Okay, some much-needed coffee and it's time for the second session of the morning.
11:00am: Joseph Conlon, "Origin and Phenomenology of Dark Radiation"
You have a microphone, no need to shout.
If dark matter, why not dark radiation? Beyond the Planck constraints, of course.
An interesting point, raised by Joseph in an earlier Q&A session, is directly about those constraints. The Planck measurements alone don't look too promising, but in terms of using the CMB alone the one-sigma deviation is consistent with pre-Planck data; while combining with direct measurements of the Hubble rate, the Planck result is still two sigma high compared to the SM expectation.
The theoretical perspective is that the inflaton decays may produce dark radiation in the form of e.g. axions or hidden photons. Irrespective of the initial conditions, the Universe passes through a phase dominated by matter with Planck-suppressed couplings (due to radiation redshifting away and Planck-suppressed couplings giving the longest lifetimes).
Specific context (large volume string theory) to get actual predictions for branching rates to dark radiation. Advantage: one modulus much lighter than the others (relates to overall volume). So can ignore all others. Additionally, always exist a light/massless axion.
Decay to axion uniquely determined by Kahler potential. Matter is a bit trickier but comes down to Higgs decays, again from Kahler potential. One "free" parameter; minimal scenario, where coupling equals 1, excluded.
Friday, 24 May 2013
Thursday, 23 May 2013
So, last night was the conference banquet and this morning we had string theory talks. A combination of events that gave me little motivation to attend and less to pay any attention, hence no blogging from me. After lunch, we have the last set of parallel talks, and I think I'll be attending the Higgs talks. My own talk here was on a similar subject, albeit off in one of the BSM sessions, and it is an obviously exciting area right now.