- Witt algebra
In
mathematics , the complex Witt algebra, named afterErnst Witt , is theLie algebra of meromorphic vector fields defined on theRiemann sphere that are holomorphic except at two fixed points. It is also the complexification of the Lie algebra of polynomial vector fields on a circle, and the Lie algebra of derivations of the ring C ["z","z"−1] . Witt algebras occur in the study ofconformal field theory .There are some related Lie algebras defined over finite fields, that are also called Witt algebras.
The complex Witt algebra was first defined by Cartan (1909), and its analogues over finite fields were studied by Witt in the 1930s.
Basis
A basis for the Witt algebra is given by the
vector field s L_n=-z^{n+1} frac{partial}{partial z}, for "n" in "mathbb Z".The Lie bracket of two vector fields is given by
:L_m,L_n] =(m-n)L_{m+n}.
This algebra has a central extension called the
Virasoro algebra that is important inconformal field theory andstring theory .Over finite fields
Over a field "k" of characteristic "p">0, the Witt algebra is defined to be the Lie algebra of derivations of the ring:"k" ["z"] /"z""p"The Witt algebra is spanned by "L""m" for −1≤ "m" ≤ "p"−2.
References
*E. Cartan, [http://www.numdam.org/numdam-bin/fitem?id=ASENS_1909_3_26__93_0 "Les groupes de transformations continus, infinis, simples."] Ann. Sci. Ecole Norm. Sup. 26, 93-161 (1909).
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