Scientific Series

Displaying 3289 - 3300 of 5164

Nonlocal cosmology

Richard Woodard University of Florida
February 27, 2014

PIRSA:14020137
Quantum Gravity
À la recherche du temps perdu - Templeton Frontiers Colloquia

Flavio Mercati University of Naples Federico II
February 26, 2014

PIRSA:14020100
Quantum Gravity
Numerical detection of symmetry protected and symmetry enriched topological phases

Frank Pollmann Max Planck Institute for Physics, Munich (Werner-Heisenberg-Institut)
February 25, 2014

PIRSA:14020140
Condensed Matter
Large Tensor-to-Scalar Ratio in Small-Field Inflation

Takeshi Kobayashi SISSA International School for Advanced Studies
February 25, 2014

PIRSA:14020152
Particle Physics

Cosmology
Probing the Small Scale Structure of Dark Matter with Indirect Detection

Sheldon Campbell Ohio State University
February 25, 2014

PIRSA:14020097
Cosmology
Quantum Liquids and Turbulent Black Holes

Allan Adams Massachusetts Institute of Technology (MIT) - Department of Physics
February 24, 2014

PIRSA:14020141
Quantum Fields and Strings
Quantum Many-body Dynamics with Matrix Product States

Martin Ganahl Sandbox AQ
February 24, 2014

PIRSA:14020156
Cosmology

Condensed Matter
Sequestering the Standard Model Vacuum Energy

Nemanja Kaloper University of California, Davis
February 21, 2014

PIRSA:14020109
Particle Physics
Quantum Raychaudhuri equation

Saurya Das University of Lethbridge
February 20, 2014

PIRSA:14020130
Quantum Gravity
The Sherrington-Kirkpatrick model and its diluted version

Dmitry Panchenko Texas A&M University
February 20, 2014

PIRSA:14020151
Mathematical physics
Causality, holography, and entanglement entropy
February 20, 2014

PIRSA:14020146
Quantum Gravity

Quantum Fields and Strings

Condensed Matter

Strong Gravity
The emergent of the chiral spin liquid in kagome Heisenberg model

Dong-Ning Sheng California State University, Northridge
February 20, 2014

PIRSA:14020149
Condensed Matter

Nonlocal cosmology

Richard Woodard University of Florida
February 27, 2014

PIRSA:14020137
Quantum Gravity
I review a class of nonlocally modified gravity models which were proposed to explain the current phase of cosmic acceleration without dark energy. Among the topics considered are deriving causal and conserved field equations, adjusting the model to make it support a given expansion history, why these models do not require an elaborate screening mechanism to evade solar system tests, degrees of freedom and kinetic stability, and the negative verdict of structure formation. Although these simple models are not consistent with data on the growth of cosmic structures many of their features are likely to carry over to more complicated models which are in better agreement with the data.
À la recherche du temps perdu - Templeton Frontiers Colloquia

Flavio Mercati University of Naples Federico II
February 26, 2014

PIRSA:14020100
Quantum Gravity
Augustine of Hippo declared he knew what time is until someone asked him. After 16 centuries we still largely ignore the true essence of time, but we made definite progress in studying its properties. The most striking, and somewhat intuitively (and tragically) obvious one is the irreversibility of its flow. And yet, our fundamental theories are time-reversal invariant, they do not distinguish between past and future. This is usually accounted for by assuming an immensely special initial condition of the Universe, dressed with statistical arguments. In this talk, I will show how an irreversible behaviour, and with it a growth of complexity and information, can emerge from time-reversal invariant laws, without assuming any special initial condition and without thermodynamical arguments. This phenomenon is present in General Relativity, our most advanced theory of the Universe. This irreversibility will also allow me to propose a solution of another puzzle associated with time, namely the incompatibility between the quantum and the general-relativistic notions of time.
Numerical detection of symmetry protected and symmetry enriched topological phases

Frank Pollmann Max Planck Institute for Physics, Munich (Werner-Heisenberg-Institut)
February 25, 2014

PIRSA:14020140
Condensed Matter
A topological phase is a phase of matter which cannot be characterized by a local order parameter. We first introduce non-local order parameters that can detect symmetry protected topological (SPT) phases in 1D systems and then show how to generalize the idea to detect symmetry enriched topological (SET) phases in 2D. SET phases are new structures that occur in topologically ordered systems in the presence of symmetries. We introduce simple methods to detect the SET order directly from a complete set of topologically degenerate ground state wave functions. We first show how to directly determine the characteristic symmetry fractionalization of the quasiparticles from the reduced density matrix of the minimally entangled states. Second, we show how a simple generalization of a non-local order parameter can be measured to detect SETs. The usefulness of the proposed approached is demonstrated by examining two concrete model states which exhibit SET: (i) a spin-1 model on the honeycomb lattice and (ii) the resonating valence bond state on a kagome lattice. We conclude that the spin-1 model and the RVB state are in the same SET phases.
Large Tensor-to-Scalar Ratio in Small-Field Inflation

Takeshi Kobayashi SISSA International School for Advanced Studies
February 25, 2014

PIRSA:14020152
Particle Physics

Cosmology
The production of gravitational waves from cosmic inflation > is normally bounded by the inflaton field excursion. This relation, > which is often referred to as the Lyth bound, claims that > observationally large gravitational waves are produced only if the > inflaton has a super-Planckian field range. In this talk I will point > out that this general belief is not necessarily true when there are > additional light fields producing density perturbations. Perturbations > seeded by the inflaton can be suppressed under such situations, thus > allow large gravitational waves to be produced even from small-field (i.e. > sub-Planckian) inflation. I will also show that the field bound is > taken over by the light field when the inflaton-induced perturbations > are suppressed, thus present a generalized form of the Lyth bound that > applies to the total field space. The calculations are rather simple, > so I will explain my work on a blackboard.
Probing the Small Scale Structure of Dark Matter with Indirect Detection

Sheldon Campbell Ohio State University
February 25, 2014

PIRSA:14020097
Cosmology
Direct observation of the small scale structure of matter in the Universe provides potentially important information about a wealth of physics, from complex galaxy evolution processes to fundamental particle properties of dark matter. Detecting this fine structure in dark matter, though, is notoriously difficult. Dark matter indirect detection--through observation of radiation products of particle annihilation--may be the most direct method for observing small scale structure. However, in an observed signal, the amount of dark matter clustering is degenerate with the annihilation cross section. This talk outlines ways this degeneracy may be broken with indirect detection alone. Scenarios are discussed where either abundant substructure leads to discovery of annihilation radiation (revealing properties of the substructure), or a discovery strongly constrains the presence of significant dark matter halo substructure.
Quantum Liquids and Turbulent Black Holes

Allan Adams Massachusetts Institute of Technology (MIT) - Department of Physics
February 24, 2014

PIRSA:14020141
Quantum Fields and Strings
The physics of black hole horizons is intimately connected to the physics of quantum liquids. In this talk I will review the connection and draw lessons about quantum turbulence from black hole dynamics and vice versa. For example, gravitational dynamics reveal that quantum turbulence can behave very differently from normal fluid turbulence in 2d, with long-wavelength excitations rapidly dissolving into small fluctuations and dissipating as in a 3d normal liquid. Meanwhile, familiar facts about turbulent flows in normal fluids imply that the horizons of certain accreting black holes evolve in time as if they have a non-trivial fractal dimension.
Quantum Many-body Dynamics with Matrix Product States

Martin Ganahl Sandbox AQ
February 24, 2014

PIRSA:14020156
Cosmology

Condensed Matter
The talk is divided into two parts: in the first, I will talk about dynamics of far-from equilibrium initial states in different lattice models. I will present results of quench dynamics of the XXZ-Heisenberg magnet, where interesting physics emerges after quenching the system. Then I will present results for scattering of solitonic objects in different integrable and non-integrable lattice models. In the second part, I will talk about dynamics of impurity systems. There I will talk about how impurity spectral functions can be calculated using the Chebyshev technique, and how MPS can serve as a high resolution impurity solver for Dynamical Mean-Field Theory. Finally, I will show some results for steady-state currents through a quantum dot device.
Sequestering the Standard Model Vacuum Energy

Nemanja Kaloper University of California, Davis
February 21, 2014

PIRSA:14020109
Particle Physics
We propose a very simple reformulation of General Relativity, which completely sequesters from gravity {\it all} of the vacuum energy from a matter sector, including all loop corrections and renders all contributions from phase transitions automatically small. The idea is to make the dimensional parameters in the matter sector functionals of the 4-volume element of the universe. For them to be nonzero, the universe should be finite in spacetime. If this matter is the Standard Model of particle physics, our mechanism prevents any of its vacuum energy, classical or quantum, from sourcing the curvature of the universe. The mechanism is consistent with the large hierarchy between the Planck scale, electroweak scale and curvature scale, and early universe cosmology, including inflation. Consequences of our proposal are that the vacuum curvature of an old and large universe is not zero, but very small, that wDE≃−1 is a transient, and that the universe will collapse in the future.
Quantum Raychaudhuri equation

Saurya Das University of Lethbridge
February 20, 2014

PIRSA:14020130
Quantum Gravity
We compute quantum corrections to the Raychaudhuri equation, by replacing classical geodesics with quantal (Bohmian) trajectories, and show that they prevent focusing of geodesics, and the formation of conjugate points. We discuss implications for the Hawking-Penrose singularity theorems, and for curvature singularities. Reference: arXiv: 1311.6539
The Sherrington-Kirkpatrick model and its diluted version

Dmitry Panchenko Texas A&M University
February 20, 2014

PIRSA:14020151
Mathematical physics
I will talk about two types of random processes -- the classical Sherrington-Kirkpatrick (SK) model of spin glasses and its diluted version. One of the main motivations in these models is to find a formula for the maximum of the process, or the free energy, in the limit when the size of the system is getting large. The answer depends on understanding the structure of the Gibbs measure in a certain sense, and this structure is expected to be described by the so called Parisi solution in the SK model and Mézard-Parisi solution in the diluted SK model. I will explain what these are and mention some results in this direction.
Causality, holography, and entanglement entropy
February 20, 2014

PIRSA:14020146
Quantum Gravity

Quantum Fields and Strings

Condensed Matter

Strong Gravity
After giving a brief overview of holographic entanglement entropy formulas, I will explore a curious feature they imply: when the bulk spacetime includes a black hole, the entanglement entropies often appear to depend on the spacetime geometry inside the horizon. I will ask whether this implies any loss of causality in the field theory. To answer this question, I will present a new general-relativity theorem concerning the causal structure of asymptotically AdS spacetimes, which implies an interesting relationship between bulk and boundary causal domains.
The emergent of the chiral spin liquid in kagome Heisenberg model

Dong-Ning Sheng California State University, Northridge
February 20, 2014

PIRSA:14020149
Condensed Matter
The quantum spin liquid is an emergent new state of matter, which has attracted a lot of recent attention. In particular, the time reversal symmetry broken spin liquid (Kalmeyer et. al. and Wen et. al.), characterized by the chiral ordering and fractionalized quasi-particle as a realization of the fractional quantum Hall state had been proposed for more than 20 years, but never identified as the true ground state in any more generic (e.g. Heisenberg spin exchange) models with time reversal symmetry. Here I will report two concrete examples where chiral spin liquid (CSL) emerge for a range of parameter space for kagome J1-J2-J3 (three nearest neighbors) model based on accurate density matrix renormalization group (DMRG) simulations. We identify long-range chiral ordering, ground state degeneracy, characteristic entanglement spectra, and the fractionalized topological Chern number to establish the topological state in such a system as the long-sought CSL. We further explicitly extract the modular matrix, which captures all the information of the fractional statistics of the quasi-particles in the system. I will also discuss the close relation of our model to some frustrated kagome antiferromagnets, and make a conjecture that J1 kagome model is near an unconventional critical point. I will conclude the talk with some discussions of the open directions.

Title	Speaker(s)	Date	Talk Type	Info link
Nonlocal cosmology	Richard Woodard	2014-02-27	Scientific Series	View details
À la recherche du temps perdu - Templeton Frontiers Colloquia	Flavio Mercati	2014-02-26	Scientific Series	View details
Numerical detection of symmetry protected and symmetry enriched topological phases	Frank Pollmann	2014-02-25	Scientific Series	View details
Large Tensor-to-Scalar Ratio in Small-Field Inflation	Takeshi Kobayashi	2014-02-25	Scientific Series	View details
Probing the Small Scale Structure of Dark Matter with Indirect Detection	Sheldon Campbell	2014-02-25	Scientific Series	View details
Quantum Liquids and Turbulent Black Holes	Allan Adams	2014-02-24	Scientific Series	View details
Quantum Many-body Dynamics with Matrix Product States	Martin Ganahl	2014-02-24	Scientific Series	View details
Sequestering the Standard Model Vacuum Energy	Nemanja Kaloper	2014-02-21	Scientific Series	View details
Quantum Raychaudhuri equation	Saurya Das	2014-02-20	Scientific Series	View details
The Sherrington-Kirkpatrick model and its diluted version	Dmitry Panchenko	2014-02-20	Scientific Series	View details
Causality, holography, and entanglement entropy		2014-02-20	Scientific Series	View details
The emergent of the chiral spin liquid in kagome Heisenberg model	Dong-Ning Sheng	2014-02-20	Scientific Series	View details

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