Ellipticity Weakens Chameleon Screening

Abstract

The chameleon mechanism enables a long range fifth force to be screened in dense environments when non-trivial self interactions of the field cause its mass to increase with the local density. To date, chameleon fifth forces have mainly been studied for spherically symmetric sources, however the non-linear self interactions mean that the chameleon responds to changes in the shape of the source differently to gravity. In this work we focus on ellipsoidal departures from spherical symmetry and compute the full form of the chameleon force, comparing it's shape dependence to that of gravity. Enhancement of the chameleon force by up to 40% is possible when deforming a sphere to an ellipsoid of the same mass, with an ellipticity $\simeq 0.99$.

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• Cluster abundance in chameleon $f(R)$ gravity I: toward an accurate halo mass function prediction
• Using Atom Interferometry to Detect Dark Energy
• A parametrisation of modified gravity on nonlinear cosmological scales
• Exact Solutions to Non-Linear Symmetron Theory: One and Two Mirror Systems
• Imprints of Chameleon f(R) Gravity on Galaxy Rotation Curves
• Constraining screened fifth forces with the electron magnetic moment
• Tests of Gravity with Galaxy Clusters
• The shape dependence of chameleon screening
• Exact Solutions to Non-Linear Symmetron Theory II: One and Two Mirror Systems
• Calculation of the critical overdensity in the spherical-collapse approximation
• SELCIE: A tool for investigating the chameleon field of arbitrary sources
• Vainshtein screening for slowly rotating stars
• Solving nonlinear Klein-Gordon equations on unbounded domains via the Finite Element Method
• Non-linear density-velocity dynamics in $f(R)$ gravity from spherical collapse
• Non-linear matter power spectrum without screening dynamics modelling in $f(R)$ gravity
• What to expect from scalar-tensor space geodesy
• Breaking the cosmological invariance of the dark matter halos shape as a new probe of modified gravity