Scientific Series

Displaying 3265 - 3276 of 5113

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
January 23, 2014

PIRSA:14010107
Cosmology
Hardness of correcting errors on a stabilizer code

Pavithran Iyer
January 22, 2014

PIRSA:14010099
Quantum Information
Does the Quantum Particle know its own Energy?

Rafael Sorkin Perimeter Institute for Theoretical Physics
January 21, 2014

PIRSA:14010106
Quantum Foundations
Boundaries and Defects in 4d N=4 SYM

Masahito Yamazaki University of Tokyo
January 21, 2014

PIRSA:14010086
Quantum Fields and Strings
Paying the price of naturalness with a supersymmetric twin Higgs

Kiel Howe Stanford University
January 21, 2014

PIRSA:14010105
Condensed Matter
The McV black hole and the scalar theories that support it

Michele Fontanini
January 21, 2014

PIRSA:14010082
Cosmology
Gaugino physics of split supersymmetry spectrum at the LHC and future proton colliders

Sunghoon Jung Korea Institute for Advanced Study
January 16, 2014

PIRSA:14010103
Particle Physics
Entanglement farming: Harnessing the properties of fixed points in quantum evolution

Eduardo Martin-Martinez University of Waterloo
January 15, 2014

PIRSA:14010104
Quantum Information

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
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."
Hardness of correcting errors on a stabilizer code

Pavithran Iyer
January 22, 2014

PIRSA:14010099
Quantum Information
Problems in computer science are often classified based on the scaling of the runtimes for algorithms that can solve the problem. Easy problems are efficiently solvable but often in physics we encounter problems that take too long to be solved on a classical computer. Here we look at one such problem in the context of quantum error correction. We will further show that no efficient algorithm for this problem is likely to exist. We will address the computational hardness of a decoding problem, pertaining to quantum stabilizer codes considering independent X and Z errors on each qubit. Much like classical linear codes, errors are detected by measuring certain check operators which yield an error syndrome, and the decoding problem consists of determining the most likely recovery given the syndrome. The corresponding classical problem is known to be NP-Complete, and a similar decoding problem for quantum codes is known to be NP-Complete too. However, this decoding strategy is not optimal in the quantum setting as it does not take into account error degeneracy, which causes distinct errors to have the same effect on the code. Here, we show that optimal decoding of stabilizer codes is computationally much harder than optimal decoding of classical linear codes, it is #P-Complete.
Does the Quantum Particle know its own Energy?

Rafael Sorkin Perimeter Institute for Theoretical Physics
January 21, 2014

PIRSA:14010106
Quantum Foundations
If a wave function does not describe microscopic reality then what does? Reformulating quantum mechanics in path-integral terms leads to a notion of ``precluded event" and thence to the proposal that quantal reality differs from classical reality in the same way as a set of worldlines differs from a single worldline. One can then ask, for example, which sets of electron trajectories correspond to a Hydrogen atom in its ground state and how they differ from those of an excited state. We address the analogous questions for simple model that replaces the electron by a particle hopping (in discrete time) on a circular lattice.
Boundaries and Defects in 4d N=4 SYM

Masahito Yamazaki University of Tokyo
January 21, 2014

PIRSA:14010086
Quantum Fields and Strings
We discuss boundary conditions and domain walls in 4d N=4 SYM, focusing on those preserving 4 supercharges. Along the way we revisit the old problem of the quantum-corrected moduli space of 3d N=2 theories.
Paying the price of naturalness with a supersymmetric twin Higgs

Kiel Howe Stanford University
January 21, 2014

PIRSA:14010105
Condensed Matter
What is the price of naturalness? In minimal extensions of the standard model, stringent limits on new colored particles and measurements of Higgs properties from the LHC severely challenge the hypothesis of naturalness of the electroweak scale. However, these measurements also provide unprecedented guidance in exploring non-minimal models of new electroweak physics. The supersymmetric twin Higgs provides a concrete example where few-percent level tuning remains compatible with superpartner limits and Higgs physics as well as gauge coupling unification and other successes of the MSSM. Studying such models in detail is crucial to understanding the role naturalness will play as a motivating principle for future searches at the 13 TeV LHC and beyond.
The McV black hole and the scalar theories that support it

Michele Fontanini
January 21, 2014

PIRSA:14010082
Cosmology
Systems in which the local gravitational attraction is coupled to the expansion of the Universe have been studied since the early stages of General Relativity as the pioneering works of McVittie show. In this talk I start reviewing the McVittie black hole solution and its variable mass generalization from a classical fluid approach to understand its properties. I then move to a field theoretical analysis to investigate the scalar theories that support such black holes.
Gaugino physics of split supersymmetry spectrum at the LHC and future proton colliders

Sunghoon Jung Korea Institute for Advanced Study
January 16, 2014

PIRSA:14010103
Particle Physics
Discovery of the Higgs boson and lack of discovery of superpartners in the first run at LHC are both predictions of split supersymmetry with thermal dark matter. We discuss what it would take to find gluinos at hadron supercolliders, including the LHC at 14 TeV center of mass energy, and future pp colliders at 100 TeV and 200 TeV. We generalize the discussion by re-expressing the search capacity in terms of gluino to lightest superpartner mass ratio, and apply results to other scenarios, such as gauge mediation and mirage mediation. In those models, distinctive gaugino mass ratios arise at leading order, but can be significantly modified by large logarithmic quantum corrections from split spectrum.
Entanglement farming: Harnessing the properties of fixed points in quantum evolution

Eduardo Martin-Martinez University of Waterloo
January 15, 2014

PIRSA:14010104
Quantum Information
We show that in certain generic circumstances the state of light of an optical cavity traversed by beams of atoms is naturally driven towards a non-thermal metastable state. This state can be such that successive pairs of unentangled particles sent through the cavity will reliably emerge significantly entangled thus providing a renewable source of quantum entanglement. Significant for possible experimental realizations is the fact that this entangling fixed point state of the cavity can be reached largely independently of the initial state in which the cavity was prepared. Our results suggest that reliable entanglement farming on the basis of such a fixed point state should be possible also in various other experimental settings, namely with the to-be-entangled particles replaced by arbitrary qudits and with the cavity replaced by a suitable reservoir system.

Title	Speaker(s)	Date	Talk Type	Info link
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
Hardness of correcting errors on a stabilizer code	Pavithran Iyer	2014-01-22	Scientific Series	View details
Does the Quantum Particle know its own Energy?	Rafael Sorkin	2014-01-21	Scientific Series	View details
Boundaries and Defects in 4d N=4 SYM	Masahito Yamazaki	2014-01-21	Scientific Series	View details
Paying the price of naturalness with a supersymmetric twin Higgs	Kiel Howe	2014-01-21	Scientific Series	View details
The McV black hole and the scalar theories that support it	Michele Fontanini	2014-01-21	Scientific Series	View details
Gaugino physics of split supersymmetry spectrum at the LHC and future proton colliders	Sunghoon Jung	2014-01-16	Scientific Series	View details
Entanglement farming: Harnessing the properties of fixed points in quantum evolution	Eduardo Martin-Martinez	2014-01-15	Scientific Series	View details

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