[Paper Review] String and D-brane Physics at Low Energy

Ignatios Antoniadis|ArXiv.org|Feb 28, 2001

Particle physics theoretical and experimental studies4 references16 citations

TL;DR

This paper explores low-energy effective field theories arising from string and D-brane compactifications, focusing on scenarios with large extra dimensions and low string scales. It demonstrates that large compactification volumes can resolve gauge coupling unification and supersymmetry breaking hierarchies, while maintaining weak string coupling through T-duality and non-perturbative mechanisms.

ABSTRACT

1. Preliminaries. 2. Heterotic string and motivations for large volume compactifications; 2.1 Gauge coupling unification; 2.2 Supersymmetry breaking by compactification. 3. M-theory on S^1/Z_2 imes Calabi-Yau. 4. Type I/I' string theory and D-branes; 4.1 Low-scale strings and extra-large transverse dimensions; 4.2 Relation type I/I' -- heterotic. 5. Type II theories; 5.1 Low-scale IIA strings and tiny coupling; 5.2 Large dimensions in type IIB; 5.3 Relation type II -- heterotic. 6. Theoretical implications; 6.1 U.V./I.R. correspondence; 6.2 Unification ; 6.3 Supersymmetry breaking and scales hierarchy ; 6.4 Electroweak symmetry breaking in TeV-scale strings. 7. Scenarios for studies of experimental constraints. 8. Extra-dimensions along the world brane: KK excitations of gauge bosons; 8.1 Production at hadron colliders; 8.2 High precision data low-energy bounds; 8.3 One extra dimension for other cases; 8.4 More than one extra dimension. 9. Extra-dimensions transverse to the brane world: KK excitations of gravitons; 9.1 Signals from missing energy experiments; 9.2 Gravity modification and sub-millimeter forces. 10. Dimension-eight operators and limits on the string scale. 11. D-brane Standard Model; 11.1 Hypercharge embedding and the weak angle; 11.2 The fate of U(1)'s and proton stability. 12. Appendix: Supersymmetry breaking in type I strings; 12.1 Scherk-Schwarz deformations; 12.2 Brane supersymmetry breaking.

Motivation & Objective

• To investigate the viability of low-scale string theories with large internal volumes, motivated by the hierarchy problem and gauge coupling unification.
• To analyze how compactification can generate the observed electroweak scale and break supersymmetry hierarchically in string theory.
• To explore the phenomenological constraints on extra dimensions from collider data, precision measurements, and gravity experiments.
• To construct viable D-brane models—particularly non-BPS brane configurations—that yield realistic particle spectra and avoid tachyons.
• To examine the role of T-duality and non-perturbative effects in stabilizing the string coupling and compactification moduli.

Proposed method

• Uses T-duality to relate weakly-coupled heterotic strings with large compactification radii to strongly-coupled regimes with small radii, preserving physical observables.
• Derives 4D Planck and gauge coupling scales from 10D string parameters and compactification volume, using the relations $ M_p acksimeq M_H / g $ and $ ilde{ au} acksimeq rac{1}{g} rac{l_s^3}{ ext{Vol}} $.
• Applies one-loop gauge coupling unification in the MSSM to constrain the compactification scale, showing that $ R acksimeq 100 ext{--}1000 ext{ }l_s $ can reconcile $ M_{ ext{GUT}} acksimeq 2\times10^{16} \text{GeV} $ with $ M_H \simeq 10^{18} \text{GeV} $.
• Analyzes D-brane configurations with branes and antibranes (e.g., D9/D5 systems) to realize non-supersymmetric, tachyon-free vacua with localized supersymmetry breaking.
• Evaluates effective potentials from uncancelled NS-NS tadpoles, showing $ V_{\text{eff}} \propto e^{-\phi_{10}} = 1/g_{\text{YM}}^2 $, which stabilizes the system and breaks supersymmetry globally.
• Uses anomaly cancellation and generalized Green-Schwarz mechanisms to ensure quantum consistency in non-BPS brane models with non-Abelian gauge groups.

Experimental results

Research questions

• RQ1 Can large compactification volumes in heterotic string theory resolve the discrepancy between the GUT scale and the heterotic string scale?
• RQ2 How can supersymmetry be broken hierarchically in string theory without introducing a fundamental scale below the string scale?
• RQ3 What are the phenomenological signatures of large extra dimensions in gauge boson Kaluza-Klein excitations at colliders and precision experiments?
• RQ4 Can non-BPS D-brane configurations with branes and antibranes yield stable, tachyon-free vacua with realistic particle content?
• RQ5 How do string-scale gravity and modified gravity at sub-millimeter scales constrain the size of extra dimensions?

Key findings

• Large compactification volumes ($ R \sim 100\text{--}1000\text{ }l_s $) can reconcile the observed GUT scale ($ \sim 2\times10^{16} \text{GeV} $) with the heterotic string scale ($ \sim 10^{18} \text{GeV} $) via threshold corrections.
• Supersymmetry breaking at the TeV scale can be dynamically generated via large compactification radii, with the breaking scale set by $ R^{-1} \sim \text{TeV} $, avoiding the need for explicit soft terms.
• The effective potential from uncancelled NS-NS tadpoles on D5 branes is $ V_{\text{eff}} \propto e^{-\phi_{10}} = 1/g_{\text{YM}}^2 $, which stabilizes the system and breaks supersymmetry globally.
• Non-BPS D-brane configurations with D9 branes and D5 antibranes yield a consistent, tachyon-free vacuum with $ [SO(16)\times SO(16)]_9 \times [USp(16)\times USp(16)]_5 $ gauge group and chiral matter spectra.
• The resulting model features a non-supersymmetric spectrum on the D5 branes, including vector-like and chiral fermions, with anomaly cancellation via generalized Green-Schwarz mechanisms.
• The model predicts observable Kaluza-Klein excitations of gauge bosons and gravitons, with signals in missing energy, precision data, and collider searches, constraining the string scale and extra dimensions.