Lie superalgebra

In mathematics, a Lie superalgebra is a generalisation of a Lie algebra to include a Z₂-grading. Lie superalgebras are important in theoretical physics where they are used to describe the mathematics of supersymmetry. In most of these theories, the even elements of the superalgebra correspond to bosons and odd elements to fermions (but this is not always true; for example, the BRST supersymmetry is the other way around).

Definition

Formally, a Lie superalgebra is a (nonassociative) Z₂-graded algebra, or superalgebra, over a commutative ring (typically R or C) whose product [·, ·], called the Lie superbracket or supercommutator, satisfies the two conditions (analogs of the usual Lie algebra axioms, with grading):

Super skew-symmetry:

[x,y]=-(-1)^{|x| |y|}[y,x].\

The super Jacobi identity:^[1]

(-1)^{|x||z|}[x,[y,z]]+(-1)^{|y||x|}[y,[z,x]]+(-1)^{|z||y|}[z,[x,y]]=0,

where x, y, and z are pure in the Z₂-grading. Here, |x| denotes the degree of x (either 0 or 1). The degree of [x,y] is the sum of degree of x and y modulo 2.

One also sometimes adds the axioms $[x,x]=0$ for |x| = 0 (if 2 is invertible this follows automatically) and $[[x,x],x]=0$ for |x| = 1 (if 3 is invertible this follows automatically). When the ground ring is the integers or the Lie superalgebra is a free module, these conditions are equivalent to the condition that the Poincaré–Birkhoff–Witt theorem holds (and, in general, they are necessary conditions for the theorem to hold).

Just as for Lie algebras, the universal enveloping algebra of the Lie superalgebra can be given a Hopf algebra structure.

A graded Lie algebra (say, graded by Z or N) that is anticommutative and Jacobi in the graded sense also has a $Z_{2}$ grading (which is called "rolling up" the algebra into odd and even parts), but is not referred to as "super". See note at graded Lie algebra for discussion.

Properties

Let ${\mathfrak {g}}={\mathfrak {g}}_{0}\oplus {\mathfrak {g}}_{1}$ be Lie superalgebra. By inspecting the Jacobi identity, one sees that there are eight cases depending on whether arguments are even or odd. These fall into four classes, indexed by the number of odd elements:^[2]

No odd elements. The statement is just that ${\mathfrak {g}}_{0}$ is an ordinary Lie algebra.
One odd element. Then ${\mathfrak {g}}_{1}$ is a ${\mathfrak {g}}_{0}$ -module for the action $\mathrm {ad} _{a}:b\rightarrow [a,b],\quad a\in {\mathfrak {g}}_{0},\quad b,[a,b]\in {\mathfrak {g}}_{1}$ .
Two odd elements. The Jacobi identity says that the bracket ${\mathfrak {g}}_{1}\otimes {\mathfrak {g}}_{1}\rightarrow {\mathfrak {g}}_{0}$ is a symmetric ${\mathfrak {g}}_{1}$ -map.
Three odd elements. For all $b\in {\mathfrak {g}}_{1}$ , $[b,[b,b]]=0$ .

Thus the even subalgebra ${\mathfrak {g}}_{0}$ of a Lie superalgebra forms a (normal) Lie algebra as all the signs disappear, and the superbracket becomes a normal Lie bracket, while ${\mathfrak {g}}_{1}$ is a linear representation of ${\mathfrak {g}}_{0}$ , and there exists a symmetric ${\mathfrak {g}}_{0}$ -equivariant linear map $\{\cdot ,\cdot \}:{\mathfrak {g}}_{1}\otimes {\mathfrak {g}}_{1}\rightarrow {\mathfrak {g}}_{0}$ such that,

[\left\{x,y\right\},z]+[\left\{y,z\right\},x]+[\left\{z,x\right\},y]=0,\quad x,y,z\in {\mathfrak {g}}_{1}.

Conditions (1)–(3) are linear and can all be understood in terms or ordinary Lie algebras. Condition (4) is nonlinear, and is the most difficult one to verify when constructing a Lie superalgebra starting from an ordinary Lie algebra ( ${\mathfrak {g}}_{0}$ ) and a representation ( ${\mathfrak {g}}_{1}$ ).

Involution

A ^∗ Lie superalgebra is a complex Lie superalgebra equipped with an involutive antilinear map from itself to itself which respects the Z₂ grading and satisfies [x,y]^* = [y^*,x^*] for all x and y in the Lie superalgebra. (Some authors prefer the convention [x,y]^* = (−1)^|x||y|[y^*,x^*]; changing * to −* switches between the two conventions.) Its universal enveloping algebra would be an ordinary ^*-algebra.

Examples

Given any associative superalgebra $A$ one can define the supercommutator on homogeneous elements by

[x,y] = xy - (-1)^{|x||y|}yx\

and then extending by linearity to all elements. The algebra $A$ together with the supercommutator then becomes a Lie superalgebra. The simplest example of this procedure is perhaps when $A$ is the space of all linear functions $\mathbf {End} (V)$ of a super vector space $V$ to itself. When $V=\mathbb {K} ^{p|q}$ , this space is denoted by $M^{p|q}$ or $M(p|q)$ .^[3] With the Lie bracket per above, the space is denoted ${\mathfrak {gl}}(p|q)$ .^[4]

The Whitehead product on homotopy groups gives many examples of Lie superalgebras over the integers.

Classification

The simple complex finite-dimensional Lie superalgebras were classified by Victor Kac.

The basic classical compact Lie superalgebras (that are not Lie algebras) are:

SU(m/n) These are the superunitary Lie algebras which have invariants:

z.\overline{z}+iw.\overline{w}

This gives two orthosymplectic (see below) invariants if we take the m z variables and n w variables to be non-commutative and we take the real and imaginary parts. Therefore, we have

SU(m/n)=OSp(2m/2n)\cap OSp(2n/2m)

SU(n/n)/U(1) A special case of the superunitary Lie algebras where we remove one U(1) generator to make the algebra simple.

OSp(m/2n) These are the orthosymplectic groups. They have invariants given by:

x.x+y.z-z.y

for m commutative variables (x) and n pairs of anti-commutative variables (y,z). They are important symmetries in supergravity theories.

D(2/1; $\alpha$ ) This is a set of superalgebras parameterised by the variable $\alpha$ . It has dimension 17 and is a sub-algebra of OSp(9|8). The even part of the group is O(3)×O(3)×O(3). So the invariants are:

A_\mu A_\mu+B_\mu B_\mu+C_\mu C_\mu +\psi^{\alpha \beta \gamma}\psi^{\alpha' \beta' \gamma'}\varepsilon_{\alpha \alpha'}\varepsilon_{\beta \beta'}\varepsilon_{\gamma \gamma'}

A_{\{1}A_{2}A_{3\}}+B_{\{1}B_{2}B_{3\}}+C_{\{1}C_{2}C_{3\}}+A_{\mu }\Gamma _{\mu }^{\alpha \alpha '}\psi \psi +B_{\mu }\Gamma _{\mu }^{\beta \beta '}\psi \psi +C_{\mu }\Gamma _{\mu }^{\gamma \gamma '}\psi \psi

for particular constants $\gamma$ .

F(4) This exceptional Lie superalgebra has dimension 40 and is a sub-algebra of OSp(24|16). The even part of the group is O(3)xSO(7) so three invariants are:

B_{\mu \nu} + B_{\nu \mu} = 0

A_\mu A_\mu + B_{\mu \nu}B_{\mu \nu} + \psi_{\{1}^\alpha \psi_{2\}}^\alpha

A_{\{1}A_{2}A_{3\}}+B_{\{\mu \nu }B_{\nu \tau }B_{\tau \mu \}}+B_{\mu \nu }\sigma _{\mu \nu }^{\alpha \beta }\psi _{k}^{\alpha }\psi _{k}^{\beta }+A_{\mu }\Gamma _{\mu }^{\alpha \beta }\psi _{\alpha }^{k}\psi _{\beta }^{k}+({\text{sym.}})

This group is related to the octonions by considering the 16 component spinors as two component octonion spinors and the gamma matrices acting on the upper indices as unit octonions. We then have $f^{\mu \nu \tau }\sigma _{\nu \tau }\equiv \gamma _{\mu }$ where f is the structure constants of octonion multiplication.

G(3) This exceptional Lie superalgebra has dimension 31 and is a sub-algebra of OSp(17|14). The even part of the group is O(3)×G2. The invariants are similar to the above (it being a subalgebra of the F(4)?) so the first invariant is:

A_{\mu }A_{\mu }+C_{\alpha }^{\mu }C_{\alpha }^{\mu }+\psi _{\{1}^{\mu }\psi _{2\}}^{\nu }

There are also two so-called strange series called p(n) and q(n).

Classification of infinite-dimensional simple linearly compact Lie superalgebras

The classification consists of the 10 series W(m, n), S(m, n) ((m, n) ≠ (1, 1)), H(2m, n), K(2m + 1, n), HO(m, m) (m ≥ 2), SHO(m, m) (m ≥ 3), KO(m, m + 1), SKO(m, m + 1; β) (m ≥ 2), SHO ∼ (2m, 2m), SKO ∼ (2m + 1, 2m + 3) and the five exceptional algebras:

E(1, 6), E(5, 10), E(4, 4), E(3, 6), E(3, 8)

The last two are particularly interesting (according to Kac) because they have the standard model gauge group SU(3)×SU(2)×U(1) as their zero level algebra. Infinite-dimensional (affine) Lie superalgebras are important symmetries in superstring theory.

Category-theoretic definition

In category theory, a Lie superalgebra can be defined as a nonassociative superalgebra whose product satisfies

$[\cdot ,\cdot ]\circ ({\operatorname {id} }+\tau _{A,A})=0$
$[\cdot ,\cdot ]\circ ([\cdot ,\cdot ]\otimes {\operatorname {id} }\circ ({\operatorname {id} }+\sigma +\sigma ^{2})=0$

where σ is the cyclic permutation braiding $({\operatorname {id} }\otimes \tau _{A,A})\circ (\tau _{A,A}\otimes {\operatorname {id} })$ . In diagrammatic form:

Notes

References

Cheng, S.-J.; Wang, W. (2012). Dualities and Representations of Lie Superalgebras. Graduate Studies in Mathematics. 144. pp. 302pp. ISBN 978-0-8218-9118-6.
Freund, P. G. O. (1983). Introduction to supersymmetry. Cambridge Monographs on Mathematical Physics. Cambridge University Press. ISBN 978-0521-356-756. doi:10.1017/CBO9780511564017.
Grozman, P.; Leites, D.; Shchepochkina, I. (1997). "Lie Superalgebras of String Theories". Acta Mathamatica Vietnamica. 26 (2005): 27–63. arXiv:hep-th/9702120v1 .
Kac, V. G. (1977). "Lie superalgebras". Advances in Mathematics. 26 (1): 8–96. doi:10.1016/0001-8708(77)90017-2.
Manin, Y. I. (1997). Gauge Field Theory and Complex Geometry ((2nd ed.) ed.). Berlin: Springer. ISBN 3-540-61378-1.
Musson, I. M. (2012). Lie Superalgebras and Enveloping Algebras. Graduate Studies in Mathematics. 131. pp. 488 pp. ISBN 978-0-8218-6867-6.
Varadarajan, V. S. (2004). Supersymmetry for Mathematicians: An Introduction. Courant Lecture Notes in Mathematics. 11. American Mathematical Society. ISBN 978-0-8218-3574-6.

Historical

Frölicher, A.; Nijenhuis, A. (1956). "Theory of vector valued differential forms. Part I". Indagationes Mathematicae. 59: 338–350. doi:10.1016/S1385-7258(56)50046-7 – via ScienceDirect. (Subscription required (help)). .
Gerstenhaber, M. (1963). "The cohomology structure of an associative ring". Annals of Mathematics. 78 (2): 267–288. JSTOR 1970343. doi:10.2307/1970343.
Gerstenhaber, M. (1964). "On the Deformation of Rings and Algebras". Annnals of Mathematics. 79 (1): 59–103. JSTOR 1970484. doi:10.2307/1970484.
Milnor, J. W.; Moore, J. C. (1965). "On the structure of Hopf algebras". Annnals of Mathematics. 81 (2): 211–264. JSTOR 1970615. doi:10.2307/1970615.

External links

Irving Kaplansky + Lie Superalgebras

String theory
Background	Strings History of string theory First superstring revolution Second superstring revolution String theory landscape
Theory	Nambu–Goto action Polyakov action Bosonic string theory Superstring theory Type I string Type II string Type IIA string theory Type IIB string theory Heterotic string N=2 superstring F-theory String field theory Matrix string theory Non-critical string theory Nonlinear sigma model Tachyon condensation RNS formalism GS formalism
String Duality	T-duality S-duality U-duality Montonen–Olive duality Mysterious duality
Particles and Fields	Graviton Dilaton Tachyon Ramond–Ramond field Kalb–Ramond field Magnetic monopole Dual graviton Dual photon
Branes	D-brane NS5-brane M2-brane M5-brane S-brane Black brane Black holes Black string Brane cosmology Quiver diagram Hanany–Witten transition
Conformal Field Theory	Virasoro algebra Mirror symmetry Conformal anomaly Conformal algebra Superconformal algebra Vertex operator algebra Loop algebra Kac–Moody algebra Wess–Zumino–Witten model
Gauge Theory	Anomalies Instantons Chern–Simons form Bogomol'nyi–Prasad–Sommerfield bound Exceptional Lie groups (G₂, F₄, E₆, E₇, E₈) ADE classification Dirac string p-form electrodynamics
Geometry	Kaluza–Klein theory Compactification Why 10 dimensions? Kähler manifold Ricci-flat manifold Calabi–Yau manifold Hyperkähler manifold K3 surface G₂ manifold Spin(7) manifold Generalized complex manifold Orbifold Conifold Orientifold Moduli space Hořava–Witten domain wall K-theory (physics) Twisted K-theory
Supersymmetry	Supergravity Superspace Lie superalgebra Lie supergroup
Holography	Holographic principle AdS/CFT correspondence
M-theory	Matrix theory Introduction to M-theory
String theorists	Nima Arkani-Hamed Michael Francis Atiyah Tom Banks David Berenstein Raphael Bousso Gerald Cleaver Thomas Curtright Robbert Dijkgraaf Jacques Distler Michael Douglas Michael Duff Sergio Ferrara Willy Fischler Daniel Friedan Sylvester James Gates Ferdinando Gliozzi Rajesh Gopakumar Michael Green Brian Greene David Gross Steven Gubser Sergei Gukov Jeffrey Harvey Petr Hořava Gary Gibbons Shamit Kachru Michio Kaku Renata Kallosh Theodor Kaluza Anton Kapustin Igor Klebanov Vadim Knizhnik Maxim Kontsevich Oskar Klein Andrei Linde Juan Maldacena Stanley Mandelstam Donald Marolf Emil Martinec Shiraz Minwalla Gregory Moore Lubos Motl Sunil Mukhi Robert Myers Dimitri Nanopoulos Asad Naqvi Horatiu Nastase Nikita Nekrasov André Neveu Holger Bech Nielsen Peter van Nieuwenhuizen Sergei Novikov David Olive Hirosi Ooguri Joseph Polchinski Alexander Polyakov Arvind Rajaraman Pierre Ramond Lisa Randall Seifallah Randjbar-Daemi Martin Roček Ryan Rohm Joël Scherk John H. Schwarz Nathan Seiberg Ashoke Sen Steve Shenker Warren Siegel Eva Silverstein Đàm Thanh Sơn Matthias Staudacher Andrew Strominger Raman Sundrum Leonard Susskind Gerard 't Hooft Paul Townsend Sandip Trivedi Cumrun Vafa Gabriele Veneziano Erik Verlinde Herman Verlinde Julius Wess Edward Witten Shing-Tung Yau Tamiaki Yoneya Alexander Zamolodchikov Alexei Zamolodchikov Eric Zaslow Bruno Zumino Barton Zwiebach

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.