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.
We introduce a two-body quantum Hamiltonian model of spin-1/2 on a 2D spatial lattice with exact topological degeneracy in all coupling regimes. There exists a gapped phase in which the low-energy sector reproduces an effective color code model. High energy excitations fall into three families of anyonic fermions that turn out to be strongly interacting. The model exhibits a Z_2xZ_2 gauge group symmetry and string-net integrals of motion, which are related to the existence of topological charges that are invisible to moving high-energy fermions.
In the 60’s, the analytic S-matrix program was developed in an attempt to describe the strong interactions – at the time, this was a theory of massive particles like pions. The S-matrix is an object that encodes the information of the probability of producing a certain set of final particles from a given set of initial particles. Eventually, the S-matrix program was replaced by Quantum Field Theory and in particular by Quantum Chromo Dynamics as the description of the strong interactions. In recent years there has been a resurrection of the S-matrix paradigm.
The essential ingredients of a quantum theory are usually a Hilbert space of states and an algebra of operators encoding observables. The mathematical operations available with these structures translate fairly well into physical operations (preparation, measurement etc.) in a non-relativistic world. This correspondence weakens in quantum field theory, where the direct operational meaning of the observable algebra structure (encoded usually through commutators) is lost.
Inflationary scenarios with detectable primordial tensor perturbations typically require symmetries that can protect the potential over a super-Planckian field excursion. An old and natural idea is for the inflaton to be an axion protected by a shift symmetry. However, this has appeared difficult to realize in string theory because axion periodicities are sub-Planckian in known examples. I will explain how in compactifications containing wrapped fivebranes, the effective axion range is increased by monodromy: a single axion period can be traversed many times.
In the past couple of years many new developments have been made in the techniques used for computing one-loop gauge theory amplitudes. These developments have mainly involved exploiting generalized unitarity techniques to construct the coefficients of the basis integral functions which make up a one-loop amplitude. I will outline these new developments along with their application to both QCD and N=8 supergravity amplitudes.
In topological quantum computation, a quantum algorithm is performed by braiding and fusion of certain quasi-particles called anyons. Therein, the performed quantum circuit is encoded in the topology of the braid. Thus, small inaccuracies in the world-lines of the braided anyons do not adversely affect the computation. For this reason, topological quantum computation has often been regarded as error-resilient per se, with no need for quantum error-correction. However, newer work [1], [2] shows that even topological computation is plagued with (small) errors.
The PAMELA satellite-borne experiment was launched from the Baikonur cosmodrome on the 15th of June 2006. It has been collecting data since July 2006. The instrument is composed of a silicon-microstrip magnetic spectrometer, a time-of-flight system, a silicon-tungsten electromagnetic calorimeter, an anticoincidence system, a shower tail counter scintillator and a neutron detector. The primary scientific goal is the measurement of the antiproton and positron energy spectrum in order to search for exotic sources, such as dark matter particle annihilations.
This course provides a thorough introduction to the bosonic string based on the Polyakov path integral and conformal field theory. We introduce central ideas of string theory, the tools of conformal field theory, the Polyakov path integral, and the covariant quantization of the string. We discuss string interactions and cover the tree-level and one loop amplitudes. More advanced topics such as T-duality and D-branes will be taught as part of the course. The course is geared for M.Sc. and Ph.D. students enrolled in Collaborative Ph.D. Program in Theoretical Physics.
This course provides a thorough introduction to the bosonic string based on the Polyakov path integral and conformal field theory. We introduce central ideas of string theory, the tools of conformal field theory, the Polyakov path integral, and the covariant quantization of the string. We discuss string interactions and cover the tree-level and one loop amplitudes. More advanced topics such as T-duality and D-branes will be taught as part of the course. The course is geared for M.Sc. and Ph.D. students enrolled in Collaborative Ph.D. Program in Theoretical Physics.
I will briefly review the construction of the graviton propagator in the context of LQG and I will show how the Barrett-Crane vertex fails to give the correct long-distance limit. The same kind of calculation however, can give the correct propagator using an alternative vertex with a specific asymptotic behavior. I will show that the BC difficulties disappear when using the EPRL model.
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