there is a conventional Lie algebra formulation, but one has to abandon manifest locality,
as we will discuss in more detail. The route taken here, which is common in physics, is
to work with fields living on the larger space but to impose a gauge redundancy. Then
there is a perfectly local formulation, but with a gauge structure that is governed by an L
∞
algebra rather than a Lie algebra. For the case at hand, we will show that the cotangent
bundle T
∗
M for any 3-manifold M equipped only with a volume form provides (a mild
generalization of) a Courant algebroid, which in turn gives rise to an L
∞
structure [19].
Thus, the gauge algebras of the SCFTs based on sdiff
3
are governed in particular by a
non-trivial ‘3-bracket’ encoding the failure of the ‘2-bracket’, the antisymmetric part of
the Leibniz product (1.1), to satisfy the Jacobi identity. Taking R to be the space of
functions on the 3-manifold, there is also the 4-tensor (1.4) and hence a trilinear bracket
on R, which turns out to be the Nambu bracket [39], but it should be emphasized that
the latter bracket is not directly related to the 3-bracket defining the gauge algebra; in
fact, they are not even defined on the same space. To illuminate this point, consider the
BLG model, for which the trilinear bracket, the ‘3-algebra’ of [2], is given by the invariant
epsilon tensor of SO(4), i.e., {φ
1
, φ
2
, φ
3
}
a
= ε
abcd
φ
1b
φ
2c
φ
3d
. The gauge algebra, on the
other hand, is the Lie algebra structure on so(4)
∗
that is transported via the embedding
tensor ϑ(
˜
t
ab
) =
1
2
ε
abcd
t
cd
from the Lie algebra so(4), where t
ab
and
˜
t
ab
are the generators
and dual generators, respectively. Being a Lie algebra, this trivially defines an L
∞
algebra
whose 3-bracket is identically zero.
The rest of this paper is organized as follows. In section 2 we develop the general
formulation of N = 8 SCFTs, starting from a Lie algebra g and constructing, via an
embedding tensor, a Leibniz-Loday algebra that is sufficient in order to define gauge the-
ories. In particular, we show that these general structures are sufficient in order to prove
N = 8 supersymmetry. In section 3 we specialize to the Lie algebra of volume-preserving
diffeomorphisms on a 3-manifold, and we show that there is a natural embedding tensor
satisfying all constraints. We then show that the resulting theories are equivalent, modulo
some topological assumptions, to the Bandos-Townsend theories. In section 4 we con-
sider truncations and deformations of the general framework. Specifically, we consider the
mode expansion of the sdiff
3
SCFTs for S
3
and show that the BLG model is a consistent
(generalized Scherk-Schwarz) truncation. Conversely, the full Bandos-Townsend theory for
S
3
provides an infinite-dimensional generalization of the BLG model. We also review the
S
2
×S
1
model, whose Scherk-Schwarz reduction on S
1
yields a 3D N = 8 super-Yang-Mills
theory with gauge group SDiff
2
, and we discuss massive deformations that preserve N = 8
supersymmetry. In the conclusion section we discuss possible generalizations.
2 Maximal 3D superconformal field theories
We define the 3D N = 8 superconformal field theory for the general data given in the
introduction. In the first subsection we review how an embedding tensor satisfying the
quadratic constraint defines a Leibniz-Loday algebra and a gauge invariant Chern-Simons
action. In the second subsection we introduce a representation R with invariant metric
and show that with these data one can universally define an invariant 4-tensor, which in
– 5 –