Theory and Phenomenology of Type I strings and M-theory

TL;DR

This review synthesizes the theory and phenomenology of Type I strings and M-theory, linking heterotic, Type I, and M-theory descriptions through dualities and D-brane physics. It details the construction rules, spectra, and consistency conditions of Type I/orientifold compactifications, and outlines how low-scale string scenarios with large extra dimensions arise and could be tested via gauge coupling unification patterns, SUSY-breaking mechanisms, and bulk-brane dynamics. A central theme is how bulk fields (neutrinos, axions) and KK towers modify low-energy observables, while string oscillator states and threshold corrections shape collider and precision phenomenology. The work underscores the potential of TeV-scale strings to address hierarchy and unification questions, while noting the need for precise background control and experimental guidance to identify the correct realization of beyond-Standard-Model physics.

Abstract

The physical motivations and the basic construction rules for Type I strings and M-theory compactifications are reviewed in light of the recent developments. The first part contains the basic theoretical ingredients needed for building four-dimensional supersymmetric models, models with broken supersymmetry and for computing low-energy actions and quantum corrections to them. The second part contains some phenomenological applications to brane world scenarios with low values of the string scale and large extra dimensions.

Figures (6)

• Figure 1: The annulus amplitude has a dual interpretation of one-loop open string propagation with vertical time $t$ and tree-level closed string propagation with horizontal time $l$.
• Figure 2: Unification of gauge couplings in the presence of extra spacetime dimensions. We consider two representative cases: $R^{-1} = 10^{5}$ GeV (left), $R^{-1} = 10^{8}$ GeV (right). In both cases we have taken $\delta=1$ and $\eta=0$.
• Figure 3: Unification of gauge couplings in the presence of extra spacetime dimensions. Here we fix $R^{-1}= 10^{12}$ GeV, $\delta=1$, and we vary $\eta$. For this value of $R^{-1}$, we see that the unification remains perturbative for all $\eta$.
• Figure 4: The disk amplitude with three open string particles and one closed string particle.
• Figure 5: The closed channel representation of the amplitude.