Hidden Sectors in String Theory: Kinetic Mixings, Fifth Forces and Quintessence

TL;DR

This paper investigates how light moduli in string compactifications interact with the visible sector via kinetic mixings, deriving bounds on extra-dimensional volume and implications for quintessence models and fine-tuning.

Contribution

It computes kinetic mixings in string compactifications, establishing lower bounds on moduli interactions and compactification volume based on fifth force constraints.

Findings

Interactions scale with inverse powers of compactification volume

Large volumes are required to evade fifth force bounds

Results inform fine-tuning for light modulus stability

Abstract

Light moduli fields in string compactifications can have interesting implications for particle physics and cosmology. Fifth force bounds impose stringent constraints on the interactions of such moduli with the visible sector. To be consistent with the bounds, they need to be part of hidden sectors which interact with the Standard Model with weaker-than-Planck suppressed interactions. We consider scenarios in which the visible sector degrees of freedom are localised in the compactification and light moduli arise as closed string degrees of freedom associated with hidden sectors which are geometrically separated (in the extra-dimensions) from the Standard Model. Kinetic mixings lead to interactions between the moduli and the visible sector - we compute these using Kaehler potentials of string/M-theory compactifications. We argue that in general these interactions provide a lower bound on the strength of the interactions between the moduli and the visible sector. The interactions scale with inverse powers of the volume of the compactification, thus fifth force bounds can be translated to lower bounds on the volume of the extra-dimensions. We find that compactification volumes have to be large to evade the bounds. This imposes interesting constraints on quintessence model building in string theory. Our results for the strength of the interactions can also be used to quantify the fine-tuning necessary for the stability of the potential of a light modulus against quantum corrections involving visible sector loops.