Conference

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Exotic Magnetism on the FCC Lattice of 5dn Double Perovskites

Edwin Kermarrec McMaster University

May 01, 2014

PIRSA:14050026
Entanglement, Ergodicity, and Many-Body Localization

Dmitry Abanin

May 01, 2014

PIRSA:14050020
Localization-Protected Quantum Order

David Huse Princeton University

May 01, 2014

PIRSA:14050013
Welcome Address

Michel Gingras University of Waterloo

May 01, 2014

PIRSA:14050012
Double scaling in tensor models

James Ryan Vinted (Germany)

April 25, 2014

PIRSA:14040114
Between Matrices and Tensors

Vincent Rivasseau University of Paris-Saclay

April 25, 2014

PIRSA:14040113
Renormalization group approach to 3d group field theory

Sylvain Carrozza University of Burgundy

April 25, 2014

PIRSA:14040112
Renormalization of entanglement entropy and the gravitational effective action

Joshua Cooperman Radboud Universiteit Nijmegen

April 25, 2014

PIRSA:14040110
Why matter matters in quantum gravity

Astrid Eichhorn Universität Heidelberg

April 25, 2014

PIRSA:14040109
The Asymptotic Safety Program: New results and an inconvenient truth

Martin Reuter Johannes Gutenberg University Mainz

April 25, 2014

PIRSA:14040108
Gravitational RG flows on foliated spacetimes

Frank Saueressig Radboud Universiteit Nijmegen

April 24, 2014

PIRSA:14040106
One-loop renormalization in a toy model of Horava-Lifshitz gravity

Dario Benedetti Ecole Polytechnique - CPHT

April 24, 2014

PIRSA:14040105

Exotic Magnetism on the FCC Lattice of 5dn Double Perovskites

Edwin Kermarrec McMaster University

May 01, 2014

PIRSA:14050026

In the search for new exotic quantum states, the impact of strong spin-orbit interaction has been recently underlined with the discovery of the Jeff = ½ spin orbital Mott state in the 5d5 layered perovskites iridates [1]. The double perovskite structure, where the magnetic ions form a face-centered-cubic (fcc) sublattice, can accommodate a large variety of 5d transition metal elements, and therefore offers an ideal playground for systematic studies of the exotic magnetic and non-magnetic ground states stabilized by strong spin-orbit coupling [2]. Here, we report time-of-flight neutron scattering measurements on the antiferromagnetic, frustrated, cubic double perovskite system Ba2YOsO6. Its non-distorted fcc lattice is decorated with magnetic Os5+ (5d3) ions which undergo a magnetic transition to a long range ordered antiferromagnetic state below TN = 70 K, as revealed by magnetic Bragg peaks occuring at the [100] and [110] positions. Our inelastic data reveals a large spin gap to the spin-wave excitations Δ = 19(2) meV, unexpected for an orbitally quenched, d3 electronic configuration. We compare this result to the recent observation of a Δ=5 meV spin gap in the related cubic double perovskite Ba2YRuO6 (Ru5+, 4d3) [3], and conclude to a stronger spin-orbit coupling present in the heavier, 5d, osmate system.

[1] B. J. Kim et al., Science 323, 1329 (2009).
[2] G. Chen, R. Pereira and L. Balents, Phys. Rev. B 82, 174440 (2010);
G. Chen and L. Balents, Phys. Rev. B 84, 094420 (2011).
[3] J. P. Carlo et al., Phys. Rev. B 88, 024418 (2013).
Entanglement, Ergodicity, and Many-Body Localization

Dmitry Abanin

May 01, 2014

PIRSA:14050020

We are used to describing systems of many particles by statistical mechanics. However, the basic postulate of statistical mechanics – ergodicity – breaks down in so-called many-body localized systems, where disorder prevents particle transport and thermalization. In this talk, I will present a theory of the many-body localized (MBL) phase, based on new insights from quantum entanglement. I will argue that, in contrast to ergodic systems, MBL eigenstates are not highly entangled. I will use this fact to show that MBL phase is characterized by an infinite number of emergent local conservation laws, in terms of which the Hamiltonian acquires a universal form. Turning to the experimental implications, I will describe the response of MBL systems to quenches: surprisingly, entanglement shows logarithmic in time growth, reminiscent of glasses, while local observables exhibit power-law approach to “equilibrium” values. I will support the presented theory with results of numerical experiments. I will close by discussing other directions in exploring ergodicity and its breaking in quantum many-body systems.
Localization-Protected Quantum Order

David Huse Princeton University

May 01, 2014

PIRSA:14050013

Systems that are many-body Anderson localized can exhibit symmetry-breaking long-range order or topological order in regimes where such order would be destroyed at equilibrium by thermal fluctuations. The ordering is dynamical: an ordered initial state stays ordered, being "protected" by the localization of all fluctuations. The simplest examples are quantum Ising models with static randomness. For the random quantum Ising chain this feature has been "known" but apparently not appreciated for close to half a century.

Ref.: Huse, et al., Phys. Rev. B 88, 014206 (2013).
Welcome Address

Michel Gingras University of Waterloo

May 01, 2014

PIRSA:14050012
Double scaling in tensor models

James Ryan Vinted (Germany)

April 25, 2014

PIRSA:14040114

I present recent work on the double scaling limit of random tensor models through the analysis of their Schwinger-Dyson equations. This study exemplifies their potential for probing the continuum phase structure of these theories.
Between Matrices and Tensors

Vincent Rivasseau University of Paris-Saclay

April 25, 2014

PIRSA:14040113

Quartic tensor models can be rewritten in terms of intermediate matrix fields. The corresponding expansion is not only simpler, it suggests also new bridges between matrices, strings and tensors.
Renormalization group approach to 3d group field theory

Sylvain Carrozza University of Burgundy

April 25, 2014

PIRSA:14040112

I will start with a brief overview of tensorial group field theories with gauge invariant condition and their relation to spin foam models. The rest of the talk will be focused on the SU(2) theory in dimension 3, which is related to Euclidean 3d quantum gravity and has been proven renormalizable up to order 6 interactions. General renormalization group flow equations will be introduced, allowing in particular to understand the behavior of the relevant couplings in the neighborhood of the Gaussian fixed point. I will close with preliminary investigations about the existence of a non-trivial fixed point.
Renormalization of entanglement entropy and the gravitational effective action

Joshua Cooperman Radboud Universiteit Nijmegen

April 25, 2014

PIRSA:14040110

The entanglement entropy associated with a spatial boundary in quantum field theory is ultraviolet divergent, its leading term being proportional to the area of the boundary. Callan and Wilczek proposed a geometrical prescription for computing this entanglement entropy as the response of the gravitational effective action to a conically singular metric perturbation. I argue that the Callan-Wilczek prescription is rigorously justified at least for a particular class of quantum states each expressible as a Euclidean path integral. I then show that the entanglement entropy is rendered ultraviolet finite by precisely the counterterms required to cancel the ultraviolet divergences in the gravitational effective action. In particular, the leading contribution to the entanglement entropy is given by the renormalized Bekenstein-Hawking formula. These results apply to a general quantum field theory coupled to a fixed background metric, holding for arbitrary entangling surfaces with vanishing extrinsic curvature in any dimension, to all orders in perturbation theory in the quantum fields, and for all ultraviolet divergent terms in the entanglement entropy. I also reconcile these results on the entanglement entropy with the existing literature, compare them to the Wald entropy, and speculate on their interpretation and implication.
Why matter matters in quantum gravity

Astrid Eichhorn Universität Heidelberg

April 25, 2014

PIRSA:14040109

I will argue that a fundamental theory of quantum gravity that is applicable to our universe must include matter degrees of freedom. In my talk I will focus on the option that these are fundamental, in contrast to low-energy effective, degrees of freedom, and must thus be included in the microscopic dynamics of spacetime.
I will present evidence that dynamical Standard Model matter is compatible with asymptotically safe quantum gravity, while several "Beyond Standard Model" scenarios are disfavored. I will also discuss how the coupling to matter opens a window into the observational quantum gravity regime.
The Asymptotic Safety Program: New results and an inconvenient truth

Martin Reuter Johannes Gutenberg University Mainz

April 25, 2014

PIRSA:14040108

We briefly review the various components and their conceptual status of the full Asymptotic Safety Program which aims at finding a nonperturbative infinite-cutoff limit of a regularized functional integral for a quantum field theory of gravity. It is explained why in the continuum formulation based on the Effective Average Action the key requirement of background independence unavoidably results in a "bi-metric" framework, and recent results on truncated RG flows of bi-metric actions are presented. They suggest that the next generation of truncations that must be explored should be of bi-metric type. As an application, a method of characterizing and counting physical states is shown to arise.
Gravitational RG flows on foliated spacetimes

Frank Saueressig Radboud Universiteit Nijmegen

April 24, 2014

PIRSA:14040106

The role of time and a possible foliation structure of spacetime are longstanding questions which lately received a lot of renewed attention from the quantum gravity community. In this talk, I will review recent progress in formulating a Wetterich-type functional renormalization group equation on foliated spacetimes and outline its potential applications. In particular, I will discuss first results concerning the RG flow of
Horava-Lifshitz gravity, highlighting a possible mechanism for a dynamical Lorentz-symmetry restoration at low energies.
One-loop renormalization in a toy model of Horava-Lifshitz gravity

Dario Benedetti Ecole Polytechnique - CPHT

April 24, 2014

PIRSA:14040105

I will present some recent results on the UV properties of a toy model of Horava-Lifshitz gravity in 2+1 dimensions. In particular, I will illustrate some details of a one-loopcalculation, leading to beta functions for the running couplings. The renormalization group flow obtained in such way shows that Newton's constant is asymptotically free. However, the DeWitt
supermetric approaches its Weyl invariant form with the same speed and the effective interaction coupling of the scalar degree of freedom remains constant along the flow. I will discuss some general lesson that we can learn from these results.

Title	Speaker(s)	Date	Talk Type	Info link
Exotic Magnetism on the FCC Lattice of 5dn Double Perovskites	Edwin Kermarrec	2014-05-01	Conference	View details
Entanglement, Ergodicity, and Many-Body Localization	Dmitry Abanin	2014-05-01	Conference	View details
Localization-Protected Quantum Order	David Huse	2014-05-01	Conference	View details
Welcome Address	Michel Gingras	2014-05-01	Conference	View details
Double scaling in tensor models	James Ryan	2014-04-25	Conference	View details
Between Matrices and Tensors	Vincent Rivasseau	2014-04-25	Conference	View details
Renormalization group approach to 3d group field theory	Sylvain Carrozza	2014-04-25	Conference	View details
Renormalization of entanglement entropy and the gravitational effective action	Joshua Cooperman	2014-04-25	Conference	View details
Why matter matters in quantum gravity	Astrid Eichhorn	2014-04-25	Conference	View details
The Asymptotic Safety Program: New results and an inconvenient truth	Martin Reuter	2014-04-25	Conference	View details
Gravitational RG flows on foliated spacetimes	Frank Saueressig	2014-04-24	Conference	View details
One-loop renormalization in a toy model of Horava-Lifshitz gravity	Dario Benedetti	2014-04-24	Conference	View details

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Exotic Magnetism on the FCC Lattice of 5dn Double Perovskites

Entanglement, Ergodicity, and Many-Body Localization

Localization-Protected Quantum Order

Welcome Address

Double scaling in tensor models

Between Matrices and Tensors

Renormalization group approach to 3d group field theory

Renormalization of entanglement entropy and the gravitational effective action

Why matter matters in quantum gravity

The Asymptotic Safety Program: New results and an inconvenient truth

Gravitational RG flows on foliated spacetimes

One-loop renormalization in a toy model of Horava-Lifshitz gravity

Exotic Magnetism on the FCC Lattice of 5dn Double Perovskites

Entanglement, Ergodicity, and Many-Body Localization

Localization-Protected Quantum Order

Welcome Address

Double scaling in tensor models

Between Matrices and Tensors

Renormalization group approach to 3d group field theory

Renormalization of entanglement entropy and the gravitational effective action

Why matter matters in quantum gravity

The Asymptotic Safety Program: New results and an inconvenient truth

Gravitational RG flows on foliated spacetimes

One-loop renormalization in a toy model of Horava-Lifshitz gravity