A division algebra is a possibly non-associative algebra , typically over a field , which has the property that for any nonzero element and any element , the equations and each have a unique solution for in the algebra.
Usually the algebra is assumed to have a multiplicative identity, in which case this condition implies that each element has a left inverse and a right inverse. These inverses necessarily coincide if the algebra is associative, but this may fail in the absence of associativity.
A sub-topic of interest is the existence of a multiplicative norm for the algebra, see at normed division algebra.
An alternative definition is used in Baez 02: The axioms given there require that the algebra is finite-dimensional over and that for any and in the algebra, implies at least one of or is already . This coincides with the definition given above for finite dimensional algebras.
Perhaps the most famous division algebras are the real numbers , the complex numbers , the quaternions , and the octonions . According to the Hurwitz theorem, these are the only normed, finite dimensional, real division algebras.
Any division ring is an associative division algebra over its center and has identity, but it may not be finite dimensional over its center.
The ring of rational polynomials is an infinite dimensional real associative division algebra.
There exists a division algebra with identity that does not have two-sided inverses for every nonzero element.
There exists a reciprocal algebra with nonzero zero divisors.
The sedenions are a finite-dimensional normed real algebra that is not a division algebra (it has zero divisors.)
The ideal generated by in the polynomial ring is an associative, commutative, infinite dimensional real algebra without identity and without zero divisors. The equation does not have a solution for in the algebra.
For many applications (also to physics) the most interesting division algebras are the normed division algebras over the real numbers: By the Hurwitz theorem these are the real numbers, complex numbers, quaternions and octonions. These have important relations to supersymmetry.
exceptional spinors and real normed division algebras
See at division algebra and supersymmetry.
See also
Wikipedia, Division algebra
John Baez, Section 1.1 Preliminaries In: The octonions, Bull. Amer. Math. Soc. 39 (2002), 145-205. (doi:10.1090/S0273-0979-01-00934-X, website)
Last revised on August 21, 2024 at 01:47:12. See the history of this page for a list of all contributions to it.