D3brane

D3-brane (often written as D3-brane) is a type of dynamical object in type IIB string theory with three spatial dimensions extending in spacetime. It is a 3+1 dimensional hypersurface on which open strings can end, and it carries Ramond-Ramond charge associated with the four-form potential C4. In a supersymmetric background it is a BPS object, preserving part of the background supersymmetry.

When N D3-branes coincide, the massless modes of open strings stretching between the branes give rise to a non-Abelian gauge theory on the common worldvolume. The low-energy theory on the worldvolume is a four-dimensional, maximally supersymmetric Yang–Mills theory with gauge group U(N) (equivalently SU(N) in the simply connected case).

In the supergravity limit, the near-horizon geometry of N coincident D3-branes is the product space AdS5 × S5 with equal radii. The radius is set by the string coupling g_s, the number of branes N, and the string length α′, and the five-form flux through S5 is quantized in terms of N.

This setup underpins the AdS/CFT correspondence, also known as gauge/gravity duality. It posits an equivalence between type IIB string theory on AdS5 × S5 and four-dimensional N=4 SU(N) super Yang–Mills theory at large N and strong coupling, providing a framework to study strongly coupled gauge dynamics via a gravity dual.

D3-branes also appear as solutions of type IIB supergravity; moving or separating branes corresponds to giving expectation values to scalars on the worldvolume and breaks the gauge symmetry via strings stretched between branes.