Levels of U(1)y in Minimal String Model on Z(N)*Z(M) Orbifolds

TL;DR

This paper investigates the levels of U(1)_Y in a minimal string model on Z(N)*Z(M) orbifolds, analyzing gauge coupling threshold corrections and experimental constraints to identify viable models.

Contribution

It provides a detailed analysis of U(1)_Y levels in minimal string models on orbifolds, including threshold corrections and experimental bounds, which was not previously explored.

Findings

Z_3×Z_3 orbifold cannot produce the minimal string model at M_Z SUSY scale.

Allowed U(1)_Y levels are constrained by LEP data.

Estimated minimum values of moduli for viable models.

Abstract

We study a minimal string model possessing the same massless spectra as the MSSM on $Z_N\times Z_M$ orbifolds. Threshold corrections of the gauge coupling constants of SU(3), SU(2) and U(1)$_Y$ are investigated in a case of an overall modulus. Using computer analyses, we search ranges of levels of U(1)$_Y$ allowed by the LEP experiments. It is found that $Z_3\times Z_3$ can not derive the minimal string model for a $M_Z$ SUSY breaking scale. The minimum values of the overall moduli are estimated within the ranges of the levels.