Scientific Series

Displaying 3553 - 3564 of 5085

Pinning of Fermionic Occupation Numbers

Christian Schilling ETH Zurich
January 21, 2013

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

Andrea Marie Albert Ohio State University
January 18, 2013

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

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

PIRSA:13010021
General Relativity & Quantum Cosmology
Einstein's gravity versus String Gravity

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

PIRSA:13010103
High Energy Physics
Superhorizon fluctuations in de Sitter and cosmological spacetimes

Guilherme Pimentel Universiteit van Amsterdam
January 15, 2013

PIRSA:13010001
High Energy Physics

Astrophysics
Boosted Multijet Resonances and New Color-Flow Variables

Brian Shuve Harvey Mudd College
January 15, 2013

PIRSA:13010104
High Energy Physics
Parameterizing dark sector perturbations

Jonathan Pearson Durham University
January 15, 2013

PIRSA:13010019
Astrophysics
Exotic topological order from quantum fractal code

Beni Yoshida Perimeter Institute for Theoretical Physics
January 14, 2013

PIRSA:13010101
Quantum Physics
New transport properties of holographic superfluids

Daniel Fernandez University of Iceland
January 10, 2013

PIRSA:13010004
General Relativity & Quantum Cosmology
Field-induced thermal transport in BEC antiferromagnets

Alexander Chernyshev University of California, Irvine
January 08, 2013

PIRSA:13010002
Condensed Matter
Worldsheet form factors in AdS/CFT

Tristan McLoughlin Trinity College Dublin
January 08, 2013

PIRSA:13010022
High Energy Physics
Fifth forces and new particles from dark energy

Amol Upadhye University of Wisconsin–Madison
January 08, 2013

PIRSA:13010023
Astrophysics

Pinning of Fermionic Occupation Numbers

Christian Schilling ETH Zurich
January 21, 2013

PIRSA:13010105
Quantum Physics
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
High Energy 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
General Relativity & Quantum Cosmology
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
High Energy Physics
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
High Energy Physics

Astrophysics
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
High Energy Physics
Parameterizing dark sector perturbations

Jonathan Pearson Durham University
January 15, 2013

PIRSA:13010019
Astrophysics
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.
Exotic topological order from quantum fractal code

Beni Yoshida Perimeter Institute for Theoretical Physics
January 14, 2013

PIRSA:13010101
Quantum Physics
We present a family of three-dimensional local quantum codes with pairs of fractal logical operators. It has two polynomials over finite fields as input parameters which generate fractal shapes of anti-commuting logical operators, and possesses exotic topological order with quantum glassiness which is beyond descriptions of conventional topological field theory. A necessary and sufficient condition for being free from string-like logical operators is obtained under which the model works as marginally self-correcting quantum memory. We also provide theoretical tools to analyze physical and coding properties of translation symmetric stabilizer Hamiltonians.
New transport properties of holographic superfluids

Daniel Fernandez University of Iceland
January 10, 2013

PIRSA:13010004
General Relativity & Quantum Cosmology
In the context of holography applied to condensed matter theory, I will present an analysis of transport properties of p-wave superfluids by means of a gravity dual. Fluctuations modes in the SU(2) Einstein-Yang-Mills theory are considered, and phenomenological implications are derived. Due to the spatial anisotropy of the system, a non-universal shear viscosity is obtained, along with a new coefficient associated to normal stress differences. I will also discuss how the transport phenomena in this model is related to the thermoelectric, flexoelectric and piezoelectric effects (mixing of electric current, heat flux and mechanical stress), which have been observed in some superconductors and crystal liquids.
Field-induced thermal transport in BEC antiferromagnets

Alexander Chernyshev University of California, Irvine
January 08, 2013

PIRSA:13010002
Condensed Matter
Recent experiments in BEC quantum magnets exhibit a dramatic evolution of the thermal conductivity of these materials in magnetic field. By considering various relaxation mechanisms of bosonic excitations in the vicinity of the BEC quantum-critical point at finite temperature we provide a detailed explanation of several unusual features of the data. We identify the leading impurity-scattering interaction and demonstrate that its renormalization due to quantum fluctuations of the paramagnetic state compensates the related mass renormalization effect. This explains the enigmatic absence of the asymmetry between the two critical points in the low-T thermal conductivity data, while such an asymmetry is prominent in many other physical quantities. The observed characteristic "migration'' of the peak in thermal conductivity away from the transition points as a function of temperature is explained as due to a competition between an increase in the number of heat carriers and an enhancement of their mutual scattering. An important role of the three-boson scattering processes within the ordered phase of these systems is also discussed. Other qualitative and quantitative features of the experiment are clarified and the future directions are sketched.
Worldsheet form factors in AdS/CFT

Tristan McLoughlin Trinity College Dublin
January 08, 2013

PIRSA:13010022
High Energy Physics
The study of the worldsheet S-matrix for AdS_5×S^5 strings was a key step in the complete determination of the non-pertubrative planar spectrum of anomalous dimensions for N=4 super-Yang-Mills. To go beyond the spectral problem it is important to consider higher-point worldsheet correlation functions and, as is standard in many integrable models, one approach is the study of form factors. We will discuss a set of consistency conditions appropriate to form factors in the light-cone gauge fixed AdS_5×S^5 string theory. We further discuss the form factors in the weakly coupled dual description, verifying that the relevant conditions naturally hold for the one-loop Heisenberg spin-chain.
Fifth forces and new particles from dark energy

Amol Upadhye University of Wisconsin–Madison
January 08, 2013

PIRSA:13010023
Astrophysics
Dark energy coupled to Standard Model fermions and gauge bosons gives rise to fifth forces and new particles, which are readily accessible to experiments from laboratory to cosmological scales. I will discuss chameleon and symmetron models, whose fifth forces are screened locally through large effective masses and symmetry-restoring phase transitions, respectively. Fifth force experiments such as the Eot-Wash torsion balance will test chameleons with small quantum corrections and gravitation-strength fifth forces, as well as symmetrons with coupling energies just beyond the Standard Model scale. A dark energy coupling to electromagnetism would imply that photons passing through a magnetic field will oscillate into particles of dark energy, a phenomenon studied by afterglow experiments such as CHASE. After constraining dark energy using laboratory experiments, I proceed to astrophysical probes. Particles of a photon-coupled dark energy could be produced in the Sun and detected in magnetic helioscopes such as CAST, while fifth forces may alter the dynamics of variable stars and the growth of large-scale structure.

Title	Speaker(s)	Date	Talk Type	Info link
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
Exotic topological order from quantum fractal code	Beni Yoshida	2013-01-14	Scientific Series	View details
New transport properties of holographic superfluids	Daniel Fernandez	2013-01-10	Scientific Series	View details
Field-induced thermal transport in BEC antiferromagnets	Alexander Chernyshev	2013-01-08	Scientific Series	View details
Worldsheet form factors in AdS/CFT	Tristan McLoughlin	2013-01-08	Scientific Series	View details
Fifth forces and new particles from dark energy	Amol Upadhye	2013-01-08	Scientific Series	View details

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Format results

Pinning of Fermionic Occupation Numbers

Indirect Searches for Dark Matter with the Fermi Large Area Telescope

The black hole information paradox and its resolution

Einstein's gravity versus String Gravity

Superhorizon fluctuations in de Sitter and cosmological spacetimes

Boosted Multijet Resonances and New Color-Flow Variables

Parameterizing dark sector perturbations

Exotic topological order from quantum fractal code

New transport properties of holographic superfluids

Field-induced thermal transport in BEC antiferromagnets

Worldsheet form factors in AdS/CFT

Fifth forces and new particles from dark energy

Pinning of Fermionic Occupation Numbers

Indirect Searches for Dark Matter with the Fermi Large Area Telescope

The black hole information paradox and its resolution

Einstein's gravity versus String Gravity

Superhorizon fluctuations in de Sitter and cosmological spacetimes

Boosted Multijet Resonances and New Color-Flow Variables

Parameterizing dark sector perturbations

Exotic topological order from quantum fractal code

New transport properties of holographic superfluids

Field-induced thermal transport in BEC antiferromagnets

Worldsheet form factors in AdS/CFT

Fifth forces and new particles from dark energy