GUT and SUSY breaking by the same field

We present a model in which the same modulus field breaks both SUSY and a s imple GUT gauge group down to the SM gauge group. The modulus is stabilized by the inverted hierarchy mechanism in a perturbative region so that the m odel is calculable. This is the first example of this kind in the literatur e. All mass scales (other than the Planck scale) are generated dynamically. In one of the models doublet-triplet splitting is achieved naturally by th e sliding singlet mechanism while another model requires fine tuning. The g auge mediation contribution to the right handed slepton (mass)(2) is negati ve. But, for the modulus vacuum expectation value close to the GUT scale, t he supergravity contribution to the slepton (mass)(2) is comparable to the gauge mediation contribution and thus a realistic spectrum can be attained. (C) 1998 Elsevier Science B.V. All rights reserved.