Braneworld cosmology

Braneworld cosmology
NASA / WMAP Science Team · Public domain · source
Name	Braneworld cosmology
Field	Cosmology
Introduced	1990s
Notable	Lisa Randall; Raman Sundrum; Arkani-Hamed; Nima Arkani-Hamed; Paul Steinhardt; Juan Maldacena

Braneworld cosmology is a framework in theoretical cosmology that embeds a lower-dimensional universe as a "brane" within a higher-dimensional bulk, proposing modifications to General relativity, Kaluza–Klein theory, and Inflation (cosmology). It emerged from developments in String theory, M-theory, and models proposed by researchers like Lisa Randall, Raman Sundrum, and Nima Arkani-Hamed, influencing investigations related to the Cosmic microwave background, Dark matter, and Dark energy. The approach connects to experimental programs at facilities such as the Large Hadron Collider and observational missions like the Planck satellite.

Introduction

Braneworld cosmology situates a four-dimensional spacetime brane within a higher-dimensional bulk described by frameworks originating in String theory, M-theory, and extensions of Kaluza–Klein theory. Historical antecedents include ideas from Paul Dirac, Theodor Kaluza, and Oskar Klein and were reinvigorated by work from Arkani-Hamed, Lisa Randall, and Raman Sundrum. The paradigm has been explored in relation to cosmological puzzles addressed by Alan Guth and Andrei Linde through variants of Inflation (cosmology), and it interfaces with observational programs led by collaborations such as WMAP and Planck.

Theoretical Background

The theoretical underpinnings draw on String theory constructions by researchers including Edward Witten, Joseph Polchinski, and Juan Maldacena, which motivate branes as dynamical objects in higher-dimensional settings. Seminal model-building used concepts from Supergravity, Type IIB string theory, and the AdS/CFT correspondence proposed by Juan Maldacena to relate bulk gravity to boundary field theories like those studied by Steven Weinberg and Gerard 't Hooft. Early phenomenological proposals invoked mechanisms studied by Nima Arkani-Hamed, Savas Dimopoulos, and Gia Dvali and later refinements involved analyses by Raman Sundrum and Lisa Randall. Mathematical tools rely on generalizations of equations formulated by Albert Einstein and techniques from differential geometry developed by figures like Élie Cartan.

Brane Models and Scenarios

Notable scenarios include the Randall–Sundrum models crafted by Lisa Randall and Raman Sundrum, the large extra dimensions framework by Arkani-Hamed et al., and compactification schemes related to Calabi–Yau manifold constructions used by Philip Candelas and Andrew Strominger. Other approaches derive from Hořava–Witten theory developed by Petr Hořava and Edward Witten, and from braneworld explorations in Type IIA string theory considered by Cumrun Vafa. Implementations link to moduli stabilization research by Shamit Kachru and Renata Kallosh and to scenarios incorporating cosmic defects studied by Tom Kibble and Alexander Vilenkin.

Cosmological Dynamics and Equations

Dynamics are governed by modified Friedmann equations that generalize relations introduced by Alexander Friedmann and further explored by Albert Einstein and Hermann Minkowski in spacetime contexts; these include contributions from bulk curvature terms studied in Anti-de Sitter space analyses associated with Juan Maldacena. The equations incorporate brane tension parameters reminiscent of tensions in D-brane analyses by Joseph Polchinski and energy exchange with bulk fields studied by Kip Thorne and Sean Carroll. Cosmological solutions have been investigated in the contexts of reheating scenarios related to Andrei Linde and phase transitions analyzed by Yoichiro Nambu and Miguel Alcubierre, while perturbation theory connects with work on cosmological perturbations by Viatcheslav Mukhanov and James Bardeen.

Observational Implications and Constraints

Predictions include modifications to the Cosmic microwave background anisotropy spectrum measured by Planck and WMAP, potential signatures in gravitational wave backgrounds relevant to efforts like LIGO and VIRGO, and collider phenomenology tested at the Large Hadron Collider by collaborations such as ATLAS and CMS. Cosmological parameter constraints have been tightened using datasets from Sloan Digital Sky Survey and supernova surveys like those involving Adam Riess and Brian Schmidt, while limits on extra-dimensional graviton emission have been constrained by analyses associated with Super-Kamiokande and IceCube. Observational tests also intersect with searches for deviations from inverse-square gravity at laboratories influenced by measurements by researchers such as Eöt-Wash group.

Connections to Particle Physics and Gravity

Braneworld frameworks interface with particle physics through mechanisms for hierarchy problem solutions proposed by Nima Arkani-Hamed and Lisa Randall, and through attempts to embed the Standard Model (SM) fields on branes as in constructions inspired by David Gross and Frank Wilczek. The approach ties to gauge/gravity duality research following Juan Maldacena and to supersymmetry investigations by Howard Georgi and Pierre Fayet, while connecting to quantum gravity programs led by Carlo Rovelli and Abhay Ashtekar. Phenomenological implications include Kaluza–Klein excitations discussed by Theodor Kaluza and Oskar Klein and implications for neutrino physics studied in contexts involving Takaaki Kajita.

Open Problems and Future Directions

Outstanding issues include consistent ultraviolet completions debated by Edward Witten and Ashoke Sen, the cosmological constant puzzle highlighted by Steven Weinberg, and nonperturbative dynamics addressed by Cumrun Vafa and Gary Horowitz. Future research directions engage gravitational wave observatories like LISA and facilities such as the High-Luminosity Large Hadron Collider, theoretical developments in AdS/CFT correspondence by Juan Maldacena and computational advances associated with groups at institutions like Perimeter Institute and Institute for Advanced Study. Cross-disciplinary programs link to observational campaigns by Euclid and to theoretical proposals from researchers including Paul Steinhardt and Neil Turok.

Category:Cosmology