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.
KeV-MeV scale dark matter particles with integer spin, very weakly unstable and super-weakly interacting, can produce an observable ionization signal in direct detection experiments. I zoom in on some sensible models and discuss their observational consequences.
The highly radiopure about 250 kg NaI(Tl) DAMA/LIBRA set-up is running at the Gran Sasso National Laboratory of the I.N.F.N.. Results exploiting the model independent annual modulation signature for Dark Matter particles in the galactic halo are presented (exposure of 0.53 ton x yr). The DAMA/LIBRA data confirm the evidence for the presence of Dark Matter particles in the galactic halo as observed by the former DAMA/NaI experiment. The combined analysis of the data of the two experiments (total exposure 0.82 ton x yr) gives a C.L. at 8.2 sigma.
The Cryogenic Dark Matter Search (CDMS) experiment employs cryogenic ionization detectors to search for nuclear recoils induced by Weakly Interacting assive dark matter particles (WIMPs). A fast readout of the thermal energy deposition and the simultaneous measurement of an ionization signal provide an excellent handle for rejection of electron recoil background events from environmental radiation. This unique technology together with passive and active shielding makes CDMS the only background free experiment in the field.
LUX (Large Underground Xenon) is a two-phase Time Projection Chamber that will instrument 350 kg of Xenon, 100 kg of which will form a fiducially active target for WIMP interactions. It will be deployed at the Sanford Underground Science and Engineering Lab at the Homestake Mine in Lead, South Dakota. The Early Implementation Program of Sanford Lab is providing space at the 4850 feet level for LUX. The first detector with 120 photomultiplier tubes is being constructed and is projected to start collecting data in late 2009.
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.