string cosmology

string cosmology
Name	String cosmology
Field	Theoretical physics
Related	String theory, M-theory, Quantum gravity

string cosmology

String cosmology is the application of String theory and M-theory ideas to the description of the Universe at cosmological scales, especially during the Big Bang and early-universe epochs. It aims to connect models proposed by researchers such as Edward Witten, Juan Maldacena, Joe Polchinski, and Cumrun Vafa to observables measured by collaborations like Planck (spacecraft), WMAP, and BICEP2. By incorporating inputs from institutions such as the Institute for Advanced Study, CERN, Perimeter Institute for Theoretical Physics, and Princeton University, the field seeks a unified account compatible with frameworks including General relativity, Quantum field theory, and proposals like the AdS/CFT correspondence.

Overview and motivation

String cosmology arises from attempts to reconcile puzzles exemplified by the Horizon problem, Flatness problem, and the Cosmic microwave background anomalies reported by COBE and Planck (spacecraft). Motivations include providing a UV-complete mechanism for inflation, explaining the origin of Dark matter and Dark energy within constructions related to Supersymmetry, and embedding scenarios compatible with constraints from experiments at Large Hadron Collider and detectors like LIGO. The field interacts with research at Stanford University, Harvard University, Caltech, and collaborations such as Strings meetings and the Kavli Institute for Theoretical Physics.

Foundations in string theory

Foundations rest on formulations of Type IIA string theory, Type IIB string theory, Heterotic string theory, and M-theory compactified on manifolds such as Calabi–Yau manifold and G2 manifold. Core technical tools derive from studies by Michael Green, John Schwarz, and David Gross on anomaly cancellation, and from dualities like T-duality and S-duality explored by Ashoke Sen and Cumrun Vafa. The AdS/CFT correspondence by Juan Maldacena and developments by Edward Witten and Steven Gubser provide nonperturbative input. Brane constructions use D-brane technology from Joe Polchinski and concepts of Orientifold introduced in string model building, while flux compactification strategies build on work by Gordon Kane, Savas Dimopoulos, and Shamit Kachru.

Early-universe models and scenarios

Proposed cosmological histories include string-inspired versions of Cosmic inflation such as Brane inflation by Shamit Kachru and collaborators, alternatives like the Ekpyrotic scenario associated with Paul Steinhardt and Neil Turok, and pre-Big Bang models advocated by Gabriele Veneziano and Maurizio Gasperini. String gas cosmology, developed by researchers including Robert Brandenberger and Cumrun Vafa, posits thermal histories on compact spaces like Toroidal compactification. Models incorporating Warped throat geometries use constructions like the Klebanov–Strassler solution and Randall–Sundrum model analogues tied to Lisa Randall and Raman Sundrum. Nonperturbative transitions draw on instanton methods explored by Sidney Coleman and Edward Witten.

Phenomenological implications and observables

Predicted signatures include distinct patterns in Cosmic microwave background polarization measured by collaborations like BICEP2 and Planck (spacecraft), primordial Gravitational waves accessible to LIGO and proposed missions such as LISA, and non-Gaussianities constrained by analyses from SDSS and DES. String-motivated particle spectra influence searches at Large Hadron Collider and dark-matter experiments like XENON1T and LUX-ZEPLIN. Moduli stabilization scenarios affect late-time acceleration and links to Lambda-CDM model tensions, while mechanisms for reheating relate to work at Fermilab and SLAC National Accelerator Laboratory. Cosmological implications have been debated in venues like Physical Review Letters and Journal of High Energy Physics.

Mathematical methods and compactifications

Mathematical infrastructure employs techniques from Algebraic geometry including study of Calabi–Yau manifold moduli spaces, tools from Differential geometry and Topology such as Betti number calculations, and stringy geometry like Noncommutative geometry referenced by Alain Connes. Compactification frameworks use fluxes, orientifolds, and brane backreaction studied through solutions like Klebanov–Strassler solution and GKP (Giddings–Kachru–Polchinski) backgrounds developed by S. B. Giddings, Shamit Kachru, and Joseph Polchinski. Mirror symmetry investigated by Philip Candelas and Strominger–Yau–Zaslow conjecture informs moduli counting; category-theoretic approaches draw on Maxim Kontsevich. Computational advances leverage algorithms used at Max Planck Institute for Gravitational Physics and collaborations with computer algebra systems employed by groups at University of Cambridge and Oxford University.

Challenges, criticisms, and open problems

Critiques center on the landscape problem exemplified by the String theory landscape and the anthropic reasoning linked to the Cosmological constant problem discussed by Steven Weinberg and Raphael Bousso. Difficulties include constructing testable, falsifiable predictions amid vast numbers of vacua, resolving the Trans-Planckian problem, and controlling backreaction in warped throat and brane setups debated in seminars at IAS and Perimeter Institute for Theoretical Physics. Open problems involve rigorous derivation of inflationary potentials from first principles, moduli stabilization compatible with low-energy supersymmetry breaking studied by Gordon Kane and Michael Dine, and embedding realistic particle physics such as Standard Model spectra into globally consistent compactifications pursued by teams at Caltech, MIT, and University of Chicago. Ongoing work connects to conjectures like the Swampland conjecture by Cumrun Vafa and collaborators, and to observational programs at Planck (spacecraft), LSST, and future gravitational-wave arrays.

Category:Cosmology