ekpyrotic model

ekpyrotic model
Name	Ekpyrotic model
Field	Cosmology
Introduced	2001
Proponents	Paul Steinhardt, Neil Turok
Related	Big Bang, Inflation, Cyclic model, Brane cosmology

ekpyrotic model

The ekpyrotic model is a cosmological scenario proposing a contracting phase prior to the Big Bang that yields the observed large-scale structure, developed as an alternative to inflation. It was motivated by ideas from Paul Steinhardt, Neil Turok, Edward Witten, Juan Maldacena, and influenced by concepts in String theory, M-theory, and Brane cosmology. Proponents contrasted it with Alan Guth's inflationary picture and engaged with critiques from researchers around Andrei Linde, Alexei Starobinsky, and Viatcheslav Mukhanov.

Introduction

The introduction situates the ekpyrotic model within debates involving Big Bang cosmology, Cosmic microwave background observations by COBE, WMAP, and Planck, and theoretical frameworks like String theory and M-theory. It frames contributions by Paul Steinhardt, Neil Turok, Raman Sundrum, Lisa Randall, and Edward Witten who sought to reconcile the hierarchy problem and cosmological initial conditions via brane interactions. Early public discussion referenced contrasts with the Inflation scenarios of Alan Guth, Andrei Linde, and Albrecht and Steinhardt.

Historical development

The historical development traces roots to Ekpyrosis-inspired literature by Khoury, Ovrut, Steinhardt, Turok and earlier brane-world proposals by Lisa Randall and Raman Sundrum. Seminal papers engaged with critiques from Andrei Linde, Paul Steinhardt's collaborators, and responses involving Juan Maldacena and Neil Turok. The model evolved through interactions with research at institutions like Princeton University, Cambridge University, Harvard University, and collaborations with groups at Perimeter Institute and IAS. Workshops at CERN, KITP, and ICTP hosted debates involving Edward Witten, Nima Arkani-Hamed, Cumrun Vafa, and Shamit Kachru that shaped refinements and cyclic extensions by Steinhardt and Turok.

Theoretical framework

The theoretical framework uses ingredients from M-theory, String theory, and Brane cosmology where our universe is a three-dimensional brane embedded in a higher-dimensional bulk, drawing on work by Horava and Witten. It invokes scalar fields studied by Andrei Linde and Paul Steinhardt with potentials analyzed by Viatcheslav Mukhanov and James Bardeen techniques for perturbations associated with Mukhanov–Sasaki equation methods developed in collaboration with researchers like Shinji Mukohyama and Misao Sasaki. The scenario relates to the Cyclic model proposed by Steinhardt and Turok and employs mechanisms analogous to the Ekpyrosis idea debated by Guth, Linde, Peter Steinhardt critics, and supporters including Ruth Gregory.

Cosmological implications

Cosmological implications involve predictions for the Cosmic microwave background anisotropies measured by Planck, the matter power spectrum constrained by SDSS, 2dF Galaxy Redshift Survey, and large-scale structure surveys led by Max Tegmark, Marc Davis, and John Peacock. It impacts expectations for primordial gravitational waves targeted by BICEP2, Advanced LIGO, LISA, and Pulsar Timing Array collaborations involving researchers like Nergis Mavalvala and Sheila Rowan. Connections to baryogenesis were discussed in contexts studied by David Gross and Helen Quinn, while dark matter implications reference experimental programs at CERN and Fermilab.

Mathematical formulation

The mathematical formulation uses higher-dimensional actions inspired by Horava–Witten heterotic constructions and effective four-dimensional descriptions employing scalar field dynamics comparable to models studied by Andrei Linde and Alexei Starobinsky. Perturbation calculations adapt the Mukhanov–Sasaki formalism with implementations by analysts like Viatcheslav Mukhanov and James Bardeen, while matching conditions across the bounce engage techniques developed by Garriga and Vilenkin, Stanford University groups, and Arkani-Hamed collaborators. Stability analyses refer to mode evolution with methods used by Juan Maldacena, Eva Silverstein, and Shamit Kachru in related string cosmology contexts.

Observational constraints

Observational constraints derive from Planck and WMAP measurements of scalar spectral index and non-Gaussianity limits analyzed by teams including Max Tegmark, David Spergel, and Charles Bennett. Constraints on tensor-to-scalar ratio come from BICEP2 controversies with involvement from John Kovac and international consortia, and from limits set by Advanced LIGO with contributions from Kip Thorne-era collaborations. Large-scale structure data from SDSS and DESI projects, and primordial element abundances informed by William Fowler-inspired nucleosynthesis studies, further constrain viable parameter space discussed in joint papers by Steinhardt, Turok, and critics including Andrei Linde.

Alternatives and extensions

Alternatives and extensions include the Inflation paradigm developed by Alan Guth, Andrei Linde, and Alexei Starobinsky; the Pre-Big Bang scenario associated with Gabriele Veneziano and Maurizio Gasperini; and cyclic cosmologies advanced by Steinhardt and Turok. Other related proposals draw on Loop Quantum Cosmology work by Abhay Ashtekar and Martin Bojowald, ekpyrosis-inspired hybrid models considered by Nima Arkani-Hamed and Eva Silverstein, and string landscape discussions by Joseph Polchinski and Raphael Bousso that inform anthropic debates engaged by Steven Weinberg and Don Page.

Category:Cosmology