D0-brane ($p=0$)

A D0-brane is a point-like D-brane in space, with a one-dimensional worldvolume consisting only of time. It belongs to type IIA superstring theory and couples electrically to its one-form Ramond–Ramond potential. “Zero” counts spatial dimensions, rather than asserting zero mass or absence of dynamics.

Its mass scales as $1/(g_s\sqrt{{\alpha }^{\prime }})$, so it is heavy at weak string coupling. Unlike an ordinary perturbative string excitation, its open-string endpoints are fixed in every spatial direction for a static brane, while the brane's own position is a dynamical collective coordinate. The low-energy description of several nearby D0-branes is quantum mechanics of their worldvolume fields; it is not a field theory with an additional extended spatial direction.^[ref]