Scientific Series

Displaying 3193 - 3204 of 5007

Firewall evasion by quantum gravity

Ted Jacobson University of Maryland, College Park
February 13, 2014

PIRSA:14020136
General Relativity & Quantum Cosmology
On null singularities in general relativity

Mihalis Dafermos Princeton University
February 13, 2014

PIRSA:14020133
General Relativity & Quantum Cosmology
Applications of Information Theory in Direct Sum and Direct Product Problems
February 12, 2014

PIRSA:14020142
Quantum Physics
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Astrophysics
Bosonic particle-correlated states

Zhang Jiang University of New Mexico
February 06, 2014

PIRSA:14020135
Quantum Physics
The Radius of Neutron Stars and the Dense Matter Equation of State

Robert Rutledge McGill University
February 06, 2014

PIRSA:14020087
General Relativity & Quantum Cosmology
The National Ignition Facility (NIF):Pathway to Energy Security and Physics of the Cosmos

Edward Moses Lawrence Livermore National Laboratory
February 05, 2014

PIRSA:14020098
Astrophysics
Towards a 1/c Expansion in 2d Conformal Field Theory
February 04, 2014

PIRSA:14020084
High Energy Physics
Cosmological constraints on complex scalar-field dark matter

Tanja Rindler-Daller University of Michigan–Ann Arbor
February 04, 2014

PIRSA:14020096
Astrophysics
Black hole entropy and the case for self-dual loop quantum gravity
January 29, 2014

PIRSA:14010098
General Relativity & Quantum Cosmology
Time, Dynamics, Chaos, and the Brain

Dean Buonomano University of California, Los Angeles

January 29, 2014

PIRSA:13010117
Mayer-Cluster Expansion of Instanton Partition Functions and Thermodynamic Bethe Ansatz

Carlo Meneghelli University of Oxford
January 28, 2014

PIRSA:14010096
High Energy Physics

Firewall evasion by quantum gravity

Ted Jacobson University of Maryland, College Park
February 13, 2014

PIRSA:14020136
General Relativity & Quantum Cosmology
It has been argued that if black hole evaporation is a unitary quantum process, then a black hole horizon must be cloaked by a "firewall", i.e. a highly excited state of local quantum fields. This reasoning is based on factorizing the Hilbert space into interior and exterior degrees of freedom. Such factorization ignores the Wheeler-deWitt constraint equation, which arises from the diffeomorphism invariance of quantum gravity. I will argue that this constraint evades the firewall.
On null singularities in general relativity

Mihalis Dafermos Princeton University
February 13, 2014

PIRSA:14020133
General Relativity & Quantum Cosmology
This talk will discuss the formation, structure and interaction of null singularities for
the Einstein equations, as well as what this all means for the singular boundary
of generic space times within black hole regions.
Applications of Information Theory in Direct Sum and Direct Product Problems
February 12, 2014

PIRSA:14020142
Quantum Physics
A fundamental question in complexity theory is how much resource is needed to solve k independent instances of a problem compared to the resource required to solve one instance. Suppose solving one instance of a problem with probability of correctness p, we require c units of some resource in a given model of computation. A direct sum theorem states that in order to compute k independent instances of a problem, it requires k times units of the resource needed to compute one instance. A strong direct product theorem states that, with o(k • c) units of the resource, one can only compute all the k instances correctly with probability exponentially small in k. In this talk, I am going to present some of recent progress on direct sum and direct product theorems in the model of communication complexity and two-prover one-round games with information-theoretic approach. The talk is based on parts of my doctoral work.
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Astrophysics
After a short introduction to open inflation and the observed large-scale cosmic microwave anomalies, which have been confirmed by the Planck satellite, I'll argue that the anomalies are naturally explained in the context of a marginally-open, negatively curved universe. I'll look in particular at the dipole power asymmetry, and motivate that this asymmetry can happen if our universe has bubble nucleated in a phase transition during a period of early inflation, and, as a result, has open geometry. Open inflation models, which are motivated by the string landscape and can excite `super-curvature' perturbation modes, can explain the presence of a very-large-scale perturbation, like the one we observe, which leads to a dipole modulation of the power spectrum. I'll provide a specific implementation of the scenario which is compatible with all existing constraints.
Bosonic particle-correlated states

Zhang Jiang University of New Mexico
February 06, 2014

PIRSA:14020135
Quantum Physics
Quantum many-body problems are notorious hard. This is partly because the Hilbert space becomes exponentially big with the particle number N. While exact solutions are often considered intractable, numerous approaches have been proposed using approximations. A common trait of these approaches is to use an ansatz such that the number of parameters either does not depend on N or is proportional to N, e.g., the matrix-product state for spin lattices, the BCS wave function for superconductivity, the Laughlin wave function for fractional quantum Hall effects, and the Gross-Pitaecskii theory for BECs. Among them the product ansatz for BECs has precisely predicted many useful properties of Bose gases at ultra-low temperature. As particle-particle correlation becomes important, however, it begins to fail. To capture the quantum correlations, we propose a new
set of states, which constitute a natural generalization of the product-state ansatz. Our state of N=d& times;n identical particles is derived by symmetrizing the n-fold product of a d-particle quantum state. For fixed d, the parameter space of our state does not grow with N. Numerically, we show that our ansatz gives the right description for the ground state and time evolution of the two-site Bose-Hubbard model.
The Radius of Neutron Stars and the Dense Matter Equation of State

Robert Rutledge McGill University
February 06, 2014

PIRSA:14020087
General Relativity & Quantum Cosmology
The equation of state of matter at and above nuclear densities remains a major theoretically uncertain prediction of QCD. Observations of the mass-radius relationship of neutron stars constrain, and can directly measure, the dense matter equation of state. I will discuss how measurements of neutron star radii have already constrained the dEOS, and how future work will directly measure the dEOS, providing an important constraint on models of the strong force.
The National Ignition Facility (NIF):Pathway to Energy Security and Physics of the Cosmos

Edward Moses Lawrence Livermore National Laboratory
February 05, 2014

PIRSA:14020098
Astrophysics
NIF is the world's most energetic laser system capable of producing over 1.8 MJ and 500 TW of ultraviolet light, about 100 times more than any other operating laser of its kind. This talk describes the unprecedented experimental capabilities of NIF, its role in fundamental science, the pathway to achieving fusion ignition and energy security missions, and the status of progress in these areas.
Towards a 1/c Expansion in 2d Conformal Field Theory
February 04, 2014

PIRSA:14020084
High Energy Physics
I will describe progress in deriving 3d gravity directly from 2d conformal field theory at large central charge 'c'. In a large class of CFTs, using general arguments like modular invariance, crossing symmetry, and the OPE expansion, the spectrum, the entanglement entropy, and certain partition functions can be computed to leading order in a 1/c expansion. The results agree with universal features of 3d gravity required by black hole thermodynamics and the Ryu-Takayanagi formula; furthermore, the relevant 3d geometries appear automatically from CFT calculations in this regime.
Cosmological constraints on complex scalar-field dark matter

Tanja Rindler-Daller University of Michigan–Ann Arbor
February 04, 2014

PIRSA:14020096
Astrophysics
The nature of dark matter is a fundamental problem in cosmology and particle physics. Many particle candidates have been devised over the course of the last decades, and are still at stake to be soon discovered or rejected. However, astronomical observations, in conjunction with the phenomenological efforts in astrophysical modeling, as well as in particle theories to explain them, have helped to pin down several key properties which any successful candidate has to have. In this talk, I will explore the possibility that dark matter is described by a complex scalar field (SFDM), while the other cosmic components are treated in the usual way, assuming a cosmological constant for the dark energy. We will see that the background evolution of a Universe with SFDM and a cosmological constant (LSFDM) complies with the concordance LCDM model, if the model parameters of the SFDM Lagrangian, mass and repulsive 2-particle self-interaction coupling strength, are properly constrained by observations of the cosmic microwave background and Big Bang nucleosynthesis (BBN). However, not only does LSFDM lead to non-standard expansion histories prior to BBN, it also exemplifies differences at small scales, which could help to resolve the discrepancies found between LCDM and certain galaxy observations. I will highlight the differences between complex SFDM and dark matter described by real fields, as for instance axion-like particles. If time permits, I will also talk about possible implementations of SFDM in the very early Universe, in the wake of its inflationary phase.
Black hole entropy and the case for self-dual loop quantum gravity
January 29, 2014

PIRSA:14010098
General Relativity & Quantum Cosmology
By focusing on aspects of black hole thermodynamics, I will present some evidences supporting the unexpected role of the complex self-dual variables in quantum gravity. This will also be the occasion of revisiting some aspects of three-dimensional gravity, and in particular the link between the BTZ black hole and the Turaev-Viro state sum model. Also the information on the website for next week needs to be modified: We will not have a seminar on Thursday (as Thursday is PI day). Instead, we will have the seminar on Wednesday, but actually would prefer a different time, namely 3.30 pm.
Time, Dynamics, Chaos, and the Brain

Dean Buonomano University of California, Los Angeles

January 29, 2014

PIRSA:13010117

Time poses a fundamental problem in neuroscience, in part, because at its core the brain is a prediction machine: the brain evolved to allow animals to anticipate, adapt, and prepare for future events. To accomplish this function the brain tells time on scales spanning 12 orders of magnitude. In contrast to most man made clocks that share a very simply underlying principle-counting the "tics" of an oscillator-evolution has devised many different solutions to the problem of telling time. On the scale of milliseconds and seconds experimental and computational evidence suggests that the brain relies on neural dynamics to tell time. For this strategy to work two conditions have to be met: the states of the neural network must evolve in a nonrepeating pattern over the relevant interval, and the sequence of states must be reproducible every time the system is reengaged. Recurrently connected networks of neurons can generate rich dynamics, but a long standing challenge is that the regimes that create computationally powerful dynamics are chaotic-and thus cannot generate reproducible patterns. We have recently demonstrated that by tuning the weights (the coupling coefficients) between the units of artificial neural networks it is possible to generate locally stable trajectories embedded within chaotic attractors. These stable patterns function as "dynamic attractors" and can be used to encode and tell time. They also exhibit a novel feature characteristic of biological systems: the ability to autonomously "return" to the pattern being generated in the face of perturbations.
Mayer-Cluster Expansion of Instanton Partition Functions and Thermodynamic Bethe Ansatz

Carlo Meneghelli University of Oxford
January 28, 2014

PIRSA:14010096
High Energy Physics
In arXiv:0908.4052, Nekrasov and Shatashvili pointed out that the N=2 instanton partition function in a special limit of the Omega-deformation parameters is characterized by certain thermodynamic Bethe ansatz (TBA) like equations.In this talk I will present an explicit derivation of this fact as well as generalizations to quiver gauge theories. The TBA equations derived entirely within gauge theory have been proposed to encode the spectrum of a large class of quantum integrable systems. I will conclude with some remarks on this correspondence.

Title	Speaker(s)	Date	Talk Type	Info link
Firewall evasion by quantum gravity	Ted Jacobson	2014-02-13	Scientific Series	View details
On null singularities in general relativity	Mihalis Dafermos	2014-02-13	Scientific Series	View details
Applications of Information Theory in Direct Sum and Direct Product Problems		2014-02-12	Scientific Series	View details
Our Lopsided Universe	Marina Cortes	2014-02-11	Scientific Series	View details
Bosonic particle-correlated states	Zhang Jiang	2014-02-06	Scientific Series	View details
The Radius of Neutron Stars and the Dense Matter Equation of State	Robert Rutledge	2014-02-06	Scientific Series	View details
The National Ignition Facility (NIF):Pathway to Energy Security and Physics of the Cosmos	Edward Moses	2014-02-05	Scientific Series	View details
Towards a 1/c Expansion in 2d Conformal Field Theory		2014-02-04	Scientific Series	View details
Cosmological constraints on complex scalar-field dark matter	Tanja Rindler-Daller	2014-02-04	Scientific Series	View details
Black hole entropy and the case for self-dual loop quantum gravity		2014-01-29	Scientific Series	View details
Time, Dynamics, Chaos, and the Brain	Dean Buonomano	2014-01-29	Scientific Series	View details
Mayer-Cluster Expansion of Instanton Partition Functions and Thermodynamic Bethe Ansatz	Carlo Meneghelli	2014-01-28	Scientific Series	View details

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Format results

Firewall evasion by quantum gravity

On null singularities in general relativity

Applications of Information Theory in Direct Sum and Direct Product Problems

Our Lopsided Universe

Bosonic particle-correlated states

The Radius of Neutron Stars and the Dense Matter Equation of State

The National Ignition Facility (NIF):Pathway to Energy Security and Physics of the Cosmos

Towards a 1/c Expansion in 2d Conformal Field Theory

Cosmological constraints on complex scalar-field dark matter

Black hole entropy and the case for self-dual loop quantum gravity

Time, Dynamics, Chaos, and the Brain

Mayer-Cluster Expansion of Instanton Partition Functions and Thermodynamic Bethe Ansatz

Firewall evasion by quantum gravity

On null singularities in general relativity

Applications of Information Theory in Direct Sum and Direct Product Problems

Our Lopsided Universe

Bosonic particle-correlated states

The Radius of Neutron Stars and the Dense Matter Equation of State

The National Ignition Facility (NIF):Pathway to Energy Security and Physics of the Cosmos

Towards a 1/c Expansion in 2d Conformal Field Theory

Cosmological constraints on complex scalar-field dark matter

Black hole entropy and the case for self-dual loop quantum gravity

Time, Dynamics, Chaos, and the Brain

Mayer-Cluster Expansion of Instanton Partition Functions and Thermodynamic Bethe Ansatz