We present a string-inspired/derived supergravity model based on the flipped
SU(5)×U(1) structure supplemented by a minimal set of additional matter
representations such that unification occurs at the string scale
(\sim10^{18}\GeV). This model is complemented by two string supersymmetry
breaking scenaria: the SU(N,1) no-scale supergravity model and a
dilaton-induced supersymmetry breaking scenario. Both imply universal soft
supersymmetry breaking parameters: m0=0,A=0 and
m_0=\coeff{1}{\sqrt{3}}m_{1/2}, A=-m_{1/2} respectively. In either case the
models depend on only three parameters: mt, tanβ, and mg~.
We present a comparative study of the sparticle and Higgs spectra of both
models and conclude that even though both can be partially probed at the
Tevatron, LEPII, and HERA, a larger fraction of the parameter space of the
no-scale model is actually accessible. In both cases there is a more
constrained version which allows to determine tanβ in terms of
mt,mg~. In the strict no-scale case we find that the value of mt
determines the sign of μ (\mu>0:\,m_t\lsim135\GeV,
\mu<0:\,m_t\gsim140\GeV) and whether the lightest Higgs boson mass is above
or below 100\GeV. In the more constrained version of the dilaton scenario,
tanβ≈1.4−1.6 and m_t\lsim155\GeV, 61\GeV\lsim m_h\lsim91\GeV
follow. Thus, continuing Tevatron top-quark searches and LEPI,II Higgs searches
could probe this restricted scenario completely.Comment: CERN-TH.6926/93, CTP-TAMU-33/93, LaTeX, 33 pages, 11 embedded
figures. Significant numerical correction to the dilaton scenario. Complete
ps file (7943 blocks,3.33MB) available via anonymous ftp from site
tamsun.tamu.edu in directory incoming, filename: CTP-TAMU-33-93.p