Talks

15697 - 15708 of 22687 Results

Is spacetime fundamentally discrete?

Bianca Dittrich Perimeter Institute for Theoretical Physics

Seth Major Hamilton College

Daniele Oriti Complutense University of Madrid

Roberto Percacci SISSA International School for Advanced Studies

Tobias Fritz Universität Innsbruck

October 24, 2012

PIRSA:12100100

Mathematical Physics
Quantum Field Theory - Lecture 12A

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 24, 2012

PIRSA:12100019

High Energy Physics
Cosmological Constant

Ivan Arraut University of Saint Joseph

Stephon Alexander Brown University

Alejandro Satz

Maïté Dupuis Perimeter Institute for Theoretical Physics

Antonino Marciano Fudan University

October 23, 2012

PIRSA:12100126

Astrophysics
Quantum Gravity Effects in Black Holes and Gravitational Waves

Giovanni Amelino-Camelia University of Naples Federico II

David Mattingly University of New Hampshire

Nicolas Yunes University of Illinois Urbana-Champaign

Avery Broderick University of Waterloo

October 23, 2012

PIRSA:12100094

General Relativity & Quantum Cosmology
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

David Jennings Imperial College London

October 23, 2012

PIRSA:12100105

Quantum Physics
Searching for Quantum Gravity with the IceCube Neutrino Observatory

John Kelley University of Wisconsin–Madison

October 23, 2012

PIRSA:12100093

General Relativity & Quantum Cosmology
From Effective Strings to the Simplest theory of Quantum Gravity

October 23, 2012

PIRSA:12100040

High Energy Physics
New Results in Jet Substructure

October 23, 2012

PIRSA:12100128

High Energy Physics
An informal discussion about topological gauge theory

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

October 23, 2012

PIRSA:12100129

High Energy Physics
Condensed Matter - Lecture 11

Assa Auerbach Technion – Israel Institute of Technology

October 23, 2012

PIRSA:12100036

Condensed Matter
Quantum Field Theory - Lecture 11B

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 23, 2012

PIRSA:12100072

High Energy Physics
Quantum Gravity Effects in the (Early and Late) Universe

Stephon Alexander Brown University

Daniel Sudarsky Universidad Nacional Autónoma De Mexico (UNAM)

Daniel Litim University of Sussex

Robert Brandenberger McGill University - Department of Physics

October 23, 2012

PIRSA:12100090

General Relativity & Quantum Cosmology

Is spacetime fundamentally discrete?

Bianca Dittrich Perimeter Institute for Theoretical Physics

Seth Major Hamilton College

Daniele Oriti Complutense University of Madrid

Roberto Percacci SISSA International School for Advanced Studies

Tobias Fritz Universität Innsbruck

October 24, 2012

PIRSA:12100100

Mathematical Physics

Modelling continuum dynamics on discrete space time
We will discuss perfect discretizations which aim at mirroring exactly continuum physics on a given lattice. Such discretizations avoid typical artifacts like Lorentz violation, energy dissipation, particle doubling and in particular breaking of diffeomorphism symmetry. Thus the question arises how to distinguish such lattice dynamics from continuum physics.

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Turning Weyl’s tile argument into a mathematically rigorous no-go theorem
Weyl's tile argument notes that if space was fundamentally discrete then the set of allowed velocities of a classical particle would not be isotropic. I will generalize Weyl's heuristic argument to a no-go theorem applying to any discrete periodic structure. Since this theorem does not take quantum mechanics into account it should only be regarded as the first step of a program of understanding the phenomenology of discrete spacetimes in a mathematically rigorous way.See arXiv:1109.1963

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On the Observability of Discrete Spatial Geometry
If quantum geometry is an accurate model of microscopic spatial geometry then two related questions arise, one observational and one theoretical: How and at what scale is the discreteness manifest? And, how is the general relativistic limit achieved? These questions will be discussed in the context of studies of a single atom of geometry. It will be shown that the effective scale of the discreteness could be much larger than the Planck scale. Before this scale can be predicted, the relations between discrete geometry, coherent states, and the semiclassical limit need to be clarified. Work towards this goal, using coherent states in spin foams and the spin geometry theorem of Penrose and Moussouris will be described.

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Asymptotic safety and minimal length
Since asymptotic safety - if true - would make a quantum field theory of gavity consistent "up to arbitrarily high energy", it would seem that this notion is incompatible with the existence of a minimal length. I will argue that this is not necessarily the case, due to ambiguity in the notion of minimal length.
Quantum Field Theory - Lecture 12A

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 24, 2012

PIRSA:12100019

High Energy Physics
Cosmological Constant

Ivan Arraut University of Saint Joseph

Stephon Alexander Brown University

Alejandro Satz

Maïté Dupuis Perimeter Institute for Theoretical Physics

Antonino Marciano Fudan University

October 23, 2012

PIRSA:12100126

Astrophysics

Dark Matter and Dark Energy as a Possible Manifestation of a Fundamental Scale
If we take the idea of the Planck length as a fundamental (minimum) scale and if additionally we impose the Cosmological Constant ($Lambda$) as and infrared (IR) cut-off parameter. Then it is possible to demonstrate that Dark Matter effects can emerge as a consequence of an IR-UV mix effect. This opens the possibility of unifying the Dark Energy and Dark matter effects in a single approach.

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Geometric Operators in Loop Quantum Gravity with a Cosmological Constant
Loop quantum gravity is a candidate to describe the quantum gravity regime with zero cosmological constant. One of its key results is that geometric operators such as area angle volume are quantized. Not much is known when the cosmological constant is not zero. It is usually believed that to introduce this parameter in the game we need to use quantum groups. However due to the complicated algebraic structure inherent to quantum groups the geometric operators are not yet properly defined (except the area operator). I will discuss how the use of tensor operators can circumvent the difficulties and allow to construct a natural set of observables. In particular I will construct the natural geometric observables such as angle or volume and discuss some of their implications.

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Interplay Between Cosmological Constant and DSR Scale
I offer brief remarks on several ways in which the cosmological constant could provide a clue toward quantum gravity. I then focus on how DSR-relativistic theories can be made compatible with spacetime expansion (possibly cosmological-constant-governed spacetime expansion), and how this interplay could manifest itself in data.

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Quantum Gravity RG Flow: A Cosmological Limit Cycle
I will discuss evidence for the existence of a limit cycle in the renormalization group for quantum gravity which is visible in a minisuperspace approximation. The emergence of the limit cycle can be studied through a tuning parameter representing the number of dimensions in which fluctuations of the conformal factor are suppressed. At the critical value of the tuning parameter all RG trajectories reaching the UV fixed point have an extended semiclassical regime with a small positive cosmological constant providing a possible model for a viable cosmology without fine-tuning.
Quantum Gravity Effects in Black Holes and Gravitational Waves

Giovanni Amelino-Camelia University of Naples Federico II

David Mattingly University of New Hampshire

Nicolas Yunes University of Illinois Urbana-Champaign

Avery Broderick University of Waterloo

October 23, 2012

PIRSA:12100094

General Relativity & Quantum Cosmology

Quantum-gravity effects as noise for gravity-wave detectors
I discuss a mechanism that can allow Planck scale effects to manifest themselves as a source of lof-frequency noise for interferometers. The mechanism requires a discrete formulation of dynamics at the Planck scale.
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Dancing in the Dark: Images of Quantum Black Holes
There have recently been a number of rather surprising suggestions that the quantum nature of black holes is manifested on macroscopic scales. This raises the question of just what the image of such an object should look like. The answer is more than simply academic; with the advent of the Event Horizon Telescope (EHT), a millimetre-wave very long baseline array, it is now possible to probe a handful of supermassive black holes with angular resolutions sufficient to image their horizons. I will discuss what we might expect to see, and how in the near future we will begin to empirically probe the existence of black hole quantum states with horizon scale curvature deviations from general relativity.
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The Irritating Persistence of Horizons
In some approaches to quantum gravity Lorentz invariance is modified. Without Lorentz invariance one can theoretically see behind the usual Killing horizon of a black hole if, for example, one allowed for superluminal propagation. This in turn raises the possibility that one could in principle probe the singularity and the quantum gravity regime. We discuss how Lorentz violating black hole solutions in Einstein-aether theory unfortunately possess another causal boundary behind the Killing horizon that is impenetrable to any superluminal mode. We also detail progress in determining the laws of black hole mechanics and the radiation spectrum from these so-called "universal horizons". Our results suggest that even if superluminal dispersion at high frequencies did exist in nature, singularities and their associated quantum gravity resolutions may very well remain locked behind horizons.
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

David Jennings Imperial College London

October 23, 2012

PIRSA:12100105

Quantum Physics

I will discuss the central role of correlations in thermodynamic directionality, how strong correlations can distort the thermodynamic arrow and contrast these distortions in both the classical and quantum regimes. These distortions constitute non-linear entanglement witnesses, and give rise to a rich information-theoretic structure. I shall explain how these results are then cast into the language of fluctuation theorems to derive a generalized exchange fluctuation theorem, and discuss the limitations of such a framework.
Searching for Quantum Gravity with the IceCube Neutrino Observatory

John Kelley University of Wisconsin–Madison

October 23, 2012

PIRSA:12100093

General Relativity & Quantum Cosmology

The IceCube Neutrino Observatory is a cubic-kilometer-scale neutrino detector built into the ice sheet at the geographic South Pole. Completed in December 2010, the detector consists of an array of photomultiplier tubes deployed along 86 cables ("strings") at depths of 1450 to 2450 m, as well as the IceTop air shower array of surface Cherenkov tanks. IceCube is detecting atmospheric neutrinos of energies above approximately 100 GeV at a rate of ~6 per hour, and is currently searching for extraterrestrial neutrinos from cosmic ray accelerators. A measurement of the atmospheric neutrino spectrum can be used to search for possible phenomenological signatures of quantum gravity (QG), such as violations of Lorentz invariance or quantum decoherence, and I present limits we have set on these phenomena in the neutrino sector. To extend the search for QG to much higher energies and cosmological baselines, we require an extraterrestrial neutrino source. In this context, I report on the status of our searches for neutrinos from gamma-ray bursts and from cosmic-ray interactions with the microwave background ("cosmogenic" neutrinos).
From Effective Strings to the Simplest theory of Quantum Gravity

October 23, 2012

PIRSA:12100040

High Energy Physics

String-like objects arise in many quantum field theories. Well known examples include flux tubes in QCD and cosmic strings. To a first approximation, their dynamics is governed by the Nambu-Goto action, but for QCD flux tubes numerical calculations of the energy levels of these objects have become so accurate that a systematic understanding of corrections to this simple description is desirable. In the first part of my talk, I discuss an effective field theory describing long relativistic strings. The construction parallels that of the chiral Lagrangian in that it is based on the pattern of symmetry breaking. To compare with previous works, I will present the results of the calculation of the S-matrix describing the scattering of excitations on the string worldsheet. In the second part of my talk, I will discuss critical strings from the same point of view and show that the worldsheet S-matrix in this case is non-trivial but can be calculated exactly. I will show that it encodes the familiar square-root formula for the energy levels of the string, the Hagedorn behavior of strings, and argue that the theory on the string worldsheet behaves like a 1+1 dimensional theory of quantum gravity rather than a field theory. If time permits, I will return to the task of computing the energy levels of flux-tubes using lessons learned from the second part of my talk.
New Results in Jet Substructure

October 23, 2012

PIRSA:12100128

High Energy Physics

We present new results on the performance of jet substructure techniques and their use in distinguishing the signatures of new boosted massive particles from the QCD background. Advanced approaches to jet reconstruction using jet grooming algorithms such as filtering, trimming, and pruning are compared. Measurements of the jet invariant mass for each jet algorithm are compared both at the particle level to multiple Monte Carlo event generators and at the detector level for several configurations of the jet grooming algorithms. The performance of these strategies and improvements in search sensitivity for new boosted hadronic particles are compared. Recent results using these techniques for both boosted RPV gluinos and top quark pairs from new particles are presented. The result is a comprehensive foundation for the use of substructure algorithms in the search for new physics at the LHC
An informal discussion about topological gauge theory

Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics

October 23, 2012

PIRSA:12100129

High Energy Physics

Reference:
Topological gauge theories and group cohomology
Robbert Dijkgraaf and Edward Witten
http://projecteuclid.org/DPubS?service=UI&version=1.0&verb=Display&handle=euclid.cmp/1104180750

Braiding statistics approach to symmetry-protected topological phases
Michael Levin, Zheng-Cheng Gu
http://arxiv.org/abs/1202.3120
Condensed Matter - Lecture 11

Assa Auerbach Technion – Israel Institute of Technology

October 23, 2012

PIRSA:12100036

Condensed Matter
Quantum Field Theory - Lecture 11B

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 23, 2012

PIRSA:12100072

High Energy Physics
Quantum Gravity Effects in the (Early and Late) Universe

Stephon Alexander Brown University

Daniel Sudarsky Universidad Nacional Autónoma De Mexico (UNAM)

Daniel Litim University of Sussex

Robert Brandenberger McGill University - Department of Physics

October 23, 2012

PIRSA:12100090

General Relativity & Quantum Cosmology

Quantum Gravity at the origin of seeds of cosmic structure?
This meeting shows a our impatience for uncovering at long last any signal of unknown physics that might have a quantum gravitational origin. I will argue that the transition from a homogenous and isotropic state characterizing the mid-early parts of inflation ( i.e. the regime after sufficient e- folds of inflation have elapsed so that all traces of the pre-inflationary state are erased), to those eras, where the primordial inhomogeneities have appears might hold ins testing clues about the nature of quantum gravity

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Quantum gravity and cosmology
In the light of upcoming high-precision data from the Planck mission and possible trans-Planckian signatures encoded in eg the microwave background radiation, and in view of possible large-distance modifications of gravity and the accelearted expansion of the universe

Title	Date	Collection	Type	Info
Is spacetime fundamentally discrete?	2012‑10‑24	Experimental Search for Quantum Gravity 2007	Conference	View details
Quantum Field Theory - Lecture 12A	2012‑10‑24	12/13 PSI - Quantum Field Theory 1	Course	View details
Cosmological Constant	2012‑10‑23	Experimental Search for Quantum Gravity 2012	Conference	View details
Quantum Gravity Effects in Black Holes and Gravitational Waves	2012‑10‑23	Experimental Search for Quantum Gravity 2012	Conference	View details
Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.	2012‑10‑23	Quantum Foundations	Scientific Series	View details
Searching for Quantum Gravity with the IceCube Neutrino Observatory	2012‑10‑23	Experimental Search for Quantum Gravity 2012	Conference	View details
From Effective Strings to the Simplest theory of Quantum Gravity	2012‑10‑23	Quantum Fields and Strings	Scientific Series	View details
New Results in Jet Substructure	2012‑10‑23	Particle Physics	Scientific Series	View details
An informal discussion about topological gauge theory	2012‑10‑23	Quantum Matter	Scientific Series	View details
Condensed Matter - Lecture 11	2012‑10‑23	12/13 PSI - Condensed Matter	Course	View details
Quantum Field Theory - Lecture 11B	2012‑10‑23	12/13 PSI - Quantum Field Theory 1	Course	View details
Quantum Gravity Effects in the (Early and Late) Universe	2012‑10‑23	Experimental Search for Quantum Gravity 2012	Conference	View details

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Format results

Is spacetime fundamentally discrete?

Quantum Field Theory - Lecture 12A

Cosmological Constant

Quantum Gravity Effects in Black Holes and Gravitational Waves

Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

Searching for Quantum Gravity with the IceCube Neutrino Observatory

From Effective Strings to the Simplest theory of Quantum Gravity

New Results in Jet Substructure

An informal discussion about topological gauge theory

Condensed Matter - Lecture 11

Quantum Field Theory - Lecture 11B

Quantum Gravity Effects in the (Early and Late) Universe

Is spacetime fundamentally discrete?

Quantum Field Theory - Lecture 12A

Cosmological Constant

Quantum Gravity Effects in Black Holes and Gravitational Waves

Thermodynamics of correlated quantum systems and a generalized exchange fluctuation theorem.

Searching for Quantum Gravity with the IceCube Neutrino Observatory

From Effective Strings to the Simplest theory of Quantum Gravity

New Results in Jet Substructure

An informal discussion about topological gauge theory

Condensed Matter - Lecture 11

Quantum Field Theory - Lecture 11B

Quantum Gravity Effects in the (Early and Late) Universe