A study of the various approaches toMGUT andαGUT

An exhaustive study is presented of the different M(GUT) and alpha(GUT) values obtained using the renormalization group equations for the evolution of the couplings, with and without the evolution of the masses, with and without light and heavy-threshold effects, using different levels of theoretical accuracy: one and two loops, simple and detailed threshold treatments. A structure of the heavy threshold with mass ratios as large as 10(6) and values of alpha3(M(Z)) as high as the world average plus 2sigma are needed in order to reach high values of M(GUT), which are still an order of magnitude below M(Planck). A discussion concludes the paper.