nLab
Green-Schwarz action functional

Context

Quantum field theory

Phyics

Super-Geometry

Idea
Definition
Properties
- Siegel- or $κ$ -symmetry
- Dimensions – the brane scan
Related concepts
References

Idea

The Green-Schwarz action functional is the action functional of a sigma-model that describes the propagation of a fundamental $p$ -brane $Σ$ on a supermanifold spacetime.

For $p = 0$ this is the Green-Schwarz superparticle.
For $p = 1$ the Green-Schwarz superstring (at the center of attention in string theory).

This model is in contrast to the NSR-string, which instead has manifest worldsheet supersymmetry. See at superstring for more on this.

Definition

The Green-Schwarz action functionals are of the standard sigma-model form for target spaces that are super-homogeneous spaces $G / H$ for $G$ a Lie supergroup and $H$ a sub-super-group, and for background gauge fields that are super-WZW-circle n-bundles with connection/bundle gerbes on $G$ .

These action functionals were first considered in (Green-Schwarz 84) for superstrings in various dimensions. The full interpretation of the action functional as an higher Wess-Zumino-Witten theory-type action controled by the Lie algebra cohomology of the super Poincaré Lie algebra (or rather of the super translation Lie algebra inside it) is due to (Azcárraga-Townsend89).

Supercoordinates

We briefly review some basics of the canonical coordinates and the super Lie algebra cohomology of the super Poincaré Lie algebra and super Minkowski space, which are referred to below (Azcárraga-Townsend 89).

By the general discussion at Chevalley-Eilenberg algebra, we may characterize the super Poincaré Lie algebra $𝔰𝔦𝔰𝔬 (D - 1, 1)$ by its CE-algebra $CE (𝔰𝔦𝔰𝔬 (D - 1, 1))$ “of left-invariant 1-forms” on its group manifold.

Definition

The Chevalley-Eilenberg algebra $CE (𝔰𝔦𝔰𝔬 (d - 1, 1))$ is generated on

elements ${e^{a}}$ and ${ω^{a b}}$ of degree $(1, even)$
and elements ${ψ^{α}}$ of degree $(1, odd)$

with the differential defined by

d_{CE} ω^{a b} = ω^{a}_{b} \land ω^{b c}

d_{CE} e^{a} = ω^{a}_{b} \land e^{b} + \frac{i}{2} \bar{ψ} Γ^{a} ψ

d_{CE} ψ = \frac{1}{4} ω^{a b} Γ_{a b} ψ .

Removing the terms involving $ω$ here this is the super translation algebra.

In this way the super-Poincaré Lie algebra and its extensions is usefully discussed for instance in (D’Auria-Fré 82) and in (Azcárraga-Townsend 89, CAIB 99). In much of the literature instead the following equivalent notation is popular, which more explicitly involves the coordinates on super Minkowski space.

Remark

The abstract generators in def. 1 are identified with left invariant 1-forms on the super-translation group (= super Minkowski space) as follows.

Let $(x^{a}, θ^{α})$ be the canonical coordinates on the supermanifold $ℝ^{d ∣ N}$ underlying the super translation group. Then the identification is

$ψ^{α} = d θ^{α}$ .
$e^{a} = d x^{a} + \frac{i}{2} \bar{θ} Γ^{a} d θ$ .

Notice that this then gives the above formula for the differential of the super-vielbein in def. 1 as

\begin{aligned} d e^{a} & = d (d x^{a} + \frac{i}{2} \bar{θ} Γ^{a} d θ) \\ = \frac{i}{2} d \bar{θ} Γ^{a} d θ \\ = \frac{i}{2} \bar{ψ} Γ^{a} ψ \end{aligned} .

Remark

The term $\frac{i}{2} \bar{ψ} Γ^{a} ψ$ is sometimes called the supertorsion of the supervielbein $e$ , because the defining equation

d_{CE} e^{a} - ω^{a}_{b} \land e^{b} = \frac{i}{2} \bar{ψ} Γ^{a} ψ

may be read as saying that $e$ is torsion-free except for that term. Notice that this term is the only one that appears when the differential is applied to “Lorentz scalars”, hence to object in $CE (𝔰𝔦𝔰𝔬)$ which have “all indices contracted”.

Notably we have

d (\bar{ψ} \land Γ^{a_{1} \dots a_{p}} ψ \land e_{a_{1}} \land \dots \land e_{a_{p}}) \propto (\bar{ψ} \land Γ^{a_{1} \dots a_{p}} ψ \land e_{a_{1}} \land \dots \land e_{a_{p - 1}}) \land (\bar{Ψ} \land Γ_{a_{p}} Ψ) .

This remaining operation ” $e \mapsto Ψ^{2}$ ” of the differential acting on Loretz scalars is sometimes denoted ” $t_{0}$ ”, e.g. in (Bossard-Howe-Stelle 09, equation (8)).

This relation is what govers all of the exceptional super Lie algebra cocycles that appear as WZW terms for the Green-Schwarz action below: for some combinations of $(D, p)$ a Fierz identity implies that the term

(\bar{ψ} \land Γ^{a_{1} \dots a_{p}} ψ \land e_{a_{1}} \land \dots \land e_{a_{p - 1}}) \land (\bar{Ψ} \land Γ_{a_{p}} Ψ)

vanishes identically, and hence in these dimensions the term

\bar{ψ} \land Γ^{a_{1} \dots a_{p}} ψ \land e_{a_{1}} \land \dots \land e_{a_{p}}

is a cocycle. See also the brane scan table below.

Kinetic term

(…)

kinetic action

\int_{Σ} ⟨ ϕ^{*} Π^{a}, ϕ^{*} Π^{b} η_{a b} ⟩

(…)

WZW term

Let $(e^{a}, ω^{a b}, ψ^{α})$ be the standard generators of the Chevalley-Eilenberg algebra $CE (𝔰𝔦𝔰𝔬 (d, 1))$ of the super Poincaré Lie algebra, as discussed there.

The part of the Lie algebra cohomology of the super translation Lie algebra that is invariant under the Lorentz transformations is spanned by closed elements of the form

μ = (d \bar{θ} Γ_{a_{1}, \dots, a_{p}} \land d θ) \land Π^{a_{1}} \land \dots \land Π^{a_{p}} .

These exist (are closed) only for certain combinations of $d$ and $p$ . The possible values are listed below.

For a bosonic WZW model the background gauge field induced by such a cocycle would be the corresponding Lie integration to a circle n-bundle with connection. Here, since the super translation group is contractible, a Poincaré lemma applies and these circle $n$ -connections are simply given by globally defined connection form $β$ satisfying

d β = μ .

The WZW part of the GS action is then

S_{WZW} : ϕ \mapsto \int_{Σ} ϕ^{*} β

(…)

Properties

Siegel- or $κ$ -symmetry

The Green-Schwarz action has an extra fermionic symmetry, on top of the genuine supersymmetry, first observed in (Siegel 83) for the superparticle and in (Siegel 84) for the superstring in 3-dimensions, and finally in (GreenSchwarz 84) for the critical superstring in 10-dimensions. This is also called $κ$ -symmetry. It has a natural interpretation in terms of the super-Cartan geometry of target space (McArthur, GKW).

Dimensions – the brane scan

The Green-Schwarz action functional of a $p$ -brane propagating on an $d$ -dimensional target spacetimes makes sense only for special combinations of $(p, d)$ , for which there are suitanble super Lie algebra cocycles on the super translation Lie algebra (see above).

The corresponding table has been called the brane scan in the literature, now often called the “old brane scan”, since it has meanwhile been further completed (see below). In (Duff 87) the “old brane scan” is displayed as follows.

The brane scan

In the $D = 10$ -row we see the critical superstring of string theory and its magnetic dual, the NS5-brane. The top row shows the M2-brane in 11-dimensional supergravity.

Moving down and left the diagonals corresponds to double dimensional reduction.

Remark

The above table considers only $N = 1$ superspace, hence that of 11-dimensional supergravity and heterotic supergravity, but not of type II supergravity.

Remark

What is missing in the table is the M5-brane in that top dimension. (See also BPST). The reason is that the M5 corresponds to a 7-cocycle not on the ordinary super Poincaré Lie algebra, but on its L-infinity algebra extension, the supergravity Lie 3-algebra. See the 7-cocycle at supergravity Lie 6-algebra. And see at The brane bouquet.

Remark

According to (D’Auria-Fré 82, equation (3.14)) there is also a 12-cocycle in $D = 11$ , $p = 10$ (in our notation, theirs differs by an offset of $p$ by one). These authors, not thinking of GS-type $p$ -brane models, “dismiss” this cocycle (on the next page) on the grounds that a 12-cocycle cannot directly appear nontrivially in an 11-dimenesional action functional. In (AETW 87, p.3) super $p$ -branes are considered, but it says parenthetically “We exclude here the degenerate case of a $p$ -brane in $d = p + 1$ dimensions.”

So (with notation as above) we have the following.

The brane scan.

The Green-Schwarz type super $p$ -brane sigma-models (see at table of branes for further links):

$\overset{D}{=}$	$p =$	1	2	3	4	5	6	7	8	9
11			M2			M5
10	D0	F1, D1	D2	D3	D4	NS5, D5	D6	D7	D8	D9
9					$*$
8				$*$
7			$*$
6		$*$		$*$
5			$*$
4		$*$	$*$
3		$*$

The corresponding exceptional super L-∞ algebra cocycles (schematically, without prefactors):

$\overset{D}{=}$	1	2	3	4	5	6	7	8	9
11		$Ψ^{2} E^{2}$ on sIso(10,1)			$Ψ^{2} E^{5} + Ψ^{2} E^{2} C_{3}$ on m2brane
10	$Ψ^{2} E^{1}$ on sIso(9,1)	$B_{2}^{2} + B_{2} Ψ^{2} + Ψ^{2} E^{2}$ on StringIIA	$\dots$ on StringIIB	$B_{2}^{3} + B_{2}^{2} Ψ^{2} + B_{2} Ψ^{2} E^{2} + Ψ^{2} E^{4}$ on StringIIA	$Ψ^{2} E^{5}$ on sIso(9,1)	$B_{2}^{4} + \dots + Ψ^{2} E^{6}$ on StringIIA	$\dots$ on StringIIB	$B_{2}^{5} + \dots + Ψ^{2} E^{8}$ in StringIIA	$\dots$ on StringIIB
9				$Ψ^{2} E^{4}$ on sIso(8,1)
8			$Ψ^{2} E^{3}$ on sIso(7,1)
7		$Ψ^{2} E^{2}$ on sIso(6,1)
6	$Ψ^{2} E^{1}$ on sIso(5,1)		$Ψ^{2} E^{3}$ on sIso(5,1)
5		$Ψ^{2} E^{2}$ on sIso(4,1)
4	$Ψ^{2} E^{1}$ on sIso(3,1)	$Ψ^{2} E^{2}$ on sIso(3,1)
3	$Ψ^{2} E^{1}$ on sIso(2,1)

Related concepts

References

General

The Green-Schwarz action functional (formulated for the superstring) is due to

Michael Green, John Schwarz, Covariant description of superstrings, Phys. Lett. B136 (1984), 367–370 (web)

A standard textbook reference is appendix 4.A of volume 1 of

Michael Green, John Schwarz, Edward Witten, Superstring theory

and a brief paragraph in Volume II, section 10.2, page 983 of

Eric D'Hoker, String theory – lecture 10: Supersymmetry and supergravity , in part 3 of

Pierre Deligne, Pavel Etingof, Dan Freed, L. Jeffrey, David Kazhdan, John Morgan, D.R. Morrison and Edward Witten, eds. Quantum Fields and Strings, A course for mathematicians, 2 vols. Amer. Math. Soc. Providence 1999. (web version)

A more recent and more comprehensive review is

Joan Simón, Brane Effective Actions, Kappa-Symmetry and Applications, Living Reviews in relativity

WZW terms, super Lie algebra cohomology and the brane scan

The WZW nature of the second term in the GS action is discussed with its Lie theoretic meaning made fully explicit in chater 8 of

José de Azcárraga, Izqierdo, Lie Groups, Lie Algebras, Cohomology and Some Applications in Physics, Cambridge monographs of mathematical physics, (1995)

The original “brane scan” classification of GS action functionals by WZW terms is due to

A. Achucarro, J. M. Evans, Paul Townsend and D. L. Wiltshire, Super $p$ -Branes, Phys. Lett. B 198 (1987) 441

For $d = 11$ the relevant super Lie algebra cocycles have also been discussed (but not related to the Green-Schwarz action functional) in

Riccardo D'Auria, Pietro Fré, Geometric Supergravity in D=11 and its hidden supergroup, Nuclear Physics B201 (1982)

A review is in

Michael Duff, Supermembranes: the first fifteen weeks CERN-TH.4797/87 (1987) (scan)

from which the above table is taken.

Symmetries

That higher WZW functionals and hence Green-Schwarz super $p$ -brane action functionals should have “higher” extended symmetry algebras in some sense… is observes in

José de Azcárraga, Jerome P. Gauntlett, J.M. Izquierdo, Paul Townsend, Topological Extensions of the Supersymmetry Algebra for Extended Objects, Phys. Rev. Lett. 63 (1989) 2443 (web)

$κ$ -Symmetry

The existence of $κ$ -symmetry was first noticed around

Warren Siegel, Hidden Local Supersymmetry In The Supersymmetric Particle Action Phys. Lett. B 128, 397 (1983)

Warren Siegel, Light Cone Analysis Of Covariant Superstring , Nucl. Phys. B 236, 311 (1984).

Michael Green, John Schwarz, Covariant Description Of Superstrings , Phys. Lett. B 136, 367 (1984) (web)

The meaning of $κ$ -symmetry in terms of the super-Cartan geometry of super-target space is discussed in

I.N. McArthur, Kappa-Symmetry of Green-Schwarz Actions in Coset Superspaces (arXiv:hep-th/9908045)

Joaquim Gomis, Kiyoshi Kamimura, Peter West, Diffeomorphism, kappa transformations and the theory of non-linear realisations (arXiv:hep-th/0607104)

Open branes ending on other branes

Discussion of the Green-Schwarz action for the open M2-brane ending on the M5-brane is in

C.S. Chu, E. Sezgin, M-Fivebrane from the Open Supermembrane, JHEP 9712 (1997) 001 (arXiv:hep-th/9710223)
Ph. Brax, J. Mourad, Open Supermembranes Coupled to M-Theory Five-Branes, Phys.Lett. B416 (1998) 295-302 (arXiv:hep-th/9707246)

GS superstrings in various backgrounds

R. R. Metsaev, Type IIB Green-Schwarz superstring in plane wave Ramond-Ramond background (arXiv:hep-th/0112044)

Revised on June 17, 2013 23:02:59 by Urs Schreiber (89.204.153.85)

nLab
Green-Schwarz action functional

Context

Quantum field theory

Contents

Phyics

Surveys, textbooks and lecture notes

Super-Geometry

Formal context

Superalgebra

Supergeometry

Structures

Applications

Contents

Idea

Definition

Supercoordinates

Definition

Remark

Remark

Kinetic term

WZW term

Properties

Siegel- or $κ$ -symmetry

Dimensions – the brane scan

Remark

Remark

Remark

Related concepts

References

General

WZW terms, super Lie algebra cohomology and the brane scan

Symmetries

$κ$ -Symmetry

Open branes ending on other branes

GS superstrings in various backgrounds

nLab Green-Schwarz action functional

Context

Quantum field theory

Contents

Phyics

Surveys, textbooks and lecture notes

Super-Geometry

Formal context

Superalgebra

Supergeometry

Structures

Applications

Contents

Idea

Definition

Supercoordinates

Definition

Remark

Remark

Kinetic term

WZW term

Properties

Siegel- or κ-symmetry

Dimensions – the brane scan

Remark

Remark

Remark

Related concepts

References

General

WZW terms, super Lie algebra cohomology and the brane scan

Symmetries

κ-Symmetry

Open branes ending on other branes

GS superstrings in various backgrounds

nLab
Green-Schwarz action functional

Siegel- or $κ$ -symmetry

$κ$ -Symmetry