Approximately -Jordan Homomorphisms on Banach Algebras
© M. Eshaghi Gordji et al. 2009
Received: 29 November 2008
Accepted: 14 January 2009
Published: 27 January 2009
Let , and let be two rings. An additive map is called -Jordan homomorphism if for all . In this paper, we establish the Hyers-Ulam-Rassias stability of -Jordan homomorphisms on Banach algebras. Also we show that (a) to each approximate 3-Jordan homomorphism from a Banach algebra into a semisimple commutative Banach algebra there corresponds a unique 3-ring homomorphism near to , (b) to each approximate -Jordan homomorphism between two commutative Banach algebras there corresponds a unique -ring homomorphism near to for all .
1. Introduction and Preliminaries
Let be two rings (algebras). An additive map is called n-Jordan homomorphism (n-ring homomorphism) if for all for all If is a linear n-ring homomorphism, we say that is n-homomorphism. The concept of n-homomorphisms was studied for complex algebras by Hejazian et al.  (see also [2, 3]). A 2-Jordan homomorphism is a Jordan homomorphism, in the usual sense, between rings. Every Jordan homomorphism is an n-Jordan homomorphism, for all (e.g., [4, Lemma 6.3.2]), but the converse is false, in general. For instance, let be an algebra over and let be a nonzero Jordan homomorphism on . Then, is a 3-Jordan homomorphism. It is easy to check that is not 2-Jordan homomorphism or 4-Jordan homomorphism. The concept of n-Jordan homomorphisms was studied by the first author . A classical question in the theory of functional equations is that "when is it true that a mapping which approximately satisfies a functional equation must be somehow close to an exact solution of ?" Such a problem was formulated by Ulam  in 1940 and solved in the next year for the Cauchy functional equation by Hyers . It gave rise to the stability theory for functional equations. Subsequently, various approaches to the problem have been introduced by several authors. For the history and various aspects of this theory we refer the reader to monographs [8–12]. Applying a theorem of Hyers , Rassias , and Gajda , Bourgin  proved the stability problem of ring homomorphisms between unital Banach algebras. Badora  proved the Hyers-Ulam-Rassias stability of ring homomorphisms, which generalizes the result of Bourgin. Recently, Miura et al.  proved the Hyers-Ulam-Rassias stability of Jordan homomorphisms. The stability problem of n-homomorphisms between Banach algebras, has been proved by the first author . In this paper, we consider the stability, in the sense of Hyers-Ulam-Rassias, of n-Jordan homomorphisms on Banach algebras.
2. Main Result
By a following similar way as in , we obtain the next theorem.
which proves , whenever This completes the proof.
Let be fixed. Suppose is a Banach algebra, which needs not to be commutative, and suppose is a semisimple commutative Banach algebra. Then, each n-Jordan homomorphism is a n-ring homomorphism.
Let be fixed. As a direct corollary, we show that to each approximate n-Jordan homomorphism from a Banach algebra into a semisimple commutative Banach algebra there corresponds a unique n-ring homomorphism near to .
It follows from Theorems 2.1, 2.2, and 2.3.
Let be fixed, be two commutative algebras, and let be a n-Jordan homomorphism. Then, is n-ring homomorphism.
Hence, is 5-ring homomorphism.
It follows from Theorems 2.1, 2.2, and 2.5.
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