nLab electric-magnetic duality




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Electric-magnetic duality is a lift of Hodge duality from de Rham cohomology to ordinary differential cohomology.


Consider a circle n-bundle with connection \nabla on a space XX. Its higher parallel transport is the action functional for the sigma-model of (n1)(n-1)-dimensional objects ((n1)(n-1)-branes) propagating in XX.

For n=1n = 1 this is the coupling of the electromagnetic field to particles. For n=2n = 2 this is the coupling of the Kalb-Ramond field to strings.

The curvature F Ω n+1(X)F_\nabla \in \Omega^{n+1}(X) is a closed (n+1)(n+1)-form. The condition that its image F \star F_\nabla under the Hodge star operator is itself closed

d dRF =0 d_{dR} \star F_\nabla = 0

is the Euler-Lagrange equation for the standard (abelian Yang-Mills theory-action functional on the space of circle n-bundle with connection.

If this is the case, it makes sense to ask if F \star F_\nabla itself is the curvature (d(n+1))(d-(n+1))-form of a circle (d(n+1)1)(d-(n+1)-1)-bundle with connection ˜\tilde \nabla, where d=dimXd = dim X is the dimension of XX.

If such ˜\tilde \nabla exists, its higher parallel transport is the gauge interaction action functional for (dn3)(d-n-3)-dimensional objects propagating on XX.

In the special case of ordinary electromagnetism with n=1n=1 and d=4d = 4 we have that electrically charged 0-dimensional particles couple to \nabla and magnetically charged (4(1+1)2)=0(4-(1+1)-2) = 0-dimensional particles couple to ˜\tilde \nabla.

In analogy to this case one calls generally the dn3d-n-3-dimensional objects coupling to ˜\tilde \nabla the magnetic duals of the (n1)(n-1)-dimensional objects coupling to \nabla.


For d=4d= 4 EM-duality is the special abelian case of S-duality for Yang-Mills theory. Witten and Kapustin argued that this is governed by the geometric Langlands correspondence.


electric-magnetic duality of D-branes/RR-fields in type II string theory:

electric chargemagnetic charge
  • M2-brane and M5-brane: the 4-form G 4G_4 which the M2-brane couples to is the Hodge-dual of the 7-form G 7G_7 which the M5-brane couples to
G 7=G 4 G_7 = \star G_4

as imposed by the equations of motion for 11d supergravity (see here). The associated C3-field and C6-field are electric-magnetic duals.

duality in physics, duality in string theory


Detailed review is in

It was originally noticed in

that where electric charge in Yang-Mills theory takes values in the weight lattice of the gauge group, then magnetic charge takes values in the lattice of what is now called the Langlands dual group.

This led to the electric/magnetic duality conjecture formulation in

According to (Kapustin-Witten 06, pages 3-4) the observation that the Montonen-Olive dual charge group coincides with the Langlands dual group is due to

See also the references at S-duality.

The insight that the Montonen-Olive duality works more naturally in super Yang-Mills theory is due to

and that it works particularly for N=4 D=4 super Yang-Mills theory is due to

  • H. Osborn, Topological Charges For N=4N = 4 Supersymmetric Gauge Theories And Monopoles Of Spin 1, Phys. Lett. B83 (1979) 321-326.

The observation that the 2\mathbb{Z}_2 electric/magnetic duality extends to an SL(2,)SL(2,\mathbb{Z})-action in this case is due to

  • John Cardy, E. Rabinovici, Phase Structure Of Zp Models In The Presence Of A Theta Parameter, Nucl. Phys. B205 (1982) 1-16;

  • John Cardy, Duality And The Theta Parameter In Abelian Lattice Models, Nucl. Phys. B205 (1982) 17-26.

  • A. Shapere and Frank Wilczek, Selfdual Models With Theta Terms, Nucl. Phys. B320 (1989) 669-695.

and specifically the embedding of this into string theory S-duality originates in

  • Ashoke Sen, Dyon - Monopole Bound States, Self-Dual Harmonic Forms on the Multi-Monopole Moduli Space, and SL(2,)SL(2,\mathbb{Z}) Invariance in String Theory (arXiv:hep-th/9402032)

The understanding of this SL(2,)SL(2,\mathbb{Z})-symmetry as a remnant conformal transformation on a 6-dimensional principal 2-bundle-theory – the 6d (2,0)-superconformal QFT – compactified on a torus is described in

The relation of S-duality to geometric Langlands duality was understood in

Exposition of this is in

  • Edward Frenkel, What Do Fermat’s Last Theorem and Electro-magnetic Duality Have in Common? KITP talk 2011 (web)

A perspective unifying EM-duality of higher gauge theories with non-abelian T-duality:

An arithmetic version of EM-duality:

Last revised on July 11, 2023 at 14:43:23. See the history of this page for a list of all contributions to it.