7 research outputs found
Non-Tachyonic Semi-Realistic Non-Supersymmetric Heterotic String Vacua
The heterotic--string models in the free fermionic formulation gave rise to
some of the most realistic string models to date, which possess N=1 spacetime
supersymmetry. Lack of evidence for supersymmetry at the LHC instigated recent
interest in non-supersymmetric heterotic-string vacua. We explore what may be
learned in this context from the quasi--realistic free fermionic models. We
show that constructions with a low number of families give rise to
proliferation of a priori tachyon producing sectors, compared to the
non--realistic examples, which typically may contain only one such sector. The
reason being that in the realistic cases the internal six dimensional space is
fragmented into smaller units. We present one example of a quasi--realistic,
non--supersymmetric, non--tachyonic, heterotic--string vacuum and compare the
structure of its massless spectrum to the corresponding supersymmetric vacuum.
While in some sectors supersymmetry is broken explicitly, i.e. the bosonic and
fermionic sectors produce massless and massive states, other sectors, and in
particular those leading to the chiral families, continue to exhibit fermi-bose
degeneracy. In these sectors the massless spectrum, as compared to the
supersymmetric cases, will only differ in some local or global U(1) charges. We
discuss the conditions for obtaining at the massless level in these
models. Our example model contains an anomalous U(1) symmetry, which generates
a tadpole diagram at one loop-order in string perturbation theory. We speculate
that this tadpole diagram may cancel the corresponding diagram generated by the
one-loop non-vanishing vacuum energy and that in this respect the
supersymmetric and non-supersymmetric vacua should be regarded on equal
footing. Finally we discuss vacua that contain two supersymmetry generating
sectors.Comment: 31 pages. 10 tables. Minor corrections. Tables are amended. Published
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