PIRSA:12100125  ( MP4 Medium Res , MP4 Low Res , MP3 , PDF ) Which Format?
Kicking Chameleons: Early Universe Challenges for Chameleon Gravity
Speaker(s): Adrienne Erickcek
Abstract: Chameleon gravity is a scalar-tensor theory that mimics general relativity in the Solar System. The scalar degree of freedom is hidden in high-density environments because the effective mass of the chameleon scalar depends on the trace of the stress-energy tensor.  In the early Universe, when the trace of the stress-energy tensor is nearly zero, the chameleon is very light and Hubble friction prevents it from reaching its potential minimum.  Whenever a particle species becomes non-relativistic, however, the trace of the stress-energy tensor is temporarily nonzero, and the chameleon begins to roll.  I will show that these "kicks" to the chameleon field have catastrophic consequences for chameleon gravity.  The velocity imparted to the chameleon is sufficiently large that the chameleon's mass changes rapidly as it slides past its potential minimum.  This nonadiabatic process shatters the chameleon field by generating extremely high-energy perturbations, casting doubt on chameleon gravity's viability as an alternative to general relativity.

Date: 25/10/2012 - 11:00 am
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