Reconciliation between Neutron Skin Thickness from PREX-2 Experiment and Neutron-Star Tidal Polarizability from GW170817 Event: The Key Role of Symmetry Energy Curvature

The GW170817 neutron star merger event and the PREX-2 experiment probing neutron skin thickness provide crucial clues for understanding the nuclear equation of state (EoS). However, an apparent inconsistency exists between the tidal polarizability Λ^{1.4} inferred from GW170817 and the neutron skin thickness R_{np}^{208} of ^{208}Pb measured by PREX-2, based on relativistic energy density functionals (EDFs). This Letter employs both relativistic and nonrelativistic EDFs to identify a multipole correlation involving Λ^{1.4}, R_{np}^{208}, and the symmetry energy curvature K_{sym} at saturation density. We demonstrate the essential role of K_{sym} in reconciling the conflicting Λ^{1.4}-R_{np}^{208} correlations derived from nonrelativistic versus relativistic EDFs and in resolving the discrepancy between the GW170817 and PREX-2 data constraints. Furthermore, we obtain a joint constraint on K_{sym} from these datasets, providing a vital constraint on the symmetry energy of the nuclear EoS.