Unweighted Hardy inequalities on the Heisenberg group and in step-two Carnot groups

We establish unweighted Hardy-type inequalities on step-two Carnot groups with one-dimensional vertical layer, with explicit lower bounds for the optimal Hardy constant. The approach is based on a quantitative integration-by-parts mechanism that replaces the non-horizontal Euler vector field by a suitably constructed horizontal vector field with controlled norm. As applications, we obtain fully explicit bounds in the Heisenberg group for both the Kor{à}nyi gauge and the Carnot--Carath{é}odory distance, and we extend the results to non-isotropic step-two structures through a generalized Kor{à}nyi-type homogeneous norm.