Tuesday, 27 May 2014

Planck 2014 Liveblog: Day Two Session 1

After yesterday's talks got a bit technical, stringy and full of context-free equations for me, today's parallel sessions look more grounded in phenomenology.  Plus, we have the first parallel session after lunch, and I should be able to find some interesting talks there.

9:00 am: Scalar Dark Matter, Genevieve Belanger

According to the title slide, this is an "alternative WIMP scenario".  Really?  If this is what I expect, I thought it was one of the standard WIMP scenarios.  Yeah, it looks like a simple model with an extended scalar sector.  Alternative seems to mean not SUSY.  Well, yes.

Okay, through the intro and to the meat.  We have a nice overview of different scalar extensions (singlet, inert doublet, doublet + singlet and so on).

Non-DM motivation: stable Higgs potential.  So this is not quite just a model of DM.

Simplest model is the scalar singlet.  Two-parameter model, one parameter fixed by relic density.  Low mass region then excluded by LUX, except around Higgs pole.  Limits from the Higgs invisible width also provide a lower limit on the mass, around 55 GeV.

First beyond-minimal model: ZN semi-annihilating model (with real scalar now).  Introduction of scalar cubic adds a third parameter relevant for DM, associated with the semi-annihilation.  The main phenomenological effect is to open parameter space with a reduced direct detection rate, allowing smaller masses.  Still, Xenon1T should probe these models.

Inert doublet model.  Efficient annihilation through SU(2) gauge bosons tends to force DM to be quite heavy, TeV scale, or nearly degenerate with the Higgs.

Doublet + Singlet: Model like the doublet that allows semi-annihilation.  Also, with Z4 symmetry have two DM candidates.  Also have DM conversion, two dark sector states annihilating to two dark sector states.  Allows doublet DM with any mass.  Two DM candidates allows most of parameter space to be probed with DD; even when DM is dominated by one state, other state might give detectable signal.

Questions: pointed out that near Higgs resonance, indirect detection can be important.

9:30 am: Indirect Dark Matter Detection: Tales of Scales, Pasquale Serpico

Astrophysics very nicely tells us that NP must exist, which is more than can be said for terrestrial particle physics.

Main theme of talk: indirect detection of DM can help identify the scale of NP; with a careful discussion of some of the problems than can occur in doing so, illustrated with case studies from current literature.

Starting point: the Hooperon.  Problem here is that signals might not cleanly break down into particle x astrophysics, as usually assumed, if prompt emission does not dominate.  This is true at low masses when we need to include Bremsstrahlung and inverse Compton.

Background problem: millisecond Pulsars.  NONE were known prior to the launch of Fermi, and they are now the most common galactic radio source.  It is thus very very hard to say that astrophysics cannot do something.

Summary: backgrounds (especially from the GC) are hard.

Second example: PeV neutrinos from IceCube.  Probably astrophysical, but some hints that it might not be, e.g. cut-off in spectra at 2 PeV, weak correlation with GC.  Could point to very heavy non-thermal DM.

Summary: not generally expected, but we must ultimately let the data lead us.  (These DM models can be tested, and should be before we conclude that this signal is DM.)

Third example: sterile neutrino, or more generally the νMSM.  Got a definite boost with the recent discovery of the 7 keV X-ray line.  Needs more study.

10:00 am: Baryogenesis from strong CP violation and the QCD axion, Geraldine Servant

Under which conditions can the QCD axion generate baryogenesis?  Currently, no known way to get baryogenesis using only SM CP violation; proven impossible for EWBG twenty years ago, possibly except for cold EWBG.

Most popular method in recent decade is leptogenesis, but BG is still worth thinking of.

Axion method based on idea that, in early universe, strong CP phase (axion VEV) can take order-1 value.  Essentially this is before axion gains mass.

These slides are full of equations.  Again, I'd like to be able to download the slides so I can figure out where I got lost.  I failed to realise that the last five minutes where talking about standard EWBG.

BG through Chern-Simonds current, somehow.  Current generated for axions through GG FF term, with GG VEV being related to axion field.

Axion can only work if EW phase transition happens after QCD phase transition.  Then need a "cold" method with high effective temperature I have no idea what those words mean in this context.

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