Reconciling Grand Unification with Strings by Anisotropic Compactifications

Understand

We analyze gauge coupling unification in the context of heterotic strings on anisotropic orbifolds.

• This construction is very much analogous to effective 5 dimensional orbifold GUT field theories.
• Our analysis assumes three fundamental scales, the string scale, $\mstring$, a compactification scale, $\mc$, and a mass scale for some of the vector-like exotics, $\mex$; the other exotics are assumed to get mass at $\mstring$.
• In the particular models analyzed, we show that gauge coupling unification is not possible with $\mex = \mc$ and in fact we require $\mex \ll \mc \sim 3 \times 10^{16}$ GeV.