∞-Lie theory (higher geometry)
Background
Smooth structure
Higher groupoids
Lie theory
∞-Lie groupoids
∞-Lie algebroids
Formal Lie groupoids
Cohomology
Homotopy
Related topics
Examples
-Lie groupoids
-Lie groups
-Lie algebroids
-Lie algebras
Let be a set of symbols and let denote the ground field.
The free associative k-algebra on the set where is a commutative unital ring, will be denoted . It is clearly graded (by the length of the word) as . The product of -modules has a natural multiplication
where and . Furthermore, has the topology of the product of discrete topological spaces. This makes a Hausdorff topological algebra, where the ground field is considered discrete and is dense in . We say that is the Magnus algebra with coefficients in . (Bourbaki-Lie gr. II.5).
An element in is invertible (under multiplication) iff it’s free term is invertible in .
The Magnus group is the (multiplicative) subgroup of the Magnus algebra consisting of all elements in the Magnus algebra with free term .
The free Lie algebra naturally embeds in (the Lie algebra corresponding to the associative algebra) ; one defines as the closure of in . The exponential series and the makes sense in ; when restricted to it gives a bijection between and a closed subgroup of the Magnus group which is sometimes called the Hausdorff group .
Hausdorff series is an element in .
The formula implies the basic symmetry of the Hausdorff series: .
The specializations of the Hausdorff series in Lie algebras which are not necessarily free are known as the Baker-Campbell-Hausdorff series and play the role in the corresponding BCH formula .
The BCH formula can be written in many ways, the most important which belong to Dynkin. The part which is linear in one of the variables involves Bernoulli numbers.
There is a decomposition where Dynkin’s Lie polynomials are defined recursively by and
where the sum over is the sum over all -tuples of strictly positive integers whose sum .
The Hausdorff series satisfies the symmetry .
First few terms of Hausdorff series are:
The following references concern the classical part of the subject. For the references connecting Hausdorff series to Drinfeld associators, the Grothendieck-Teichmueller group and the Kashiwara-Vergne conjecture see there.
Early discussion:
Rüdiger Achilles, Andrea Bonfiglioli: The early proofs of the theorem of Campbell, Baker, Hausdorff, and Dynkin, Arch. Hist. Exact Sci. 66 (2012) 295–358 [doi:10.1007/s00407-012-0095-8]
Eugene B. Dynkin, Calculation of the coefficents in the Campbell-Hausdorff formula, Doklady Akad. Nauk SSSR (N.S.) 57 (1947) 323-326
Wilhelm Magnus, A connection between the Baker-Hausdorff formula and a problem of Burnside, Ann. of Math. 52 (1950) 111-126
Kuo-Tsai Chen, Integration of paths, geometric invariants and a generalized Baker–Hausdorff formula, Annals of Mathematics 65:1 (1957) 163–178 doi jstor
Most monographs on Lie algebras discuss the Hausdorff series, for instance:
Jean-Pierre Serre, Section IV.7 in: Lie Algebras and Lie Groups – 1964 Lectures given at Harvard University, Lecture Notes in Mathematics 1500, Springer (1992) [doi:10.1007/978-3-540-70634-2]
Nicolas Bourbaki, Chapter 2 of: Lie groups and Lie algebras, Springer (1975, 1989) [ISBN:9783540642428]
Gerhard P. Hochschild, p. 226 in: Basic theory of algebraic groups and Lie algebras, Graduate Texts in Mathematics 75, Springer (1981) [doi:10.1007/978-1-4613-8114-3_16]
M. M. Postnikov, Lectures on geometry: Semester V, Lie groups and algebras (1986) [ark:/13960/t4cp9jn4p]
Hans Duistermaat, Johan A. C. Kolk, Dynkin’s formula, Section 1.7 in: Lie groups, Springer (2000) [doi:10.1007/978-3-642-56936-4]
Shlomo Sternberg: The Campbell Baker Hausdorff Formula, Section 1 of: Lie Algebras (2004) [pdf, pdf]
James Milne, p. 260 in: Algebraic Groups – The theory of group schemes of finite type over a field, Cambridge University Press (2017) [doi:10.1017/9781316711736, webpage, pdf]
Richard Borcherds, Mark Haiman, Theo Johnson-Freyd, Nicolai Reshetikhin, Vera Serganova: §3.3 in: Berkeley Lectures on Lie Groups and Quantum Groups (2020-2024) [pdf]
See also:
Wikipedia: Baker–Campbell–Hausdorff formula
Terence Tao, 254A, Notes 1: Lie groups, Lie algebras, and the Baker-Campbell-Hausdorff formula, blog entry (2011)
Terence Tao: The Baker-Campbell-Hausdorff formula, blog entry (2011)
See also:
V. Kurlin, The Baker-Campbell-Hausdorff formula in the free metabelian Lie algebra [arXiv:math/0606330]
Federico Zadra et al. The flow method for the Baker-Campbell-Hausdorff formula: exact results, J. Phys. A: Math. Theor. 56 (2023) 385206 [doi:10.1088/1751-8121/acf102]
Last revised on September 3, 2024 at 10:15:27. See the history of this page for a list of all contributions to it.