Root Bundles and Towards Exact Matter Spectra of F-theory MSSMs

TL;DR

This paper investigates root bundles in F-theory compactifications, linking them to gauge potentials and constraining matter spectra to avoid vector-like exotics in MSSM models.

Contribution

It provides a systematic analysis of root bundle constraints on matter curves in F-theory MSSMs, extending diagrammatic methods to determine cohomologies and physical spectra.

Findings

Derived lower bounds for root bundle and spin bundle combinations satisfying physical constraints.

Extended diagrammatic description of root bundles on nodal and blown-up curves.

Constrained vector-like spectra in F-theory MSSMs to avoid exotics.

Abstract

Motivated by the appearance of fractional powers of line bundles in studies of vector-like spectra in 4d F-theory compactifications, we analyze the structure and origin of these bundles. Fractional powers of line bundles are also known as root bundles and can be thought of as generalizations of spin bundles. We explain how these root bundles are linked to inequivalent F-theory gauge potentials of a $G_4$-flux. While this observation is interesting in its own right, it is particularly valuable for F-theory Standard Model constructions. In aiming for MSSMs, it is desired to argue for the absence of vector-like exotics. We work out the root bundle constraints on all matter curves in the largest class of currently-known F-theory Standard Model constructions without chiral exotics and gauge coupling unification. On each matter curve, we conduct a systematic "bottom"-analysis of all solutions to the root bundle constraints and all spin bundles. Thereby, we derive a lower bound for the number of combinations of root bundles and spin bundles whose cohomologies satisfy the physical demand of absence of vector-like pairs. On a technical level, this systematic study is achieved by a well-known diagrammatic description of root bundles on nodal curves. We extend this description by a counting procedure, which determines the cohomologies of so-called limit root bundles on full blow-ups of nodal curves. By use of deformation theory, these results constrain the vector-like spectra on the smooth matter curves in the actual F-theory geometry.