Canuto, V. M.Owen, J. R.Narlikar, J. V.2012-03-152012-03-151980-04-24http://hdl.handle.net/11007/1524In this paper we analyze the contribution of QSO's, BL-Lac's and Seyfert galaxies to the diffuse gamma-ray background within the framework of the Hoyle-Narlikar theory. It is shown that the inconsistency reported in standard theory, namely that the evolutionary function needed to explain the gamma-ray data is very different from the one derived from the optical part of the spectrum, is no longer present. It is also shown that the contribution of a variable gravitational "constant" to the expression for the diffuse background is the same as that of a density evolution function.enCosmologyGamma-raysArticle