nLab noncommutative open string theory

Context

String theory

Noncommutative geometry

Contents

Idea

It is known since Chu & Ho 1999 (and widely appreciated since Seiberg & Witten 1999) that limits of open string dynamics on D-branes with constant B-field potential effectively yield noncommutative field theories. Specifically, in the default case considered here, of spacelike B-field potential, there exists a clean limit where the string length scale α\alpha' goes to zero, and only point-particle excitations remains.

This is crucially different when the B-field potential BB has non-vanishing timelike components B 0iB_{0i} (corresponding to electric flux density of the Chan-Paton gauge field on the D-brane): In this case (Seiberg, Susskind & Toumbas 2000) there is a limiting critical field value, which keeps the string tension from diverging, while closed string interactions and hence gravity decouples. Therefore at the critical electric field strength one is left (not just with a noncommutative effective field theory but) with a pure open string theory on noncommutative space.

This decoupling limit is hence called noncommutative open string theory, abbreviated NCOS.

At least for open strings on D4-branes, this NCOS has a lift to M-theory (Bergshoeff, Berman, van der Schaar & Sundell 2000), namely to open membranes ending on M5-branes with critical self-dual 3-form flux density.

The corresponding decoupling limit should hence be a noncommutative open membrane theory and as such ought to be abbreviated NCOM but has come to be known just as “OM theory” (GMSS’00, apparently for the sake of the pun).

Properties

Parellel/dissolved M2-branes

In this OM theory limit, the angle vanishes between the M5-brane and the open M2-brane that ends on it (Berman & Sundell 2000 §3, Michishita 2000 p 9), making the M2-branes be parallel (lie entirely inside, be dissolved into) the M5 brane (not just their boundary M-strings). Cf. also Hanazawa & Sakaguchi 2018 §4.1.

References

NCOS Theory

The original observation of effective noncommutative geometry seen by open strings ending on D-branes with constant B-field gauge potential:

The original consideration of electric background flux and its NCOS limit:

Review:

Further discussion:

OM Theory

Precursor discussion:

The original discussion of the OM theory lift of NCOS to M-theory:

Further discussion:

Review:

The variant of lightlike instead of timelike flux:

and tentatively relating this to engineering of quantum Hall systems:

On the M2/M5-brane interaction angle, generally and in the OM theory limit, where the M2 is parallel to (lies inside, “dissolves” into) the M5

Last revised on April 20, 2026 at 20:36:50. See the history of this page for a list of all contributions to it.