1. Michael Doran Institute for Theoretical Physics Universität Heidelberg Dark Energy in the lab?

2. Outline Dark Energy A lab proposal...... and why it cannot work Another ‘lab’ proposal that could work...... but only if we are really lucky

3. Dark Energy What is dark energy? Some would say: Vaccum Energy, i.e. cosmological constant Non-interacting scalar field(s) Scalar fields with interactions with (dark) matter Modifications to Einstein gravity...

4. A lab proposal by C. Beck and M.C. Mackey (2004) Measure spectrum of noise in current through shunting resistor in a Josephson junction circuit. Prediction: we should see frequency cut-off corresponding to vacuum energy. Theoretical prediction from the very general fluctuation-dissipation theorem of Callen & Welton (1951):

5. Looks like vacuum contribution, but is it? Unfortunately not! Reviewing derivation of Callan & Welton, you would find that: Result invariant under shift of Hamiltonian depends on density of states of the system under considerations. This is not directly related to density of states of vacuum. Won’t work!

6. Casimir effect does not see such a cut-off The cut-off proposed by Beck & Mackey has not been observed by Casimir measurements which have already probed the relevant range Yet, Casimir effect unable to probe vaccum energy anyhow: measures only derivative of energy blind to particles not coupled electro- magnetically

7. Dark Energy at Colliders If world has extra dimensions, mini black holes might form at collider.

8. Mini Black holes are larger and cooler

9. Example Black holes radiate all particles coupled to gravity. Depending on mass and spin, emissivity is slightly different. Counting degrees of freedom only known way to exclude light scalar field!

10. Emissivity depends on mass perfect black body n=7 M.D, J. Jäckel (2005) n=1

11. Counting effective degrees of freedom n=7 n=3 n=1 Temperature drops Kinematics

12. All known experiments only sensitive to EM-particles Josephson junction invariant under Casimir effect sees no cut-off Casimir effect also invariant under Only know possibility to rule out additional light degrees of freedom is a miniature black hole Black holes might form at colliders, however several if’s: –Needs large extra dimensions –LHC won’t reach precision necessary On the positive side, however: –If black holes produced at LHC, next generation collider could reach precision target of Conclusions