Chameleon Fields Reconciling Quintessence with Gravity Bounds

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1 Chameleon Fields Reconciling Quintessence with Gravity Bounds David F. Mota University of Heidelberg March 2008

2 What is the nature of Dark Energy?! The answer may be in physics beyond Standard Model?

3 Dark Energy: New Field and/or Modified Gravity?

4 Dark Energy: New Field and/or Modified Gravity? Whatever it is... constraints are very strong! Solar System Bounds (Modified Gravity) Astrophysical Bounds (Coupling to Dark Matter) Cosmology, Astrophysics Laboratory Bounds (Coupling to ordinary matter) V (r) = G m 1m 2 (1 + β 1 β 2 e r/λ ) r Amendola PRD (1999) Long et al. Nature (2004)

5 Chameleon Fields Self-interacting scalar fields strongly coupled to matter Chameleons have a matter dependent effective potential Cosmology:

6 Chameleon Mass Not Constant A chameleon field has mass: Not constant but changes with local matter density Large Mass (short range) Small Mass (long range) The stronger the matter coupling, the faster adapt and the better hide from experiments

7 The Thin Shell Effect R

8 The Thin Shell Effect R Khoury&Weltman PRL (2004)

9 The Thin Shell Effect R Khoury&Weltman PRL (2004)

10 The Thin Shell Effect R Field reaches effective minimum almost everywhere in the body All field variations confined to small region near body surface This region is called a thin-shell

11 Fifth Force on Body with Thin-Shell

12 Fifth Force on Body with Thin-Shell

13 Fifth Force on Body with Thin-Shell

14 Fifth Force on Body with Thin-Shell Thin shell Fifth force produced in a body with thin-shell becomes very small

15 Bounds on Chameleon Fields

16 Bounds on Chameleon Fields

17 Bounds on Chameleon Fields Parameter space increased enormously!

18 Bounds on Chameleon Fields Parameter space increased enormously! (! shell No major changes for small couplings (no thin

19 Bounds on Chameleon Fields Parameter space increased enormously! (! shell No major changes for small couplings (no thin (! effect Major changes for large couplings (thin shell

20 Bounds on Chameleon Fields Parameter space increased enormously! (! shell No major changes for small couplings (no thin (! effect Major changes for large couplings (thin shell Parameter space increases for highly non-linear Potentials

21 Bounds on Chameleon Fields Small couplings: best constraints from short-range lab tests

22 Bounds on Chameleon Fields Small couplings: best constraints from short-range lab tests The problem: β >10 4, BeCu electromagnetic shield develops a thin-shell

23 Bounds on Chameleon Fields Small couplings: best constraints from short-range lab tests The problem: β >10 4, BeCu electromagnetic shield develops a thin-shell Best upper bounds on β come from Cosmology

24 Bounds on Chameleon Fields Small couplings: best constraints from short-range lab tests The problem: β >10 4, BeCu electromagnetic shield develops a thin-shell Best upper bounds on β come from Cosmology Particle Colliders could rule out already very large couplings

25 Conclusions

26 Conclusions Chameleon fields are able to evade a whole range of experiments and constraints on WEP and fifth forces Due to environmental dependent mass Thin-Shell Effect Non-Linear terms in the bare potential

27 Conclusions Chameleon fields are able to evade a whole range of experiments and constraints on WEP and fifth forces Due to environmental dependent mass Thin-Shell Effect Non-Linear terms in the bare potential Bounds from laboratories, solar system and astrophysical experiments are exponentially relaxed Improvements can be made doing space base experiments and redesigning some earth experiments

28 Conclusions Chameleon fields are able to evade a whole range of experiments and constraints on WEP and fifth forces Due to environmental dependent mass Thin-Shell Effect Non-Linear terms in the bare potential Bounds from laboratories, solar system and astrophysical experiments are exponentially relaxed Improvements can be made doing space base experiments and redesigning some earth experiments Chameleons are a candidate for dark energy Can reconcile quintessence and gravity experiments

29 Conclusions Chameleon fields are able to evade a whole range of experiments and constraints on WEP and fifth forces Due to environmental dependent mass Thin-Shell Effect Non-Linear terms in the bare potential Bounds from laboratories, solar system and astrophysical experiments are exponentially relaxed Improvements can be made doing space base experiments and redesigning some earth experiments Chameleons are a candidate for dark energy Can reconcile quintessence and gravity experiments Chameleon dark energy can be probed in the lab Will be tested soon via optical measurements Next generation of Casimir force test should detect them See Amanda Weltman s talk for probes in the Lab!