testing chameleon dark energy
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Testing Chameleon Dark Testing Chameleon Dark EnergyEnergy
Amanda WeltmanAmanda Weltman
University of University of CambridgeCambridge
Portsmouth June 2008Portsmouth June 2008
University of Cape TownUniversity of Cape Town
MotivationMotivation• Massless scalar fields are abundant in String and SUGRA theories• Massless fields generally couple directly to matter with gravitational strength
• Unacceptably large Equivalence Principle violations
• Coupling constants can vary
• Masses of elementary particles can vary
Gravitational strength coupling+Light scalar field
Tension between theory and observationsOpportunity! - Connect to Cosmology
ObservationsObservations
• Dark Energy p < 0
• Cosmological Constant,
• Dynamical e.o.s w -1
Accelerated expansion of the Universe
Quintessence Need light scalar fieldlight scalar field
Chameleon EffectChameleon Effect
Mass of scalar field depends on local matter density
In region of high density mass is large EP viol suppressed
In solar system density much lower fields essentially free
On cosmological scales density very low m ~ H0
Field may be a candidate for acc of universe
astro-ph/0309300 PRL J. Khoury and A.W astro-ph/0309411 PRD J. Khoury and A.W
IngredientsIngredients
Matter Fields
Reduced Planck Mass
Einstein Frame MetricConformally Coupled
Potential is of the runaway form
Coupling to photons
astro-ph/0408415 PRD P. Brax, C. van de Bruck, J.Khoury, A. Davis and A.W
Effective Effective PotentialPotential
Equation of
motion :
Dynamics governed by Effective potential :
Energy density in the ith form of matter
Predictions for Tests in Predictions for Tests in SpaceSpace
Different behaviour in space
STEP ~ 10-18
GG ~ 10-17
MICROSCOPE ~ 10-15
Tests for UFF
Near- future experiments in space :
We predict
New Feature !!
SEE Capsule
Corrections of O(1) to Newton’s Constant
Eöt-Wash Bound < 10-13
RE/RE< 10-710-15 <
Cosmological EvolutionCosmological Evolution
What do we need?
• attractor solution
If field starts at min, will follow the min
• Slow rolls along the attractor
• must join attractor before current epoch
• Variation in m is constrained to be less than ~ 10%. Constrains BBN the initial energy density of the field.
Weaker bound than usual quintessence
astro-ph/0408415 PRD P. Brax, C. van de Bruck, J.Khoury, A. Davis and A.W
Strong CouplingStrong Coupling
Thin shell suppression
Where :
Effective coupling is independent of !!
If an object satisfies thin shell condition - the force is independent independent
Mota and ShawStrong coupling not ruled out by local experiments!
>> 1 thin shell more likely suppresses space signal
LabLab tests on earth can probe a range of parameter space that is complementarycomplementary to space tests.
Opportunity?Opportunity?Loophole!
Coupling to PhotonsCoupling to PhotonsRemember :
Introduces a new mass scale :
Effective potential :
We can probe this term in quantum vacuum experiments
• Use a magnetic field to disturb the vacuum• Probe the disturbance with photons
Test the F2 term
To explain unexpected birefringence and dichroism results
requires and
Conflicts with astrophysical bounds e.g. CAST (solar cooling)
Chameleons - naturally evade CAST bounds and explain PVLASBrax, Davis, van de Bruck
(g = 1/M)
(Polarizzazione del Vuoto con LASer)
PVLAS and CASTPVLAS and CAST
Too heavy to produce CAST bounds easily satisfied
But +
(CERN Axion Solar Telescope)
Particles Trapped in a JarParticles Trapped in a Jar
See also - Gies et. Al. + Ahlers et. Al. (DESY) Alps at DESY, LIPSS at JLab, OSQAR at CERN, BMV
A. Chou et. Al. 0806.2438 [hep-ex]
“ [Photon]-[dilaton-like chameleon particle] regeneration using a "particle trapped in a jar" technique “
Idea : • Send a laser through a magnetic field• Photons turn into chameleons via F2 coupling
• Turn of the laser• Chameleons turn back into photons
• Observe the afterglow
Failing which - rule out chunks of parameter space!
http://gammev.fnal.gov
GammeVGammeV
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a) Chameleon production phase: photons propagating through a region of magnetic field oscillate into chameleons
Nd:YAG laser at 532nm, 5ns wide pulses, power 160mJ, rep rate 20Hz
Tevatron dipole magnet at 5T
PMT with single photon sensitivity
Glass window
b) Afterglow phase: chameleons in chamber gradually decay back into photons and are detected by a PMT
• Photons travel through the glass
• Chameleons see the glass as a wall - trapped
A. Uphadye
http://gammev.fnal.gov
SchematicSchematic
AfterglowAfterglow
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Observing window
Stronger coupling decays too fast
Excluded RegionExcluded Region
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PseudoscalarScalar
Fast afterglow decay rates prevent excluding large coupling
Excluded regions
Using minimum afterglow predictions, the sensitivity at low coupling is determined by the PMT noise rate.
ComplicationsComplications• Not longitudinal motion - chameleons and photons bounce• absorption of photons by the walls• reflections don’t occur at same place
• Photon penetrates into wall by skin depth• Chameleon bounces before it reaches the wall
Phase difference at each reflection. V dependent
• Other loss modes. Chameleon could decay to other fields?• Fragmentation?
• Vacuum design is ineficient for constraining models • Roughing pump decreases Pgas 10-3 Torr • Turbo molecular pump decreases to 10-7 Torr but removes gas volume. I.e. can remove chameleons.
Conclusions/OutlookConclusions/Outlook
Complementary Complementary tools of probing fundamental physics
• SpaceSpace tests of gravity
• Dark Energy Dark Energy candidate
• LabLab tests can probe a range of parameter space that is complementarycomplementary to space tests (qm vacuum and casimir)
• Chameleon fieldsChameleon fields: Concrete, testable predictions
• New bounds from AstrophysicsAstrophysics and CosmologyCosmology
• First results now out• Potential to dramatically improve these constraints in next generation experiment
• ChameleonsChameleons weaken bounds on f(R) modelsf(R) models(Hu and Sawicki 2007)
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