Bayesian inference on isospin splitting of nucleon effective mass from giant resonances in ~(208)Pb

From a Bayesian analysis of the electric dipole polarizability, the constrained energy of isovector giant dipole resonance, the peak energy of isocalar giant quadrupole resonance, and the constrained energy of isocalar giant monopole resonance in ²⁰⁸Pb, we extract the isoscalar and isovector effective masses in nuclear matter at saturation density begin{document}$ rho_0 $end{document} as begin{document}$ m_{s,0}^{ast}/m = 0.87_{-0.04}^{+0.04} $end{document} and begin{document}$ m_{v,0}^{ast}/m = 0.78_{-0.05}^{+0.06} $end{document}, respectively, at 90% confidence level. The constraints obtained on begin{document}$ m_{s,0}^{ast} $end{document} and begin{document}$ m_{v,0}^{ast} $end{document} lead to a positive isospin splitting of nucleon effective mass in asymmetric nuclear matter of isospin asymmetry begin{document}$ delta $end{document} at begin{document}$ rho_0 $end{document} as begin{document}$ m_{n-p}^* / m = (0.20^{+0.15}_{-0.14})delta $end{document}. In addition, the symmetry energy at the subsaturation density begin{document}$ rho^{ast} = 0.05; mathrm{fm}^{-3} $end{document} is determined to be begin{document}$ E_{mathrm{sym}}(rho^{ast}) = 16.7pm1.3 $end{document} MeV at 90% confidence level.