Michael Doran

Institute for Theoretical Physics

Universität Heidelberg

Dark Energy in the lab?

Outline

• Dark Energy

• A lab proposal ...

• ... and why it cannot work

• Another ‘lab’ proposal that could work ...

• ... but only if we are really lucky

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

• ...

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):

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!

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

Dark Energy at Colliders

If world has extra dimensions, mini black holes might form at collider.

Mini Black holes are larger and cooler

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!

Emissivity depends on mass

perfect black body

n=7

M.D, J. Jäckel (2005)

n=1

Counting effective degrees of freedom

n=7

n=3

n=1 Temperature drops

Kinematics

• 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