Some Topics in the Low-Energy Physics from Superstrings

Abstract

The recent revival of string theories^1-5 was mostly motivated by purely phenomenological reasons. The experimental results obtained during the last decades indicate that quarks and leptons come in chiral (complex) representations of a gauge group SU(3) × SU(2) × U(1) (or some extension). The important point of the heterotic E₈ × E₈ superstring⁴ is that, since it contains explicit gauge bosons, one may obtain chiral low-energy fermions which transform like the standard quarks and leptons under an SU(3) × SU(2) × U(1) subgroup of E₈ × E₈ Still, the theory has no gauge or gravitational anomalies as shown for the field theory limit by Green and Schwarz². To some extent, the parity-breaking world we observe now is related to the left-right asymmetric construction of the heterotic string. This asymmetric construction is required to have explicit gauge bosons, which in turn are required to get low-energy chiral fermions (quarks and leptons). It is obvious that the possible phenomeno logical applications of the E₈ × E₈ string are at the root of the present interest for this theory. Other strings (e. g., the anomaly- free chiral type IIb superstring) are simpler and have less contrived constructions, but are certainly less popular, since their phenomenological uses do not seem very bright.