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.
Observations are opening new windows to test general relativity at cosmological scales. In this talk, I will discuss how gravity determines the expansion and structure formation of the universe, what smoking guns of gravity in the cosmos we are expecting, what difficulties we are facing to perform unambiguous tests of gravity and what are possible ways to overcome these difficulties.
Non-linear structures in the universe leave characteristic imprints in the cosmic microwave background. These include Compton scattering (Sunyaev-Zeldovich effects) and gravitational lensing. The South Pole Telescope now has a catalog of massive galaxy clusters that were discovered this way, along with a measure of the background fluctuations generated by smaller clusters, that can be used to chart the growth of structure in the universe.
We have announced the results from 7 years of observations of the Wilkinson Microwave Anisotropy Probe (WMAP) on January 26. In this talk we will present the cosmological interpretation of the WMAP 7-year data, including the detection of primordial helium, images of polarization of microwave background around temperature peaks, and new limits on inflation and properties of neutrinos. We also report a significant detection of the Sunyaev-Zel'dovich effect and discuss implications for the gas pressure in clusters of galaxies.
A systematic method to construct 4d N=2 supersymmetric theories by compactifying M5-branes on a Riemann surface was found by Gaiotto last year.
This suggests that any physical quantity of the 4d theory should be reflected in another physical quantity of the 2d theory living on the Riemann surface.
Indeed, one finds that the instanton partition function of the 4d theories equals the conformal blocks of the 2d theory.
I would like to illustrate this construction through explicit examples.
Many putative explanations in physics rely on idealized models of physical systems. These explanations are inconsistent with standard philosophical accounts of explanation. A common view holds that idealizations can underwrite explanation nonetheless, but only when they are what have variously been called Galilean, approximative, traditional or controllable. Controllability is the least vague of these categories, and this paper focuses on the relation between controllability and explanation. Specifically, it argues that the common view is an untenable half-measure.
Gauge Invariant Cosmological Perturbation theory from 3+1 formulation of General Relativity. This course will aim to study in detail the 3+1 decomposition in General Relativity and use the formalism to derive Gauge invariant perturbation theory at the linear order. Some applications will be studied.
We point out and explicitly demonstrate a close connection that exists between featureless Mott insulators and fractional quantum Hall liquids. Using magnetic Wannier states as the single-particle basis in the lowest Landau level (LLL), we demonstrate that the Hamiltonian of interacting bosons in the LLL maps onto a Hamiltonian of a featureless Mott insulator on triangular lattice, formed by the magnetic Wannier states. The Hamiltonian is remarkably simple and consists only of short-range repulsion and ring-exchange terms.
The heavy fermion URu2Si2 boasts a 25 year old mystery. Its ''hidden order'' phase transition at Tc=17.5K has eluded the onslaught of theory and experiment to describe the complex underlying mechanism. Whether the transition is due to conventional ordering of k-space heavy electrons or to a change in hybridization of the r-space states at each magnetic-moment-contributing U atom is unknown. Addressing the problem requires a probe which can simultaneously measure the real space and momentum space structure, making spectroscopic imaging STM (SI-STM) the natural choice.