Thursday, 8 May 2014

Pheno 2014 Liveblog: Day Three Session 2

We come at last to the final session of Phenomenology 2014.  Sadly, I may well not be able to stay for the whole session because I have a plane to catch.  This is especially true given that we have Nima giving the last talk, so that'll run long, and I was not able to check in to my flight online.

This session is kind of two; we start with some BICEP/cosmology talks, then finish with discussion on the general summary and outlook of the field.

11:00 am: Evidence for Inflationary Gravitational Waves from BICEP2, Clem Pryke

This should be interesting, except I've seen two other BICEP talks on this trip.

BICEP is a gravitational wave experiment.  We cannot probe the universe before recombination directly with light; it is opaque.  But gravitational waves can provide a probe, and while we cannot (yet) directly observe them we can see them indirectly.

The gravitational wave pattern is a clear prediction of inflation.

CMB polarisation arises at last scattering from a local radiation quadrupole.  Conventional (non-gravity) quadrupoles make E-modes, where polarisation is aligned parallel or perpendicular to the intensity.  B-modes do not respect this, and are generated by gravity waves.  (Gravity also generates E-modes, but they are obviously not a clear signal.)

Experiment focuses on small range of l that is most sensitive.  On ground, best for deep focus and allows in situ control of systematics.  Experiment at the south pole because it is dry.

Systematics are an issue.  Important trick is to compare sums and differences of half of data.  Differences should be noise, and not only are they but they have the correct decaying dependence with exposure time.

Perform numerical simulations to see if find genuine signal, or just noise.  Even by eye, clear that signal is stronger than expected from just noise.  More advanced statistical techniques support this.

In situ calibration impressive, really makes you believe that the detector exists.

Looks very convincing that we have found a celestial (non-terrestial) signal.  What is it?  Is it CMB, or dust?  (This has been the main challenge to the BICEP results that I've heard.)  Hard to say without access to the full pre-existing dust models, but using what is available in the literature the dust signal is consistently far, far too low to explain the data.

Another check: use BICEP one data at different frequency to estimate power spectrum of signal.  More consistent with CMB than backgrounds (though only at 2 to 3 σ).

Independent tests?  Planck should be able to say if dust (end of year), might not be able to see signal. SPT should also have information.  Keck is same technology, but will give more information on spectral index.  Once confirmed, we need to measure on larger patch of sky to push the uncertainty on r down (currently sample-limited).

Question from Nima on dust: what about Planck public data?  Answer: available data is just awful, pdfs from talks.  Have used that, but undoubtedly their are unquantifiable systematic errors.

11:30 am: Cosmology: dark energy and beyond, Bhuv Jain

Now we talk about the late time universe.  In particular, we are looking at dark energy (beyond the minimal scenario) and tests of gravity at a range of scales.

A lot of discussion about the open questions here.  It kind of feels like a list at times.  "Here's another question... and another..."

Theorem: The CC is the unique modification to GR that does not introduce new degrees of freedom.  Modified gravity theories typically can be expressed as involving a new scalar degree of freedom.  Essentially three screening methods to protect this from solar system measurements (small coupling, large mass, large kinetic term; but all are dependent on local background!)  Different screening mechanisms lead to different observable effects, so in principle distinguishable experimentally.

Limits on modified gravity.  Apart from solar system, nearly all limits from last five years.

We're already a good ten minuted behind schedule (thanks to the morning session as well).  So I will definitely skip the last talk.  Looking at the slides, it looks like Nima is talking about stuff I've seen before (such as at SUSY last year); the importance of a 100 TeV collider, the profundity of the amplituhedron, the fundamental and difficult nature of the challenges that face us.

12:00 pm: Physics Potential at the ILC, Keisuke Fuji

Slides of texttexttexttexttexttextttex

Measure Higgs couplings with high precision: bottom-up reconstruction of EWSB sector.

Key thresholds to measure:
  1. ~ 250 GeV, ZH, for Higgs mass and width
  2. ~ 350 GeV, ttbar, for Higgs-top coupling and precision top mass
  3. ??, ννH, why is this a threshold?  On-shell Ws?  What?
First is real flagship measurement.  Precision measurement of ZZH coupling, Higgs mass.  Additionally, ZZH coupling plus BR for Higgs to ZZ gives total Higgs width.  This, however, is easier at large energies ...?

Higgs self-coupling from e.g. ZHH final state.  Unfortunately, several channels contribute so extracting HHH coupling difficult.

Worth remembering that ILC is also an energy frontier, probing physics that is not coloured.  For example, in SUSY can serve as Higgsino factory.

ILC TDR is complete, and preferred candidate site in Japan has been chosen.  Site specific design is starting.  But needs international support at all levels to make sure it happens!

Given the time, I think I will skip both of the last two talks, actually.  Unfortunately the last set of slides are not yet online, but I think I will be happier to leave now.

I may write a summary for Pheno as a whole when I arrive in the UK.  In general, though, I enjoyed it again and have definitely got some ideas to take away with me.

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