Link invariants of electromagnetic fields

Hanno v. Bodecker, Gunnar Hornig

    Research output: Contribution to journalArticlepeer-review

    17 Citations (Scopus)


    The cross-helicity integral is known in fluid dynamics and plasma physics as a topological invariant which measures the mutual linkage of two divergence-free vector fields, e.g., magnetic fields, on a three-dimensional domain. Generalizing this concept, a new topological invariant is found which measures the mutual linkage of three closed two-forms, e.g., electromagnetic fields, on a four-dimensional domain. The integral is shown to detect a separation of the cross helicity between two of the fields with the help of the third field. It can be related to the triple linking number known in knot theory. Furthermore, it is shown that the well-known three-dimensional cross helicity and the new four-dimensional invariant are the first two examples of a series of topological invariants which are defined by n-1 field strengths F=dA on a simply connected n-dimensional manifold Mn.
    Original languageEnglish
    Pages (from-to)030406
    Number of pages1
    JournalPhysical Review Letters
    Issue number3
    Publication statusPublished - Jan 2004


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