Research Journal of Applied Sciences, Engineering and Technology 6(22): 4129-4137, 2013 ISSN: 2040-7459; e-ISSN: 2040-7467 © Maxwell Scientific Organization, 2013 Submitted: November 19, 2012 Accepted: May 07, 2013 Published: December 05, 2013 The θ-Centralizers of Semiprime Gamma Rings 1 1 M.F. Hoque, 1H.O. Roshid and 2A.C. Paul Department of Mathematics, Pabna University of Science and Technology, Pabna-6600, Bangladesh 2 Department of Mathematics, Rajshahi University, Rajshahi-6205, Bangladesh Abstract: Let M be a 2-torsion free semiprime Γ-ring satisfying a certain assumption and θ be an endomorphism of M. Let T : M M be an additive mapping such that T ( xy x ) ( x )T ( y ) ( x ) holds for all x, y M and , . Then we prove that T is a θ-centralizer. We also show that T is a θ-centralizer if M contains a multiplicative identity 1. 2010 Mathematics Subject Classification, Primary 16N60, Secondary 16W25, 16U80. Keywords: Centralizer, θ-centralizer, Jordan centralizer, Jordan θ-centralizer, left centralizer, left θ-centralizer, semiprime Γ-ring, INTRODUCTION The notion of a Γ -ring was first introduced as an extensive generalization of the concept of a classical ring. From its first appearance, the extensions and generalizations of various important results in the theory of classical rings to the theory of Γ-rings have been attracted a wider attentions as an emerging field of research to the modern algebraists to enrich the world of algebra. Many prominent mathematicians have worked out on this interesting area of research to determine many basic properties of Γ-rings and have extended numerous remarkable results in this context in the last few decades. All over the world, many researchers are recently engaged to execute more productive and creative results of Γ-rings. We begin with the definition. Let M and Γ be additive abelian groups. If there exists a mapping ( x, , y) xy of MM M , which satisfies the conditions: ( xy ) M ( x y )z xz yz , x( ) z xz xz , ( x α y ) β z = x α ( y β z ) for x ( y z ) xy xz all and , , then M is called a Let M be a Γ -ring. Then an additive subgroup U of M is called a left (right) ideal of M if MU U (UM U ) . If U is a left and a right ideal, then we say U is an ideal of M . Suppose again that M is a Γ.-ring. Then M is said to be a 2-torsion free if 2x 0 implies x 0 for all x M . An ideal P1 of a Γ -ring M is said to be a prime if for any ideals A and B of M, AB P1 implies A P1 or B P1 . An ideal P2 of a Γ-ring M is said to be semiprime if for any ideal U of M, UU P2 implies U P2 . A Γ-ring M is said to be prime if a M b ( 0 ) with, a, b M implies a 0 or b 0 and semiprime if a 0. implies aMa (0) with a M Furthermore, M is said to be commutative Γ-ring if xy yx for all x, y M and . Moreover, the set Z(M) {x M : xy yx for all If M is a -ring, then [ x, y ] x y y x is , where x, y M and commutator identities: -ring. Every ring M is a Γ-ring with M = Γ. However a Γ -ring need not be a ring. Gamma rings, more general than rings, were introduced by Nobusawa (1964). Bernes (1966) weakened slightly the conditions in the definition of Γ-ring in the sense of Nobusawa (1964). and y M } is called the centre of the Γ-ring M. known as the commutator of x and x, y , z M y with respect to . We make the basic [ xy, z] [ x, z] y x[ , ] z y x[ y, z] and [ x , y z ] [ x , y ] z y[ , ] x z y [ x , z ] for all x , y , z M and , . We consider the following assumption: Corresponding Author: M.F. Hoque, Department of Mathematics, Pabna University of Science and Technology, Pabna-6600, Bangladesh 4129 Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 x y z x y z ………….. x, y , z M and , . (A) for all According to the assumption (A), the above two identities reduce to [ xy, z ] [ x, z ] y x [ y, z ] and [ x, yz ] [ x, y ] z y [ x, z ] ,which we extensively used. An additive mapping T : M M is a left (right) centralizer if T ( xy ) T ( x)y[T ( xy ) xT ( y )] holds for all x, y, z M and , . A centralizer is an additive mapping which is both a left and a right centralizer. For any fixed and Г,, the mapping is a left centralizer and is a right centralizer. We shall restrict our attention on left centralizer, since all results of right centralizers are the same as left centralizers. An additive mapping ∶ ⟶ is called a derivation if holds for all , Гand is called a Jordan derivation if for all and Г. An additive mapping ∶ ⟶ is Jordan left (right) centralizer if for all and Г. Every left centralizer is a Jordan left centralizer but the converse is not in general true. An additive mappings ∶ ⟶ is called a Jordan centralizer if , for all , and Г. Every centralizer is a Jordan centralizer but Jordan centralizer is not in general a centralizer. Bernes (1966), Luh (1969) and Kyuno (1978) studied the structure ofГ -rings and obtained various generalizations of corresponding parts in ring theory. Zalar (1991) worked on centralizers of semiprime rings and proved that Jordan centralizers and centralizers of this rings coincide. Vukman (1997, 1999, 2001) developed some remarkable results using centralizers on prime and semiprime rings. Ceven (2002) worked on Jordan left derivations on completely prime Г -rings. He investigated the existence of a nonzero Jordan left derivation on a completely prime Г-ring that makes the Г-ring commutative with an assumption. With the same assumption, he showed that every Jordan left derivation on a completely prime Г-ring is a left derivation on it. The commutativity condition of a prime ring has been studied by Mayne (1984) by means of a Lie ideal of R and with a nontrivial automorphism or derivation. Ullah and Chaudhary (2010) proved that if T is an additive mapping of a 2-torsion free semiprime ring with involution * satisfying T (xx* ) T (x) (x* ) (x* )T (x) , then t is a -centralizer. Hoque and Paul (2011) have proved that every Jordan centralizer of a 2-torsion free semiprime Г -ring satisfying a centain assumption is a centralizer. Hoque and Paul (2012) have proved that if T is an additive mapping on a 2-torsion free semiprimeГ -ring M with a certain assumption such that , for all , and , Г, then is a centralizer. Ullah and Chaudhary (2012), have proved that every Jordan -centralizer of a 2-torsion free semiprime Г -ring is a -centralizer. Hoque et al. (2012) proved that T is a -centralizer by using a relation 2T (aba) T (a)(b)(a) (a)(b)T (a) , where T is an additive mapping on a 2-torsion free semiprimeГ -ringM. Our research works inspired by the works of Hoque et al. (2012) in Г -rings with -centralizers. Here we prove that if is a 2-torsion free semiprime Г-ring satisfying the assumption (A) and if ∶ ⟶ is an additive mapping such that: (1) For all , , , Гand an endomorphism on , then is -centralizer. Also we show that is a centralizer if contains a multiplicative identity 1. THE -CENTRALIZER OF SEMIPRIME GAMMA RINGS In this section, we have given the following definitions: Let be a 2-torsion free semiprime Г -ring and let be an endomorphism of . An additive mapping ∶ ⟶ is a left (right) -centralizer if holds for all , and Г. If t is a left and a right -centralizer, then it is natural to call a -centralizer. Let be a Г-ring and let and Гbe fixed element. Let ∶ ⟶ be an endomorphism. Define a mapping ∶ ⟶ by . Then it is clear that is a left -centralizer. If is defined, then is a right -centralizer. An additive mapping ∶ ⟶ is a Jordan left (right) -centralizer if = holds for all and Г. It is obvious that every left -centralizer is a Jordan left -centralizer but in general Jordan left -centralizer is not a left -centralizer. Example 2.1 Let be a Г-ring and let ∶ ⟶ be a left -centralizer, where ∶ ⟶ is an endomorphism. Define , ∶ and Γ , ∶ Γ . The addition and multiplication on are defined as follows: , , , and , , , , . 4130 Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 Under these addition and multiplication, it is clear that is a Γ -ring. , Define , , and , . Then T is an additive mapping on and is an endomorphism on . Now, let , , , ,then we have: , , , , , , , , , , , . , , , , , , Example 2: Let be a Γ-ring satisfying the assumption (A) and let be a fixed element of such that , the centre of . Define a mapping ∶ ⟶ by , where ∶ ⟶ is an endomorphism and Гis a fixed element.Then for all , and Г , we have: , , Therefore, T is a Jordan left -centralizer which is not a left -centralizer. Let be a Γ-ring and let be an endomorphism on . An additive mapping ∶ ⟶ is called a Jordan -centralizer if , for all , and Г. It is clear that every -centralizer is a Jordan -centralizer but the converse is not in general a -centralizer. An additive mapping ∶ ⟶ is a , derivation if holds for all , and Гand is called a Jordan , -derivation if , holds for all and Г.Now we begin with two examples which are ensure that a centralizer and a Jordan -centralizer exist in Γ-ring. Also, , , . Under these addition and multiplication is a Γ -ring.Define , , and , , .Then is is an endomorphism on . additive mapping and Let , , , , , . Then we have: , , , , , , , , , , , , , , , Therefore, is a Jordan -centralizer on which is not a -centralizer. For proving our main results, we need the following Lemmas: Lemma 1: (7, Lemma 1) Suppose is a semiprime Γring satisfying the assumption . Suppose that the relation 0 holds for all ∈ , some , , ∈ and , ∈ Γ. Then 0 is satisfied for all ∈ and , ∈ Γ. Lemma 2: Let be a 2-torsion free semiprimeΓ –ring satisfying the assumption and let ∶ → be an additive mapping. Suppose that holds for all , ∈ and , ∈ Γ. Then: , , , , , , 0 0. 0 Proof: We prove (i) T x , x , x 0 . Therefore, is a left and right is a . 0 0 For linearization, we put relation(1),we obtain: centralizer, so Example 3: Let be a Γ-ring and let ∶ → be a -centralizer, where ∶ → is an endomorphism. , : ∈ and Γ , : ∈Γ . Define as follows: Define addition and multiplication on , , , and , , (2) xz for x in T x y z z y x x T y z z T y x Replacing y for x and z for y in (3), we have: (3) T x x y y x x x T x x y T x x 4131 (4) Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 For z x x in relation (3) reduces to: , 2 2 2 T x xyx x xyx x T xxy yxx x , , , , 0 , follows, i.e., 0 (12) , , , , , , , (8) Putting , , , , 0 in the above relation, we have: , Using Lemma 2 in the above relation , we have: , , , , x y T x x x x y x T x x x T x , x y x 0 , , , , , , , 0 Adding the above two relations, we have: , , 2 2 0 , , 0 , 0 , , 2 0 , , , , , 0 0 9 , , , (13) 0 , , (9) , , , , , , Putting for y in (13) and using (1), (2), (13) and assumption (A), we have: 0 , , , Since M is 2-torsion free semiprime Г-ring, so, we have: 0 , , Let The linearization of (2) gives: y x x y T x , x x 0 2 Since is semiprime, so , 0 , Now, we prove the relation ∶ Combining (6) and (7), we arrive at: T x T x , x , , T x x y x x y x x 2 x T x y x x y T x x x (7) 2 , (11) which gives because of (4): 2 gives: Subtracting 11 from 10 one obtains: The substitution xx y yxx for y in the relation (1) gives: 2 , 0 (6) 2 (10) Right multiplication of 9 by T x xyx x y x xT xx yx x yxT x x 2 , 0 T x y x x x x y x 2 2 x T y x x x x T y x (5) Putting y xyx in (4), we obtain: 2 , , 4132 , Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 , [T x , x x x ] T x , x x x y T x , x 0 , , , , , , , , , which reduces to: x T x , x x x x , T x , x y T x , x , , , , , Relation \ , , makes it possible to write instead of x T x , x , which means that x x T x , x can be , replaced by x T x , x x in the above relation. Thus we have: x T x , x x y T x , y 0 Right multiplication of the above relation by and substitution for gives finally, , 0 , (2) T x , x x , , T x , θ x βθ y β\θ x γθ x θ x γθ x βθ y β T x , θ x θ x γθ y βθ x β T x , θ x _α T x , θ x _αβθ x βθ y γθ x . Therefore, we have: , 0 0 Hence For all x,y ∈ , ∈ , which reduces because of (3) and (8) to: Left multiplication of the above relation by xβ gives: x T x , x y x x y T x , x 0 One can replace in the above relation according to (15), θ(x)β[T(x), θ(x)]α βθ(y)βθ(x) by x y T x , x x which gives: x y T x , x x x x x x y T x , x 0 by of M, we , 0, ∈ , First, we putting because of (12): ∈ for (17) in (8), gives , (14) 0 (18) for in (25), we have: , αθ 0 (19) , Right multiplication of (18) by , (15) have Next we prove the relation (iii): T x x y T x , x x x 0 (20) Subtracting (20) from (19), we have: The substitution T(x)αθ(y) for y in (14), we have: , 0 x T x y T x , x x x ⇒ x x x T x y T x , x 0 (16) , , 0 ⇒ Subtracting (16) from (15), we obtain: T x , x y T x , x x x T x , x x x y T x , x semiprimeness 0. The substitution Left multiplication of the above relation by T(x)α gives: T x x x x y T x , x 0 , ⇒ 0 From the above relation and Lemma-2.1, it follows that: According , gives: 4133 , , , , to , 0 , 0 (2), by one can , replaced which Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 , 0, , ∈ , , ∈ ( x ) (T ( xy yx ) T ( y ) ( x ) , ( x )T ( y )) ( x) 0. Hence by semiprimenessof M, ( x) [T ( x), ( x)] 0 , We define: Finally, we prove the equation (u) : G ( ( x ), ( y )) T ( xy yx ) T ( y ) ( x ) ( x )T ( y ). x, y M , , . T ( x ), ( x) = 0 Then it is clear that: (21) ( x )G ( ( x ), ( y )) ( x) 0 and G ( ( x ), ( y )) G ( ( y ), ( x )). From (2) and (17), it follows that: [T ( x ), ( x)] ( x) = 0, x M , , . Replacing x for y and using (22), we have: The linearization of the above relation gives (see how relation (13) was obtained from (2)): ( y )G ( ( x), ( y )) ( y ) 0. We can also easily prove the following results : [T ( x ), ( x )] ( y ) [T ( x ), ( y )] (1) G ( ( x) ( z ), ( y )) G ( ( x), ( y )) G ( ( z), ( y)) (2) G ( (x), ( y) (z)) G ( (x), ( y)) G ( ( x), ( z )) ( x ) [T ( y ), ( x )] ( x ) 0 (3) G ( ( x), ( y )) G ( ( x), ( y )) G ( ( x), ( y )) (4) G ( ( x), ( y)) G ( ( x), ( y)) (5) G ( ( x), ( y )) G ( ( x), ( y )) . Right multiplication of the above relation by [T ( x), x] gives because of (17): [T ( x), ( x)] ( y ) [T ( x), ( x)] 0 which implies [T ( x ), ( x )] 0. Lemma 3: Let M be - ring satisfying the assumption (A) and let T : M M be an additive mapping such that T ( xyx) ( x)T ( y ) ( x) holds for all x, y, M and , . Then: (a) [G ( ( x), ( y )), ( x)] 0 ( x) (T ( xy yx) T ( y) ( x) ( x)T ( y)) ( x) 0 (22) Proof: The substitution gives: xy yx for Lemma 4: Let M be a 2-torsion free semiprime Γring satisfying the assumption (A) and let T : M M be an additive mapping. Suppose that T ( xyx) ( x)T ( y) ( x) holds for all x, y M and , . Then: (b) Gα(θ(x),θ)) = 0 Proof: First we prove the relation (a): y in (1) T ( xxyx xyxx) ( x)T ( xy yx) ( x) [G ( ( x), ( y)), ( x)] 0 The linearization of (21) gives: (23) On the other hand, we obtain by putting z xx in (3), we have: T ( xxy x xy xx ) ( x)T ( y ) ( x ) ( x) ( x) ( x)T ( y ) ( x) T ( xxyx xyxx) ( x)T ( y ) ( x) ( x) ( x) ( x)T ( y ) ( x) (24) By comparing (23) and ( 24), we have: (25) [T ( x), ( y )] [T ( y ), ( x)] 0 (26) Putting xy yx for y in the above relation and using (21), we obtain: [T ( x), ( x) ( y) ( y) ( x)] [T ( xy yx), ( x)] 0 xT x, y T x, y x T xy yx, x 0 T xy yx, x x T x, y T x, y x 0 4134 Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 According to (26) one can replace T x , y by T y , x which gives G ( ( x ), ( y )) 0 i.e., in the above relation. We have T ( xy yx) T ( y) ( x) ( x)T ( y) therefore: T xy yx , x x T y , x T y , x x 0 i.e., G x , y , x 0 Hence the proof is complete. Theorem 1: Let M be a 2-torsion free semiprime Γ-ring satisfying the assumption (A) and let T : M M be an additive mapping. Suppose that T(xαxβx) = θ(x)αT(x)βθ(x) holds for all x M and , . The proof is therefore complete. Finally, we prove the relation (b): Then T is a -centralizer. G x , y 0 Proof: In particular for reduces to: (27) From (22) one obtains (see how (13) was obtained from (2)), we have: x G x , y z x G z , y x z G x , y 0 y x, the relation (32) 2T ( x x ) T ( x ) ( x ) ( x ) T ( x ) Combining the above relation with (21), we arrive at: Right multiplication of the above relation by G x , y x gives because of (22): x G x , y z G x , y x 0 2T ( xx) 2T ( x) ( x), xM , 2T ( xx) 2 ( x)T ( x), x M , . And Since (28) Relation (25) makes it possible to replace in (28), x G x , y by G x , y x . Thus we have: M is 2-torsion free, so we have: T ( xx) T ( x) ( x), T xx xT x, x M, x M , G x , y x z G x , y x 0 (29) By theorem 3.5 in Ullah and Chaudhary (2012), it follows that T is a left and also right θ–centralizer which completes the proof of the theorem. Putting y = x in relation (1), we obtain: Therefore by semiprimeness of M: T x x x x T x x , x M , , T (33) G x , y x 0 The question arises whether in a2-torsion free semi-prime Γ–ring the above relation implies that T is a θ-centralizer. Unfortunately we were unable to answer affirmative if M has an identity element. (30) Of course, we have also: ( x )G ( ( x), ( y )) 0 Theorem 2: Let M be a 2-torsion free semi-prime Γ– ring with identity element 1 satisfying the assumption (A) and let T : M M be an additive mapping. Suppose that T xxx xT x x holds for The linearization of (30) with respect to x gives: G ( ( x), ( y)) ( z) G ( ( z), ( y)) ( x) 0 all x M and , . Then T is a Right multiplication of the above relation by G ( ( x), ( y)) gives because of (31): -centralizer. Proof: Putting x+1 for x in relation (33), one obtains after some calculations: 3T xx 2T x T x x x T x x a x a x x a G ( ( x), ( y )) ( z )G ( ( x), ( y )) 0 4135 Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 where a stands for T(1). Putting –x for x in the relation above and comparing the relation so obtain with the above relation we have: 6T xx 2T x x 2 x T x 2 x a x (34) and θ be an endomorphism of M. Suppose there exists an additive mapping T : M M such that m n m n holds for all T (( x ) ( x ) x) ( x ) T ( x) ( x ) x M , , , where m 1, n 1 are some integers. Thus T is a θ-centralizer. CONCLUSION and 2T x a x x (35) We shall prove that a Z M .According to (35) one can replace 2T x on the right side of (41) by a x x and 6T xx on the left side by 3a x x 3 x x a , which gives after some calculation: In this study, we have given some examples which have shown that θ-centralizer exists in Γ-rings. We proved that if T is an additive mapping on a 2-torsion free semiprime Γ-ring M satisfying the assumption (A) such that T ( x y x ) ( x ) T ( y ) ( x ) for all x, y M , , and θ an endomorphism on M,then T is a θ-centralizer. We have also showed that T is a θcentralizer if M contains a multiplicative identity 1. a x x x x a 2 x a x 0 REFERENCES The above relation can be written in the form: [[ a , ( x )] , ( x )] 0; x M , , (36) The linearization of the above relation gives: [[ a, ( x )] , ( y )] [[ a, ( y )] , ( x )] 0 (37) Putting y x y in (37), we obtain because of (36) and (37): 0 [[a, ( x)] , ( x) ( y)] [[ , ( x) ( y)] , ( x)] [[a, ( x)] , ( x)] ( y)] ( x) )[[a, ( x)], ( y)] [[a, ( x)] ( y) ( x)[a, ( y)] , ( x)] ( x)[[a, ( x)] , ( y)] [[a, ( x)] ( y), ( x)] [ ( x)[a, ( y)] , ( x)] ( x) [[a, ( x)] , ( y)] [[a, ( x) ( x)] ( y) [a, ( x)] [ ( y), ( x)] [ ( x) [a, ( y)] , ( x)] [a, ( x)] [ ( y), ( x)] The substitution ( y ) a for ( y) in the above relation gives: [ a, ( x )] ( y ) [a, ( x)] 0 Hence it follows a Z (M ) , which reduces (35) to the form T ( x) a ( x), x M , . The proof of the theorem is complete. We conclude with the following conjecture: let M be a semiprime Γ-ring with suitable torsion restrictions Bernes, W.E., 1966. On the Γ-rings of nobusawa. Pacific J. Math., 18: 411-422. Ceven, Y., 2002. Jordan left derivations on completely prime Г-rings. Ç.U. Art. Sci. J. Sci. Technol. (Turkish), 23(2): 39-43. Hoque, M.F. and A.C. Paul, 2011. On centralizers of semiprime gamma rings. Int. Math. Forum, 6(13): 627-638. Hoque, M.F. and A.C. Paul, 2012. Centralizers of semiprime gamma rings. Italian J. Pure Appl. Math., 30(To Appear). Retrieved from: http:// www. researchmathsci. org/ apamart/ apam- v1n17. pdf. Hoque, M.F., H.O. Roshid and A.C. Paul, 2012. An equation related to θ-centralizers in semiprime gamma rings. Int. J. Math. Combin., 4: 17-26. Kyuno, S., 1978. On prime gamma ring. Pacific J. Math., 75: 185-190. Luh, L., 1969. On the theory of simple gamma rings. Michigan Math. J., 16: 65-75. Mayne, J.H., 1984. Centralizing mappings of prime rings. Canad. Math. Bull., 27(1): 122-126. Nobusawa, N., 1964. On the generalization of the ring theory. Osaka J. Math., 1: 81-89. Ullah, Z. and M.A. Chaudhary, 2010. θ-centralizers of rings with involution. Int. J. Algera, 4(17): 843-850. Ullah, Z. and M.A. Chaudhary, 2012. On K centralizers of semiprime gamma rings. Int. J. Algera, 6(21): 1001-1010. Vukman, J., 1997. Centralizers in prime and semiprime comment. Math. Univ., Carolinae, 38: 231-240. Vukman, J., 1999. An identity related to centralizers in semiprime rings. Comment. Math. Univ., Carolinae, 40(3): 447-456. 4136 Res. J. Appl. Sci. Eng. Technol., 6(22): 4129-4137, 2013 Vukman, J., 2001. Centralizers on Semiprime rings. Comment. Math. Univ., Carolinae, 42(2): 237-245. Zalar, B., 1991. On centralizers of semiprime rings. Comment. Math. Univ., Carolinae, 32: 609-614. 4137