D-term spectroscopy in realistic heterotic-string models - art. no. 016010

The recent emergence of free fermionic heterotic string models with solely the MSSM charged spectrum below the string scale reinforces the motivation to investigate the pheneomelogical characteristics of this class of string models, which possess an underlying Z(2) x Z(2) orbifold structure. An impo rtant property of the Z(2) x Z(2) orbifold is the cyclic permutation symmet ry between the three twisted sectors. If preserved in the three-generation models the cyclic permutation symmetry results in a family universal anomal ous U(1)(A), which is instrumental in explaining squark degeneracy, provide d that the dominant component of supersymmetry breaking arises from the U(1 )(A) D term. Interestingly, the contribution of the family-universal D-A te rm to the squark masses may be intrafamily nonuniversal, and may differ fro m the usual (universal) boundary conditions assumed in the MSSM. We contemp late how D-A-term spectroscopy may be instrumental in studying superstring models irrespective of our ignorance of the details of supersymmetry breaki ng. We examine the possible effect of the intrafamily nonuniversality on th e resulting SUSY spectrum and the values of the strong coupling, effective weak mixing angle, and W-gauge boson mass; up to a two-loop accuracy, in th e two models (universal and nonuniversal). We find that nonuniversality rel axes the constraint of color and charge breaking minima which appears in th e universal case. In addition, it predicts a 3% smaller value of alpha(s) d ue to different threshold masses obtained in the latter scenario. Finally, we present the experimentally allowed predictions of the two models in an M -0 and M-1/2 parameter space.