# Representation of a Lie superalgebra

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Representation of a Lie superalgebra

In the mathematical field of representation theory, a representation of a Lie superalgebra is an action of Lie superalgebra "L" on a Z2-graded vector space "V", such that if "A" and "B" are any two pure elements of "L" and "X" and "Y" are any two pure elements of "V", then

:$\left(c_1 A+c_2 B\right) \left[X\right] =c_1 A \left[X\right] + c_2 B \left[X\right] ,$

:$A \left[c_1 X + c_2 Y\right] =c_1 A \left[X\right] + c_2 A \left[Y\right] ,$

:$\left(-1\right)^\left\{A \left[X\right] \right\}=\left(-1\right)^A\left(-1\right)^X,$

:$\left[A,B\right) \left[X\right] =A \left[B \left[X\right] -\left(-1\right)^\left\{AB\right\}B \left[A \left[X\right] .,$

Equivalently, a representation of "L" is a Z2-graded representation of the universal enveloping algebra of "L" which respects the third equation above.

Unitary representation of a star Lie superalgebra

A * Lie superalgebra is a complex Lie superalgebra equipped with an involutive antilinear map * such that * respects the grading and

: [a,b] *= [b*,a*]

A unitary representation of such a Lie algebra is a Z2 graded Hilbert space which is a representation of a Lie superalgebra as above together with the requirement that self-adjoint elements of the Lie superalgebra are represented by Hermitian transformations.

This is a major concept in the study of supersymmetry together with representation of a Lie superalgebra on an algebra. Say A is an *-algebra representation of the Lie superalgebra (together with the additional requirement that * respects the grading and L [a] *=-(-1)LaL* [a*] ) and H is the unitary rep and also, H is a unitary representation of A.

These three reps are all compatible if for pure elements a in A, |ψ> in H and L in the Lie superalgebra,

:L [a|ψ>)] =(L [a] )|ψ>+(-1)Laa(L [|ψ>] )

Sometimes, the Lie superalgebra is embedded within A in the sense that there is a homomorphism from the universal enveloping algebra of the Lie superalgebra to A. In that case, the equation above reduces to

:L [a] =La-(-1)LaaL

This approach avoids working directly with a Lie supergroup, and hence avoids the use of auxiliary Grassmann numbers.

ee also

* Lie algebra representation
* Representation theory of Hopf algebras

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