Scientific Series

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Cosmological Constraints on theories of Modified Gravity

Alexandre Barreira Durham University
October 16, 2014

PIRSA:14100074
Astrophysics
Quantum Fields and Strings at Finite Coupling

Pedro Vieira Perimeter Institute for Theoretical Physics

October 15, 2014

PIRSA:14100050
The Minimal Modal Interpretation of Quantum Theory
- David Kagan University of Massachusetts Dartmouth
- Jacob Barandes Harvard University
October 14, 2014

PIRSA:14100001
Quantum Physics
Bulk Entanglement Spectrum: From Topological States to Quantum Criticality

Timothy Hsieh Perimeter Institute for Theoretical Physics
October 14, 2014

PIRSA:14100075
Condensed Matter
QQ-CHARACTERS, GAUGE THEORY and non-perturbative Dyson-Schwinger equations

Nikita Nekrasov Stony Brook University

October 14, 2014

PIRSA:14100066
(Non)perturbative QCD and Jet Substructure

Jesse Thaler Massachusetts Institute of Technology (MIT)

October 14, 2014

PIRSA:14100046
Gravitational lensing of the CMB

Gilbert Holder University of Illinois Urbana-Champaign
October 14, 2014

PIRSA:14100084
Astrophysics
Bogomolov and beyond for Calabi-Yau 3-folds

Peng Gao ExodusPoint Capital
October 08, 2014

PIRSA:14100083
High Energy Physics
Non local weak measurements

Aharon Brodutch Institute for Quantum Computing (IQC)
October 07, 2014

PIRSA:14100073
Quantum Physics
On reducing 3d supersymmetric theories to two dimensions

Brian Willett Institute for Advanced Study (IAS)
October 07, 2014

PIRSA:14100005
High Energy Physics
De Sitter Wavefunctionals and the Resummation of Time

Matthew Baumgart Carnegie Mellon University
October 07, 2014

PIRSA:14100051
High Energy Physics
Flux Compactifications Grow Lumps

Claire Zukowski University of California, Berkeley
October 07, 2014

PIRSA:14100081
Astrophysics

Cosmological Constraints on theories of Modified Gravity

Alexandre Barreira Durham University
October 16, 2014

PIRSA:14100074
Astrophysics
Recently, research in cosmology has seen a growing interest in theories of gravity beyond General Relativity (GR). From an observational point of view, there are two main reasons for this. Firstly, the law of gravity has never been directly tested on scales larger than the Solar System. Hence, by understanding better the various signatures that different gravity models can leave on cosmological observables, one can improve the chances of identifying any departures from GR, or alternatively, extend the model's observational success into a whole new regime. Secondly, theories of modified gravity can arise also as an alternative to the cosmological constant (or any other form of dark energy) to explain the current accelerated expansion of the Universe. Using my results from suitably modified Boltzmann, N-body codes and semi-analytical models of structure formation, I will describe the way modified gravity models typically impact a series of cosmological observables. I will use two popular models as examples, which are known as Galileon and Nonlocal Gravity. In the Galileon model, the modifications to gravity on large scales are driven by nonlinear derivative interactions of a scalar field, which can nevertheless be suppressed in the Solar System by means of a mechanism known as Vainshtein screening. This model can provide a good fit to the latest CMB, BAO and SNIa data, although with different cosmological parameters than the standard LCDM model. Specifically, unlike LCDM, the Galileon model predicts nonzero neutrino masses (over 5sigma) and the constraints on the Hubble rate are compatible with its local determinations. The results from my N-body simulations and Halo Occupation Distribution analysis also show that the model can describe the measured clustering amplitude of Luminous Red Galaxies and that the screening mechanism can be very efficient in "hiding" the modifications to gravity on small scales. However, these results also show that the observational viability of the model may be under pressure due to the combined constraints derived from the sign of the ISW effect and from Solar System tests. In the Nonlocal model, the acceleration of the universe is driven by terms that involve the inverse of a derivative operator acting on curvature tensors. This model is also likely to pass large-scale structure constraints with the same flying colors as Galileon gravity, but the lack of a screening mechanism in this model makes it unclear on whether or not it is able to satisfy Solar System constraints. These steps I will describe for the cases of the Galileon and Nonlocal models can be viewed as guidelines for one to place constraints on other (or not yet invented) models of modified gravity. References: The results I will describe are based on the following papers: arXiv:1208.0600, arXiv:1302.6241, arXiv:1306.3219, arXiv:1308.3699, arXiv:1401.1497, arXiv:1404.1365, arXiv:1406.0485, arXiv:1408.1084
Quantum Fields and Strings at Finite Coupling

Pedro Vieira Perimeter Institute for Theoretical Physics

October 15, 2014

PIRSA:14100050

Gauge theories lie at the heart of our understanding of three of the four known forces in nature: the electromagnetic, weak and strong forces. Moreover, our best understood non-perturbative definition of a theory of quantum gravity is also given by a gauge theory. Yet, despite their absolutely central role in physics, gauge theories are still far from being tamed with our current theoretical tools. In this colloquium we shall explore the realm of quantum fields and strings at finite coupling and survey some of the exciting recent developments which are improving this state of affairs. The main character in our incursions will be a most symmetric gauge theory known as N=4 super Yang-Mills theory, often referred to as the harmonic oscillator of the twenty first century or, as it was most recently coined, as the Darth Vader theory.
The Minimal Modal Interpretation of Quantum Theory
- David Kagan University of Massachusetts Dartmouth
- Jacob Barandes Harvard University
October 14, 2014

PIRSA:14100001
Quantum Physics
A persistent mystery of quantum theory is whether it admits an interpretation that is realist, self-consistent, model-independent, and unextravagant in the sense of featuring neither multiple worlds nor pilot waves. In this talk, I will present a new interpretation of quantum theory -- called the minimal modal interpretation (MMI) -- that aims to meet these conditions while also hewing closely to the basic structure of the theory in its widely accepted form. The MMI asserts that quantum systems -- whether closed or open -- have actual states that evolve along kinematical trajectories through their state spaces, and that those trajectories are governed by specific (if approximate) dynamical rules determined by a general new class of conditional probabilities, and in a manner that differs significantly from the de Broglie-Bohm formulation. The MMI is axiomatically parsimonious, leaves the usual dynamical content of quantum theory essentially intact, and includes only metaphysical entities that are either already a standard part of quantum theory or that have counterparts in classical physics. I will also address a number of important issues and implicit assumptions in the foundations community that I believe merit reconsideration and re-evaluation going forward.
Bulk Entanglement Spectrum: From Topological States to Quantum Criticality

Timothy Hsieh Perimeter Institute for Theoretical Physics
October 14, 2014

PIRSA:14100075
Condensed Matter
A quantum phase transition is usually achieved by tuning physical parameters in a Hamiltonian at zero temperature. Here, we demonstrate that the ground state of a topological phase itself encodes critical properties of its transition to a trivial phase. To extract this information, we introduce a partition of the system into two subsystems both of which extend throughout the bulk in all directions. The resulting bulk entanglement spectrum (BES) has a low-lying part that resembles the excitation spectrum of a bulk Hamiltonian, which allows us to probe a topological phase transition from a single wavefunction by tuning either the geometry of the partition or the entanglement temperature. As an example, this remarkable correspondence between topological phase transition and entanglement criticality is rigorously established for integer quantum Hall states. We also implement BES using tensor networks, derive the universality classes of topological phase transitions from the spin-1 chain Haldane phase, and demonstrate that the AKLT wavefunction (and its generalizations) remarkably contains critical six-vertex (and in general eight-vertex) models within it.
QQ-CHARACTERS, GAUGE THEORY and non-perturbative Dyson-Schwinger equations

Nikita Nekrasov Stony Brook University

October 14, 2014

PIRSA:14100066

We report on recent advances in understanding the non-local symmetries of quantum field theory, notably gauge theory. The symmetries relate topologically distinct sectors of the field space. We study these symmetries in some detail in the context of the BPS/CFT correspondence. We also introduce a notion of qq-characters, which generalize the q-characters of quantum affine algebras, introduced by E. Frenkel and N. Reshetikhin, and conjecturally are related to the (q, t)-characters introduced by H. Nakajima. We show that the qq-characters can be used to derive an infinite set of Dyson-Schwinger type relations which imply that the supersymmetric partition functions of four dimensional gauge theory (with surface operators) obey BPZ and KZB-type equations.
(Non)perturbative QCD and Jet Substructure

Jesse Thaler Massachusetts Institute of Technology (MIT)

October 14, 2014

PIRSA:14100046

With the remarkable performance of the ATLAS and CMS detectors, jets at the LHC can now be characterized not just by their overall direction and energy but also by their substructure. At the same time, there has been substantial progress in predicting the properties of jets from first principles. In this talk, I highlight the ways that theoretical studies of jet substructure have enhanced our understanding of QCD, including examples that blur the boundary between perturbative and nonperturbative physics.
Gravitational lensing of the CMB

Gilbert Holder University of Illinois Urbana-Champaign
October 14, 2014

PIRSA:14100084
Astrophysics
Gravitational lensing of the cosmic microwave background is emerging as a useful cosmological tool. Recent measurements have been made by several experiments (including the South Pole Telescope, which will be featured), with rapidly improving precision. These measurements can be used for many purposes, including studying the connection between dark matter and galaxies on large scales, measuring the clustering of matter at z~3, and improving the precision of possible measurements of gravitational radiation from inflation.
Bogomolov and beyond for Calabi-Yau 3-folds

Peng Gao ExodusPoint Capital
October 08, 2014

PIRSA:14100083
High Energy Physics
Non local weak measurements

Aharon Brodutch Institute for Quantum Computing (IQC)
October 07, 2014

PIRSA:14100073
Quantum Physics
Weak measurement is increasingly acknowledged as an important theoretical and experimental tool. Weak values- the results of weak measurements- are often used to understand seemingly paradoxical quantum behavior. Until now however, it was not known how to perform a weak non-local measurement of a general operator. Such a procedure is necessary if we are to take the associated `weak values' seriously as a physical quantity. We propose a novel scheme for performing non-local weak measurement which is based on the principle of quantum erasure. This method can be used for a large class of observables including those related to Hardy's paradox.
On reducing 3d supersymmetric theories to two dimensions

Brian Willett Institute for Advanced Study (IAS)
October 07, 2014

PIRSA:14100005
High Energy Physics
We study the dimensional reduction of 3d QFTs with N=2 supersymmetry. In particular, we are interested in deriving dualities between 2d N=(2,2) theories starting from 3d dualities. Our main tool is the supersymmetric index, ie, the partition function on S^2 x S^1, which formally reduces to the partition function on S^2 as the radius of the circle goes to zero. There are various technical subtleties in this limit of the index which reflect physical subtleties in the reduction of the theories. We reproduce several known 2d N=(2,2) dualities and find evidence for some new ones.
De Sitter Wavefunctionals and the Resummation of Time

Matthew Baumgart Carnegie Mellon University
October 07, 2014

PIRSA:14100051
High Energy Physics
The holographic RG of Anti-De Sitter gives a powerful clue about the underlying AdS/CFT correspondence. The question is whether similar hints can be found for the heretofore elusive holographic dual of De Sitter. The framework of stochastic inflation uses nonperturbative insight to tame bad behavior in the perturbation series of a massless scalar in DS at late times. Remarkably, this fully quantum system loses phase information in the leading approximation, but retains a probabilistic character and allows for a controlled prediction of late time Green's functions. Recasting this as a "resummation of time", we wish understand whether the distributions that result can be thought of as an attractive UV fixed point of a theory
living on a spacelike slice of DS. We derive stochastic inflation via the wavefunctional approach to Quantum Field Theory. This allows for the straightforward implementation of corrections to the original framework.
Flux Compactifications Grow Lumps

Claire Zukowski University of California, Berkeley
October 07, 2014

PIRSA:14100081
Astrophysics
The simplest flux compactifications are highly symmetric—a q-form flux is wrapped uniformly around an extra-dimensional q-sphere. I will discuss a family of solutions that break the internal SO(q+1) symmetry of these solutions down to SO(q)×Z_2, and show that often at least one of them has lower vacuum energy, larger entropy, and is more stable than the symmetric solution. I will describe the phase diagram of lumpy solutions and provide an interpretation in terms of an effective potential. Finally, I will provide evidence that the perturbatively stable vacua have a non-perturbative instability to spontaneously sprout lumps; generically this new decay is exponentially faster than all other known decays of the model.

Title	Speaker(s)	Date	Talk Type	Info link
Cosmological Constraints on theories of Modified Gravity	Alexandre Barreira	2014-10-16	Scientific Series	View details
Quantum Fields and Strings at Finite Coupling	Pedro Vieira	2014-10-15	Scientific Series	View details
The Minimal Modal Interpretation of Quantum Theory	David Kagan, Jacob Barandes	2014-10-14	Scientific Series	View details
Bulk Entanglement Spectrum: From Topological States to Quantum Criticality	Timothy Hsieh	2014-10-14	Scientific Series	View details
QQ-CHARACTERS, GAUGE THEORY and non-perturbative Dyson-Schwinger equations	Nikita Nekrasov	2014-10-14	Scientific Series	View details
(Non)perturbative QCD and Jet Substructure	Jesse Thaler	2014-10-14	Scientific Series	View details
Gravitational lensing of the CMB	Gilbert Holder	2014-10-14	Scientific Series	View details
Bogomolov and beyond for Calabi-Yau 3-folds	Peng Gao	2014-10-08	Scientific Series	View details
Non local weak measurements	Aharon Brodutch	2014-10-07	Scientific Series	View details
On reducing 3d supersymmetric theories to two dimensions	Brian Willett	2014-10-07	Scientific Series	View details
De Sitter Wavefunctionals and the Resummation of Time	Matthew Baumgart	2014-10-07	Scientific Series	View details
Flux Compactifications Grow Lumps	Claire Zukowski	2014-10-07	Scientific Series	View details

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Format results

Cosmological Constraints on theories of Modified Gravity

Quantum Fields and Strings at Finite Coupling

The Minimal Modal Interpretation of Quantum Theory

Bulk Entanglement Spectrum: From Topological States to Quantum Criticality

QQ-CHARACTERS, GAUGE THEORY and non-perturbative Dyson-Schwinger equations

(Non)perturbative QCD and Jet Substructure

Gravitational lensing of the CMB

Bogomolov and beyond for Calabi-Yau 3-folds

Non local weak measurements

On reducing 3d supersymmetric theories to two dimensions

De Sitter Wavefunctionals and the Resummation of Time

Flux Compactifications Grow Lumps

Cosmological Constraints on theories of Modified Gravity

Quantum Fields and Strings at Finite Coupling

The Minimal Modal Interpretation of Quantum Theory

Bulk Entanglement Spectrum: From Topological States to Quantum Criticality

QQ-CHARACTERS, GAUGE THEORY and non-perturbative Dyson-Schwinger equations

(Non)perturbative QCD and Jet Substructure

Gravitational lensing of the CMB

Bogomolov and beyond for Calabi-Yau 3-folds

Non local weak measurements

On reducing 3d supersymmetric theories to two dimensions

De Sitter Wavefunctionals and the Resummation of Time

Flux Compactifications Grow Lumps