Monday, 23 May 2016

Planck 2016 Liveblog: Day One Session One

It's that time of year again, the time I write most of my posts here: Conference Season!  I skipped Pheno this year for a variety of reasons, so I'm starting things off at Planck 2016, in the city of Valencia.  I've never been to this part of Spain before, but what little of the city I've seen so far does look very nice.

After the usual opening remarks, it seems we start with a session on astrophysics and cosmology.

09:30 am: Results from the Planck Satellite and implications for particle physics, Julien Lesgourges

"Very happy to open Planck with some Planck."

Direct observations: temperature and polarisation.  Derived map: lensing.  Four independent two-point correlation functions: TT, EE, TE, φφ.  Four (complicated) functions to fit gives information from early Universe.  Minimal ΛCDM means six parameter fit.  Fit is good.

Planck satellite stopped taking data some time ago, but analysis is difficult and still ungoing.  TT data is now as good as it can be for l > 30 or so (cosmic variance limited).  Last month, TE/EE data from LFI detector at low multipoles.  Still some systematics in TE/EE/φφ spectra, hope to have finished work by 2017.

Most recent results at low multipoles: information on reionisation at small redshift.  Preference to relatively recent reionisation.  Resolves small prior tension between CMB and astrophysics (Quasars, Lyman-α) data.  Also, increases bounds on neutrino masses: Planck alone at < 140 meV.  Puts greater pressure on inverted hierarchy.

Bounds on WIMP annihilation improved with Planck polarisation data release.  Depending on annihilation channel, exclude the region 10 to 40 GeV.

Most interesting facet might be the affect on inflation.  ``The'' inflationary model, φ2, is in increasing tension with the most recent Planck polarisation results; needs official analysis.  Would be more interesting if I worked on this type of model-building.  Convex models in general more and more disfavoured.  Preferred models: hilltop (some fine-tuning, connection to SSB); flat direction lifted by radiative corrections (SUSY); exponential potential (moduli stabilisation).  Last are interesting in that they give lower bound on r of 0.01.  This can be tested within a decade or so.

What of Higgs inflation?  Currently disfavoured due to instability of potential.
Sterile neutrinos?  Cannot improve the quality of the fit.  (Can avoid the bounds in various ways.)
Tension in Hubble parameter?  Increasing with more data.  Now at 3σ, cannot be ignored.  Could, of course, be systematic.  Some have suggested a systematic between local and global measurements; but not part of standard cosmology.  Could be model: CMB measurement requires some type of extrapolation.
Extensions beyond ΛCDM?  Must keep good fit.  e.g. WDM can not be distinguished using CMB data.  Occam's razor.

10:00 am: The new era of gravitational wave astronomy, Alicia Sintes

Now that we have discovered them, GW opens a new avenue of observations.  High frequencies correspond to low energies here.  High-frequencies (stellar masses) are the only things that can be probed with ground-based experiments.

First science run of Advanced LIGO was still well short of design sensitivity.  Observation targets: coalescing binaries, bursts (core collapse plus ??), continuous signals (spinning neutron stars) and stochastic searches (primordial GW).

Advanced LIGO will ultimately increase sensitivity over LIGO by a factor of 10; hence volume of space accessible increases by 1000.  Improvement is even more dramatic at low frequency end.  Gain so far by factor of 3+.

Second observed candidate; only at 2σ (compare 5 for initial event).

Observation requires spectral matching to be robust.  Final fraction of a second before merger can only be done with numerical relativity.  This can take weeks to generate.

Only half of initial run released so far.  90% chance of a second event.  Expect 5 to 10 events from run 2 this autumn.

10:30 am: Constraining non-standard neutrinos with cosmic microwave background observations, Massimiliano Lattanzi

Possible extensions to standard picture obviously broad, but primary focus: non-standard interactions; non-thermal distribution; steriles; and large lepton asymmetries.  For time reasons, only can cover first two.

NSI: basically neutrinos plus coupling to either light/massless scalar or light pseudoscalar.  Cross section then goes like T-2.  This leads to a recoupling of neutrinos as late time: σv/H ~ 1/T, 1/T3/2 depending on era.  Collisions drive power from higher moments to only monopole (density) and dipole (pressure).

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