Thermal conductivity of dense $np\mathrm{\Lambda }$ matter in neutron star cores

The possible presence of hyperons in the cores of massive neutron stars has important implications for their microscopic transport properties and thermal evolution. Despite recent progress in modelling core transport, a dedicated analysis regarding the thermal conductivity of a specific $np\mathrm{\Lambda }$ mixture remains absent from the existing literature. In this work, we investigate the thermal conductivity of dense, $\beta$-equilibrated $np\mathrm{\Lambda }$ matter within the framework of the variational linearized Boltzmann kinetic approach, employing the density-dependent DDME2 equation of state across a baryon density range of $(0.5\text{–}4.5)n_0$. We find that neutrons still dominate thermal transport, while the onset of $\mathrm{\Lambda }$ hyperons induces only a remarkably small reduction in neutron conductivity compared to pure nucleonic matter. These results suggests that the core thermal relaxation timescale remains practically unaltered in the presence of $\mathrm{\Lambda }$ hyperons.