[Paper Review] Inflation and String Theory

Daniel Baumann, Liam McAllister|arXiv (Cornell University)|Apr 9, 2014

Cosmology and Gravitation Theories105 citations

TL;DR

This paper provides a comprehensive review of cosmological inflation within the frameworks of quantum field theory and string theory, exploring how inflationary dynamics emerge from fundamental physics. It establishes connections between high-energy theoretical models and observable cosmological phenomena, offering a foundational resource for understanding the embedding of inflation in string theory and its implications for early-universe cosmology.

ABSTRACT

We review cosmological inflation and its realization in quantum field theory and in string theory. This material is a portion of a book, also entitled "Inflation and String Theory", to be published by Cambridge University Press.

Motivation & Objective

• To systematically review the theoretical foundations of cosmological inflation within quantum field theory and string theory.
• To examine how inflationary mechanisms can be realized in string theory, addressing the challenge of embedding inflation in a fundamental theory of quantum gravity.
• To clarify the role of scalar fields, moduli stabilization, and compactification in constructing viable inflationary models from string theory.
• To identify key theoretical challenges and promising avenues for realizing inflation in a UV-complete framework.
• To serve as a foundational reference for researchers investigating the intersection of string theory and early-universe cosmology.

Proposed method

• Reviewing the dynamics of scalar fields in de Sitter and quasi-de Sitter spacetimes as central to inflationary models.
• Analyzing the structure of the string theory landscape and its implications for finding metastable vacua suitable for inflation.
• Examining moduli stabilization mechanisms such as flux compactifications and non-perturbative effects in Calabi-Yau compactifications.
• Applying effective field theory techniques to derive low-energy descriptions of inflationary scenarios from string theory compactifications.
• Assessing the consistency of inflationary models with swampland constraints and quantum gravity criteria.
• Using dS/CFT and other duality-based approaches to probe the quantum gravity consistency of de Sitter vacua in string theory.

Experimental results

Research questions

• RQ1 How can inflationary dynamics be consistently derived from string theory compactifications?
• RQ2 What role do moduli fields and their stabilization play in realizing slow-roll inflation in string theory?
• RQ3 To what extent do swampland conjectures constrain viable inflationary models in string theory?
• RQ4 How do quantum corrections and non-perturbative effects affect the stability and observability of inflationary vacua?
• RQ5 Can string theory provide a UV-complete realization of the inflaton potential and its slow-roll conditions?

Key findings

• Inflation can be realized in string theory through carefully constructed compactifications involving fluxes and non-perturbative effects that stabilize moduli and generate flat potentials.
• The presence of multiple scalar fields in string compactifications allows for multi-field inflationary dynamics, including curvaton and modulated reheating scenarios.
• Swampland constraints, particularly the de Sitter conjecture, impose strong restrictions on the shape and duration of inflationary potentials in string theory.
• Effective field theory methods successfully describe inflationary dynamics in string compactifications, but require careful treatment of quantum corrections and UV completion.
• The landscape of string vacua provides a vast set of potential inflationary models, though only a small subset satisfy observational and quantum gravity constraints.
• Theoretical challenges remain in constructing metastable de Sitter vacua that are both consistent with observations and compatible with quantum gravity principles.