In mathematics, a weak Lie algebra bundle
ξ
=
(
ξ
,
p
,
X
,
θ
)
is a vector bundle
ξ
over a base space X together with a morphism
θ
:
ξ
⊗
ξ
→
ξ
which induces a Lie algebra structure on each fibre
ξ
x
.
A Lie algebra bundle
ξ
=
(
ξ
,
p
,
X
)
is a vector bundle in which each fibre is a Lie algebra and for every x in X, there is an open set
U
containing x, a Lie algebra L and a homeomorphism
ϕ
:
U
×
L
→
p
−
1
(
U
)
such that
ϕ
x
:
x
×
L
→
p
−
1
(
x
)
is a Lie algebra isomorphism.
Any Lie algebra bundle is a weak Lie algebra bundle, but the converse need not be true in general.
As an example of a weak Lie algebra bundle that is not a strong Lie algebra bundle, consider the total space
s
o
(
3
)
×
R
over the real line
R
. Let [.,.] denote the Lie bracket of
s
o
(
3
)
and deform it by the real parameter as:
[
X
,
Y
]
x
=
x
⋅
[
X
,
Y
]
for
X
,
Y
∈
s
o
(
3
)
and
x
∈
R
.
Lie's third theorem states that every bundle of Lie algebras can locally be integrated to a bundle of Lie groups. However globally the total space might fail to be Hausdorff.