Antisymmetric tensor

Antisymmetric tensor

In mathematics and theoretical physics, a tensor is antisymmetric on two indices i and j if it flips sign when the two indices are interchanged:

T_{ijkdots} = -T_{jikdots}

An antisymmetric tensor is a tensor for which there are two indices on which it is antisymmetric. If a tensor changes sign under the exchange of any pair of indices, then the tensor is completely antisymmetric and it is also referred to as a differential form.

A tensor A which is antisymmetric on indices i and j has the property that the contraction with a tensor B, which is symmetric on indices i and j, is identically 0.

For a general tensor U with components U_{ijkdots} and a pair of indices i and j, U has symmetric and antisymmetric parts defined as:

U_{(ij)kdots}=frac{1}{2}(U_{ijkdots}+U_{jikdots}) (symmetric part)

U_{[ij]kdots}=frac{1}{2}(U_{ijkdots}-U_{jikdots}) (antisymmetric part)

Similar definitions can be given for other pairs of indices. As the term "part" suggests, a tensor is the sum of its symmetric part and antisymmetric part for a given pair of indices, as in U_{ijkdots}=U_{(ij)kdots}+U_{[ij]kdots}

An important antisymmetric tensor in physics is the electromagnetic tensor F in electromagnetism.

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