The closing session of the Perimeter workshop on "New ideas in low-energy tests of fundamental physics" was a stimulating discussion on open questions at the intersection of precision measurements and fundamental physics.  The discussion was guided by Derek Kimball's  list of questions that he kindly shares with you below. The video/audio record of the entire discussion can be found online here: part1 and part2.

Are there boring answers to exciting mysteries?

If one assumes, from the experimental perspective, the most boring solutions to mysteries: for example, a cosmological constant driving the accelerating expansion of the universe and dark matter that has no couplings to Standard Model particles, what mysteries still cannot be resolved?

Interaction of DM/DE with Standard Model particles/fields

Is non-gravitational interaction of DM/DE with Standard Model particles/fields well-motivated? (From astrophysical and cosmological measurements?)

Energy scale of new physics

Technical naturalness: for now should we not be overly concerned about this issue for experiments?

Hierarchy problem and its relation to the observed Higgs mass, cosmological constant, BICEP-2, Planck scale: how does this relate to the scale of new physics and where we should search?

New (?) idea of searching for fast-varying constants: could this be done in an astrophysical spectroscopic search?

It was noted that a phase transition process (or evolving couplings) could be introduced “avoid” technical naturalness problems... could there be phase transitions with very small effects that occur frequently, perhaps even today? (Something for GNOME or clock networks to look for?)

Impact of BICEP-2 results

BICEP-2 results: if assumed to be correct, what do they imply about the best regimes/scenarios/experiments to search for new physics?

Does BICEP-2 imply that lots of interesting new physics stuff inflates away?

How plausible is scale evolution of physics to avoid BICEP-2 “problems” and what are experimental signatures of scale evolution?

Relation between astrophysical and laboratory searches

Ideas like chameleon fields: what kind of mechanisms exist to hide interactions in laboratory tests and allow astrophysically, or allow in laboratory tests and hide astrophysically? How plausible are these, and how seriously should constraints be taken?

What is the state of knowledge about coupling between dark matter particles? Would coupling between DM particles make some difference between laboratory vs. astrophysical bounds? What if DM is more complex (not just one species) and 5% is coupled strongly to itself: could one have, for example, axion stars, etc.? Could such objects give transient signals?

Transient and time-dependent new physics signals

What kind of new physics can GNOME, clock network, CASPEr, or related experiments access that laboratory experiments cannot access?

Is there anything that can be said about scale of domains, time between transient signals?

Higher dimension topological defects and textures were mentioned. What are these, and what are interesting signatures and characteristics?

It was noted that the photon mass could be altered inside a topological defect: could this be measured with the GNOME or the clock network experiment?

Symmetry tests of gravity

How do we test if standard gravity violates parity or time-reversal invariance?

Tests involving gravito-magnetic fields were mentioned, also chirality in gravitational waves?

Could G measurements (torsion pendulum or atom interferometer) test somehow?

Clocks are sensitive to general relativity effects: could GR effects be used to test P- and T-invariance of gravity somehow?

Antimatter

What new physics might anti-hydrogen experiments be sensitive to that experiments with ordinary matter are not?

What are other possibilities beyond Peccei-Quinn symmetry breaking (QCD axion) to explain strong-CP problem? What are signatures?

What is the present status of the connection between CPT violation and local Lorentz invariance violation?

Variation of fundamental constants and physical laws

Are there viable ways to test variation of other constants besides \alpha, proton/electron mass ratio? For example, Fermi constant? G (lunar laser ranging was suggested)? Strong coupling constant?

What about violation/variation of other sacred laws: angular momentum conservation? energy conservation? charge conservation?

Electric dipole moments (EDMs)

What is the impact of the ThO electron EDM constraint (also Hg and neutron EDM limits) on new physics scenarios?

Dark Energy (DE)

What are the range of viable ideas outside of the cosmological constant, and among these which have the best motivation? What “hand-waving arguments” motivate where to search?

What is relation of inflation to CP problem and baryogenesis (does CP-violating inflaton do anything, or are Sakharov conditions not satisfied)?

What is connection between inflaton and dark-energy?

Non-quantum fields?

It was noted that loop corrections complicate the physics of light scalar fields. Can one imagine “non-quantizable” fields (something like gravity that can’t be quantized simply)? For example, torsion or chiral gravity that is not quantized (at least in the usual way)?

Do such fields have distinct signatures compared to quantized spin-0, spin-1 quantum fields? What is plausibility, for example, of long-range torsion gravity?

Transients in astronomical spectroscopy

Could we detect new physics “passing through” the line of sight between earth and astrophysical object?

Could we search for transients using a telescope? There was a suggestion to use an astro-comb…

For example, it was suggested that quintessence field coupled electromagnetically and generated Faraday rotation: if \phi is clumped or forms topological defect, is this something observable?

Impact of proton radius measurements

What kind of new physics might it imply?

Hidden sector

There are previous and future tests of the spin-statistics connection being conducted. Could these be sensitive to some of the hidden sector physics?

What are observable signatures of hidden sector supersymmetry?

Large extra dimensions

What is the present status and is there strong motivation to go to particular length scales in tests? Is 100 microns a special length? What would show up in atoms?

Experimentally, what is the status of patch potential systematics?

Lense-Thirring effect for intrinsic spins

Comparison of Lense-Thirring effect for intrinsic spin vs. orbital angular momentum? Is there a way to test?