The Return of the Phoenix Universe (2009)
Lehners, Jean-Luc, Steinhardt, Paul J., Turok, Neil
Georges Lemaitre introduced the term "phoenix universe" to describe an oscillatory cosmology with alternating periods of gravitational collapse and expansion. This model is ruled out observationally...
Non-Gaussianity Generated by the Entropic Mechanism in Bouncing Cosmologies Made Simple (2009)
Lehners, Jean-Luc, Steinhardt, Paul J.
Non-gaussianity in the microwave background radiation is bound to play a key role in giving us clues about the physics of the very early universe. However, the associated calculations, at second and...
Multifield Cosmological Perturbations at Third Order and the Ekpyrotic Trispectrum (2009)
Lehners, Jean-Luc, Renaux-Petel, Sébastien
Using the covariant formalism, we derive the equations of motion for adiabatic and entropy perturbations at third order in perturbation theory for cosmological models involving two scalar fields. We...
Dark Energy and the Return of the Phoenix Universe (2008)
Lehners, Jean-Luc, Steinhardt, Paul J.
In cyclic universe models based on a single scalar field (e.g., the radion determining the distance between branes in M-theory), virtually the entire universe makes it through the ekpyrotic smoothing...
Ekpyrotic and Cyclic Cosmology (2008)
Ekpyrotic and cyclic cosmologies provide theories of the very early and of the very late universe. In these models, the big bang is described as a collision of branes - and thus the big bang is not...
Intuitive understanding of non-gaussianity in ekpyrotic and cyclic models (2008)
Lehners, Jean-Luc, Steinhardt, Paul J.
It has been pointed out by several groups that ekpyrotic and cyclic models generate significant non-gaussianity. In this paper, we present a physically intuitive, semi-analytic estimate of the...
Lehners, Jean-Luc, Steinhardt, Paul J.
We analyze the non-gaussian density perturbations generated in ekpyrotic/cyclic models based on heterotic M-theory. In this picture, two scalar fields produce nearly scale-invariant entropic...
Bouncing and Colliding Branes (2007)
In a braneworld description of our universe, we must allow for the possibility of having dynamical branes around the time of the big bang. Some properties of such domain walls in motion are discussed...
Bouncing Negative-Tension Branes (2007)
Lehners, Jean-Luc, Turok, Neil
Braneworlds, understood here as double domain wall spacetimes, can be described in terms of a linear harmonic function, with kinks at the locations of the boundary branes. In a dynamical setting,...
Kaluza-Klein Induced Supersymmetry Breaking for Braneworlds in Type IIB Supergravity (2007)
Lehners, Jean-Luc, Smyth, Paul, Stelle, K. S.
We consider Z_2-symmetric braneworlds arising from 5-sphere compactifications with 5-form flux in type IIB supergravity. This Kaluza-Klein reduction produces a D=5 theory which supports...
Generating Ekpyrotic Curvature Perturbations Before the Big Bang (2007)
Lehners, Jean-Luc, McFadden, Paul, Turok, Neil, Steinhardt, Paul J.
We analyze a general mechanism for producing a nearly scale-invariant spectrum of cosmological curvature perturbations during a contracting phase preceding a big bang, that can be entirely described...
Effective Actions for Heterotic M-Theory (2006)
Lehners, Jean-Luc, McFadden, Paul, Turok, Neil
We discuss the moduli space approximation for heterotic M-theory, both for the minimal case of two boundary branes only, and when a bulk brane is included. The resulting effective actions may be used...
Colliding Branes in Heterotic M-theory (2006)
Lehners, Jean-Luc, McFadden, Paul, Turok, Neil
We study the collision of two flat, parallel end-of-the-world branes in heterotic M-theory. By insisting that there is no divergence in the Riemann curvature as the collision approaches, we are able...
D=5 M-theory radion supermultiplet dynamics (2002)
Lehners, Jean-Luc, Stelle, K. S.
We show how the bosonic sector of the radion supermultiplet plus d=4, N=1 supergravity emerge from a consistent braneworld Kaluza-Klein reduction of D=5 M--theory. The radion and its associated...