Improved hard-thermal-loop effective actions

Hard thermal loop effective actions furnish the building blocks of resummed thermal perturbation theory, which is expected to work as long as the quantities under consideration are not sensitive to the nonperturbative (chromo-)magnetostatic sector. A different breakdown of perturbation theory occurs whenever external momenta are light-like, because the hard thermal loops themselves develop collinear singularities. By additionally resumming asymptotic thermal masses for hard modes these singularities are removed while leaving the gauge invariance of the effective action intact.