Imperial College London
Talks by Joao Magueijo
The problem of time meets the problem of constants: could Quantum Cosmology be happening now?
Joao Magueijo
Imperial College London
Abstract: TBD
The cosmological nonconstant and Cartan's spiral staircase
Joao Magueijo
Imperial College London
We review recent efforts to turn the cosmological constant into a dynamical variable without an ungainly proliferation of free parameters. In a cosmological setting where parity invariance is imposed (along with homogeneity and isotropy) this leads to phenomenological disaster. However, in this theory it is possible to construct parity violating Friedman models due to torsion, a reenactment of "Cartan's spiral staircase".
Fundamental Time

Laurent Freidel Perimeter Institute for Theoretical Physics

Lee Smolin Perimeter Institute for Theoretical Physics

Joao Magueijo Imperial College London
Lorentz symmetry: Broken, intact or deformed?

Rafael Sorkin Perimeter Institute for Theoretical Physics

Sabine Hossenfelder Frankfurt Institute for Advanced Studies (FIAS)

David Mattingly University of New Hampshire

Niayesh Afshordi University of Waterloo

Daniel Sudarsky Universidad Nacional Autónoma De Mexico (UNAM)

Stefano Liberati SISSA Scuola Internazionale Superiore di Studi Avanzati

Joao Magueijo Imperial College London
Is aether technically natural?
I will discuss whether higher energy Lorentz violation should be considered a natural expectation in theories of quantum gravity with a preferred frame.
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If spacetime is a causal set then Lorentz symmetry is unbroken
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Quantum superpositions of the speed of light
I will discuss whether higher energy Lorentz violation should be considered a natural expectation in theories of quantum gravity with a preferred frame.
_____________________________
If spacetime is a causal set then Lorentz symmetry is unbroken
_____________________________
Quantum superpositions of the speed of light
Photons and Quantum Gravity in Astrophysics

Robert Nemiroff Michigan Technological University

Giovanni AmelinoCamelia Sapienza Università di Roma  Dipartimento di Fisica

Niayesh Afshordi University of Waterloo

Joao Magueijo Imperial College London

Alfio Bonanno INAF, Catania

Robert Brandenberger McGill University  Department of 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 deSitter vacua emerges from an effective quantum gravitational action. In this framework, the possibility of detecting specific signaturesof a nongaussian fixed point of the gravitational interactions in the CMB polarization spectrum will then be discussed.
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 deSitter vacua emerges from an effective quantum gravitational action. In this framework, the possibility of detecting specific signaturesof a nongaussian fixed point of the gravitational interactions in the CMB polarization spectrum will then be discussed.
Is Nothing Sacred? The Cosmological Pay Off from Breaking Lorentz and Diffeormorphism Invariance
Joao Magueijo
Imperial College London
I show how the local Lorentz and/or diffeomorphism invariances may be broken by a varying c, softly or harshly, depending on taste. Regardless of the fundamental implications of such dramas, these symmetry breakings may be of great practical use in cosmology. They may solve the horizon and flatness problems. A near scaleinvariant spectrum of fluctuation may arise, even without inflation. Distinct imprints may be left, teaching us an important lesson: our foundations may be flimsier than we like to think.
Cosmology Meets Quantum Gravity: a Chiral Signature in the CMB?
Joao Magueijo
Imperial College London
Cosmology and quantum gravity have not always had the smoothest of interactions. As a case in point I'll summarize the calculation behind the prediction of tensor modes in inflationary universes and discuss the difficulties found in recasting this calculation in terms of AshtekarBarberoImmirzi variables. Contrary to the belief that ``inflation is shielded from quantum gravity'', novelties are found, leading to the interesting prediction of a chiral signature in the gravitational wave background, proportional to the imaginary part of the Immirzi parameter.
Generating scaleinvariant fluctuations without inflation
Joao Magueijo
Imperial College London
I describe a number of techniques that allow for the generation of (near) scaleinvariant fluctuations in the early Universe without inflation or ekpyrosis. The basic ingredient is a decaying maximal speed of propagation, for which a Universal law is found. Connections are made with kessence, the cuscaton, and the DBI action. However the simplest realizations result from bimetric theories and deformed dispersion relations and DSR. A number of implications to theories of quantum gravity are discussed.
Cosmic Microwave Background and the Structure of the Universe
Joao Magueijo
Imperial College London
Cosmic Microwave Background and the Structure of the Universe
Joao Magueijo
Imperial College London