Where are the Walls?

TL;DR

This paper investigates whether spatial variations in the fine-structure constant can be explained by the presence of one or two domain walls, finding that two-wall models fit the data significantly better than simpler models, though the standard model remains plausible.

Contribution

It introduces a two-domain wall model to explain spatial variations in the fine-structure constant and compares its fit to observational data against simpler models.

Findings

Two-wall solution provides a significantly better fit than single-wall or dipole models.

Including extra random error improves the fit of domain wall models to the data.

Standard Model still has a reasonable p-value (~20%) despite alternative explanations.

Abstract

The reported spatial variation in the fine-structure constant at high redshift, if physical, could be due to the presence of dilatonic domains, and one or more domain walls inside our horizon. An absorption spectrum of an object in a different domain from our own would be characterized by a different value of alpha. We show that while a single wall solution is statically comparable to a dipole fit, and is a big improvement over a weighted mean (despite adding 3 parameters), a two-wall solution is a far better fit (despite adding 3 parameters over the single wall solution). We derive a simple model accounting for the two-domain wall solution. The goodness of these fits is however dependent on the extra random error which was argued to account for the large scatter in most of the data. When this error is omitted, all the above solutions are poor fits to the data. When included, the solutions that exhibit a spatial dependence agree with the data much more significantly than the Standard Model; however, the Standard Model itself is not a terrible fit to the data, having a p-value of ~ 20 %.