# Effects on the CMB from Compactification Before Inflation

## TL;DR

This paper explores how a compactification mechanism in theories with extra dimensions could leave observable signatures on the CMB, potentially explaining low multipole anomalies.

## Contribution

It introduces a model where extra dimensions are compactified before inflation, affecting CMB anisotropies and aligning with recent low multipole anomalies.

## Key findings

- Compactification affects low l multipole amplitudes.
- Models with expanding or contracting extra dimensions are consistent with observations.
- Potential explanation for CMB anomalies at low multipoles.

## Abstract

Many theories beyond the Standard Model include extra dimensions, though these have yet to be directly observed. In this work we consider the possibility of a compactification mechanism which both allows extra dimensions and is compatible with current observations. This compactification is predicted to leave a signature on the CMB by altering the amplitude of the low l multipoles, dependent on the amount of inflation. Recently discovered CMB anomalies at low multipoles may be evidence for this. In our model we assume the spacetime is the product of a four-dimensional spacetime and flat extra dimensions. Before the compactification, both the four-dimensional space- time and the extra dimensions can either be expanding or contracting independently. Taking into account physical constraints, we explore the observational consequences and the plausibility of these different models.