EJTP 8, No. 25 (2011) 1–8 Electronic Journal of Theoretical Physics Some Bianchi type-I Cosmic strings in a Scalar –Tensor Theory of Gravitation R.Venkateswarlu 1 , J.Satish 2 and K.Pavan Kumar 3∗ 1 GITAM School of International Business, GITAM University, Visakhapatnam 530045, India 2 Vignan’s Institute of Engineering for Women, Duvvada, . Vadlapudi, Visakhapatnam 530046, India 3 Swarnandhra College of Engg. & Tech, Narsapur 534 280, India Received 6 July 2010, Accepted 10 February 2011, Published 10 May 2011 Abstract: The field equations are obtained in Sen–Dunn theory of gravitation with the help of LRS Bainchi type-I in the context of cosmic strings. We have solved the field equations when the shear σ is proportional to the scalar expansion θ. It is found that the cosmic do not exist with the scalar field except for some special cases and hence vacuum solutions are presented and discussed. c ⃝ Electronic Journal of Theoretical Physics. All rights reserved. Keywords: Gravitation; General Relativity; Bianchi type-I PACS (2010): 95.30.Sf; 04.20.-q 1. Introduction Brans and Dicke [1] have formulated a scalar-tensor theory of gravitation in which the tensor field alone is geometrised and the scalar field is alien to the geometry. Sen and Dunn [2] have proposed a new scalar-tensor theory of gravitation in which both the scalar and tensor fields have intrinsic geometrical significance. The scalar field in this theory is characterized by the function ϕ = ϕ(x i ) where x i are coordinates in the four – dimensional Lyra manifold and the tensor field is identified with the metric tensor g ij of the manifold. The field equations given by Sen and Dunn for the combined scalar and tensor fields are R ij − 1 2 g ij R = ωϕ -2 (ϕ ,i ϕ ,j − 1 2 g ij ϕ ,k ϕ ,k ) − ϕ -2 T ij (1) * rangavajhala v@yahoo.co.in