# Wydawnictwa / Czasopisma IMPAN / Studia Mathematica / Wszystkie zeszyty

## On the uniqueness of uniform norms and $C^{\ast }$-norms

### Tom 191 / 2009

Studia Mathematica 191 (2009), 263-270 MSC: 46J05, 46K05, 22D15. DOI: 10.4064/sm191-3-7

#### Streszczenie

We prove that a semisimple, commutative Banach algebra has either exactly one uniform norm or infinitely many uniform norms; this answers a question asked by S. J. Bhatt and H. V. Dedania [Studia Math. 160 (2004)]. A similar result is proved for $C^\ast$-norms on $\ast$-semisimple, commutative Banach $\ast$-algebras. These properties are preserved if the identity is adjoined. We also show that a commutative Beurling $\ast$-algebra $L^1(G,\omega )$ has exactly one uniform norm if and only if it has exactly one $C^\ast$-norm; this is not true in arbitrary $\ast$-semisimple, commutative Banach $\ast$-algebras.

#### Autorzy

• P. A. DabhiDepartment of Mathematics
Sardar Patel University
Vallabh Vidyanagar 388 120
Gujarat, India
e-mail
• H. V. DedaniaDepartment of Mathematics
Sardar Patel University
Vallabh Vidyanagar 388 120
Gujarat, India
e-mail

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