Hunting for Chameleons Hunting for Chameleons

Centre for Theoretical CosmologyCentre for Theoretical CosmologyUniversity of CambridgeUniversity of Cambridge

Moriond 2008 Moriond 2008

astro-ph/0309300 PRL J. Khoury and A.W astro-ph/0309411 PRD J. Khoury and A.Wastro-ph/0408415 PRD P. Brax, C. van de Bruck, J.Khoury, A. Davis and A.W hep-ph in progress A. Chou, J. Steffen, W. Wester, A. Uphadye and A.Wastro-ph in progress A. Uphadye and A. W

Amanda WeltmanAmanda Weltman

PlanPlan• Motivation - Theoretical + Observational

• Chameleon idea and thin shell effect

• Predictions for tests in space

• Dark Energy Candidate

• Quantum vacuum polarisation experiments

• The GammeV experiment and Chameleons

We can learn about fundamental physics using low energy and low cost techniques.

See Mota talk

See Mota talk

See Mota talk

• 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

MotivationMotivation

Tension between theory and observationsOpportunity! - Connect to Cosmology

Solutions?Solutions?

• String loop effects Damour & Polyakov

• Approximate global symmetry Carroll

• Invoke a potential

1. Suppress the coupling strength :

2. Field acquires mass due to some mechanism :

• Chameleon Mechanism Khoury & A.W• Flux Compactification KKLT• Special points in moduli space - new d.o.f become light Greene, Judes, Levin, Watson & A.W

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

IngredientsIngredients

Matter Fields

Reduced Planck Mass

Einstein Frame MetricConformally Coupled

Potential is of the runaway form

Coupling to photons

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 <

Strong CouplingStrong Coupling

Thin shell suppression

Remember :

Effective coupling is independent of !!

If an object satisfies thin shell condition - the force is independent independent

Lab experiments are compatible with large - strong couplingstrong coupling!!

Thin shell possible in space suppress signal

Mota and ShawStrong coupling not ruled out by local experiments!

>> 1 more likely to satisfy thin shell condition

Strong coupling is not ideal for space tests - loophole

Coupling to PhotonsCoupling to Photons

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• Expect small birefringence• Polarisation : Linear elliptical

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 PVLASDavis, Brax, van de Bruck

(g = 1/M)

(Polarizzazione del Vuoto con LASer)PVLASPVLAS

Too heavy to produce CAST bounds easily satisfied

But +

GammeVGammeV

“ [Photon]-[dilaton-like chameleon particle] regeneration using a "particle trapped in a jar" technique “ - http://gammev.fnal.gov

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 - at least rule out chunks of parameter space!

A. Chou, J. Steffen, A. Uphadye, A.W. and W. Wester

See also - Gies et. Al. + Ahlers et. Al.

Alps at DESY, LIPSS at JLab, OSQAR at CERN, BMV, PVLAS

GammeVGammeV

QuickTime™ and aTIFF (Uncompressed) decompressor

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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

AfterglowAfterglow

QuickTime™ and aTIFF (Uncompressed) decompressor

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QuickTime™ and aTIFF (Uncompressed) decompressor

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Decay time vs couplingDecay time vs coupling Afterglow vs timeAfterglow vs time

B = 5T, L = 6M, E = 2.3eV

Transition probability :

Flux of photons :

Integration time:

Afterglow 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?

Data Analysis is under way!

• Bounds from Astrophysics and Cosmology A.W and A. Uphadye in progress

Conclusions/OutlookConclusions/Outlook

• Complementary Complementary tools of probing fundamental physics

• SpaceSpace tests of gravity

• Intriguing cosmological consequencescosmological consequences : chameleon could be causing current accelerated expansionaccelerated expansion

• 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

A lot to learn from probes of the low energy low energy frontierfrontierusing spare parts from the high energy high energy frontierfrontier

SupplementarySupplementary

Constraints on Model Constraints on Model ParametersParameters

+

Coincides with Energy scale of Dark Coincides with Energy scale of Dark EnergyEnergy

Fifth ForceFifth Force5th Force:

Separation

Strength of interaction,

Potential :

Range of interaction

Thin shell

Require both earth and atmosphere display thin shell effect

Hoskins et. Al. < 10-3

Quantum VacuumQuantum Vacuum

• Use a magnetic field to disturb the vacuum• Probe the disturbance with photons

Classical Vacuum Quantum Vacuum

BirefringenceBirefringence

Quantum vacuum behaves like a birefringent medium

Vacuum region

Linearly polarised light

• Different index of refraction for different components of polarisation

• Different components of polarisation vector travel with different velocity• Result: same amplitude but out of phase• Polarisation : Linear elliptical

Elliptically polarised light

http://www.ts.infn.it/physics/experiments/pvlas/

DichroismDichroismDifferential absorption of polarisation components

• One component of polarisation vector preferentially absorbed• Result: same phase but different amplitude• Polarisation : Rotation in polarisation plane

In vacuum :• Birefringence expected to be v. small• No dichroism expected

PVLAS : anomolous signals for both rotation and ellipticity

New Physics?

PVLASPVLAS(Polarizzazione del Vuoto con LASer)

ALP interpretation photon splits into neutral scalar

pseudoscalar scalar

or

: Angle betw pol and B

Extract information about m and g and about parity!

Ellipticity:

Rotation:

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

Davis, Brax, van de Bruck, Khoury and A.W.