Particle Physics and Cosmology in Auckland

Cosmic Variance
By Mark Trodden
Jul 14, 2012 4:13 AMMay 17, 2019 8:42 PM


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As I mentioned in my last post, I’m now in Auckland. Richard Easther, a repatriated Kiwi who came here from Yale last year to head up the physics department, has organized a workshop on “The LHC, Particle Physics and the Cosmos“, at which I gave a talk this morning.

This is a very different affair to ICHEP. In Melbourne there were 800 or so participants, filling a gigantic conference hall for the plenary talks, whereas there are something like 30 44 participants at this workshop, roughly split between New Zealand academics (faculty, postdocs and students), and those of us from abroad. ICHEP was a terrific conference, but more usually I strongly prefer these small, intimate workshops to huge meetings. They tend to be more focused and I typically seem to leave having learned more from the talks.

This meeting kicked off with a public lecture on Thursday evening, at which Mark Kruse from Duke University gave a skilled account of “Why do we care about the Large Hadron Collider”.

There were something like 400 people at his talk, and the thing that struck me was the quality of the questions that people asked at the end. There was even a question that was essentially about triggers, and the risk that one might miss important physics due to them. As you'll have seen discussed before, the sheer volume of data produced by each collision at the LHC, combined with the frequency of these collisions means that it is just impossible to save each individual event. Instead, a decision has to be made extremely rapidly whether to save a given event, understanding that doing this means that many other events will then be missed. This decision is based on the expectations we have of the kind of signals that we expect the new physics to exhibit. Of course, a consequence is that there exist possible signals of new physics that will evade these triggers. This is a subtle question and one that I'm surprised to hear asked in a public lecture.

Yesterday the research talks began. The topics have spanned quite a number of topics, including talks from people on ATLAS and CMS on their Higgs, and other results. There have been talks on dark matter, neutrinos, variance in the Hubble flow in cosmology, and a number of other topics, including one on the Phenomenological Minimal Supersymmetric Standard Model from Tom Rizzo from SLAC. I particularly enjoyed a talk from Pat Scott, who is a postdoc at McGill, about cosmology with ultracompact minihalos of dark matter. These potentially provide a way to probe the extent to which the statistics of structure formation deviates from that expected from gaussian primordial seeds. As such, it seems that it may provide another way to look at non-gaussianity beyond that we usually think of in the microwave background, and about which we hope to see interesting results from the Planck mission.

This morning Tom Appelquist (Yale) and Jay Wacker (SLAC/Stanford) gave interesting theory talks, and our own JoAnne spoke about the physics that may be probed through a program of physics at the intensity frontier. This afternoon Michele Redi from CERN gave an interesting talk on the implications of a light Higgs for composite models. It is one thing to find the object that breaks the electroweak symmetry, but another to pin down whether it is a fundamental or composite particle. Compositeness is attractive in some ways, since it may provide a way to tackle the hierarchy problem, but finding the Higgs at the rather light mass announced last week presents particular challenges to models in which the Higgs is composite, and leads to some specific predictions. Michele is interested in models in which the Higgs is a pseudo-Goldstone boson and showed that in many such models, naturalness, coupled with a 125 GeV Higgs implies that there should also be new fermions in the model that are quite light, and may be within the reach of the LHC.

Well I'm off to have tea and then chair a parallel session in which there will be a lot of theory talks, about which I may report soon.

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