Structural Implications of the Chameleon Mechanism on White Dwarfs

We study the impact of the chameleon mechanism on the structure of white dwarfs. Using a shooting method of our design, we solve the corresponding scalar-tensor equilibrium equations for a Chandrasekhar equation of state, exploring various energy scales and couplings of the chameleon field to matter. We find the chameleon field to be in a thick-shell configuration, identifying for the first time in the literature a similarity relation for the radially normalised scalar field gradient. Our analysis reveals that the chameleon mechanism significantly alters the internal pressure of white dwarfs, leading to a notable reduction in the stellar radii and masses and shifting the mass-radius curves below those predicted by Newtonian gravity. Finally, we derive parametric expressions from our results to expedite future analyses of white dwarfs in scalar-tensor theories.