Draft:Pro-Lie Group
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A pro-Lie group is in mathematics a topological group that can be written in a certain sense as a limit of Lie groups.[1]
The class of all pro-Lie groups contains all Lie groups[2], compact groups[3] and connected locally compact groups[4], but is closed under arbitrary products[5], which often makes it easier to handle than, for example, the class of locally compact groups[6]. Locally compact pro-Lie groups have been known since the solution of the fifth Hilbert problem by Andrew Gleason, Deane Montgomery and Leo Zippin, the extension to nonlocally compact pro-Lie groups is essentially due to the book The Lie-Theory of Connected Pro-Lie Groups by Karl Heinrich Hofmann and Sidney Morris, but has since attracted many authors.
Definition
[edit]A topological group is a group with multiplication and neutral element provided with a topology such that both (with the product topology on ) and the inverse map are continuous.[7] A Lie group is a topological group on which there is also a differentiable structure such that the multiplication and inverse are smooth. Such a structure – if it exists – is always unique.
A topological group is a pro-Lie group if and only if it has one of the following equivalent properties:[8]
- The group is the projective limit of a family of Lie groups, taken in the category of topological groups.
- The group is topologically isomorphic to a closed subgroup of a (possibly infinite) product of Lie groups.
- The group is complete (with respect to its left uniform structure) and every open neighborhood of the unit element of the group contains a closed normal subgroup , so that the quotient group is a Lie group.
Note that in this article — as well as in the literature on pro-Lie groups — a Lie group is always finite-dimensional and Hausdorffian, but need not be second-countable. In particular, uncountable discrete groups are, according to this terminology (zero-dimensional) Lie groups and thus in particular pro-Lie groups.
Examples
[edit]- Every Lie group is a pro-Lie group.[9]
- Every finite group becomes a (zero-dimensional) Lie group with the discrete topology and thus in particular a pro-Lie group.
- Every profinite group is thus a pro-Lie group.[10]
- Every compact group can be embedded in a product of (finite-dimensional) unitary groups and is thus a pro-Lie group.[11]
- Every locally compact group has an open subgroup that is a pro-Lie group, in particular every connected locally compact group is a pro-Lie group (theorem of Gleason-Yamabe).[12][13]
- Every abelian locally compact group is a pro-Lie group.[14]
- The Butcher group from numerics is a pro-Lie group that is not locally compact.[15]
- More generally, every character group of a (real or complex) Hopf algebra is a Pro-Lie group, which in many interesting cases is not locally compact.[16]
- The set of all real-valued functions of a set is, with pointwise addition and the topology of pointwise convergence (product topology), an abelian Pro-Lie group, which is not locally compact for infinite .[17]
- The projective special linear group over the field of -adic numbers is an example of a locally compact group that is not a Pro-Lie group. This is because it is simple and thus satisfies the third condition mentioned above.
Citations
[edit]- ^ Hofmann, Morris 2007, p. vii
- ^ Hofmann, Morris 2007, p. 8, Theorem 6
- ^ Hofmann, Morris 2006, p. 45, Corollary 2.29
- ^ Hofmann, Morris 2007, p. 165
- ^ Hofmann, Morris 2007, p. 165
- ^ Hofmann, Morris 2007, p. 165
- ^ Hofmann, Morris 2006, p. 2, Definition 1.1(i)
- ^ Hofmann, Morris 2007, p. 161, Theorem 3.39
- ^ Hofmann, Morris 2007, p. 8, Theorem 6
- ^ Hofmann, Morris 2007, p. 2
- ^ Hofmann, Morris 2006, p. 45, Corollary 2.29
- ^ Hofmann, Morris 2007, p. 165
- ^ "254A, Notes 5: The structure of locally compact groups, and Hilbert's fifth problem". 8 October 2011.
- ^ Hofmann, Morris 2007, p. 165
- ^ Bogfjellmo, Geir; Schmeding, Alexander, The Lie group structure of the Butcher group, Found. Comput. Math. 17, No. 1, 127-159 (2017).
- ^ Geir Bogfjellmo, Rafael Dahmen & Alexander Schmeding: Character groups of Hopf algebras as infinite-dimensional Lie groups. in: Annales de l’Institut Fourier 2016. Theorem 5.6
- ^ Hofmann, Morris 2007, p. 5
References
[edit]- Karl H. Hofmann, Sidney Morris (2006): The Structure of Compact Groups, 2nd Revised and Augmented Edition. Walter de Gruyter, Berlin, New York.
- Karl H. Hofmann, Sidney Morris (2007): The Lie-Theory of Connected Pro-Lie Groups. European Mathematical Society (EMS), Zürich, ISBN 978-3-03719-032-6.