D2branes

D2-branes are two-dimensional Dirichlet branes in type IIA string theory. They are extended objects on which open strings can end with Dirichlet boundary conditions in two spatial directions, giving them a three-dimensional worldvolume (two spatial dimensions plus time). A D2-brane carries Ramond-Ramond charge under the RR 3-form C3 and has a tension T2 = 1/((2π)^2 α'^{3/2} g_s) in string units.

In the low-energy limit with N coincident D2-branes, the dynamics on the worldvolume is described by a 2+1 dimensional U(N) supersymmetric Yang-Mills theory with 16 supercharges; the field content includes a U(N) gauge field, seven scalar fields representing transverse fluctuations, and fermions. The worldvolume action is given by the Dirac-Born-Infeld form supplemented by a Wess-Zumino term that encodes the coupling to RR potentials. The seven transverse scalars parameterize the motion in the seven directions perpendicular to the D2-brane.

D2-branes can form bound states with lower-dimensional branes, such as D0-branes, through the Chern-Simons couplings in the worldvolume action, and they can polarize in background RR fields via the Myers effect. They are also related to M-theory; under dimensional reduction of M-theory on a circle, M2-branes map to D2-branes in type IIA.

In brane constructions and holography, stacks of D2-branes realize 2+1 dimensional gauge theories and provide a setting for studying gauge/gravity duality. D2-branes, like other D-branes, are non-perturbative objects whose properties are constrained by supersymmetry, dualities, and RR charge conservation.