Talks

10885 - 10896 of 18093 Results

12/13 PSI Researcher Presentation

Matthew Johnson York University

October 24, 2012

PIRSA:12100050

Astrophysics
Astrophysical Searches for Quantum Gravity Signals

Jonathan Granot University of Hertfordshire

October 24, 2012

PIRSA:12100058

General Relativity & Quantum Cosmology
Dynamical Dimensional Reduction

Dejan Stojkovic State University of New York (SUNY)

Astrid Eichhorn University of Southern Denmark

Martin Reuter Johannes Gutenberg University Mainz

October 24, 2012

PIRSA:12100104

General Relativity & Quantum Cosmology
Quantum Field Theory - Lecture 12B

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 24, 2012

PIRSA:12100073

High Energy Physics
Condensed Matter - Lecture 12

Assa Auerbach Technion – Israel Institute of Technology

October 24, 2012

PIRSA:12100037

Condensed Matter
Is spacetime fundamentally discrete?

Bianca Dittrich Perimeter Institute for Theoretical Physics

Seth Major Hamilton College

Daniele Oriti Ludwig-Maximilians-Universität München (LMU)

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 Sapienza Università di Roma - Dipartimento di Fisica

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
From Effective Strings to the Simplest theory of Quantum Gravity

October 23, 2012

PIRSA:12100040

High Energy 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

12/13 PSI Researcher Presentation

Matthew Johnson York University

October 24, 2012

PIRSA:12100050

Astrophysics
Astrophysical Searches for Quantum Gravity Signals

Jonathan Granot University of Hertfordshire

October 24, 2012

PIRSA:12100058

General Relativity & Quantum Cosmology

Some recent searches for quantum gravity signatures using observations of distant astrophysical sources will be discussed, focusing on the search for Lorentz invariance violation (LIV) in the form of a dependence of the photon propagation speed on its energy. Fermi gamma-ray space telescope observations of ~8 keV to ~30 GeV photons from a short (< 1 s) gamma-ray burst (GRB 090510) at a cosmological distance (z = 0.903), enabled for the first time to put a direct time of flight limit on a possible linear variation of the speed of light with photon energy that is beyond the Planck scale. Parameterizing |v/c-1| = E/E_{QG} our most conservative limits are E_{QG}/E_{Planck} > 1.2, while less conservative limits are up to 1-2 orders of magnitude stricter. Other types of astrophysical searches for LIV will be briefly outlined, along with some prospects for the future.
Dynamical Dimensional Reduction

Dejan Stojkovic State University of New York (SUNY)

Astrid Eichhorn University of Southern Denmark

Martin Reuter Johannes Gutenberg University Mainz

October 24, 2012

PIRSA:12100104

General Relativity & Quantum Cosmology

Dynamical dimensional reduction and Asymptotic Safety
The effective average action approach to Quantum Einstein Gravity (QEG) is discussed as a natural framework for exploring the scale dependent Riemannian geometry and multifractal micro-structure of the effective spacetimes predicted by QEG. Their fractal properties are related to the functional RG flow on theory space, and the special role of the running cosmological constant is emphasized. The prospects of an experimental verification will also be discussed.
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Vanishing dimension: theory and phenomenology
Lower-dimensionality at higher energies has manifold theoretical advantages as recently pointed out. Moreover, it appears that experimental evidence may already exists for it - a statistically significant planar alignment of events with energies higher than TeV has been observed in some earlier cosmic ray experiments. If this alignment is not a fluke, then the LHC should be able to see effects associated with the dimensional crossover. Further, (2+1)-dimensional spacetimes have no gravitational degrees of freedom, and gravity waves cannot be produced in that epoch in the early universe. This places a universal maximum frequency at which primordial gravity waves can propagate, which may be accessible to future gravitational wave detectors such as LISA. In this talk, the theoretical motivation for "vanishing dimensions" as well as generic experimental and observational signature will be discussed
Quantum Field Theory - Lecture 12B

Konstantin Zarembo Nordic Institute for Theoretical Physics

October 24, 2012

PIRSA:12100073

High Energy Physics
Condensed Matter - Lecture 12

Assa Auerbach Technion – Israel Institute of Technology

October 24, 2012

PIRSA:12100037

Condensed Matter
Is spacetime fundamentally discrete?

Bianca Dittrich Perimeter Institute for Theoretical Physics

Seth Major Hamilton College

Daniele Oriti Ludwig-Maximilians-Universität München (LMU)

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 Sapienza Università di Roma - Dipartimento di Fisica

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.
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.
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).

Title	Date	Collection	Type	Info
12/13 PSI Researcher Presentation	2012‑10‑24	12/13 PSI Researcher Presentations	Course	View details
Astrophysical Searches for Quantum Gravity Signals	2012‑10‑24	Experimental Search for Quantum Gravity 2012	Scientific Series	View details
Dynamical Dimensional Reduction	2012‑10‑24	Experimental Search for Quantum Gravity 2012	Conference	View details
Quantum Field Theory - Lecture 12B	2012‑10‑24	12/13 PSI - Quantum Field Theory 1	Course	View details
Condensed Matter - Lecture 12	2012‑10‑24	12/13 PSI - Condensed Matter	Course	View details
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
From Effective Strings to the Simplest theory of Quantum Gravity	2012‑10‑23	Quantum Fields and Strings	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

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Format results

12/13 PSI Researcher Presentation

Astrophysical Searches for Quantum Gravity Signals

Dynamical Dimensional Reduction

Quantum Field Theory - Lecture 12B

Condensed Matter - Lecture 12

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.

From Effective Strings to the Simplest theory of Quantum Gravity

Searching for Quantum Gravity with the IceCube Neutrino Observatory

12/13 PSI Researcher Presentation

Astrophysical Searches for Quantum Gravity Signals

Dynamical Dimensional Reduction

Quantum Field Theory - Lecture 12B

Condensed Matter - Lecture 12

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.

From Effective Strings to the Simplest theory of Quantum Gravity

Searching for Quantum Gravity with the IceCube Neutrino Observatory