show that, without the second-order operator, the agreement with the exact solution becomes worse as the excitation energy increases, but that, with the second-order operator included, the exact solution is well reproduced even for highly excited states. We also reconsider which equations one should adopt as the basic equations in the case where only the first-order operator is taken into account, and suggest an alternative set of fundamental equations instead of the conventional ASCC equations. Moreover, we briefly discuss the gauge symmetry of the new basic equations we propose in this paper.
nucl-thPTEP(2018)·2 citations
03
A nuclear matter calculation with the tensor optimized Fermi sphere method using central interaction
Taiichi Yamada🇯🇵 · Takayuki Myo🇯🇵 · Hisashi Horiuchi🇯🇵 · Kiyomi Ikeda🇯🇵 · Hiroshi Toki🇯🇵
The tensor optimized Fermi sphere (TOFS) method is applied first for the study of the property of nuclear matter using the Argonne V4' $N N$ potential. In the TOFS method, the correlated nuclear matter wave function is taken to be a power-series-type of the correlation function $F$ , where $F$ can induce central, spin-isospin, tensor, etc.~correlations. This expression has been ensured by a cluster expansion theory. In the TOFS calculation, we take into account the contributions from all the many body terms arising from the product of the nuclear-matter Hamiltonian $H$ and $F$ . It is found that the density dependence of the energy per particle in nuclear matter is reasonably reproduced, in comparison with other methods such as the Brueckner-Hartree-Fock (BHF) approach.
nucl-thcond-mat.otherPTEP(2019)·10 citations
04
Exploring Bayesian parameter estimation for chiral effective field theory using nucleon-nucleon phase shifts
S. Wesolowski🇺🇸 · R. J. Furnstahl🇺🇸 · J. A. Melendez🇺🇸 · D. R. Phillips🇺🇸
We recently developed a Bayesian framework for parameter estimation in general effective field theories. Here we present selected results from using that framework to estimate parameters with a nucleon-nucleon (NN) potential derived using chiral effective field theory ( $χ$ EFT): the semi-local NN potential of Epelbaum, Krebs, and Meißner (EKM). There are many NN scattering data, up to high energies, and with rather small errors, so imposing a penalty for unnatural low-energy constants (LECs) usually has a small effect on the fits. In contrast, we have found that including an estimate of higher orders in $χ$ EFT plays an important role in robust parameter estimation.We present two case studies where our Bayesian machinery illuminates physics issues. The first involves the EKM potential at fourth order in the $χ$ EFT expansion: the two-dimensional posterior probability density function (pdf) for the fourth-order $s$ -wave LECs obtained from the Nijmegen PWA93 phase shifts indicates these parameters in the NN potential are degenerate. We trace this feature of the pdf to the presence of an operator in the fourth-order NN potential that vanishes on-shell. The second case study examines the stability of LEC extractions as more data at higher energies are included in the fit. We show that as long as $χ$ EFT truncation errors are properly accounted for in the parameter estimation, the LEC values extracted using our Bayesian approach are not sensitive to the maximum energy chosen for the fit.Uncorrelated and fully correlated models for the truncation errors are compared, pointing the way to the use of Gaussian processes to more generally model the correlation structure.
nucl-thJ.Phys.G(2019)·115 citations
05
$e^{+} e^{-}$ angularity distributions at NNLL $^{'}$ accuracy
Guido Bell🇩🇪 · Andrew Hornig🇺🇸 · Christopher Lee🇺🇸 · Jim Talbert🇩🇪
We present predictions for the $e^{+} e^{-}$ event shape angularities at NNLL $^{'}$ resummed and $O (α_{s}^{2})$ matched accuracy and compare them to LEP data at center-of-mass energies $Q = 91.2$ GeV and $Q = 197$ GeV. We perform the resummation within the framework of Soft-Collinear Effective Theory, and make use of recent results for the two-loop angularity soft function. We determine the remaining NNLL $^{'}$ and $O (α_{s}^{2})$ ingredients from a fit to the EVENT2 generator, and implement a shape function with a renormalon-free gap parameter to model non-perturbative effects. Using values of the strong coupling $α_{s} (m_{Z})$ and the universal non-perturbative shift parameter $Ω_{1}$ that are consistent with those obtained in previous fits to the thrust and $C$ -parameter distributions, we find excellent agreement between our predictions and the LEP data for all angularities with $a \in [- 1, 0.5]$ . This provides a robust test of the predictions of QCD, factorization, and the universal scaling of the non-perturbative shift across different angularities. Promisingly, our results indicate that current degeneracies in the ${α_{s} (m_{Z}), Ω_{1}}$ parameter space could be be alleviated upon fitting these parameters to experimental data for the angularity distributions.
↳ hep-phhep-exnucl-thJHEP(2019)·69 citations
06
Dynamical topological transitions in the massive Schwinger model with a {\theta}-term
T. V. Zache🇩🇪 · N. Mueller🇺🇸 · J. T. Schneider🇩🇪 · F. Jendrzejewski🇩🇪 · J. Berges🇩🇪 · P. Hauke🇩🇪
Aiming at a better understanding of anomalous and topological effects in gauge theories out-of-equilibrium, we study the real-time dynamics of a prototype model for CP-violation, the massive Schwinger model with a $θ$ -term. We identify dynamical quantum phase transitions between different topological sectors that appear after sufficiently strong quenches of the $θ$ -parameter. Moreover, we establish a general dynamical topological order parameter, which can be accessed through fermion two-point correlators and, importantly, which can be applied for interacting theories. Enabled by this result, we show that the topological transitions persist beyond the weak-coupling regime. Finally, these effects can be observed with table-top experiments based on existing cold-atom, superconducting-qubit, and trapped-ion technology. Our work, thus, presents a significant step towards quantum simulating topological and anomalous real-time phenomena relevant to nuclear and high-energy physics.
↳ quant-phcond-mat.quant-gascond-mat.str-elhep-ph+1PRL(2019)·121 citations
07
Stationary and non-stationary solutions of the evolution equation for neutrino in matter
A. V. Chukhnova🇷🇺 · A. E. Lobanov🇷🇺
We study solutions of the equation which describes the evolution of a neutrino propagating in dense homogeneous medium in the framework of the quantum field theory. In the two-flavor model the explicit form of Green function is obtained, and as a consequence the dispersion law for a neutrino in matter is derived. It is shown that there exist both the solutions describing the stationary states and the solutions describing the spin-flavor coherent states of the neutrino. The stationary states may be different from the mass eigenstates, and the wave function of a state with a definite flavor should be constructed as a linear combination of the wave functions of the stationary states with coefficients, which depend on the mixing angle in matter. In the ultra-relativistic limit the wave functions of the spin-flavor coherent states coincide with the solutions of the quasi-classical evolution equation. Quasi-classical approximation of the wave functions of spin-flavor coherent states is used to calculate the probabilities of transitions between neutrino states with definite flavor and helicity.
↳ hep-phhep-thnucl-thEPJ Web Conf.(2018)·1 citation
08
Density Renormalization Group for Classical Liquids
Satoshi Iso🇯🇵 · Kiyoharu Kawana🇯🇵
We study response of liquid to a scale transformation, which generates a change of the liquid density, and obtain a set of differential equations for correlation functions. The set of equations, which we call density renormalization group equations (DRGEs), is similar to the BBGKY hierarchy as it relates different multiple-point correlation functions. In particular, we derive DRGEs for one-particle irreducible vertex functions of liquid by performing Legendre transformations, which enables us to calculate properties of liquid at higher density in terms of correlation functions at lower density.
↳ cond-mat.stat-mechhep-thnucl-thPTEP(2019)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE