Tuesday, 21 May 2013

Planck 2013 Day Two Live Blog 2

Second Plenary session, first after the crucial coffee break.  Conference website.

11:00 am: Daniel Baumann, "Probing High-Scale Physics with Planck"

I think that's the first time I've heard a Plenary talk open with "this is based on the following paper..."

Planck accuracy, blah blah blah, bispectrum (three-point function).  High precision measurements imply constraints on high-scale operators, as is done every day in particle physics.  In this case the scale is the inflationary Hubble scale, and we non-Gaussianities at the observed scale gives us sensitivity to 100 to 100000 times higher energies.

This seems to be a natural follow-up to the first part of the previous talk: constraining realistic models of inflation (which will have more than just the inflaton and its potential).  This is further done through the language of effective field theory.

Three-scale problem: inflationary Hubble scale, Planck scale and scale of symmetry breaking (associated with time dependence of inflaton).  Inflationary models: slow-roll at Planck scale; DBI below symmetry breaking scale; and mixing with hidden sector, between Planck and symmetry breaking scales.  Focus is the last of these.

Approximate inflaton shift symmetry constrains mixing with hidden sector; leading term is dimension-five coupling involving inflaton kinetic term.  (Dimension-four kinetic mixing can be rotated away; shift symmetry makes it small.)

Result: mixing scale must be at least 1000 times the inflationary Hubble scale, and (up to 100 times) higher for large hidden-sector cubic couplings.  The large cubic coupling is "natural" for gravity-mediated SUSY breaking.  We can generalise this approach for other mixings, or gauge fields; similar results follow.

The summary seems to be that the Planck observations strongly constrain gravity-suppressed operators, and doubly so if gravity waves are observed.

Q&A: Constraints are even stronger on string theory models of inflation, since these operators are suppressed by the string scale, which is likely below the Planck scale.

Q&A: Low-scale inflation might avoid these constraints.

11:30 am: Dan Hooper, "Dark Matter in the Discovery Age"

This has the potential to be fun.  I'll save my snark till I see what Dan actually says.  Somewhat irritatingly, the slides are not available online yet and the projection difficult to see.

Emphasis: LHC, direct and indirect detection experiments are now able to probe the most plausible models.  Hence, "discovery age".

Direct detection: we will probe and discover or rule out Higgs-mediated scattering of dark matter in the next decade; some exclusions already exist.  If no discovery is made in 5 to 10 years, WIMPs will be very constrained, forcing us to highly baroque models.

Review of the anomalies.  A cross section-mass plot for CoGeNT I haven't seen, looks to fit constraints but Xenon not shown.  CDMS-Si pretty much overlaps with CoGeNT, again I hadn't seen that plot before.  Low-mass CDMS-Ge events (from Juan Collar) apparently also overlap.  These claims are much stronger than I have seen elsewhere.

Ah, constraints.  The CDMS constraints are consistent with the CoGeNT and CDMS signals.  Xenon-10 marginally consistent; Xenon-100 less so, but what's the theoretical uncertainty?

Three experiments should see this by the end of the year: LUX, SuperCDMS and COUPP-lite.  I wasn't aware that the latter two experiments could also resolve this question.

Indirect detection: First constraints on thermal WIMP annihilation cross sections.  Great strength of FERMI; three days to supersede EGRET!  Dwarf galaxies as excellent sources due to low backgrounds.  Ruling out annihilation to bottom or tau for masses below about 20 GeV.

Galactic centre data: Dan's long-standing point about an "excess" at the galactic centre.  Part of the claim rests on the source being spatially extended, not a point source.  Requires a steeper dark matter profile than NFW, which is a bit worrying.

Attempts to address criticisms by looking away from the galactic centre; bump appears as you move towards the galactic centre, but still several degrees away.  Too few pulsars, and give the wrong spectrum.  Some of his papers are in my to-read list, but I haven't gotten to them yet.

One thing; is the statement about ruling out WIMPs in five to ten years true for e.g. 2 TeV SU(2) doublets?

Q&A:  LHC constraints from monophotons/monojets?  Model-dependent, can't say.

Q&A: Direct Detection expts.  CoGeNT: could be unknown background, but not anything known or electrons.  CDMS: events are at edge of box, as expected.  Analysis threshold chosen to control backgrounds; detector threshold ten times lower.  Xenon: should have seen events; saw two, but do those mean anything?  (Wrong cross section.)

CDMS: Ionisation cut is now being argued over.

12:00pm: Zygmunt Lalak, "Exponential hierarchy of scales and cosmology"

Strong coupling as the origin of hierarchies, inflation and vacuum selection.  Higgs mass/μ term comes from fermion condensation.

This is a bad talk for the last one before lunch.  I can feel myself nodding off already.

Well, I got nothing out of that talk.

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