## Wednesday, April 19, 2006

### Michele Papucci: neutrino optics

Michele Papucci from Berkeley gave a talk about neutrino optics. There will be a preprint about it with Gilad Perez, Hitoshi Murayama, and one more author whose name will be completed here if necessary.

When we test cosmological models, we rely on regular optics of photons. Are there other "eyes" we could use? They must be weakly interacting, so the only possibilities are
• gravitational waves
• neutrinos
Michele only focused on the last ones, the neutrinos. More precisely, it is the electron antineutrinos he is interested in. They are produced by supernovae (yes, there is some neutrino oscillation physics you must take into account); on the other hand, the Sun only creates neutrinos so the solar neutrino backgrounds does not affect their proposed experiments.

You can't really measure the direction from which they come (pretty fuzzy optics) because the particles created in the inverse beta decay have a momentum that is virtually uncorrelated with the antineutrinos' momenta. So the only thing you can measure is the distribution of energies.

In reality, we detect 15 neutrinos a year or so, which means that the one-pixel multi-frequency photograph of the skies won't be terribly sharp. ;-)

They expect the spectrum of the antineutrinos from supernovae (type I, type II, as well as heterotic supersymmetric novae) to look like a black body curve with a peak around 20 MeV, and they are produced by supernovae at redshift equal at most "z=2". The curve has a certain shape that depends on the precise distribution of supernovae in the Universe as a function of time and their size, and also depends on the expansion of the Universe.

Most of these things are rather uncertain. The main question he wants to ask is whether the neutrino "eyes" are able to distinguish the cold dark matter cosmological models with and without the cosmological constant. By a rather accurate analysis of the error margins, his conclusion is that the correct or wrong model will only be confirmed or eliminated at the two sigma confidence level which is comparable to climate science - not terribly convincing. But on the other hand, their project is cheap because it will just use data from other experiments that exist anyway.

They just need some extra gadolinium, and one liter of it costs like one liter of coffee, so their new tools are inexpensive.