Scientific Series

Displaying 3229 - 3240 of 5012

New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT
November 11, 2013

PIRSA:13110081
Cosmology
Matter matters in asymptotically safe quantum gravity
November 07, 2013

PIRSA:13110048
Quantum Gravity
Dynamical Emergence of Universal Horizons during the formation of Black Holes

Mehdi Saravani
Goldman Sachs (United States)
November 07, 2013

PIRSA:13110087
Strong Gravity
Fractional statistics in two-dimensions: Anyon there?

Smitha Vishveshwara
University of Illinois Urbana-Champaign
November 06, 2013

PIRSA:13110062
Mathematical physics
A note on emergent classical behavior and approximations to decoherence functionals

Henrique Gomes
University of Oxford
November 05, 2013

PIRSA:13110085
Quantum Foundations
Z2 spin liquid in kagome Heisenberg antiferromagnet

Yuan Wan
Chinese Academy of Sciences
November 05, 2013

PIRSA:13110086
Condensed Matter
From the symmetric group to giant gravitons in super Yang-Mills theory
November 05, 2013

PIRSA:13110084
Quantum Fields and Strings
Induced Electroweak Symmetry Breaking and Supersymmetry

Jamison Galloway
New York University (NYU)
November 05, 2013

PIRSA:13110050
Particle Physics
Feedback-regulated star formation on galactic and cosmological scales

Claude-André Faucher-Giguère
University of California System
November 05, 2013

PIRSA:13110056
Cosmology
Split Dirac Supersymmetry and a Higgsino LSP
November 01, 2013

PIRSA:13110052
Particle Physics
A causal set action

Lisa Glaser
University of Vienna
October 31, 2013

PIRSA:13100063
Quantum Gravity
New lessons about hydrodynamics from gravity

Michal Heller
Ghent University
October 31, 2013

PIRSA:13100064
Strong Gravity

New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT
November 11, 2013

PIRSA:13110081
Cosmology
Galaxy clusters form from the rarest peaks in the initial matter distribution, and hence are a sensitive probe of the amplitude of density fluctuations (sigma_8), the amount of matter in the universe, and the growth rate of structure. Galaxy clusters have the potential to constrain dark energy and neutrino masses. However, cluster cosmology is currently limited by systematic uncertainties due to poorly understood intracluster gas physics. I will present new statistical approaches to understand clusters and improve their cosmological constraining power through the thermal Sunyaev-Zel'dovich (tSZ) effect. First, I will describe a forthcoming first detection of the cross-correlation of the tSZ signal reconstructed from Planck data with the large-scale matter distribution traced by the Planck CMB lensing potential. This statistic measures the amount of hot gas found in moderately massive groups and clusters (M ~ 10^13-10^14.5 M_sun), a mass scale below that probed by direct cluster detections. Second, I will describe the first measurement of the PDF of the tSZ field using ACT 148 GHz maps. This measurement contains information from all (zero-lag) moments of the tSZ field, beyond simply the 2- or 3-point functions. It is a very sensitive probe of sigma_8 and may also provide a method with which to break the degeneracy between sigma_8 and uncertainties in the physics of the intracluster gas.
Matter matters in asymptotically safe quantum gravity
November 07, 2013

PIRSA:13110048
Quantum Gravity
The Functional Renormalisation Group technique has received great attention in recent times proving itself as a powerful tool to describe the high energy behaviour of gravitational interactions.
Its key ingredient is a nontrivial fixed point of the theory renormalization group flow which controls the behavior of the coupling constants in the ultraviolet regime and ensures that physical quantities are safe from divergences. I will briefly review the main ingredients of the gravitational asymptotic safety framework before focusing on the effect of massless minimally coupled scalars, fermions and vector fields on the gravitational fixed point. I will then set bounds on the type and number of such fields requiring the existence of a UV attractive fixed point. I will also discuss the dynamically generated quantum-gravity scale in asymptotic safety, which is the transition scale to the fixed-point regime, and its variation as a function of matter degrees of freedom. To conclude I will also consider the case of higher dimensional models.
Dynamical Emergence of Universal Horizons during the formation of Black Holes

Mehdi Saravani
Goldman Sachs (United States)
November 07, 2013

PIRSA:13110087
Strong Gravity
In many theories with fundamental preferred frame, such as Einstein-Aether or Gravitational Aether theories, K-essence, Cuscuton theory, Shape Dynamics, or (non-projectable) Horava-Lifshitz gravity, the low energy theory contains a fluid with superluminal or incompressible excitations. In this talk, I study the formation of black holes in the presence of such a fluid. In particular, I focus on the incompressible limit of the fluid (or Constant Mean Curvature foliation) in the space-time of a spherically collapsing shell within an asymptotically cosmological space-time. In this case, I show that an observer inside 3/4 of the Schwarzschild radius cannot send a signal outside, after a stage in collapse, even using signals that propagate infinitely fast in the preferred frame. This confirms the dynamical emergence of universal horizons that have been previously found in static solutions [arXiv:1110.2195, arXiv:1104.2889, arXiv:1212.1334].
Fractional statistics in two-dimensions: Anyon there?

Smitha Vishveshwara
University of Illinois Urbana-Champaign
November 06, 2013

PIRSA:13110062
Mathematical physics
A fascinating aspect of the two dimensional world is the possible existence of anyons, particles which obey 'fractional' statistics different from fermionic and bosonic statistics. In this colloquium, following an introduction to fractional particles in the context of quantum Hall systems, some of the tantalizing experiments for detecting the fractional charge of these particles will be described. Probes of fractional statistics in these systems will be discussed, drawing from analogies with the bosonic behavior of light studied by Hanbury Brown and Twiss in the 1950's as well as in the more recent beam-splitter settings in quantum optics. Finally, the exciting prospect of detecting fractional statistics in the context of superconductors will be explored.
A note on emergent classical behavior and approximations to decoherence functionals

Henrique Gomes
University of Oxford
November 05, 2013

PIRSA:13110085
Quantum Foundations
Although it can only be argued to have become consequential in the study of quantum cosmology, the question ``Why do we observe a classical world? " has been one of the biggest preoccupations of quantum foundations. In the consistent histories formalism, the question is shifted to an analysis of the telltale sign of quantum mechanics: superposition of states. In the consistent histories formalism, histories of the system which ``decohere", i.e. fall out of superposition or have negligible interference can be subjected to a notion of classical probability. In this paper we use an extension of Kirchoff's diffraction formula for wave functions on configuration spaces to give a different analysis and an approximation of decoherence. The Kirchoff diffraction formula lies conveniently at the midway between path integrals, wave equations, and classical behavior. By using it, we formulate an approximate dampening of the amplitude of superposition of histories. The dampening acts on each middle element of the fine-grained history {c_\alpha}, and is a function of the angle formed between {c_{n-1},c_n} and {c_n,c_{n+1}}, as classical trajectories in configuration space. As an example we apply the formalism to a modified gravity theory in the ADM gravitational conformal superspace.
Z2 spin liquid in kagome Heisenberg antiferromagnet

Yuan Wan
Chinese Academy of Sciences
November 05, 2013

PIRSA:13110086
Condensed Matter
A quantum spin liquid is a hypothesized ground state of a magnet without long-range magnetic order. Similar to a liquid, which is spatially uniform and strongly correlated, a quantum spin liquid preserves all the symmetries and exhibits strong correlations between spins. First proposed by P. W. Anderson in 1973, it has remained a conjecture until recently. In the past couple of years, numerical studies have provided strong evidences for quantum spin liquid in a simple model, the kagome Heisenberg antiferromagnet. In this talk, I will describe a low-energy effective theory for this magnet in terms of a lattice gauge theory with the simplest possible mathematical structure (a group of two elements, namely Z2). I will show that the theory reproduces many characteristic features observed numerically, thereby providing a bridge between the numeircs and the analytics. Furthermore, I will present theoretical predictions which could be tested in future numerical studies.
From the symmetric group to giant gravitons in super Yang-Mills theory
November 05, 2013

PIRSA:13110084
Quantum Fields and Strings
In this talk we will discuss how giant gravitons and their open string interactions emerge from super Yang-Mills Theory. This is accomplished by diagonalizing the one loop dilatation operator on a class of operators with bare dimension of order N. From the result of this diagonalization, the Gauss Law governing the allowed open string excitations of giant gravitons is clearly visible. In addition, we show that this sector of the theory is integrable.
Induced Electroweak Symmetry Breaking and Supersymmetry

Jamison Galloway
New York University (NYU)
November 05, 2013

PIRSA:13110050
Particle Physics
I'll discuss a class of supersymmetric models in which the physical Higgs mass is freed from the quartic coupling, thereby allowing for a 125 GeV Higgs state whose self-interaction can be much smaller than in the SM via a mechanism of 'induced EWSB'. This class of models provides a unique alternative to other realizations of natural SUSY, and the simplest realizations necessitate additional characteristic scalars below the TeV scale, thus altering phenomenological predictions for additional Higgses at the LHC.
Feedback-regulated star formation on galactic and cosmological scales

Claude-André Faucher-Giguère
University of California System
November 05, 2013

PIRSA:13110056
Cosmology
A central problem in galaxy formation is to understand why star formation is so inefficient. Within individual galaxies, gas is converted into stars at a rate two orders of magnitude slower than unimpeded gravitational collapse predicts, a fact embodied in the low normalization of the observed Kennicutt-Schmidt (K-S) relationship between star formation rate surface density and gas surface density. Star formation in galaxies is also globally inefficient in the sense that the stellar mass in dark matter halos is a small fraction of the universal baryon fraction. I will show that these two facts can be explained by the self-regulation of star formation by feedback from massive stars. Within galaxies, stellar feedback drives turbulence that supports the interstellar medium against collapse and the K-S law is set by the low strength of gravity relative to stellar feedback. The energy input from the same stellar feedback processes drive powerful galactic outflows that remove most of the gas accreted from the intergalactic medium before it has time to turn into stars. Using cosmological hydrodynamical simulations from our FIRE project ("Feedback In Realistic Environments"), I will show that gas removal by star formation-driven galactic winds successfully explains the observed galaxy stellar mass function, at least for galaxies less massive than the Milky Way. Feedback from massive black holes may be required to explain the quenching of more massive galaxies. Motivated by recent observations, I will discuss the physics of galactic winds driven by active galactic nuclei.
Split Dirac Supersymmetry and a Higgsino LSP
November 01, 2013

PIRSA:13110052
Particle Physics
TBA
A causal set action

Lisa Glaser
University of Vienna
October 31, 2013

PIRSA:13100063
Quantum Gravity
Causal set theory is discrete, fully covariant theory of quantum gravity. The discrete framework makes it necessary to reformulate continuum concepts. One of these concepts is that of a derivative operator. It is possible to define a derivative operator in causal sets that in the continuum limit agrees with the d'Alembertian for a scalar field. This operator can be used to define a causal set action, which enables Monte-Carlo simulations. In this seminar I will present this operator and action and then show some results of Monte-Carlo simulations in 2 dimensions.
New lessons about hydrodynamics from gravity

Michal Heller
Ghent University
October 31, 2013

PIRSA:13100064
Strong Gravity
Hydrodynamics of relativistic plasmas received, within the last 10 years, a lot of attention. The reason for it, on one hand, is the quest for theoretical understanding of the quark-gluon plasma created in heavy ion collisions and, on the other, advances in holographic duality and black hole physics in anti-de Sitter spacetimes. I will describe recent progress in answering foundational issues in hydrodynamics of strongly coupled systems, i.e. questions about its applicability and the character of hydrodynamic gradient expansion, that was achieved with the use of numerical techniques in anti-de Sitter spacetimes in the strong gravity regime.

Title	Speaker(s)	Date	Talk Type	Info link
New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT		2013-11-11	Scientific Series	View details
Matter matters in asymptotically safe quantum gravity		2013-11-07	Scientific Series	View details
Dynamical Emergence of Universal Horizons during the formation of Black Holes	Mehdi Saravani	2013-11-07	Scientific Series	View details
Fractional statistics in two-dimensions: Anyon there?	Smitha Vishveshwara	2013-11-06	Scientific Series	View details
A note on emergent classical behavior and approximations to decoherence functionals	Henrique Gomes	2013-11-05	Scientific Series	View details
Z2 spin liquid in kagome Heisenberg antiferromagnet	Yuan Wan	2013-11-05	Scientific Series	View details
From the symmetric group to giant gravitons in super Yang-Mills theory		2013-11-05	Scientific Series	View details
Induced Electroweak Symmetry Breaking and Supersymmetry	Jamison Galloway	2013-11-05	Scientific Series	View details
Feedback-regulated star formation on galactic and cosmological scales	Claude-André Faucher-Giguère	2013-11-05	Scientific Series	View details
Split Dirac Supersymmetry and a Higgsino LSP		2013-11-01	Scientific Series	View details
A causal set action	Lisa Glaser	2013-10-31	Scientific Series	View details
New lessons about hydrodynamics from gravity	Michal Heller	2013-10-31	Scientific Series	View details

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