Talks by Joao Magueijo

The cosmological non-constant 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 re-enactment of "Cartan's spiral staircase".

Lorentz symmetry: Broken, intact or deformed?

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.

If spacetime is a causal set then Lorentz symmetry is unbroken

Quantum superpositions of the speed of light

Photons and Quantum Gravity in Astrophysics

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.

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 scale-invariant 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 Ashtekar-Barbero-Immirzi 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 scale-invariant fluctuations without inflation

Joao Magueijo Imperial College London
I describe a number of techniques that allow for the generation of (near) scale-invariant 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 k-essence, 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.