Question

Schur multipliers for group extensions and for Lie groups also Where are they written for Lie algebras?

Answer 1

Take a look at the Ph.D. Thesis of P.G. Batten:

http://www4.ncsu.edu/~stitz/Multipliers%20and%20Covers%20of%20Lie%20Algebras.pdf

Answer 2

Another answer to your interest in analogues between groups and Lie algebras is in

Ellis, Graham J. Nonabelian exterior products of Lie algebras and an exact sequence in the homology of Lie algebras. J. Pure Appl. Algebra 46 (1987), no. 2-3, 111–115.

which gives $H_2(L)$ for a Lie algebra as the kernel of a morphism $L \wedge L \to L$ where $L \wedge L$ is a nonabelian exterior product. This is the Lie algebra analogue of a result for groups proved in

Miller, Clair, `The second homology of a group', Proc. American Math. Soc. 3 (1952) 588-595.

This is part of the development of nonabelian tensor products of groups (and Lie algebras). More references to this are in

http://pages.bangor.ac.uk/~mas010/nonabtens.html

Answer 3

Throwing a bunch of more references, for what it's worth (haven't looked thoroughly at them). But frankly, for me the "Schur multiplier", at least in the Lie-algebraic context, was always a synonym for the "second (co)homology with trivial coefficients", just defined via the Hopf formula, though probably I am missing some additional data coming by analogy from group theory.

• J. Bichon, G. Carnovale, Lazy cohomology: an analogue of the Schur multiplier for arbitrary Hopf algebras, J. Pure Appl. Algebra 204 (2006), no.3, 627-665
• L.R. Bosko, On Schur multipliers of Lie algebras and groups of maximal class, Intern. J. Algebra Comput. 20 (2010), N6, 807-821; DOI:10.1142/S0218196710005881
• L.R. Bosko, E.L. Stitzinger, Schur multipliers of nilpotent Lie algebras, arXiv:1103.1812
• H. Mohammadzadeh, B. Edalatzadeh, Some properties on Schur multiplier and cover of a pair of Lie algebras, arXiv:1105.0077
• P. Niroomand, On dimension of the Schur multiplier of nilpotent Lie algebras, Centr. Eur. J. Math. 9 (2011), no.1, 57-64 MR:2011m:17031
• P. Niroomand, F. Russo, A note on the Schur multiplier of a nilpotent Lie algebra, Comm. Algebra 39 (2011), N4, 1293-1297; arXiv:1001.0176; DOI:10.1080/00927871003652660
• P. Niroomand, F. Russo, A restriction on the Schur multiplier of nilpotent Lie algebras, Electron. J. Lin. Algebra 22 (2011), 1-9 http://www.math.technion.ac.il/iic/ela/ela-articles/22.html#1
• F. Saeedi, A. Salemkar, B. Edalatzadeh, The commutator subalgebra and Schur multiplier of a pair of nilpotent Lie algebras, J. Lie Theory 21 (2011), No.2, 491-498 http://www.heldermann.de/JLT/JLT21/JLT212/jlt21021.htm
• A. Salemkar, V. Alamian, H. Mohammadzadeh, Some properties of the Schur multiplier and covers of Lie algebras, Comm. Algebra 36 (2008), no.2, 697-707; DOI:10.1080/00927870701724193