This event provides an opportunity for top young physicists to enjoy a multidisciplinary conference, and interact with resident scientists. In addition, participants will have an opportunity to learn more about Perimeter Institute. http://pirsa.org/podcast/C06016 Science 2008 http://blogs.law.harvard.edu/tech/rss en-ca Sun, 23 Nov 2008 10:26:11 -0500 sbradwell@perimeterinstitute.ca Sun, 23 Nov 2008 10:26:11 -0500 G 180 pirsa-admin@perimeterinstitute.ca Steve Bradwell's - Podcast Generator I discuss two instances in which nonlinear perturbations in cosmological models are important. First, in de Sitter space-time, the bare necessity that the perturbations should be part of a consistent Taylor expansion of the field equations leads to the requirement, using the 'linearization stability' arguments of the '70's, that the quantum field theory of a scalar field on de Sitter space-time is manifestly de Sitter invariant (not covariant). Second, the concern that in slow-roll inflation the effect of second order perturbations on the long wavelength (super Hubble) perturbations could be much stronger than that of the first order perturbations, for a wide range of slow-roll conditions, is explored in the context of a linear inflation potential and chaotic inflation. Bojan Losic http://streamer.perimeterinstitute.ca/mp3/b11ecdc1-9eab-44d4-9948-a7112d14cd05.mp3 Science http://streamer.perimeterinstitute.ca/mp3/b11ecdc1-9eab-44d4-9948-a7112d14cd05.mp3 Mon, 04 Dec 2006 09:00:00 -0500 I consider a six dimensional space-time, in which two of the dimensions are compactified by a flux. Matter can be localized on a codimension one brane coupled to the bulk gauge field and wrapped around an axis of symmetry of the internal space. By studying the linear perturbations around this background, I show that the gravitational interaction between sources on the brane is described by Einstein 4d gravity at large distances. This is one of the first complete study of gravity in a realistic brane model with two extra dimensions, in which the mechanism of stabilization of the extra space is fully taken into account. Gianmassimo Tasinato http://streamer.perimeterinstitute.ca/mp3/83d0cf9a-fd63-4dc1-a2c6-c61f526af278.mp3 Science http://streamer.perimeterinstitute.ca/mp3/83d0cf9a-fd63-4dc1-a2c6-c61f526af278.mp3 Mon, 04 Dec 2006 10:30:00 -0500 At large scales the CMB spectrum measured by WMAP appears to have an anomalously low power of the quadrupole and an asymmetry of power at l < 40. We show that with an initial stage of fast roll of the inflation and a gradient in the initial conditions a simple chaotic inflation model may be capable of explaining both anomalies. Andreas Ross http://streamer.perimeterinstitute.ca/mp3/37fca4dc-ec75-4966-b991-46c7c3df0448.mp3 Science http://streamer.perimeterinstitute.ca/mp3/37fca4dc-ec75-4966-b991-46c7c3df0448.mp3 Mon, 04 Dec 2006 11:30:00 -0500 The description of noncommutative space will be given. I will show the relation between field theory on kappa-Minkowski space and the one in Minkowski. This construction leads to deformed energy momentum conservation law for energies close to the Planck scale. Sebastian Nowak http://streamer.perimeterinstitute.ca/mp3/12f65d3f-6091-4239-af7d-b496684fb85b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/12f65d3f-6091-4239-af7d-b496684fb85b.mp3 Mon, 04 Dec 2006 14:00:00 -0500 A classical Hamiltonian system can be reduced to a subsystem of "relevant observables" using the pull-back under a Poisson embedding of the "relevant phase space" into the "full phase space". Since a quantum theory can be thought of a noncommutative phase space, one encounters the problem of the embedding of noncommutative spaces, when one tries to extend the reduction via a pull-back to a quantum theory. This problem can be solved for a class of physically interesting quantum systems and embeddings using an analogy to finding the base space of an embedded fibre bundle via the projection in the full fibre bundle. The resulting construction is then applied to Loop Quantum Gravity to extract a cosmological sector. This sector turns out to be similar but not equivalent to Loop Quantum Cosmology. Tim Koslowski http://streamer.perimeterinstitute.ca/mp3/056c1a6b-a78b-4e6e-8d76-30be15c50d6b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/056c1a6b-a78b-4e6e-8d76-30be15c50d6b.mp3 Mon, 04 Dec 2006 15:00:00 -0500 TBA Willem Westra http://streamer.perimeterinstitute.ca/mp3/be09b1ef-2d6e-4d05-8060-2ea7bd22c7dd.mp3 Science http://streamer.perimeterinstitute.ca/mp3/be09b1ef-2d6e-4d05-8060-2ea7bd22c7dd.mp3 Mon, 04 Dec 2006 16:30:00 -0500 Non-Gaussianities are a generic prediction of multi-field inflationary models and within reach of upcoming experiments. After reviewing current observational limits and the physical origin of a non-zero three point correlation function, I will discuss the possibility of detectable non-Gaussian signatures in a certain class of multi-field inflationary models, upon which assisted inflation/N-flation lies. Using the delta-N formalism within the slow roll approximation and focusing on N-flation (quadratic potentials without cross-coupling), we will see that said signatures are suppressed as the number of e-foldings grows, and that this suppression is increased in models with a broad spectrum of masses. We thus conclude that the production of a large non-Gaussian signal in models of this type is very unlikely. Thorsten Battefeld http://streamer.perimeterinstitute.ca/mp3/b2fd29d0-e575-4a6d-a5bd-39e72f6f6738.mp3 Science http://streamer.perimeterinstitute.ca/mp3/b2fd29d0-e575-4a6d-a5bd-39e72f6f6738.mp3 Tue, 05 Dec 2006 09:00:00 -0500 A number of mechanisms have been introduced in previous literature that might be responsible for transitions between metastable minima in a scalar field theory coupled to gravity. The connection between these transition mechanisms has remained unclear, and current formulations of eternal inflation only include a subset of the allowed processes. In the first part of this talk, I will discuss how a number of transition mechanisms can be unified in the thin-wall limit, with interesting consequences for quantum cosmology and eternal inflation. I will then discuss making predictions in an eternally inflating universe, and introduce a measure for eternal inflation that is based on transitions rather than vacua. Matthew Johnson http://streamer.perimeterinstitute.ca/mp3/078ad56b-ed60-40b7-bb1b-d1a3f115c761.mp3 Science http://streamer.perimeterinstitute.ca/mp3/078ad56b-ed60-40b7-bb1b-d1a3f115c761.mp3 Tue, 05 Dec 2006 10:30:00 -0500 Alex Vikman http://streamer.perimeterinstitute.ca/mp3/03072a3e-1524-4de2-8a29-e9696054bf23.mp3 Science http://streamer.perimeterinstitute.ca/mp3/03072a3e-1524-4de2-8a29-e9696054bf23.mp3 Tue, 05 Dec 2006 11:30:00 -0500 TBA Brian Wecht http://streamer.perimeterinstitute.ca/mp3/c43f33e8-097d-4388-96ec-c0be766e15de.mp3 Science http://streamer.perimeterinstitute.ca/mp3/c43f33e8-097d-4388-96ec-c0be766e15de.mp3 Tue, 05 Dec 2006 13:30:00 -0500 We will discuss applications of the recently developed twistor-space methods in perturbative quantum field-theory. The two central topics will be 1) the unitarity bootstrap approach to hard scattering amplitudes in QCD and 2) the analysis of the UV structure of N=8 supergravity. Harald Ita http://streamer.perimeterinstitute.ca/mp3/481fa81f-216a-472f-afde-c94d74510593.mp3 Science http://streamer.perimeterinstitute.ca/mp3/481fa81f-216a-472f-afde-c94d74510593.mp3 Tue, 05 Dec 2006 14:30:00 -0500 Quantum gravity in an AdS space-time is described by an SU(N) Yang-Mills theory on a sphere, a bounded many-body system. We argue that in the high temperature phase the theory is intrinsically non-perturbative in the large N limit. At any nonzero value of the \'t Hooft coupling $lambda$, an exponentially large (in N^2) number of free theory states of wide energy range (of order N) mix under the interaction. As a result the planar perturbation theory breaks down. We argue that an arrow of time emerges and the dual string configuration should be interpreted as a stringy black hole Guido Festuccia http://streamer.perimeterinstitute.ca/mp3/63a83e24-08a0-4755-b662-b30f029653d1.mp3 Science http://streamer.perimeterinstitute.ca/mp3/63a83e24-08a0-4755-b662-b30f029653d1.mp3 Tue, 05 Dec 2006 15:45:00 -0500 Due to recent, as well as less recent, work on perturbative N=8 supergravity and N=4 super Yang-Mills in 4d, the two theories are appearing more and more closely related. These relations include similar "MHV-rule" constructions, one-loop structure and, perhaps, the same UV behavior, namely UV finiteness. This talk introduces some of the methods to study the relations. Kasper Larsen http://streamer.perimeterinstitute.ca/mp3/3008c0cd-cc58-48f8-96bc-649c9a26f686.mp3 Science http://streamer.perimeterinstitute.ca/mp3/3008c0cd-cc58-48f8-96bc-649c9a26f686.mp3 Tue, 05 Dec 2006 16:45:00 -0500 TBA Eleonora Dell'Aquila http://streamer.perimeterinstitute.ca/mp3/ce1a1202-bf9d-4387-883f-3f61fc78ba6f.mp3 Science http://streamer.perimeterinstitute.ca/mp3/ce1a1202-bf9d-4387-883f-3f61fc78ba6f.mp3 Wed, 06 Dec 2006 08:30:00 -0500 In the context of AdS/CFT, it has been recently proposed that Wilson loops in higher representation of the gauge group have a dual description in terms of D-branes in AdS_5xS^5. After reviewing this new dictionary, I will present a computation of correlators between chiral primaries of N=4 SYM and Wilson loops in large symmetric and antisymmetric representations. These correlators can be computed both in supergravity using D-branes and in gauge theory from a matrix model, with precise agreement between the two sides Simone Giombi http://streamer.perimeterinstitute.ca/mp3/a6b124ed-f8c7-438a-bcec-2ddf39002bfe.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a6b124ed-f8c7-438a-bcec-2ddf39002bfe.mp3 Wed, 06 Dec 2006 10:00:00 -0500 It has been conjectured that maximally supersymmetric SU(N) Yang-Mills theory is dual to a String Theory on asymptotically AdS_5 times S^5 backgrounds. This is known as the AdS/CFT correspondence. In this talk I will show how using one-loop calculations in the gauge theory, one can study the emergence of the dual String Theory. We will see, quite explicitly, the emergence of closed strings, D-branes, open strings and space-time itself. This is done in a reduced sector (SU(2) sector), where the gauge theory can be written as Matrix Quantum Mechanics. This simple sector provides a toy model of a non-perturbative quantum theory of gravity. Samuel Vazquez http://streamer.perimeterinstitute.ca/mp3/a0c6e7af-cb24-4e91-8844-301d83c27899.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a0c6e7af-cb24-4e91-8844-301d83c27899.mp3 Wed, 06 Dec 2006 11:00:00 -0500 TBA Dario Benedetti http://streamer.perimeterinstitute.ca/mp3/a5bcb014-907a-46ef-8f5d-0cc793a7f142.mp3 Science http://streamer.perimeterinstitute.ca/mp3/a5bcb014-907a-46ef-8f5d-0cc793a7f142.mp3 Wed, 06 Dec 2006 13:00:00 -0500 David Archer http://streamer.perimeterinstitute.ca/mp3/97d6805d-776c-432d-bcf7-b32f60dc5d14.mp3 Science http://streamer.perimeterinstitute.ca/mp3/97d6805d-776c-432d-bcf7-b32f60dc5d14.mp3 Wed, 06 Dec 2006 14:00:00 -0500 TBA Andy Randono http://streamer.perimeterinstitute.ca/mp3/0e201666-c181-4406-a4ba-7693e23fc8ad.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0e201666-c181-4406-a4ba-7693e23fc8ad.mp3 Wed, 06 Dec 2006 15:30:00 -0500 Hints from quantum gravity suggest that a preferred frame may actually exist. One way to accommodate such a frame in general relativity without sacrificing diffeomorphism invariance is to couple the metric to a dynamical, time like, unit-norm vector field--the "aether". I will discuss properties and observational tests of a class of such theories, including post-Newtonian effects and radiation from binary pulsar systems. Brendan Foster http://streamer.perimeterinstitute.ca/mp3/46063c3a-e27b-478b-9b96-21cd86d4004b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/46063c3a-e27b-478b-9b96-21cd86d4004b.mp3 Wed, 06 Dec 2006 16:30:00 -0500 Although entanglement constitutes one of the most remarkable differences between classical and quantum mechanics, and entanglement does have directly observable consequences, entanglement is not a regular observable like momentum or energy. It is rather a non-linear functional of a typically large set of such observables. Therefore, one often needs to perform many different measurements, in order to determine the degree of entanglement of a given quantum state. We show, how the number of measurement can be reduced -- sometimes to a single one -- if collective observables are measured, that respect the natural invariance properties of entangled states. Finally, we discuss the implementation of this approach in a laboratory experiment. Nature 440, 1022 (2006) PRL 79, 050501 (2006) quant-ph/0605250 Florian Mintert http://streamer.perimeterinstitute.ca/mp3/0e201666-c181-4406-a4ba-7693e23fc8ad.mp3 Science http://streamer.perimeterinstitute.ca/mp3/0e201666-c181-4406-a4ba-7693e23fc8ad.mp3 Wed, 06 Dec 2006 16:30:00 -0500 The Everett (many-worlds) interpretation has made great progress over the past 20-30 years, largely due to the role of decoherence in providing a solution to the preferred basis problem. This makes it a serious candidate for a realist solution to the measurement problem. A remaining objection to the Everett interpretation (and one that is often considered fatal) is that that interpretation cannot make adequate sense of quantum probabilities. Dvaid Deutsch and David Wallace have argued that, by applying decision theory to the case of a rational agent who believes in the many-worlds interpretation, we can prove that such agents _act as if_ the theory predicted objective probabilities in the sense of fundamental indeterminism, or ignorance of initial conditions. I raise the issue of whether or not this, if true, is all that the many-worlds theorist needs from 'probability'. I first suggest a reason for thinking that the answer might be 'no': the reason is that knowing how to act on the assumption that a given theory is true is prima facie irrelevant to the question of whether we have any reason to believe the theory in the first place. I then go on to offer a solution to this problem, drawing on resources from Bayesian confirmation theory. My conclusion is that the problem of probability in the Everett interpretation has been solved. Hilary Greaves http://streamer.perimeterinstitute.ca/mp3/e46a70e9-1b30-4dce-aec0-62f1ac19ff94.mp3 Science http://streamer.perimeterinstitute.ca/mp3/e46a70e9-1b30-4dce-aec0-62f1ac19ff94.mp3 Thu, 07 Dec 2006 03:00:00 -0500 Ancillary state construction is a necessary component of quantum computing. Ancillae are required both for error correction and for performing universal computation in a fault-tolerant way. Computation to an arbitrary accuracy, however, is effectively achieved by increasing the number of qubits in order to suppress the variance in the expected number of errors. Thus, it is important to be able to construct very large ancillary states. Concatenated quantum coding provides a means of constructing ancillae of any size, but, this fact aside, concatenation is not a particularly efficient form of coding. More efficient codes exist, but these codes lack the substructure of concatenated codes that enables fault-tolerant preparation of large ancillae. In this talk I will discuss the advantages of coding in large blocks, both from the perspective of efficiency and analysis, and I will describe my progress in developing construction procedures for moderately large ancillae. Bryan Eastin http://streamer.perimeterinstitute.ca/mp3/bf74fc55-a736-4a0d-95e6-ce35deb23ff8.mp3 Science http://streamer.perimeterinstitute.ca/mp3/bf74fc55-a736-4a0d-95e6-ce35deb23ff8.mp3 Thu, 07 Dec 2006 09:15:00 -0500 It is a fundamental property of quantum mechanics that non-orthogonal pure states cannot be distinguished with certainty, which leads to the following problem: Given a state picked at random from some ensemble, what is the maximum probability of success of determining which state we actually have? I will discuss two recently obtained analytic lower bounds on this optimal probability. An interesting case to which these bounds can be applied is that of ensembles consisting of states that are themselves picked at random. In this case, I will show that powerful results from random matrix theory may be used to give a strong lower bound on the probability of success, in the regime where the ratio of the number of states in the ensemble to the dimension of the states is constant. I will also briefly discuss applications to quantum computation (the oracle identification problem) and to the study of generic entanglement. Ashley Montanaro http://streamer.perimeterinstitute.ca/mp3/05aee4e1-bb13-47a2-8642-820b063ba817.mp3 Science http://streamer.perimeterinstitute.ca/mp3/05aee4e1-bb13-47a2-8642-820b063ba817.mp3 Thu, 07 Dec 2006 10:20:00 -0500 Quantum information theory has two equivalent mathematical conjectures concerning quantum channels, which are also equivalent to other important conjectures concerning the entanglement. In this talk I explain these conjectures and introduce recent results. Motohisa Fukuda http://streamer.perimeterinstitute.ca/mp3/5f2beeba-868a-43ab-99a5-e96f2d070f09.mp3 Science http://streamer.perimeterinstitute.ca/mp3/5f2beeba-868a-43ab-99a5-e96f2d070f09.mp3 Thu, 07 Dec 2006 11:05:00 -0500 TBA Tony Short http://streamer.perimeterinstitute.ca/mp3/57f72a2d-13c0-4dee-be55-fdf6d7e8ea6b.mp3 Science http://streamer.perimeterinstitute.ca/mp3/57f72a2d-13c0-4dee-be55-fdf6d7e8ea6b.mp3 Thu, 07 Dec 2006 14:00:00 -0500 In stochastic treatments of the ERRB set-up, it is equivalent to impose Bell's inequalities, a local causality condition, or a certain "non-contextual hidden variables" condition. But these conditions are violated by quantum mechanics. On the other hand, it is possible to view quantum mechanics as part of "quantum measure theory", a generalization of probability measure theory that allows pair wise interferences between histories whilst banning higher order interference. In this setting, is may be possible find quantum analogues of the three stochastic conditions. Following this line of inquiry, we will see that quantum measure theory allows no stronger violations of Bell's inequalities than does standard quantum theory. We also gain some insights into how to define causality in quantum theory. Joe Henson http://streamer.perimeterinstitute.ca/mp3/9e290909-60d9-4398-8fd3-650640b48985.mp3 Science http://streamer.perimeterinstitute.ca/mp3/9e290909-60d9-4398-8fd3-650640b48985.mp3 Thu, 07 Dec 2006 16:30:00 -0500 TBA Sarah Croke http://streamer.perimeterinstitute.ca/mp3/17e15c34-dfe8-4351-82ca-e8344559bfe4.mp3 Science http://streamer.perimeterinstitute.ca/mp3/17e15c34-dfe8-4351-82ca-e8344559bfe4.mp3 Fri, 08 Dec 2006 09:15:00 -0500 TBA Joseph Fitzsimons http://streamer.perimeterinstitute.ca/mp3/f1296436-ba2c-41dd-adce-304f330ab5d0.mp3 Science http://streamer.perimeterinstitute.ca/mp3/f1296436-ba2c-41dd-adce-304f330ab5d0.mp3 Fri, 08 Dec 2006 10:20:00 -0500 Inferring a quantum system's state, from repeated measurements, is critical for verifying theories and designing quantum hardware. It's also surprisingly easy to do wrong, as illustrated by maximum likelihood estimation (MLE), the current state of the art. I'll explain why MLE yields unreliable and rank-deficient estimates, why you shouldn't be a quantum frequentist, and why we need a different approach. I'll show how operational divergences -- well-motivated metrics designed to evaluate estimates -- follow from quantum strictly proper scoring rules. This motivates Bayesian Mean Estimation (BME), and I'll show how it fixes most of the problems with MLE. I'll conclude with a couple of speculations about the future of quantum state and process estimatio Robin Blume-Kohout http://streamer.perimeterinstitute.ca/mp3/d0ad8fd9-6019-4e22-8045-f43c934706ab.mp3 Science http://streamer.perimeterinstitute.ca/mp3/d0ad8fd9-6019-4e22-8045-f43c934706ab.mp3 Fri, 08 Dec 2006 11:05:00 -0500