Detecting Dark Energy in the Laboratory

Transcription

1 Detecting Dark Energy in the Laboratory Collaboration with C. van de Bruck, A. C. Davis, D.Mota and D. Shaw. Astroparticle Toulouse 2007 hep-ph/ arxiv:0707/2801,

2 Outline Chameleon fields and dark energy Gravity and astrophysical tests Casimir force Chameleon optics

3 Cosmic Acceleration

4 Nearly Massless Fields very fast roll implies that indistinguishable from a cosmological constant If then Nearly massless field Leads to strong gravitational constraints

5 Gravity Tests Fifth force experiments Equivalence principle

6 Effective field theories with gravity and scalars coupling constant to matter gravitational coupling constant: Geodesics deviate from general relativity

7 Chameleon Fields When coupled to matter, moduli have matter dependent effective potential In cosmology coupling to nonrelativistic matter only

8 Typical example: Ratra-Peebles potential Constant coupling to matter

9 Chameleon field: field with a matter dependent mass A way to reconcile gravity tests and cosmology: Nearly massless field on cosmological scales Massive field in the atmosphere Allow large gravitational coupling constant of order one or more Possible non-trivial effects in the solar system (satellite experiments)

10 The Thin Shell Effect The field outside a compact body of radius R interpolates between the minimum inside and outside the body Inside the solution is nearly constant up to the boundary of the object and jumps over a thin shell Outside the field is given by The thin shell is determined by

11 Thin shell: deviations from Newton s law are given by for large objects (sun, earth, moon), Newton s potential is large and a thin shell is always present Planetary motion unaffected by the chameleon field (no anomaly in lunar ranging experiment) Thick shell: for small objects, large deviations from Newton s law if field essentially massless

12 Detecting Chameleon Fields dark energy on your desk top with Casimir Force

13 Detecting Chameleons Chameleon force looks very similar to the Casimir force:

14 Casimir Force

15 Casimir Force Experiments Measure force between Two parallel plates Difficult to keep plates parallel A plate and a sphere Harder to calculate analytically. R. S. Decca et al.,prd 75 (2007) S. K. Lamoreaux, PRL 78 (1997)

16 What the future holds

17 New Experiments

18 New Experiments

19 Optical Experiments: Probing Scalar Fields?

20 The original PVLAS experiment claimed to have observed a signal for the birefrigence (ellipticity) and the dichroism (rotation) of a polarised laser beam going through a static magnetic field. The phenomenon could be interpreted as a result of the mixing between photons and scalars. More precisely: a coupling between 2 photons and a scalar can induce two effects: Rotation: : a photon can be transformed in a scalar. Ellipticity: : a photon can be transformed into a scalar and then regenerated as a photon (delay)

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22 PVLAS: new results New runs looking for experimental artifacts have contradicted the experimental results. No rotation signal observed at 2.3 T and 5.5 T No ellipticity signal at 2.3 T and a large positive signal at 5.5 T Ellipticity incompatible with a traditional scalar/axion interpretation ( scaling).

23 PVLAS vs CAST Putative PVLAS experimental results could be seen as a result of the coupling: Limits on mass of scalar quite stringent: No contradiction with CAST experiments on scalar emitted from the sun What if? CHAMELEON?

24 The energy density depends on the magnetic field: The mass of the chameleon is given by: No chameleon production in the sun if massive enough: For a density the mass in the sun is: Hence chameleons evade the CAST bound.

25 Testing Chameleons Gravitational tests: earth: solar system: Cosmology: modification of growth factor at short distance: cosmological variation of the fine structure constant

26 One might wonder if the chameleon affected precision experiments like the anomalous magnetic moment of the muon via the interaction When one evaluates the diagram, it is which is much less than the direct contribution. Other corrections are smaller eg to hyperfine splitting

27 Chameleon Optics Chameleons never leave the cavity (outside mass too large, no tunnelling) Chameleons do not reflect simultaneously with photons. Chameleons propagate slower in the no-field zone within the cavity

28 Rotation

29 Ellipticity

30 Predictions Ellipticity always larger than rotation by a factor N (number of passes)

31 Can fit the new data with various values of n and M: We know that these parameters lead to a full compatibility with gravity tests, cosmology, CAST. BMV (and others) should give us more clues.

32 Conclusions Chameleon fields can reconcile quintessence and gravity experiments. Will be tested soon via Casimir and optical measurements. Exciting time??

33 Radiative corrections In the Einstein frame, below the electron mass, the effective theory obtained by integration out matter fields involves only photons and chameleons with a correction the scalar potential determined solely by covariance: Fine tuning of the cosmological constant implies that the corrections to the mass of the chameleons are suppressed too. In the Jordan frame, all radiative processes involving only standard model fields (not gravity) do not involve the chameleon at all. Hence the form of the coupling of the chameleon to matter is stable.