Inflation, String Theory and Cosmology

Abstract

At its very beginning, the universe is believed to have grown exponentially in size via the mechanism of inflation. The almost scale-invariant density perturbation spectrum predicted by inflation is strongly supported by cosmological observations, in particular the cosmic microwave background radiation. However, the universe's precise inflationary scenario remains a profound problem for cosmology and for fundamental physics. String theory, the most-studied theory as the final physical theory of nature, should provide an answer to this question. Some of the proposals on how inflation is realized in string theory are reviewed. Since everything is made of strings, some string loops of cosmological sizes are likely to survive in the hot big bang that followed inflation. They appear as cosmic strings, which can have intricate properties. Because of the warped geometry in flux compactification of the extra spatial dimensions in string theory, some of the cosmic strings may have tensions substantially below the Planck or string scale. Such strings cluster in a manner similar to dark matter leading to hugely enhanced densities. As a result, numerous fossil remnants of the low tension cosmic strings may exist within the galaxy. They can be revealed through the optical lensing of background stars in the near future and studied in detail through gravitational wave emission. We anticipate that these cosmic strings will permit us to address central questions about the properties of string theory as well as the birth of our universe.

61 pages, 10 figures Added references and summary section; expanded introduction

References in corpus (26)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Cosmic Structure as the Quantum Interference of a Coherent Dark Wave
• Monodromy in the CMB: Gravity Waves and String Inflation
• Flux Compactification
• Cosmological parameters from combining the Lyman-alpha forest with CMB, galaxy clustering and SN constraints
• Upper bounds on the low-frequency stochastic gravitational wave background from pulsar timing observations: current limits and future prospects
• Gravitational wave stochastic background from cosmic (super)strings
• Gravitational-Wave Stochastic Background from Kinks and Cusps on Cosmic Strings
• CMB power spectrum contribution from cosmic strings using field-evolution simulations of the Abelian Higgs model
• Gravitational wave bursts from cosmic (super)strings: Quantitative analysis and constraints
• Stochastic Gravitational Wave Background from Light Cosmic Strings
• Analytic Study of Small Scale Structure on Cosmic Strings
• Cosmic String Structure at the Gravitational Radiation Scale
• Chasing Brane Inflation in String-Theory
• First LIGO search for gravitational wave bursts from cosmic (super)strings
• The (p,q) String Tension in a Warped Deformed Conifold
• Gravitational Waves from Light Cosmic Strings: Backgrounds and Bursts with Large Loops
• Implications of fast radio bursts for superconducting cosmic strings
• Cosmic string Y-junctions: a comparison between field theoretic and Nambu-Goto dynamics
• On quantifying and resolving the BICEP2/Planck tension over gravitational waves
• Cosmic Necklaces from String Theory
• Search for Cosmic Strings in the COSMOS Survey
• Effect of extra dimensions on gravitational waves from cosmic strings
• Search for Cosmic Strings in the GOODS Survey
• Constructing warm inflationary model in brane-antibrane system
• Kinks, extra dimensions, and gravitational waves