Book contents
- Frontmatter
- Contents
- Preface
- A note on choice of metric
- Text website
- Part 1 Effective field theory: the Standard Model, supersymmetry, unification
- Part 2 Supersymmetry
- Part 3 String theory
- 20 Introduction
- 21 The bosonic string
- 22 The superstring
- 23 The heterotic string
- 24 Effective actions in ten dimensions
- 25 Compactification of string theory I. Tori and orbifolds
- 26 Compactification of string theory II. Calabi–Yau compactifications
- 27 Dynamics of string theory at weak coupling
- 28 Beyond weak coupling: non-perturbative string theory
- 29 Large and warped extra dimensions
- 30 Coda: where are we headed?
- Part 4 The appendices
- References
- Index
27 - Dynamics of string theory at weak coupling
from Part 3 - String theory
Published online by Cambridge University Press: 17 May 2010
- Frontmatter
- Contents
- Preface
- A note on choice of metric
- Text website
- Part 1 Effective field theory: the Standard Model, supersymmetry, unification
- Part 2 Supersymmetry
- Part 3 String theory
- 20 Introduction
- 21 The bosonic string
- 22 The superstring
- 23 The heterotic string
- 24 Effective actions in ten dimensions
- 25 Compactification of string theory I. Tori and orbifolds
- 26 Compactification of string theory II. Calabi–Yau compactifications
- 27 Dynamics of string theory at weak coupling
- 28 Beyond weak coupling: non-perturbative string theory
- 29 Large and warped extra dimensions
- 30 Coda: where are we headed?
- Part 4 The appendices
- References
- Index
Summary
In previous chapters, we have seen that string theory at the classical level shows promise of describing the Standard Model, and can realize at least one scenario for physics beyond: low-energy supersymmetry. But there are many puzzles, most importantly the existence of moduli and the related question of the cosmological constant. At tree level, in the Calabi–Yau solutions, the cosmological constant vanishes. But whether this holds in perturbation theory and beyond requires understanding of the quantum theory.
In studying string theory, we have certain tools:
(1) weak coupling expansions,
(2) long-wavelength (low-momentum, α′) expansions.
We have exploited both of these techniques up to this point. In analyzing string spectra, we have worked in a weak coupling limit. There are corrections to the masses and couplings, for example, in string perturbation theory, and most of the states that we have studied have finite lifetimes. At weak coupling, these effects are small, but at strong coupling, the theories presumably look dramatically different.
In asserting that Calabi–Yau vacua are solutions of the string equations, we used both types of expansions. We wrote the string equations both in lowest order in the string coupling, and also with the fewest number of derivatives (two). Even at weak coupling and in the derivative expansion, we can ask whether Calabi–Yau spaces are actually solutions of the string equations, both classically and quantum mechanically. For example, we have seen that, at lowest order in both expansions, there are typically many massless particles. We might expect tadpoles to appear for these fields, both in the α′ and in loops.
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- Supersymmetry and String TheoryBeyond the Standard Model, pp. 429 - 440Publisher: Cambridge University PressPrint publication year: 2007