Let $mathfrak{s} = mathfrak{s}_0 oplus mathfrak{s}_1$ be a real Lie superalgebra. (The ground field does not matter much, but at least one formula will not work as written if the characteristic is 2 or 3.) Recall that this means that there is a bilinear 2-graded bracket $[-,-]$ with three components
(a) $mathfrak{s}_0 times mathfrak{s}_0 to mathfrak{s}_0$ (skewsymmetric)
(b) $mathfrak{s}_0 times mathfrak{s}_1 to mathfrak{s}_1$
(c) $mathfrak{s}_1 times mathfrak{s}_1 to mathfrak{s}_0$ (symmetric)
satisfying the Jacobi identity, which splits into 4 components, which can be paraphrased as
(1) $mathfrak{s}_0$ is a Lie algebra under (a)
(2) $mathfrak{s}_1$ is an $mathfrak{s}_0$-module under (b)
(3) the map in (c) is $mathfrak{s}_0$-equivariant
(4) $[[x,x],x] = 0$ for all $x in mathfrak{s}_1$
The fact that the first three components can be written using words, whereas the fourth is easiest via a formula, suggests that they should perhaps be treated differently.
Indeed, over time I have come across many examples of superalgebras where the first three components of the Jacobi identity are satisfied but not the fourth. I'd like to call them 3/4-Lie superalgebras. I would like to know how far can this notion be pushed and in particular how much of the theory of Lie superalgebras still works in the 3/4 case.
To motivate this seemingly random question, let me end by pointing out one generic example where they arise. There are others, but they are lengthier to describe.
Let $mathfrak{g}$ be a metric Lie algebra; that is, a Lie algebra with an ad-invariant inner product $(-,-)$ and let $V$ be a symplectic $mathfrak{g}$-module; that is, one possessing a $mathfrak{g}$-invariant symplectic form $langle-,-rangle$. Now let $mathfrak{s} = mathfrak{g} oplus V$. Then maps (a) and (b) are obvious: given by the Lie bracket on $mathfrak{g}$ and the action of $mathfrak{g}$ on $V$, respectively. Map (c) is the transpose of map (b) using the inner products of both $mathfrak{g}$ and $V$; in other words, if $x,y in V$ then $[x,y] in mathfrak{g}$ is defined by
$$([x,y],a) = langle acdot x,yrangle$$
for all $a in mathfrak{g}$.
Then it is easy to see that $[x,y] = [y,x]$ and that (1)-(3) are satisfied, whereas in general (4) is not satisfied and instead defines a subclass of symplectic $mathfrak{g}$-modules.
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