Scientific Series

Displaying 3397 - 3408 of 5085

ΛCDM Large Scale Triumphs and Small Scale Challenges

Joel Primack University of California, Santa Cruz
September 17, 2013

PIRSA:13090066
Astrophysics
Edge states at domain wall junctions in supersymmetric gauge theory

Davide Gaiotto Perimeter Institute for Theoretical Physics
September 13, 2013

PIRSA:13090074
Condensed Matter
Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Donald Marolf University of California, Santa Barbara
September 12, 2013

PIRSA:13090060
General Relativity & Quantum Cosmology
Quantum States are Consistent Probability Distributions

Nadish de Silva University of Oxford
September 12, 2013

PIRSA:13090070
Quantum Physics
The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe
September 11, 2013

PIRSA:13090065
High Energy Physics
Quantum Observables as Real-valued Functions and Quantum Probability
September 10, 2013

PIRSA:13090068
Quantum Physics
From dlogs to dilogs

Arthur Lipstein Durham University
September 10, 2013

PIRSA:13090049
High Energy Physics
The local Callan-Symanzik equation: structure and applications

Boaz Keren-Zur L'Ecole Polytechnique Federale de Lausanne (EPFL)
September 06, 2013

PIRSA:13090067
High Energy Physics
A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?
- Niayesh Afshordi University of Waterloo
- Elizabeth Gould Arthur B. McDonald Canadian Astroparticle Physics Research Institute
September 03, 2013

PIRSA:13090064
Quantum Physics
Peaks, excursion sets and the distribution of dark matter haloes

Vincent Desjacques Université de Genève
September 03, 2013

PIRSA:13090062
Astrophysics
Wavelets and MERA

Steven White University of California, Irvine
August 30, 2013

PIRSA:13080057
Condensed Matter
Bottom-up Naturalness

Sonia El Hedri Stanford University
August 27, 2013

PIRSA:13080056
High Energy Physics

ΛCDM Large Scale Triumphs and Small Scale Challenges

Joel Primack University of California, Santa Cruz
September 17, 2013

PIRSA:13090066
Astrophysics
ΛCDM has become the standard cosmological model because its predictions agree so well with observations of the cosmic microwave background and the large-scale structure of the universe. However ΛCDM has faced challenges on smaller scales. Some of these challenges, including the “angular momentum catastrophe" and the absence of density cusps in the centers of small galaxies, may be overcome with improvements in simulation resolution and feedback. Recent simulations appear to form realistic galaxies in agreement with observed scaling relations. Although dark matter halos start small and grow by accretion, the existence of a star-forming band of halo masses naturally explains why the most massive galaxies have the oldest stars, a phenomenon known as galactic “downsizing." The discovery of many faint galaxies in the Local Group is consistent with the large number of subhalos in ΛCDM simulations. There is increasing evidence for such substructure in galaxy dark matter halos from gaps in cold stellar streams in the Milky Way and Andromeda and from gravitational lensing flux anomalies, with the prospect of rapidly increasing data on that from ALMA. The “too big to fail" (TBTF) problem is the latest apparent challenge to ΛCDM. It arose from analysis of the Aquarius and Via Lactea very-high-resolution ΛCDM simulations of Milky-Way-mass dark matter halos. Each simulated halo has ∼10 subhalos so massive and dense that they would appear to be too big to fail to form lots of stars. The TBTF problem is that none of the observed dwarf satellite galaxies of the Milky Way or Andromeda have stars moving as fast as would be expected in these densest subhalos. This may indicate the need for a more complex theory of dark matter – but several recent papers have shown that subhalos in pure dark matter simulations like Aquarius or Via Lactea are significantly modified when baryonic effects are included, so as to solve the TBTF problem. Higher resolution simulations are needed to verify this.
Edge states at domain wall junctions in supersymmetric gauge theory

Davide Gaiotto Perimeter Institute for Theoretical Physics
September 13, 2013

PIRSA:13090074
Condensed Matter
Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Donald Marolf University of California, Santa Barbara
September 12, 2013

PIRSA:13090060
General Relativity & Quantum Cosmology
A defining feature of holographic dualities is that, along with the bulk equations of motion, boundary correlators at any given time t determine those of observables deep in the bulk. We argue that this property emerges from the bulk gravitational Gauss law together with bulk quantum entanglement as embodied in the Reeh-Schlieder theorem. Stringy bulk degrees of freedom are not required and play little role even when they exist. As an example we study a toy model whose matter sector is a free scalar field. The energy density (\rho) sources what we call a pseudo-Newtonian potential (\Phi) through Poisson's equation on each constant time surface, but there is no back-reaction on the matter. We show the Hamiltonian to be essentially self-adjoint on the domain generated from the vacuum by acting with boundary observables localized in an arbitrarily small neighborhood of the chosen time t. Since the Gauss law represents the Hamiltonian as a boundary term, the model is holographic in the sense stated above.
Quantum States are Consistent Probability Distributions

Nadish de Silva University of Oxford
September 12, 2013

PIRSA:13090070
Quantum Physics
We describe a notion of state for a quantum system which is given in terms of a collection of empirically realizable probability distributions and is formally analogous to the familiar concept of state from classical statistical mechanics. We first demonstrate the mathematical equivalence of this new notion to the standard quantum notion of density matrix. We identify the simple logical consistency condition (a generalization of the familiar no-signalling condition) which a collection of distributions must obey in order to reconstruct the unique quantum state from which they arise. In this way, we achieve a formal expression of the common intuition of a quantum state as being classical distributions on compatible observables.
The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe
September 11, 2013

PIRSA:13090065
High Energy Physics
Despite being one of the most abundant constituents of the Universe and more than a half a century of study, some of the most fundamental properties of the neutrino have only been recently uncovered, and others still remain unresolved. I will discuss important developments in the phenomenon of neutrino oscillations, a transmutation process that allows neutrinos to change between three types as they propagate in time. In particular, recent discoveries have opened up the possibility of CP violation in neutrino oscillations, asymmetries in the behavior of neutrinos and their anti-matter counterparts. CP violation, along with other unresolved properties of the neutrino, may play a central role in how the universe came to a matter-dominated state. I will also discuss a new generation of experiments that may allow us to establish whether CP violation does indeed occur in neutrino oscillations.
Quantum Observables as Real-valued Functions and Quantum Probability
September 10, 2013

PIRSA:13090068
Quantum Physics
Quantum observables are commonly described by self-adjoint operators on a Hilbert space H. I will show that one can equivalently describe observables by real-valued functions on the set P(H) of projections, which we call q-observable functions. If one regards a quantum observable as a random variable, the corresponding q-observable function can be understood as a quantum quantile function, generalising the classical notion. I will briefly sketch how q-observable functions relate to the topos approach to quantum theory and the process called daseinisation. The topos approach provides a generalised state space for quantum systems that serves as a joint sample space for all quantum observables. This is joint work with Barry Dewitt.
From dlogs to dilogs

Arthur Lipstein Durham University
September 10, 2013

PIRSA:13090049
High Energy Physics
In this talk, I will describe a new form of hidden simplicity in the planar scattering amplitudes of N=4 super-Yang-Mills theory, notably that the loop integrands can be expressed in dlog form. I will explain how this form arises geometrically from computing the scattering amplitudes using a holomorphic Wilson loop in twistor space. I will also describe a systematic method for evaluating such integrals and use it to obtain a new formula for the 1-loop MHV amplitude. These techniques can be extended to higher loop amplitudes and may lead to a simple and efficient method for computing scattering amplitudes more generally.
The local Callan-Symanzik equation: structure and applications

Boaz Keren-Zur L'Ecole Polytechnique Federale de Lausanne (EPFL)
September 06, 2013

PIRSA:13090067
High Energy Physics
The local Callan-Symanzik equation describes the response of a quantum field theory to local scale transformations in the presence of background sources. The consistency conditions associated with this anomalous equation can be used to derive powerful constraints on RG flows. We will discuss various aspects of the equation and present new results regarding the structure of the anomaly. We then use the equation to write correlation functions of the trace of the energy-momentum tensor off-criticality.
A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?
- Niayesh Afshordi University of Waterloo
- Elizabeth Gould Arthur B. McDonald Canadian Astroparticle Physics Research Institute
September 03, 2013

PIRSA:13090064
Quantum Physics
A century after the advent of Quantum Mechanics and General Relativity, both theories enjoy incredible empirical success, constituting the cornerstones of modern physics. Yet, paradoxically, they suffer from deep-rooted, so-far intractable, conflicts. Motivations for violations of the notion of
relativistic locality include the Bell's inequalities for hidden variable theories, the cosmological horizon problem, and Lorentz-violating approaches to quantum geometrodynamics, such as Horava-Lifshitz gravity. Here, we explore a recent proposal for a ``real ensemble'' non-local description of quantum mechanics, in which ``particles'' can copy each others' observables AND phases, independent of their spatial separation. We first specify the exact theory, ensuring that it is consistent and has (ordinary) quantum mechanics as a fixed point, where all particles with the same observables have the same phases. We then study the stability of this fixed point numerically, and analytically, for simple models. We provide evidence that most systems (in our study) are locally stable to small deviations from quantum mechanics, and furthermore, the phase variance per observable, as well as systematic deviations from quantum mechanics, decay as ~ (EnergyXTime)^{-n}, where n > 2. Interestingly, this convergence is controlled by the absolute value of energy (and not energy difference). Finally, we discuss different issues related to this theory, as well as potential implications for early universe, and the cosmological constant problem.
Peaks, excursion sets and the distribution of dark matter haloes

Vincent Desjacques Université de Genève
September 03, 2013

PIRSA:13090062
Astrophysics
I will review recent developments in our theoretical understanding of the abundance and clustering of dark matter haloes. In the first part of this talk, I will discuss a toy model based on the statistics of peaks of Gaussian random field (Bardeen et al 1986) and show how the clustering properties of such a point set can be easily derived from a generalised local bias expansion. In the second part, I will explain how this peak formalism relates to the excursion set approach and present parameter-free predictions for the mass function and bias of dark matter halos.
Wavelets and MERA

Steven White University of California, Irvine
August 30, 2013

PIRSA:13080057
Condensed Matter
Some of the key insights that led to the development of DMRG stemmed from studying the behavior of real space RG for single particle wavefunctions, a much simpler context than the many-particle case of main interest. Similarly, one can gain insight into MERA by studying wavelets. I will introduce basic wavelet theory and show how one of the most well-known wavelets, a low order orthogonal wavelet of Daubechies, can be realized as the fixed point of a specific MERA (in single-particle direct-sum space). Higher order wavelets and the conflict between compactness in real and Fourier space may provide insight into generalized MERAs for many particle systems.
Bottom-up Naturalness

Sonia El Hedri Stanford University
August 27, 2013

PIRSA:13080056
High Energy Physics
We study the naturalness problem using a model independent bottom up approach by considering models where only the interaction terms needed to cancel the Higgs quadratic divergences are present. If quadratic divergences are canceled by terms linear in the Higgs field, then the collider phenomenology is well covered by current electroweakino and fourth generation searches. If quadratic divergences are canceled by terms bilinear in the Higgs field, then the signatures are highly dependent on the quantum numbers of the new particles. Precision Higgs measurements can reveal the presence of new particles with either vevs or Standard Model charges. If the new particles are scalar dark matter candidates, their direct and indirect detection signatures will be highly correlated and within the reach of XENON100 and Fermi. Observation at one of these experiments would imply observation at the other one. Observable LHC decay channels can also arise if the new particles mix with lighter states. This decay channel involves only the Higgs boson and not the gauge bosons. Observation of such decays would give evidence that the new particle is tied to the naturalness problem.

Title	Speaker(s)	Date	Talk Type	Info link
ΛCDM Large Scale Triumphs and Small Scale Challenges	Joel Primack	2013-09-17	Scientific Series	View details
Edge states at domain wall junctions in supersymmetric gauge theory	Davide Gaiotto	2013-09-13	Scientific Series	View details
Holography without Strings - Joint Quantum Gravity and String Theory Seminar	Donald Marolf	2013-09-12	Scientific Series	View details
Quantum States are Consistent Probability Distributions	Nadish de Silva	2013-09-12	Scientific Series	View details
The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe		2013-09-11	Scientific Series	View details
Quantum Observables as Real-valued Functions and Quantum Probability		2013-09-10	Scientific Series	View details
From dlogs to dilogs	Arthur Lipstein	2013-09-10	Scientific Series	View details
The local Callan-Symanzik equation: structure and applications	Boaz Keren-Zur	2013-09-06	Scientific Series	View details
A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?	Niayesh Afshordi, Elizabeth Gould	2013-09-03	Scientific Series	View details
Peaks, excursion sets and the distribution of dark matter haloes	Vincent Desjacques	2013-09-03	Scientific Series	View details
Wavelets and MERA	Steven White	2013-08-30	Scientific Series	View details
Bottom-up Naturalness	Sonia El Hedri	2013-08-27	Scientific Series	View details

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ΛCDM Large Scale Triumphs and Small Scale Challenges

Edge states at domain wall junctions in supersymmetric gauge theory

Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Quantum States are Consistent Probability Distributions

The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe

Quantum Observables as Real-valued Functions and Quantum Probability

From dlogs to dilogs

The local Callan-Symanzik equation: structure and applications

A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?

Peaks, excursion sets and the distribution of dark matter haloes

Wavelets and MERA

Bottom-up Naturalness

ΛCDM Large Scale Triumphs and Small Scale Challenges

Edge states at domain wall junctions in supersymmetric gauge theory

Holography without Strings - Joint Quantum Gravity and String Theory Seminar

Quantum States are Consistent Probability Distributions

The Era of Three Generations: Possible hints from neutrinos in elucidating the matter/antimatter asymmetry of the Universe

Quantum Observables as Real-valued Functions and Quantum Probability

From dlogs to dilogs

The local Callan-Symanzik equation: structure and applications

A Non-Local Reality: Is there a Phase Uncertainty in Quantum Mechanics?

Peaks, excursion sets and the distribution of dark matter haloes

Wavelets and MERA

Bottom-up Naturalness