Gut model-building with fermionic four-dimensional strings

Physics Letters B, 1988

Physics Letters B, 1988

In this letter, the problems of the up-quark and neutrmo mass matrix, as well as the lepton non-conservation are dlscussed wthm the N= 1 supersymmetric SU (5 ) x U ( 1) model derived from the four-dlmenslonal fermlomc superstrmg

Physics Letters B, 1989

Physics Letters B, 1988

Physics Letters B, 1996

We present a model based on the gauge group SU(2) L ×SU(2) R ×SU(4) C with gauge couplings that are found to be unified at a scale M G near the string unification scale. The model breaks to the minimal supersymmetric standard model at a scale M I ∼ 10 12 GeV, which is instrumental in producing a neutrino in a mass range that can serve as hot dark matter and this scale can also solve the strong CP problem via the Peccei-Quinn (PQ) mechanism with an invisible harmless axion. We show how this model can accommodate low and high values of tan β and "exotic" representations that often occur in string derived models. We show that this model has lepton flavor violation which can lead to processes which are one or two orders of magnitude below the current experimental limits.

Physics Letters B, 1990

Many low-energy superstring models contain a pseudo-anomalous U (1) as a global symmetry. We investigate the possibility of having the ensuing axion solve the strong CPproblem. We conclude that in heterotic strings with non-abelian hidden gauge groups, this axion cannot solve the strong CP problem. We also comment on alternative solutions to the strong CP puzzle in strings, based on approximate global symmetries of the low-energy lagrangian. We point out potential problems this mechanism would face when applied to realistic models. We find the massless up quark solution to the strong CP problem quite satisfactory. As an example, we work out all the details behind our general remarks for the flipped SU (5) × U (1) model. Previous studies of the hierarchical fermion mass spectrum in this model offer substantial support to our proposed solution to the puzzle.

Physics Letters B, 1989

We study lepton-number violations in the flipped SU (5) X U (1) model m the context of no-scale supergravlty We find that the experimental hmlts on g~e'/, g-,ee~, and g conversmn in nuclei generally imply an upper bound on the top quark mass and a lower bound on the gaugmo mass. We conclude that the seed of supersymmetry breaking in no-scale models (gauglno masses) radically changes some results obtained m "mimmal" N= 1 supergrawty m the leptonlc sector, while results m the hadromc sector (e.g. K-I(, B-13 mlxmgs, and b~ s3,) remam essentially unchanged

Physics Letters B, 1989

Nuclear Physics B, 1989

A string-loop generated Fayet-Iliopoulos term can trigger, in four-dimensional superstring models with an anomalous U(1), the presence of global and local cosmic strings and, depending on the values of the string parameters M s (string scale) and M c (compactification scale), a period of inflationary expansion of the universe. The observational effects of inflation (density inhomogeneities) and cosmic strings (gravitational radiation, etc.) put severe bounds on the values of M~ and Me.

Physics Letters B, 1989

In the low-energy theory, of four-dimensional superstrings the spontaneous breakdown of a pseudo-anomalous [J (1) can trigger (but not necessarily) the formation of global and/or local cosmic strings. When cosmic strings are formed, supersymmetry is broken inside the string cores with a positive cosmological constant and an exponential growth of the cosmic scale factor. Strings are conformally stretched with the inflationary expansion, never enter the physics horizon and can have no observable (e.g. optical) effects. Off-string regions are in a (radiation-dominated) FRW universe. Most of our observable universe would still be inflating today unless a late (conventional) period of inflation transforms an off-string region into our present universe. The required amount of inflation coincides with the one needed to solve the usual flatness and horizon problems of the standard cosmological model. We consider, as an example, the chaotic inflation associated with the low-energy breaking (~ 1 TeV) of supersymmetry.

Physical Review D, 1995

Ioannis Giannakis (a),(b) , D.V. Nanopoulos (a),(b),(c) and Kajia Yuan (a),(b)

Physics Letters B, 1988

Physics Letters B, 1988