Scientific Series

Displaying 3349 - 3360 of 5012

Loop quantization of a weak-coupling limit of Euclidean gravity

Casey Tomlin
Pennsylvania State University
April 25, 2013

PIRSA:13040104
Quantum Gravity
Constraining neutron star interior properties with transient events from accreting neutron stars and magnetars

Andrew Cumming
McGill University
April 25, 2013

PIRSA:13040138
Strong Gravity
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems
April 24, 2013

PIRSA:13040116
Condensed Matter
On memory in exponentially expanding spaces

Douglas Stanford
Stanford University
April 23, 2013

PIRSA:13040127
Cosmology
Quantum transport in one dimension: from integrability to many-body localization and topology

Joel Moore
University of California, Berkeley
April 23, 2013

PIRSA:13040125
Condensed Matter
The continuum limit of tensor networks: a path integral representation

David Jennings
Imperial College London
April 22, 2013

PIRSA:13040113
Quantum Foundations
The imaginary part of the gravitational action and black hole entropy

Yasha Neiman
Okinawa Institute of Science and Technology Graduate University
April 18, 2013

PIRSA:13040106
Quantum Gravity
Energy and the Environment - What Physicists Can Do

John Baez
University of California, Riverside
April 17, 2013

PIRSA:13040030
Mathematical physics
The theory of composition in physics

Lucien Hardy
Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040121
Quantum Foundations
Results and highlights from Planck

Kendrick Smith
Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040123
Cosmology
Continuous-variable entanglement distillation and non-commutative central limit theorems

Earl Campbell
University of Sheffield
April 15, 2013

PIRSA:13040122
Quantum Information
Quantum causal dynamics without absolute space or time
April 11, 2013

PIRSA:13040083
Quantum Gravity

Loop quantization of a weak-coupling limit of Euclidean gravity

Casey Tomlin
Pennsylvania State University
April 25, 2013

PIRSA:13040104
Quantum Gravity
I will describe recent work in collaboration with Adam Henderson, Alok Laddha, and Madhavan Varadarajan on the loop quantization of a certain $G_{\mathrm{N}}\rightarrow 0$ limit of Euclidean gravity, introduced by Smolin. The model allows one to test various quantization choices one is faced with in loop quantum gravity, but in a simplified setting. The main results are the construction of finite-triangulation Hamiltonian and diffeomorphism constraint operators whose continuum limits can be evaluated in a precise sense, such that the quantum Dirac algebra of constraints closes nontrivially and free of anomalies. The construction relies heavily on techniques of Thiemann's QSD treatment, and lessons learned applying such techniques to the loop quantization of parameterized scalar field theory and the diffeomorphism constraint in loop quantum gravity. I will also briefly discuss the status of the quantum constraint algebra in full LQG, and how some of the lessons learned from the present model may guide us in that setting.
Constraining neutron star interior properties with transient events from accreting neutron stars and magnetars

Andrew Cumming
McGill University
April 25, 2013

PIRSA:13040138
Strong Gravity
The last few years have seen new opportunities for constraining the physics of neutron star interiors. I will first discuss the current state of neutron star radius measurements and then go on to discuss thermal tomography as a probe of the nuclear, magnetic, and transport properties of neutron star crusts. In each case, I will emphasize the astrophysics that must be understood to make reliable inferences about the properties of dense matter from observations of neutron stars.
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems
April 24, 2013

PIRSA:13040116
Condensed Matter
In one extreme, where the interactions are sufficiently weak compared to the interactions, electrons form a “Fermi liquid” – the state that accounts for the properties of simple metals. In the other extreme, where the interactions are dominant, the electrons form various “Mott” insulating or “Wigner crystalline” phases, often characterized by broken spatial and/or magnetic symmetries. Corresponding charge and/or magnetically ordered insulating phases are common in nature. Between these two extremes lie highly correlated electronic fluids, and correspondingly a host of interesting and perplexing materials, including such diverse systems as the cuprate and iron-based high temperature superconductors, the failed metamagnet Sr3Ru2O7, and a variety of quantum Hall fluids. Some insight into electron fluids in this rich intermediate coupling regime can be obtained from viewing them as partially melted electron solids, rather than as strongly interacting gases. Here, analogies with the liquid crystalline phases of complex classical fluids provide useful guidance for a new approach to this key problem in condensed matter physics.
On memory in exponentially expanding spaces

Douglas Stanford
Stanford University
April 23, 2013

PIRSA:13040127
Cosmology
I will present recent work, done in collaboration with Daniel Roberts, on the global memory of initial conditions that is sometimes, but not always, retained by fluctuating fields on de Sitter space, Euclidean anti de Sitter space, and regular infinite trees. I will discuss applications to the structure of configuration space in de Sitter space and eternal inflation.
Quantum transport in one dimension: from integrability to many-body localization and topology

Joel Moore
University of California, Berkeley
April 23, 2013

PIRSA:13040125
Condensed Matter
Recent advances in analytical theory and numerical methods enable some long-standing questions about transport in one dimension to be answered; these questions are closely related to transport experiments in quasi-1D compounds. The spinless fermion chain with nearest-neighbor interactions at half-filling, or equivalently the XXZ model in zero magnetic field, is an example of an integrable system in which no conventional conserved quantity forces dissipationless transport (Drude weight); we show that there is nevertheless a Drude weight and that at some points its contribution is from a new type of conserved quantity recently constructed by Prosen. Adding an integrability-breaking perturbation leads to a scaling theory of conductivity at low temperature. Adding disorder, we study the question of how Anderson localization is modified by interactions when the system remains fully quantum coherent ("many-body localization"). We find that even weak interactions are a singular perturbation on some quantities: entanglement grows slowly but without limit, suggesting that dynamics in the possible many-body localized phase are glass-like. If time permits, some results on the fractional Luttinger's theorem and the 1D limit of quantum Hall states will be presented.
The continuum limit of tensor networks: a path integral representation

David Jennings
Imperial College London
April 22, 2013

PIRSA:13040113
Quantum Foundations
I will discuss a path-integral representation of continuum tensor networks that extends the continuous MPS class for 1-D quantum fields to arbitrary spatial dimensions while encoding desirable symmetries. The physical states can be interpreted as arising through a continuous measurement process by a lower dimensional virtual field with Lorentz symmetry. The resultant physical states naturally obey entropy area laws, with the expectation values of observables determined by the dissipative dynamics of the boundary field. The class offers the prospect of powerful new analytical and computational tools to describe the physics of strongly interacting field systems.
The imaginary part of the gravitational action and black hole entropy

Yasha Neiman
Okinawa Institute of Science and Technology Graduate University
April 18, 2013

PIRSA:13040106
Quantum Gravity
I present a candidate for a new derivation of black hole entropy. The key observation is that the action of General Relativity in bounded regions has an imaginary part, arising from the boundary term. The formula for this imaginary part is closely related to the Bekenstein-Hawking entropy formula, and coincides with it for certain classes of regions. This remains true in the presence of matter, and generalizes appropriately to Lovelock gravity. The imaginary part of the action is a versatile notion, requiring neither stationarity nor any knowledge about asymptotic infinity. Thus, it may provide a handle on quantum gravity in finite and dynamical regions. I derive the above results, make connections with standard approaches to black hole entropy, and speculate on the meaning of it all. Implications for loop quantum gravity are also discussed.
Energy and the Environment - What Physicists Can Do

John Baez
University of California, Riverside
April 17, 2013

PIRSA:13040030
Mathematical physics
The global warming crisis is part of a bigger transformation in which humanity realizes that the Earth is a finite system and that our population, energy usage, and the like cannot continue to grow exponentially. While politics and economics pose the biggest challenges, physicists are in a good position to help make this transition a bit easier. After a quick review of the problems, we discuss a few ways physicists can help.
The theory of composition in physics

Lucien Hardy
Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040121
Quantum Foundations
We develop a theory for describing composite objects in physics. These can be static objects, such as tables, or things that happen in spacetime (such as a region of spacetime with fields on it regarded as being composed of smaller such regions joined together). We propose certain fundamental axioms which, it seems, should be satisfied in any theory of composition. A key axiom is the order independence axiom which says we can describe the composition of a composite object in any order. Then we provide a notation for describing composite objects that naturally leads to these axioms being satisfied. In any given physical context we are interested in the value of certain properties for the objects (such as whether the object is possible, what probability it has, how wide it is, and so on). We associate a generalized state with an object. This can be used to calculate the value of those properties we are interested in for for this object. We then propose a certain principle, the composition principle, which says that we can determine the generalized state of a composite object from the generalized states for the components by means of a calculation having the same structure as the description of the generalized state. The composition principle provides a link between description and prediction.
Results and highlights from Planck

Kendrick Smith
Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040123
Cosmology
Cosmological results from Planck, a third-generation satellite mission to measure the cosmic microwave background, have just been announced. These results improve constraints on essentially all cosmological parameters, and have implications for several preexisting sources of tension with the standard cosmological model, while also raising new puzzles. I will discuss these results and their significance, as well as the next steps forward.
Continuous-variable entanglement distillation and non-commutative central limit theorems

Earl Campbell
University of Sheffield
April 15, 2013

PIRSA:13040122
Quantum Information
Entanglement distillation transforms weakly entangled noisy states into highly entangled states, a primitive to be used in quantum repeater schemes and other protocols designed for quantum communication and key distribution. In this work, we present a comprehensive framework for continuous-variable entanglement distillation schemes that convert noisy non-Gaussian states into Gaussian ones in many iterations of the protocol. Instances of these protocols include the recursive Gaussifier protocol and the pumping Gaussifier protocol. The flexibility of these protocols give rise to several beneficial trade-offs related to success probabilities or memory requirements that can be adjusted to reflect experimental specifics. Despite these protocols involving measurements, we relate the convergence in this protocols to new instances of non-commutative central limit theorems. Implications of the findings for quantum repeater schemes are discussed.
Quantum causal dynamics without absolute space or time
April 11, 2013

PIRSA:13040083
Quantum Gravity
I will describe a discrete model of spacetime which is quantum-mechanical, causal, and background free. The kinematics is described by networks whose vertices are labelled with arrows. These networks can be evolved forwards (or backwards) in time by using unitary replacement rules. The arrow structure permits one to define dynamics without using an absolute time parameter. Based on arXiv:1201.2489.

Title	Speaker(s)	Date	Talk Type	Info link
Loop quantization of a weak-coupling limit of Euclidean gravity	Casey Tomlin	2013-04-25	Scientific Series	View details
Constraining neutron star interior properties with transient events from accreting neutron stars and magnetars	Andrew Cumming	2013-04-25	Scientific Series	View details
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems		2013-04-24	Scientific Series	View details
On memory in exponentially expanding spaces	Douglas Stanford	2013-04-23	Scientific Series	View details
Quantum transport in one dimension: from integrability to many-body localization and topology	Joel Moore	2013-04-23	Scientific Series	View details
The continuum limit of tensor networks: a path integral representation	David Jennings	2013-04-22	Scientific Series	View details
The imaginary part of the gravitational action and black hole entropy	Yasha Neiman	2013-04-18	Scientific Series	View details
Energy and the Environment - What Physicists Can Do	John Baez	2013-04-17	Scientific Series	View details
The theory of composition in physics	Lucien Hardy	2013-04-16	Scientific Series	View details
Results and highlights from Planck	Kendrick Smith	2013-04-16	Scientific Series	View details
Continuous-variable entanglement distillation and non-commutative central limit theorems	Earl Campbell	2013-04-15	Scientific Series	View details
Quantum causal dynamics without absolute space or time		2013-04-11	Scientific Series	View details

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