Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
The PICASSO experiment searches for cold dark matter through the direct detection of weakly interacting massive particles (WIMPs) via their spin-dependent interactions with fluorine at SNOLAB, Sudbury - ON, Canada. The detection principle is based on the superheated droplet technique; the detectors consist of a gel matrix with millions of droplets of superheated fluorocarbon (C4F10) dispersed in it.
Dark matter (DM) annihilation around the redshift of last scattering can alter the recombination history of the universe, broaden the last scattering surface, and influence the observed temperature and polarization fluctuations of the cosmic microwave background (CMB). Unlike other indirect astrophysical signals of DM annihilation, these CMB signatures are free of the significant uncertainties inherent in modeling galactic physics, and provide an independent method to test and constrain models of dark matter.
The spectra of cosmic ray electrons and positrons should have contributions from known sources such as particles accelerated in supernova remnants and from the cosmic rays interactions. Besides these guaranteed contributions, any evidence for an additional component may carry hints of a new phenomenon. Most recently PAMELA and ATIC experiments hinted an overabundance of these particles as compared to model expectations and generated much interest on astrophysical and exotic explanations.
The positron excess measured by PAMELA may be the long waited hint of the presence of dark matter particles in the Milky Way halo. But before we rejoice, we need to examine the other Possible astrophysical explanations. Whatever the sources -- DM or conventional -- a crucial ingredient is the transport of cosmic rays in the magnetic fields of the Galaxy to which I will pay particular attention in this presentation.
The cosmic-ray excess observed by PAMELA in the positron fraction and by FERMI and HESS in the electron + positron flux can be interpreted in terms of DM annihilations or decays into leptonic final states. Final states into tau's or 4mu give the best fit to the excess. However, in the annihilation scenario, they are incompatible with photon and neutrino constraints, unless DM has a quasi-constant density profile.
Recent data from the PAMELA satellite and a number of balloon experiment have reported unexpected excesses in the measured fluxes of cosmic rays. Are these the first direct evidences for Dark Matter? If yes, which DM models and candidates can explain these anomalies and what do they imply for future searches?
The balloon-borne Advanced Thin Ionization Calorimeter (ATIC) experiment has measured the cosmic-ray electron spectrum over the energy range from 20 GeV to 3 TeV. The totally active Bismuth Germanate (BGO) calorimeter provides energy measurements with resolution of ~2%. The finely segmented Silicon matrix provides charge measurements with an excellent resolution of ~0.2 e. Below 100 GeV, the ATIC spectrum agrees with previous data and with a calculated spectrum based on a conventional galactic propagation model.
New results on the antiproton-to-proton and positron-to-all electron ratios over a wide energy range (1 – 100 GeV) have been obtained by the PAMELA mission. These data are mainly interpreted in terms of dark matter annihilation or pulsar contribution. The instrument PAMELA, in orbit since June 15th, 2006 on board the Russian satellite Resurs DK1, is daily delivering to ground 16 Gigabytes of data.