Entanglement entropy of Wilson loops: Holography and matrix models
Simon Gentle University of California, Los Angeles
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Discovering the QCD Axion with Black Holes and Gravitational Waves
Masha Baryakhtar University of Washington
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Numerical Study of a Bosonic Topological Insulator in Three Dimensions
Scott Geraedts California Institute of Technology
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Fundamental physics with muons
PIRSA:14100115 -
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Spinning Black Holes and the Membrane Paradigm
Robert Penna Massachusetts Institute of Technology (MIT)
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Superconformal Indices, AdS/CFT, and Cyclic Homologies
Richard Eager University of Tokyo
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Cosmological Constraints on theories of Modified Gravity
Alexandre Barreira Durham University
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Quantum Fields and Strings at Finite Coupling
Pedro Vieira Perimeter Institute for Theoretical Physics
PIRSA:14100050
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Entanglement entropy of Wilson loops: Holography and matrix models
Simon Gentle University of California, Los Angeles
A half-BPS circular Wilson loop in maximally supersymmetric SU(N) Yang-Mills theory in an arbitrary representation is described by a Gaussian matrix model with a particular insertion. The additional entanglement entropy of a spherical region in the presence of such a loop was recently computed by Lewkowycz and Maldacena using exact matrix model results. In this talk I will utilise the supergravity solutions that are dual to such Wilson loops in large representations to calculate this entropy holographically. Employing the results of Gomis, Matsuura, Okuda and Trancanelli to express this holographic entanglement entropy in a matrix model language, I will demonstrate complete agreement with the formula derived by Lewkowycz and Maldacena. -
Discovering the QCD Axion with Black Holes and Gravitational Waves
Masha Baryakhtar University of Washington
In the next few years, Advanced LIGO will be the first experiment to detect gravitational waves. Through superradiance of stellar black holes, it may also be the first experiment to discover the QCD axion with decay constant around or above the GUT scale. When an axion's Compton wavelength is comparable to the size of a black hole, the axion binds to the black hole, forming a "gravitational atom". Due to superradiance, the number of axions occupying the bound levels grows exponentially, extracting energy and angular momentum from the black hole. I will discuss the promising gravitational wave signals from axions transitioning between levels of the gravitational atom and axions annihilating to gravitons. Events for axions in the range 10^−13 to 10^−10 eV can be visible at aLIGO. The signals produced are long-lasting, monochromatic, and can be distinguished from ordinary astrophysical sources. These signatures are also promising for lighter axions at future, lower-frequency, GW observatories. I will also present our updated exclusion on the QCD axion mass range of 6*10^−13 eV < ma < 1.5*10^−11 eV imposed by black hole spin measurements. -
Beyond slow-roll - Daan Meerburg
We live in exciting times for cosmologists. There is a plethora of cosmological experiments that allow us to reconstruct the earliest moments in the Universe and test our ideas on how the Universe came into existence. Current data appear to favor an inflationary model that produces adiabatic, scale free, Gaussian fluctuations with an amplitude of 10^-5 in units of mK. WIthin the realm of cosmological models, it appears that such conditions are easily accomplished if we have a single light field slowly rolling down its potential. In this talk, I will investigate the possibility to what extend our current observations would allow for a deviation from slow-roll: several class of models predicts that the fluctuation spectra will contain superimposed features on top of their slow-roll solution. I will discuss these models and explain a novel way of extract these features from the data, both in the power spectrum as well as in the bispectrum. I will give the latest constraints from current cosmological surveys. In light of the possible detection of primordial gravitational waves, I will show that there exists evidence (3 sigma) that the data prefer a long wavelength feature driven by axion monodromy, a model that naturally predicts large tensor modes. From this I will derive a constraint on the axion decay constant. I will conclude with a discussion on how observations of higher order statistics and large scale structure could further constrain these models. -
Disturbance in weak measurements and the difference between quantum and classical weak values
The role of measurement induced disturbance in weak measurements is of central importance for the interpretation of the weak value. Uncontrolled disturbance can interfere with the postselection process and make the weak value dependent on the details of the measurement process. Here we develop the concept of a generalized weak measurement for classical and quantum mechanics. The two cases appear remarkably similar, but we point out some important differences. A priori it is not clear what the correct notion of disturbance should be in the context of weak measurements. We consider three different notions and get three different results: (1) For a `strong' definition of disturbance, we find that weak measurements are disturbing. (2) For a weaker definition we find that a general class of weak measurements are non-disturbing, but that one gets weak values which depend on the measurement process. (3) Finally, with respect to an operational definition of the `degree of disturbance', we find that the AAV weak measurements are the least disturbing, but that the disturbance is still non-zero. -
Numerical Study of a Bosonic Topological Insulator in Three Dimensions
Scott Geraedts California Institute of Technology
We construct a model which realizes a (3+1)-dimensional symmetry-protected topological phase of bosons with U(1) charge conservation and time reversal symmetry, envisioned by A. Vishwanath and T. Senthil [PRX 4 011016]. Our model works by introducing an additional spin degree of freedom, and binding its hedgehogs to a species of charged bosons. We study the model using Monte Carlo and determine its bulk phase diagram; the phase where the bound states of hedgehogs and charges condense is the topological phase, and we demonstrate this by observing a Witten effect. We also study the surface phase diagram on a (2+1)-dimensional boundary between the topological and trivial insulators. We find a number of exotic phases on the surface, including exotic superfluids, a phase with a Hall conductivity quantized to half the value possible in 2D, and a phase with intrinsic topological order. We also find a new bulk phase with intrinsic topological order. -
Three-Point Function in N=4 SYM and Spin Vertex
In this talk I will explain how to compute three-point functions of N=4 SYM theory in the planar limit for tree level and one-loop in perturbation theory. First I will recall how to formulate the problem of computing the three-point function of operators with determined R-charges in the language of integrable spin chains. In the su(2) sector, the tree-level three point function can be obtained in terms of determinants, whose large R-charge limit can be taken explicitly. Then I will report a systematic method to compute the su(2) three point function at higher loops. In particular, we are able to take the semi-classical limit, and we can compare our result with the calculation from string theory. In the Frolov-Tseytlin limit we find a perfect match at one-loop. Finally I will present a new formalism of computing three-point functions called the spin vertex formalism, which is the weak coupling counter-part of the string vertex in the string field theory. I will describe how to construct the spin vertex and discuss its important properties. -
Fundamental physics with muons
PIRSA:14100115I will review applications of the muon as a probe for new phenomena. Topics to be discussed include the free muon decay and the determination of the Fermi constant; the anomalous magnetic moment of the muon; and searches for lepton flavor violation such as mu->e+gamma, mu->3e, and the muon-electron conversion, with special emphasis on the modification of the muon decay by the atomic binding. -
Schroedinger method as field theoretical model to describe structure formation
Cora Uhlemann Bielefeld University
We investigate large-scale structure formation of collisionless dark matter in the phase space description based on the Vlasov equation whose nonlinearity is induced solely by gravitational interaction according to the Poisson equation. Determining the time-evolution of density and velocity demands solving the full Vlasov hierarchy for the cumulants of the distribution function. In the presence of long-range interaction no consistent truncation is known apart from the dust model which is incapable of describing the formation of bound structures due to the inability to generate higher cumulants like velocity dispersion. Our goal is to find a simple ansatz for the phase space distribution function that approximates the full Vlasov distribution function and can serve as theoretical N-body double to replace the dust model. We present the Schroedinger method which is based on the coarse-grained Wigner probability distribution obtained from a wave function fulfilling the Schroedinger-Poisson equation as sought-after model. We show that its evolution equation approximates the Vlasov equation in a controlled way, cures the shell-crossing singularities of the dust model and is able to describe multi-streaming which is crucial for halo formation. This feature has already been employed in cosmological simulations of large-scale structure formation by Widrow & Kaiser (1993). We explain how the coarse-grained Wigner ansatz allows to calculate higher cumulants like velocity dispersion analytically from density and velocity in a self-consistent manner. On this basis we show that instead of solving the Vlasov-Poisson system one can use the Schrödinger method and solve the Schrödinger-Poission equation to directly determine density and velocity and all higher cumulants. As a first application we study the coarse-grained dust model, which is a limiting case of the Schrödinger method, within Eulerian and Lagrangian perturbation theory. -
Spinning Black Holes and the Membrane Paradigm
Robert Penna Massachusetts Institute of Technology (MIT)
There are about nine astrophysical black holes with measurements of the black hole's spin via the continuum fitting method. Several of these black holes drive powerful jets, which appear to extract the black hole's rotational energy. I will discuss the theory behind these observations, with a particular focus on the black hole membrane paradigm. The membrane paradigm is useful on a practical level for understanding black hole jets. However, it may also be related to fundamental physics through holography and AdS/CFT. This suggests new opportunities for interactions between fundamental physics and astrophysics. -
Superconformal Indices, AdS/CFT, and Cyclic Homologies
Richard Eager University of Tokyo
We explain how to obtain the spectrum of operators with protected scaling dimensions in a four-dimensional superconformal field theory from cyclic homology. Additionally, we show that the superconformal index of a quiver gauge theory equals the Euler characteristic of the cyclic homology of the Ginzburg dg algebra associated to the quiver. For quiver gauge theories which are dual to type IIB string theory on the product of an arbitrary smooth Sasaki-Einstein manifold with five-dimensional AdS space, the index is calculated both from the gauge theory and gravity viewpoints. We find complete agreement. Finally we show how to match the spectrum of protected operators on a supergravity compactification involving generalized complex geometry. -
Cosmological Constraints on theories of Modified Gravity
Alexandre Barreira Durham University
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
PIRSA:14100050Gauge 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.