On the residual Monge-Ampère mass of plurisubharmonic functions with symmetry in ${\mathbb{C}}^2$

The aim of this paper is to study the residual Monge-Ampère mass of a plurisubharmonic function with isolated singularity at the origin in ${\mathbb{C}}^2$. We prove that the residual mass is zero if its Lelong number is zero at the origin, provided that it is $S^1$-invariant. This result answers the zero mass conjecture raised by Guedj and Rashkovskii in this special case. More generally, we obtain an estimate on the residual mass by the maximal Lelong number and Lelong number at the origin.