Chameleon dark energy - University of California, Los Angeles · Chameleon dark energy GammeV-CHASE...

Chameleon dark energyGammeV-CHASE

Chameleon and thin-shell effectsOscillation

Introduction

1 Cosmic acceleration is the greatest mystery in cosmology.

cosmological constant?scalar field, modified gravity ⇒ w(z) 6= −1, fifth forces, etc.

2 Chameleon dark energy

looks like cosmological constant on large scalesevades fifth force constraints by becoming massive inhigh-density environmentsphoton coupling ⇒ oscillation

3 GammeV-CHASE afterglow experiment

produce chameleon particles through oscillationtrap particles inside chamber“afterglow” as particles oscillate back into photonsconstraints on chameleon parameter space published

Amol Upadhye How dark is dark energy?



Chameleon scalar field

Action for a photon-coupled chameleon field:

S =

∫d4x

[− 1

2(∂φ)2 − V (φ) + Lmat(e

βmφMPl gµν) − 1

4 eβγφ

MPl FµνFµν]

nonlinear V ′

⇒ nonlinear e.o.m.

linear matter coupling

∼ βmρφ/MPl

photon coupling

∼ 12βγφ(B2 − E 2)/MPl

mass of field depends on matterdistribution

effective mass meff higher in denserenvironments

⇒ chameleon and thin-shell effects

chameleon-photonoscillation inbackgroundmagnetic field




Chameleon and thin-shell effects

(AU, Gubser, Khoury 2006)Amol Upadhye How dark is dark energy?

0

0.2

0.4

0.6

0.8

1

-20 -15 -10 -5 0 5 10 15 20

φ(x)

/φbu

lk

x [m-1eff]

0.3131030

thickness[m

eff-1 ]

force on test particle:F ∝ dφ/dx

vacuum



Chameleon-photon oscillation

γ ↔ φ conversion in background ~B field(from φF 2 interaction)

Oscillation probability

massless limit, parallel to ~B: Pγ↔φ =β2γB

2t2

4M2Pl

(AU, Steffen, Weltman 2010)

conversion rate for a chameleon particle

propagate through ~Bmeasure particle content after time ∆t

conversion rate Γ =Pγ↔φ(∆t)

∆taverage over particles to get total rate




Window as a quantum measurement device

0 5 10 15 20x [meff

-1]

density ρbackground φ0φ0 + δφphoton



Experimental setupConstraints

A simple afterglow experiment

(a) Production phase: photons streamed through ~B0 region; someoscillate into chameleons

(b) Afterglow phase: chameleons slowly oscillate back intophotons, escaping chamber




GammeV-CHASE apparatus

1 Multiple magnetic field runs

2 Partitioning of magnetic field region

3 Modulation of detector

4 Vacuum maintained by ion pump




Conversion rate in GammeV-CHASE

(AU, et. al., 2012 (in prep.))Amol Upadhye How dark is dark energy?

1e-16

1e-14

1e-12

1e-10

1e-08

1e-06

0.0001

0.0001 0.001 0.01 0.1

rate

[Hz]

meff(chamber) [eV]

decay

afterglow

ξref

0 (V∝ φ 4)π/3 (V∝ 1/φ )π (V∝ exp φ)



Expected afterglow signal


0.01

1

100

10000

1e+06

1e+08

1e+10

1e+12

-1500 -1000 -500 0 500 1000 1500 2000 2500 3000

afte

rglo

w ra

te [s

ec-1

]

time [sec]

0.2 T

0.45 T

1.0 T

2.2 T

5.0 T

observation period βγ=3e11





0.01

1

100

10000

1e+06

1e+08

1e+10

1e+12

-1500 -1000 -500 0 500 1000 1500 2000 2500 3000

afte

rglo

w ra

te [s

ec-1

]

time [sec]

0.05 T0.09 T

0.2 T

0.45 T

1.0 T

2.2 T

5.0 T






0.01

1

100

10000

1e+06

1e+08

1e+10

1e+12

-1500 -1000 -500 0 500 1000 1500 2000 2500 3000

afte

rglo

w ra

te [s

ec-1

]

time [sec]

0.05 T0.09 T

0.2 T0.45 T1.0 T2.2 T5.0 T






0.01

1

100

10000

1e+06

1e+08

1e+10

1e+12

-1500 -1000 -500 0 500 1000 1500 2000 2500 3000

afte

rglo

w ra

te [s

ec-1

]

time [sec]

0.05 T0.09 T0.2 T0.45 T1.0 T2.2 T5.0 T




GammeV-CHASE constraints

(Steffen, AU, et. al., 2010)Amol Upadhye How dark is dark energy?

effective mass meff [eV]

phot

on c

oupl

ing

β γ

scalarpseudoscalar

Collider constraints

GammeVconstraints

1e-05 0.0001 0.001 0.01 0.1 1e+10

1e+11

1e+12

1e+13

1e+14

1e+15

1e+16

1e+17

CHASE constraints

effective mass meff [eV]

phot

on c

oupl

ing

β γ

scalarpseudoscalar


GammeVconstraints

1e-05 0.0001 0.001 0.01 0.1 1e+10

1e+11

1e+12

1e+13

1e+14

1e+15

1e+16

1e+17

CHASE constraints



Constraints on dark energy, V (φ) ≈ M4Λ + M4−N

Λ φN

(Steffen, AU, et. al., 2010)Amol Upadhye How dark is dark energy?

matter coupling βm

phot

on c

oupl

ing

β γ


g γ =

βγ /

MP

l [G

eV-1

]

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

10000 1e+08 1e+12 1e+16 1e+20 1e+24 1e+10

1e+11

1e+12

1e+13

1e+14

1e+15

1e+16

1e+17

N=-1N=-2N=-4N=4, λ=10-2

N=4, λ=10-4

matter coupling βm

phot

on c

oupl

ing

β γ


g γ =

βγ /

MP

l [G

eV-1

]

1e-8

1e-7

1e-6

1e-5

1e-4

1e-3

1e-2

10000 1e+08 1e+12 1e+16 1e+20 1e+24 1e+10

1e+11

1e+12

1e+13

1e+14

1e+15

1e+16

1e+17

N=-1N=-2N=-4N=4, λ=10-2

N=4, λ=10-4



Conclusions

1 Laboratory searches for dark energy are complementary tocosmological probes.

2 GammeV and GammeV-CHASE attempted to produce, trap,and detect chameleon dark energy through its afterglow.

3 GammeV was a simple modification of an axion experiment,suggesting possibilities for future experiments.

4 GammeV-CHASE published constraints in Steffen, AU,Baumbaugh, Chou, Mazur, Tomlin, Weltman, Wester 2010.

excluded 4 orders of magnitude in βγ at meff = MΛ

bridged gap between GammeV and collider constraints




The End.


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