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The spectral theorem in Banach algebras

  • Stephen Plafker (a1)
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The concept of a hermitian element of a Banach algebra was first introduced by Vidav [21] who proved that, if a Banach algebra π’œ has β€œenough” hermitian elements, then π’œ can be renormed and given an involution to make it a stellar algebra. (Following Bourbaki [5] we shall use the expression β€œstellar algebra” in place of the term β€œC*-algebra”.) This theorem was improved by Berkson [2], Glickfeld [10] and Palmer [17]. The improvements consist of removing hypotheses from Vidav's original theorem and in showing that Vidav's new norm is in fact the original norm of the algebra. Lumer [13] gave a spatial definition of a hermitian operator on a Banach space E and proved it to be equivalent to Vidav's definition when one considers the Banach algebra 𝓛(E) of continuous linear mappings of E into E.

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References
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1.Berkson, E., A characterization of scalar type operators on reflexive Banach spaces, Pacific J. Math. 13 (1963), 365–373.
2.Berkson, E., Some characterizations of C*-algebras, Illinois J. Math. 10 (1966), 1–8.
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21.Vidav, I., Eine metrische Kennzeichnung der selbstadjungierten Operatoren, Math. Zeit. 66 (1956), 121–128.
22.Wermer, J., Commuting spectral measures on Hilbert space, Pacific J. Math. 4 (1954), 355–361.
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Glasgow Mathematical Journal
  • ISSN: 0017-0895
  • EISSN: 1469-509X
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