The shape dependence of chameleon screening

TL;DR

This paper introduces a numerical method to analyze how the shape of objects affects chameleon screening of fifth forces, revealing that non-spherical shapes can significantly alter the screening effect.

Contribution

It provides a numerical tool to compute chameleon fields around arbitrary shapes, extending understanding beyond simple geometries and showing shape-dependent variations in screening.

Findings

Deviations from spherical symmetry can increase chameleon acceleration by up to a factor of 3.

Objects minimizing internal dimensions are less effectively screened.

Numerical solutions for arbitrary shapes are now feasible with the introduced code.

Abstract

Chameleon scalar fields can screen their associated fifth forces from detection by changing their mass with the local density. These models are an archetypal example of a screening mechanism, and have become an important target for both cosmological surveys and terrestrial experiments. In particular there has been much recent interest in searching for chameleon fifth forces in the laboratory. It is known that the chameleon force is less screened around non-spherical sources, but only the field profiles around a few simple shapes are known analytically. In this work we introduce a numerical code that solves for the chameleon field around arbitrary shapes with azimuthal symmetry placed in a spherical vacuum chamber. We find that deviations from spherical symmetry can increase the chameleon acceleration experienced by a test particle by up to a factor of $\sim 3$, and that the least screened objects are those which minimize some internal dimension.