Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chameleons in the Early Universe: Kicks, Rebounds, and Particle
  Production   Chameleon gravity is a scalar-tensor theory that includes a non-minimal
coupling between the scalar field and the matter fields and yet 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 matter stress-energy tensor is nearly zero, the chameleon is
very light, and Hubble friction prevents it from reaching the minimum of its
effective potential. Whenever a particle species becomes non-relativistic,
however, the trace of the stress-energy tensor is temporarily nonzero, and the
chameleon begins to roll. We show that these "kicks" to the chameleon field
have catastrophic consequences for chameleon gravity. The velocity imparted to
the chameleon by the kick is sufficiently large that the chameleon's mass
changes rapidly as it slides past its potential minimum. This nonadiabatic
evolution shatters the chameleon field by generating extremely high-energy
perturbations through quantum particle production. If the chameleon's coupling
to matter is slightly stronger than gravitational, the excited modes have
trans-Planckian momenta. The production of modes with momenta exceeding 1e7 GeV
can only be avoided for small couplings and finely tuned initial conditions.
These quantum effects also significantly alter the background evolution of the
chameleon field, and we develop new analytic and numerical techniques to treat
quantum particle production in the regime of strong dissipation. This analysis
demonstrates that chameleon gravity cannot be treated as a classical field
theory at the time of Big Bang Nucleosynthesis and casts doubt on chameleon
gravity's viability as an alternative to general relativity.

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The categories of this paper are: chem-ph
21
The categories of this paper are: adap-org
17
The categories of this paper are: q-fin
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
30
The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
24
The categories of this paper are: dg-ga
12
The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: econ
5
The categories of this paper are: gr-qc
27
The categories of this paper are: comp-gas