Path integral Monte Carlo calculations of dense hydrogen and helium thermodynamics

This paper is devoted to first-principles calculations of hydrogen and helium thermodynamics. We use the direct path integral Monte Carlo method to compute isochors and isotherms in a wide range of parameters in comparison with available theoretical and experimental results. New results for hydrogen and hydrogen-helium plasmas with the mass concentration of helium Y=0.988 are analysed with the help of a model based on the chemical picture.