Conference

Displaying 2977 - 2988 of 4904

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
Quantum Gravity
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
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
Cosmology
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
Quantum Gravity
Searching for Quantum Gravity with the IceCube Neutrino Observatory

John Kelley
University of Wisconsin–Madison
October 23, 2012

PIRSA:12100093
Quantum Gravity
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
Quantum Gravity
The highest-energy particles of the Universe as viewed by the Pierre Auger Observatory

Markus Risse
University of Siegen

October 23, 2012

PIRSA:12100089
Photons and Quantum Gravity in Astrophysics
- Robert Nemiroff
  Michigan Technological University
- Giovanni Amelino-Camelia
  Sapienza Università di Roma - Dipartimento di Fisica
- Niayesh Afshordi
  University of Waterloo
- Joao Magueijo
  Imperial College London
- Alfio Bonanno
  National Institute for Astrophysics (INAF)
- Robert Brandenberger
  McGill University - Department of Physics
October 22, 2012

PIRSA:12100085
Quantum Gravity

Particle Physics
Lorentz Invariance Violation searches with HESS

Julien Bolmont
Sorbonne University

October 22, 2012

PIRSA:12100084
Is there a MesoScale in Quantum Gravity? Is it a Non-Locality Scale?
- Laurent Freidel
  Perimeter Institute for Theoretical Physics
- Stefano Liberati
  SISSA International School for Advanced Studies
- Dionigi Benincasa
October 22, 2012

PIRSA:12100082
Quantum Gravity
The cosmological constant and the emergence of the continuum

Lorenzo Sindoni
Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
October 22, 2012

PIRSA:12100081
Cosmology
An analogue model lesson for the cosmological constant

Stefano Liberati
SISSA International School for Advanced Studies
October 22, 2012

PIRSA:12100080
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
Quantum Gravity
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
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.
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
Cosmology
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
Quantum Gravity
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.
Searching for Quantum Gravity with the IceCube Neutrino Observatory

John Kelley
University of Wisconsin–Madison
October 23, 2012

PIRSA:12100093
Quantum Gravity
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).
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
Quantum Gravity
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
The highest-energy particles of the Universe as viewed by the Pierre Auger Observatory

Markus Risse
University of Siegen

October 23, 2012

PIRSA:12100089

One century after the seminal balloon flights of Victor Hess, the Pierre Auger Observatory aims at unveiling some of the mysteries of the highest-energy cosmic rays: what are their sources? Is there an end to the spectrum? What kind of particles are they? Are there signatures of new physics or of a violation of fundamental laws of physics? The Auger Observatory measures cosmic rays with energies of 10^20 eV or more by observing the giant air showers created when the particles hit the atmosphere. Located in Argentina, two complementary detector systems are used: an array of 1600 water-Cherenkov detectors distributed over 3000 sqkm, and fluorescence telescopes which monitor the atmosphere above the array in clear nights. Since 2005, data of unprecedented quantity and quality could be taken. In the talk, the observation principles, successes and limitations are described. Current, partly surprising results are presented. Data interpretations related to the search for violation of Lorentz invariance are mentioned.
Photons and Quantum Gravity in Astrophysics
- Robert Nemiroff
  Michigan Technological University
- Giovanni Amelino-Camelia
  Sapienza Università di Roma - Dipartimento di Fisica
- Niayesh Afshordi
  University of Waterloo
- Joao Magueijo
  Imperial College London
- Alfio Bonanno
  National Institute for Astrophysics (INAF)
- Robert Brandenberger
  McGill University - Department of Physics
October 22, 2012

PIRSA:12100085
Quantum Gravity

Particle Physics
Asymptotically safe inflation and CMB polarization
The presence of complex critical exponents in the scaling behavior of the Newton constant and Cosmological constant has dramatic consequences at the inflation scale. In particular an infinite number of unstable de-Sitter vacua emerges from an effective quantum gravitational action. In this framework, the possibility of detecting specific signaturesof a non-gaussian fixed point of the gravitational interactions in the CMB polarization spectrum will then be discussed.

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Cosmological windows such as CMB polarization and 21cm redshift surveys to probe Planck-scale physics

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Quantum gravity and a chiral signature in gravity waves
I show how quantum gravity could lead to a chiral signature in the graviational wave background, proportional to the imaginary part of the Immirzi parameter. This would leave a distinctive imprint in the polarization of the cosmic microwave background. I will discuss how this isue is closely related to that of identifying the ground of base state for quantum gravity.

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A Possible Bound on Spectral Dispersion from Fermi-Detected Gamma Ray Burst 090510A
Three photons spanning about 30 GeV arrived within about one millisecond from the Fermi-detected GRB 090510A at a redshift of about 0.9. Although conceivably a > 3Ïƒ statistical fluctuation when taken at face value this photon bunch -- quite possibly a classic GRB pulse -- leads to a relatively tight bound on the ability of our universe to disperse high energy photons. Specifically given a generic dispersion relation where the time delay is proportional to the photon energy to the first power the limit on the dispersion strength is k1 < 1.61Ã—10-5 sec Gpc-1 GeV-1. In the context of some theories of quantum gravity this conservative bound translates into an minimum energy scale greater than 525 m_Planck suggesting that spacetime is smooth at energies perhaps three orders of magnitude over the Planck mass.
Lorentz Invariance Violation searches with HESS

Julien Bolmont
Sorbonne University

October 22, 2012

PIRSA:12100084

The high flux and variability of the blazar PKS 2155-304 as observed by H.E.S.S. during the night of 28 July 2006 allowed a very high precision search for Quantum Gravity-induced energy-dependent time lags. In this talk, I will review the results published by the H.E.S.S. collaboration on this topic. In particular, I will emphasize the latest results obtained using a likelihood fit to study individual photon data. With this method and a proper error calibration procedure, a very high precision measurement was achieved leading to the best constraints on linear and quadratic terms of the dispersion relations obtained with an AGN so far.
Is there a MesoScale in Quantum Gravity? Is it a Non-Locality Scale?
- Laurent Freidel
  Perimeter Institute for Theoretical Physics
- Stefano Liberati
  SISSA International School for Advanced Studies
- Dionigi Benincasa
October 22, 2012

PIRSA:12100082
Quantum Gravity
The cosmological constant and the emergence of the continuum

Lorenzo Sindoni
Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
October 22, 2012

PIRSA:12100081
Cosmology
Naturalness problems that could be signaling the necessity a completion of an effective field theory with the introduction of an otherwise overlooked ingredient. The cosmological constant problem can be seen as a signal that the EFT for gravity, general relativity, is not correctly including the gravitational properties of the vacuum. Starting from the discussion of the a possible solution to this naturalness problem for a cc-like term in a BEC analogue model, I will briefly discuss how this particular mechanism can be extended, albeit in a preliminary form, to more genuine quantum gravity models like GFT, connecting in particular the problem of the determination of the gravitational couplings (and hence the hierarchies involved) to the appearance of a semiclassical space-time
An analogue model lesson for the cosmological constant

Stefano Liberati
SISSA International School for Advanced Studies
October 22, 2012

PIRSA:12100080
Cosmology
Analogue models of gravity have been a test field for many phenomena in quantum field theory on curved spacetimes. It was recently recognized that in some situations they can also provide toy models of emergent gravity. We shall review here such a model and address within it the nature and scale of the cosmological constrant trying to draw general lessons for emergent gravity scenarios.

Title	Speaker(s)	Date	Talk Type	Info link
Dynamical Dimensional Reduction	Dejan Stojkovic, Astrid Eichhorn, Martin Reuter	2012-10-24	Conference	View details
Is spacetime fundamentally discrete?	Bianca Dittrich, Seth Major, Daniele Oriti, Roberto Percacci, Tobias Fritz	2012-10-24	Conference	View details
Cosmological Constant	Ivan Arraut, Stephon Alexander, Alejandro Satz, Maïté Dupuis, Antonino Marciano	2012-10-23	Conference	View details
Quantum Gravity Effects in Black Holes and Gravitational Waves	Giovanni Amelino-Camelia, David Mattingly, Nicolas Yunes, Avery Broderick	2012-10-23	Conference	View details
Searching for Quantum Gravity with the IceCube Neutrino Observatory	John Kelley	2012-10-23	Conference	View details
Quantum Gravity Effects in the (Early and Late) Universe	Stephon Alexander, Daniel Sudarsky, Daniel Litim, Robert Brandenberger	2012-10-23	Conference	View details
The highest-energy particles of the Universe as viewed by the Pierre Auger Observatory	Markus Risse	2012-10-23	Conference	View details
Photons and Quantum Gravity in Astrophysics	Robert Nemiroff, Giovanni Amelino-Camelia, Niayesh Afshordi, Joao Magueijo, Alfio Bonanno, Robert Brandenberger	2012-10-22	Conference	View details
Lorentz Invariance Violation searches with HESS	Julien Bolmont	2012-10-22	Conference	View details
Is there a MesoScale in Quantum Gravity? Is it a Non-Locality Scale?	Laurent Freidel, Stefano Liberati, Dionigi Benincasa	2012-10-22	Conference	View details
The cosmological constant and the emergence of the continuum	Lorenzo Sindoni	2012-10-22	Conference	View details
An analogue model lesson for the cosmological constant	Stefano Liberati	2012-10-22	Conference	View details

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