38 research outputs found
Chameleon Fragmentation
A scalar field dark energy candidate could couple to ordinary matter and
photons, enabling its detection in laboratory experiments. Here we study the
quantum properties of the chameleon field, one such dark energy candidate, in
an "afterglow" experiment designed to produce, trap, and detect chameleon
particles. In particular, we investigate the possible fragmentation of a beam
of chameleon particles into multiple particle states due to the highly
non-linear interaction terms in the chameleon Lagrangian. Fragmentation could
weaken the constraints of an afterglow experiment by reducing the energy of the
regenerated photons, but this energy reduction also provides a unique signature
which could be detected by a properly-designed experiment. We show that
constraints from the CHASE experiment are essentially unaffected by
fragmentation for and potentials, but are weakened for
steeper potentials, and we discuss possible future afterglow experiments.Comment: 27 pages, 7 figure
Dark energy fifth forces in torsion pendulum experiments
The chameleon scalar field is a matter-coupled dark energy candidate whose
nonlinear self-interaction partially screens its fifth force at laboratory
scales. Nevertheless, small-scale experiments such as the torsion pendulum can
provide powerful constraints on chameleon models. Here we develop a simple
approximation for computing chameleon fifth forces in torsion pendulum
experiments such as Eot-Wash. We show that our approximation agrees well with
published constraints on the quartic chameleon, and we use it to extend these
constraints to a much wider range of models. Finally, we forecast the
constraints which will result from the next-generation Eot-Wash experiment, and
show that this experiment will exclude a wide range of quantum-stable models.Comment: 15 pages, 17 figures; matches version accepted by PR
Designing dark energy afterglow experiments
Chameleon fields, which are scalar field dark energy candidates, can evade
fifth force constraints by becoming massive in high-density regions. However,
this property allows chameleon particles to be trapped inside a vacuum chamber
with dense walls. Afterglow experiments constrain photon-coupled chameleon
fields by attempting to produce and trap chameleon particles inside such a
vacuum chamber, from which they will emit an afterglow as they regenerate
photons. Here we discuss several theoretical and systematic effects underlying
the design and analysis of the GammeV and CHASE afterglow experiments. We
consider chameleon particle interactions with photons, Fermions, and other
chameleon particles, as well as with macroscopic magnetic fields and matter.
The afterglow signal in each experiment is predicted, and its sensitivity to
various properties of the experimental apparatus is studied. Finally, we use
CHASE data to exclude a wide range of photon-coupled chameleon dark energy
models.Comment: 29 pages, 31 figures, 1 tabl
Quantum Stability of Chameleon Field Theories
Chameleon scalar fields are dark energy candidates which suppress fifth
forces in high density regions of the universe by becoming massive. We consider
chameleon models as effective field theories and estimate quantum corrections
to their potentials. Requiring that quantum corrections be small, so as to
allow reliable predictions of fifth forces, leads to an upper bound eV for gravitational strength coupling
whereas fifth force experiments place a lower bound of \,eV. An
improvement of less than a factor of two in the range of fifth force
experiments could test all classical chameleon field theories whose quantum
corrections are well-controlled and couple to matter with nearly gravitational
strength regardless of the specific form of the chameleon potential.Comment: 5 pages, 3 figures. Matches version accepted by PR
On the anomalous afterglow seen in a chameleon afterglow search
We present data from our investigation of the anomalous orange-colored
afterglow that was seen in the GammeV Chameleon Afterglow Search (CHASE). These
data includes information about the broad band color of the observed glow, the
relationship between the glow and the temperature of the apparatus, and other
data taken prior to and during the science operations of CHASE. While differing
in several details, the generic properties of the afterglow from CHASE are
similar to luminescence seen in some vacuum compounds. Contamination from this,
or similar, luminescent signatures will likely impact the design of
implementation of future experiments involving single photon detectors and high
intensity light sources in a cryogenic environment.Comment: 6 pages, 5 figures, submitted to PR