Scientific Series

Displaying 3157 - 3168 of 5012

Our Lopsided Universe

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

PIRSA:14020139
Cosmology
Bosonic particle-correlated states

Zhang Jiang
University of New Mexico
February 06, 2014

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

Robert Rutledge
McGill University
February 06, 2014

PIRSA:14020087
Strong Gravity
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
Cosmology
Towards a 1/c Expansion in 2d Conformal Field Theory
February 04, 2014

PIRSA:14020084
Quantum Fields and Strings
Cosmological constraints on complex scalar-field dark matter

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

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

PIRSA:14010098
Quantum Gravity
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
Quantum Fields and Strings
New light on 21cm intensity fluctuations from the dark ages
January 28, 2014

PIRSA:14010097
Cosmology
Wilson Lines in Higher Spin Gravity

Alejandra Castro
University of Cambridge
January 23, 2014

PIRSA:14010081
Quantum Gravity
Cosmic Variance from Superhorizon Mode Coupling

Elliot Nelson
IBM (United States)
January 23, 2014

PIRSA:14010107
Cosmology

Our Lopsided Universe

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

PIRSA:14020139
Cosmology
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 Information
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
Strong Gravity
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
Cosmology
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
Quantum Fields and Strings
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
Cosmology
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
Quantum Gravity
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
Quantum Fields and Strings
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.
New light on 21cm intensity fluctuations from the dark ages
January 28, 2014

PIRSA:14010097
Cosmology
Fluctuations of the 21 cm brightness temperature before the formation of the first stars hold the promise of becoming a high-precision cosmological probe in the future. The growth of over densities is very well described by perturbation theory at that epoch and the signal can in principle be predicted to arbitrary accuracy for given cosmological parameters. Recently, Tseliakhovich and Hirata pointed out a previously neglected and important physical effect, due to the fact that baryons and cold dark matter (CDM) have supersonic relative velocities after recombination. This relative velocity suppresses the growth of matter fluctuations on scales k∼10−10^3 Mpc^−1. In addition, the amplitude of the small-scale power spectrum is modulated on the large scales over which the relative velocity varies, corresponding to k∼0.005−1 Mpc^−1. In this talk, I will describe the effect of the relative velocity on 21 cm brightness temperature fluctuations from redshifts z≥30. I will show that the 21 cm power spectrum is affected on most scales. On small scales, the signal is typically suppressed several tens of percent, except for extremely small scales (k≳2000 Mpc−1) for which the fluctuations are boosted by resonant excitation of acoustic waves. On large scales, 21 cm fluctuations are enhanced due to the non-linear dependence of the brightness temperature on the underlying gas density and temperature. The enhancement of the 21 cm power spectrum is of a few percent at k∼0.1 Mpc−1 and up to tens of percent at k≲0.005 Mpc−1, for standard ΛCDM cosmology. In principle this effect allows to probe the small-scale matter power spectrum not only through a measurement of small angular scales but also through its effect on large angular scales.
Wilson Lines in Higher Spin Gravity

Alejandra Castro
University of Cambridge
January 23, 2014

PIRSA:14010081
Quantum Gravity
In this talk I will review the interpretation of Wilson line operators in the context of higher spin gravity in 2+1 dim and holography. I will show how a Wilson line encapsulates the thermodynamics of black holes. Furthermore it provides an elegant description of massive particles. This opens a new window of observables which will allow us to probe the true geometrical nature of higher spin gravity.
Cosmic Variance from Superhorizon Mode Coupling

Elliot Nelson
IBM (United States)
January 23, 2014

PIRSA:14010107
Cosmology
We observe a finite subvolume of the universe, so CMB and large scale structure data may give us either a representative or a biased sample of statistics in the larger universe. Mode coupling (non-Gaussianity) in the primordial perturbations can introduce a bias of parameters measured in any subvolume due to coupling to superhorizon background modes longer than the size of the subvolume. This leads to a "cosmic variance" of statistics on smaller scales, as the long-wavelength background modes vary around the global mean. We study this bias for local non-Gaussianity and quantify how observed statistics such as the power spectrum of the primordial perturbations, spectral index (scale-dependence in the power spectrum), amplitude of non-Gaussianity, dark matter halo power spectrum, and primordial tensor modes, can differ from the same quantities averaged throughout a volume much larger than the observable universe. More general kinds of mode coupling can change the relative sensitivity to different background modes. Finally, we consider what observations can tell us about the possibility of biasing from superhorizon modes."

Title	Speaker(s)	Date	Talk Type	Info link
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
New light on 21cm intensity fluctuations from the dark ages		2014-01-28	Scientific Series	View details
Wilson Lines in Higher Spin Gravity	Alejandra Castro	2014-01-23	Scientific Series	View details
Cosmic Variance from Superhorizon Mode Coupling	Elliot Nelson	2014-01-23	Scientific Series	View details

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