D-brane

A D-brane is a dynamical object in string theory on which open strings can end. Dirichlet boundary conditions fix the strings’ endpoints in directions transverse to the brane.

Open string: A string with two endpoints, whose allowed boundary conditions shape its spectrum and interactions. Its endpoints can be constrained to lie on a D-brane.
String theory: A framework in which fundamental particles are modeled as one-dimensional strings whose vibrational states represent different particles. D-branes arise as dynamical objects in this framework.
Joseph Polchinski: An American theoretical physicist whose work established the role of D-branes in string theory. His 1995 work identified D-branes as carriers of Ramond–Ramond charge.
D-brane gauge theory: A gauge theory arising from open strings ending on a stack of coincident D-branes. The massless open-string modes describe gauge fields on the branes.
Neumann boundary condition: A boundary condition that sets a field’s normal derivative to zero at a boundary. Open-string directions along a D-brane obey Neumann rather than Dirichlet conditions.
Worldvolume: The space traced out by an object through time, including its spatial dimensions. Fields living on a D-brane are described over its worldvolume.
Superstring theory: String theory incorporating supersymmetry, with consistent versions requiring ten spacetime dimensions. D-branes are especially central to its open-string sectors and dualities.
Dirichlet boundary condition: A boundary condition that fixes a field’s value at a boundary; for open strings, it fixes endpoint positions in transverse directions. The name D-brane comes from this condition on open-string endpoints.
AdS/CFT correspondence: A duality relating a gravitational theory in anti-de Sitter space to a conformal field theory on its boundary. A stack of D3-branes provides the canonical setting for its gauge/gravity correspondence.
NS5-brane: A five-dimensional spatial brane carrying magnetic charge under the Neveu–Schwarz two-form field. Unlike a D-brane, it is magnetically charged under an NS–NS field rather than a Ramond–Ramond field.

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BraneBroader topic: D-branes are a well-studied class of branes that make the general idea concrete.