Scientific Series

Displaying 3433 - 3444 of 5012

Cosmic Tides

Ue-Li Pen
Canadian Institute for Theoretical Astrophysics (CITA)
January 29, 2013

PIRSA:13010114
Cosmology
What is motion? What is time?

Flavio Mercati
University of Naples Federico II
January 23, 2013

PIRSA:13010003
Quantum Gravity
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.

Juan Carrasquilla
ETH Zurich
January 22, 2013

PIRSA:13010107
Condensed Matter
A monodromy defect in the 3d Ising model.

Roberto Pellegrini
National Institute for Nuclear Physics
January 22, 2013

PIRSA:13010106
Quantum Fields and Strings
Holographic description of cosmological singularity

Misha Smolkin
Hebrew University of Jerusalem
January 22, 2013

PIRSA:13010111
Cosmology
Pinning of Fermionic Occupation Numbers

Christian Schilling
ETH Zurich - Institut für Theoretische Physik
January 21, 2013

PIRSA:13010105
Quantum Information
Indirect Searches for Dark Matter with the Fermi Large Area Telescope

Andrea Marie Albert
Ohio State University
January 18, 2013

PIRSA:13010102
Particle Physics
The black hole information paradox and its resolution

Ted Jacobson
University of Maryland, College Park
January 17, 2013

PIRSA:13010021
Quantum Gravity
Einstein's gravity versus String Gravity

Barton Zwiebach
Massachusetts Institute of Technology (MIT) - Department of Physics
January 16, 2013

PIRSA:13010103
Quantum Fields and Strings
Superhorizon fluctuations in de Sitter and cosmological spacetimes

Guilherme Pimentel
Universiteit van Amsterdam
January 15, 2013

PIRSA:13010001
Quantum Fields and Strings

Cosmology
Boosted Multijet Resonances and New Color-Flow Variables

Brian Shuve
Harvey Mudd College
January 15, 2013

PIRSA:13010104
Particle Physics
Parameterizing dark sector perturbations

Jonathan Pearson
Durham University
January 15, 2013

PIRSA:13010019
Cosmology

Cosmic Tides

Ue-Li Pen
Canadian Institute for Theoretical Astrophysics (CITA)
January 29, 2013

PIRSA:13010114
Cosmology
We apply CMB lensing techniques to large scale structure and solve for the 3-D cosmic tidal field. We use small scale filamentary structures to solve for the large scale tidal shear and gravitational potential. By comparing this to the redshift space density field, one can measure the gravitational growth factor on large scales without cosmic variance. This potentially enables accurate measurements of neutrino masses and reconstruction of radial modes lost in 21 cm intensity mapping, which are essential for CMB and other cross correlations. We relate the tidal fields to the squeezed limit bispectrum, and present initial results from simulations and data from the SDSS.
What is motion? What is time?

Flavio Mercati
University of Naples Federico II
January 23, 2013

PIRSA:13010003
Quantum Gravity
I give an account of the Machian approach to dynamics, from Mach's critique of Newton to the work of Barbour, Bertotti, York and O'Murchadha, which culminated in the theory of Shape Dynamics, a new and original way of thinking about General Relativity. I conclude commenting on the present research lines in Shape Dynamics, and the opportunity it offers to solve the problem of time in quantum gravity.

Support for this colloquium is provided by The Templeton Frontiers Program.
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.

Juan Carrasquilla
ETH Zurich
January 22, 2013

PIRSA:13010107
Condensed Matter
Using quantum Monte Carlo simulations, we investigate the finite-temperature phase diagram of hard-core bosons (XY model) in two- and three-dimensional square lattices. To determine the phase boundaries, we perform a finite-size scaling analysis of the condensate fraction and/or the superfluid stiffness. We then discuss how this diagrams can be measured in experiments with trapped ultracold gases, where the systems are inhomogeneous. For that, we introduce a method based on the measurement of the zero-momentum occupation, which is adequate for experiments dealing with both homogeneous and trapped systems. Finally, we provide an analytical argument that demonstrates that the Bose-Hubbard model does not exhibit ﬁnite-temperature BEC in two dimensions, provided that density remains finite across the entire system in the thermodynamic limit.
A monodromy defect in the 3d Ising model.

Roberto Pellegrini
National Institute for Nuclear Physics
January 22, 2013

PIRSA:13010106
Quantum Fields and Strings
A conformal defect is a d-dimensional geometrical object that breaks the SO(D+1,1) symmetry, of a D-dimensional conformal field theory, down to those transformations that leave the defect invariant i.e. SO(D-d) X SO(d+1,1).
We studied the 3D critical Ising model in presence of a special kind of these defects, a monodromy line defect.
In particular we computed, using Montecarlo simulations, the anomalous dimensions of the lowest dimensional operators living at the defect, as well as correlation functions of operators in the bulk with operators at the defect.
We found a good agreement between our results and the expectations of conformal field theory.
Holographic description of cosmological singularity

Misha Smolkin
Hebrew University of Jerusalem
January 22, 2013

PIRSA:13010111
Cosmology
In my talk I will discuss our recent paper hep-th/1211.1322 where we construct a 3D conformal field theory dual to asymptotically AdS cosmology in four dimensions. Due to the scale invariance this dual theory allows an infinite family of instantons each of which breaks the conformal group O(3,2) down to O(3,1). These instantons are dual to bulk instantons responsible for nucleating an O(3,1) invariant cosmological bubble. Presumably they indicate an infinite instability rate, however we are able to sum over all of them completely. The resulting theory is manifestly stable, unitary and finite.
Pinning of Fermionic Occupation Numbers

Christian Schilling
ETH Zurich - Institut für Theoretische Physik
January 21, 2013

PIRSA:13010105
Quantum Information
The problem of determining and describing the family of 1-particle reduced density operators (1-RDO) arising from N-fermion pure states (viapartial trace) is known as the fermionic quantum marginal problem. We present its solution, a multitude of constraints on the eigenvalues of the 1-RDO, generalizing the Pauli exclusion principle. To explore the relevance of these constraints we study an analytically solvable model of N fermions in a harmonic potential and determine the spectral `trajectory' corresponding to the ground state as function of the fermion-fermion interaction strength.Intriguingly, we find that the occupation numbers are almost, but not exactly, pinned to the boundary of the allowed region (quasi-pinned). Our findings suggest a generalization of the Hartree-Fock approximation.

see also: http://arxiv.org/abs/1210.5531
Indirect Searches for Dark Matter with the Fermi Large Area Telescope

Andrea Marie Albert
Ohio State University
January 18, 2013

PIRSA:13010102
Particle Physics
There is overwhelming evidence that non-baryonic dark matter constitutes ~23% of the energy density of the universe. Weakly Interacting Massive Particles (WIMPs) are promising dark matter candidates that may produce gamma rays via annihilation or decay detectable by the Fermi Large Area Telescope (Fermi LAT). A detection of WIMPs would also indicate the existence of physics beyond the Standard Model. I will present recent results from indirect WIMP searches by the Fermi LAT Collaboration. I will focus on our recent search for gamma-ray spectral lines from WIMP annihilations with 4 years of data. There has been recent excitement with the report of a line-like feature localized in the galactic center around 130 GeV. I will be discussing what our search finds and the systematic checks we've performed on potential signals.
The black hole information paradox and its resolution

Ted Jacobson
University of Maryland, College Park
January 17, 2013

PIRSA:13010021
Quantum Gravity
Both AdS/CFT duality and more general reasoning from quantum gravity point to a rich collection of boundary observables that always evolve unitarily. The physical quantum gravity states described by these observables must be solutions of the spatial diffeomorphism and Wheeler-deWitt constraints, which implies that the state space does not factorize into a tensor product of localized degrees of freedom. The "firewall" argument that unitarity of black hole evaporation is incompatible with a regular near horizon region is based on such a factorization, hence is not applicable in quantum gravity. A version of black hole complementarity resolves the apparent conflict. (I will also discuss doubts and questions.)
Einstein's gravity versus String Gravity

Barton Zwiebach
Massachusetts Institute of Technology (MIT) - Department of Physics
January 16, 2013

PIRSA:13010103
Quantum Fields and Strings
Gravity in string theory is a generalized version of Einstein's theory with some universal features that call for a reformulation of the key geometrical concepts. In addition to the metric tensor, for example, string theory contains an antisymmetric tensor and a dilaton that allow for extra symmetries. A new branch of mathematics, Generalized Geometry, suggests a framework that finds a realization in the recent Double Field Theory formulation of string gravity. I will describe the main ideas, the progress, and the mysteries that remain in the search for a proper description of string gravitation.
Superhorizon fluctuations in de Sitter and cosmological spacetimes

Guilherme Pimentel
Universiteit van Amsterdam
January 15, 2013

PIRSA:13010001
Quantum Fields and Strings

Cosmology
I will discuss superhorizon fluctuations in de Sitter space. The first part of the talk will focus on computing entanglement entropies of field theories in a fixed de Sitter background. Those computations are done for free theories and also theories with gravity duals. If time permits, I will also discuss superhorizon fluctuations in cosmological backgrounds. In particular, I focus on showing that subhorizon fluctuations can not produce any significant backreaction on superhorizon modes. If those late time effects existed, one in principle could not trust the scale invariant spectrum of inflationary theories to be the source of the spectrum of thermal fluctuations of the CMB.
Boosted Multijet Resonances and New Color-Flow Variables

Brian Shuve
Harvey Mudd College
January 15, 2013

PIRSA:13010104
Particle Physics
Parameterizing dark sector perturbations

Jonathan Pearson
Durham University
January 15, 2013

PIRSA:13010019
Cosmology
When recent observational evidence and the GR+FRW+CDM model are combined we obtain the result that the Universe is accelerating, where the acceleration is due to some not-yet-understood "dark sector". There has been a considerable number of theoretical models constructed in an attempt to provide an "understanding" of the dark sector: dark energy and modified gravity theories. The proliferation of modified gravity and dark energy models has brought to light the need to construct a "generic" way to parameterize the dark sector. We will discuss our new way of approaching this problem, looking at linearised perturbations. Our approach is inspired by that taken in particle physics, where the most general modifications to the standard model are written down for a given field content that is compatible with some assumed symmetry (which we take to be isotropy of the background spatial sections). Our emphasis is on constructing a theoretically motivated toolkit which can be used to extract meaningful information about the dark sector (such as its field content). We find, for example, that the observational impact of very broad classes of theories can be encoded by a very small (less than 5) number of parameters. It is these parameters which we hope to measure with observational data.

Title	Speaker(s)	Date	Talk Type	Info link
Cosmic Tides	Ue-Li Pen	2013-01-29	Scientific Series	View details
What is motion? What is time?	Flavio Mercati	2013-01-23	Scientific Series	View details
Superfluid to normal phase transition in strongly interacting bosons in two and three dimensions.	Juan Carrasquilla	2013-01-22	Scientific Series	View details
A monodromy defect in the 3d Ising model.	Roberto Pellegrini	2013-01-22	Scientific Series	View details
Holographic description of cosmological singularity	Misha Smolkin	2013-01-22	Scientific Series	View details
Pinning of Fermionic Occupation Numbers	Christian Schilling	2013-01-21	Scientific Series	View details
Indirect Searches for Dark Matter with the Fermi Large Area Telescope	Andrea Marie Albert	2013-01-18	Scientific Series	View details
The black hole information paradox and its resolution	Ted Jacobson	2013-01-17	Scientific Series	View details
Einstein's gravity versus String Gravity	Barton Zwiebach	2013-01-16	Scientific Series	View details
Superhorizon fluctuations in de Sitter and cosmological spacetimes	Guilherme Pimentel	2013-01-15	Scientific Series	View details
Boosted Multijet Resonances and New Color-Flow Variables	Brian Shuve	2013-01-15	Scientific Series	View details
Parameterizing dark sector perturbations	Jonathan Pearson	2013-01-15	Scientific Series	View details

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