Overview of "Lectures on the Swampland Program in String Compactifications"
The document titled "Lectures on the Swampland Program in String Compactifications" provides an extensive coverage of the Swampland program, a key area of research in theoretical physics that deals with effective field theories (EFTs) and their viability when embedded in a consistent theory of quantum gravity such as string theory. The paper serves as a detailed pedagogical guide on various Swampland conjectures, exploring their significance, implications, and the connections between them.
Introduction
The authors begin by positing the Swampland program's goal: identifying which EFTs can be consistently included in a quantum gravity framework. The program emphasizes that certain phenomena allowed in effective field theories, such as global symmetries, are disallowed when considering quantum gravity theories, aligning with the hypothesized constraints of the Swampland program.
Swampland Conjectures
Key conjectures within the Swampland program are articulated in detail:
- No Global Symmetries Conjecture posits that quantum gravity does not permit exact global symmetries, which has implications for phenomenology and has been supported by various string theoretical and holographical evidence.
- Completeness Hypothesis states that all gauge charges must be realized by physical states, with numerous implications for the structure of possible gauge groups and the nature of dualities in string theory.
- Weak Gravity Conjecture (WGC) introduces the notion that gravity should be the weakest force. This conjecture is explored in various contexts including black hole physics and its implications for gauge theories; it suggests that certain charged states must exist within any given EFT.
- Distance Conjecture suggests that as one moves towards infinite boundaries in moduli space, there exists a tower of light states that constrains large field ranges in field space, providing critical insights into string dualities and geometrical structures of moduli spaces.
Implications for Cosmology and Phenomenology
The paper discusses the impact of these conjectures on cosmology, particularly focusing on the Swampland's constraints on inflationary models. For instance, the WGC's implications for axion models pose significant challenges to large-field inflation scenarios, suggesting a failure in accommodating trans-Planckian field excursions in quantum gravity.
Moreover, the Distance Conjecture and its implications for scalar field variations highlight limitations in EFTs when attempting to describe cosmological phenomena such as quintessence or de Sitter solutions, often proposing a "runaway" as a generic feature at the moduli space's boundaries.
Swampland Distance Conjecture and Emergence Proposal
The Swampland Distance Conjecture is further explored with evidence from string compactifications revealing how light towers of states manifest in various moduli spaces, reinforcing the interplay between quantum gravity and low-energy EFTs. This section is linked to the Emergence Proposal which hypothesizes that kinetic terms in effective theories emerge from integrating out massive fields, intimating at a unified description at higher energy scales.
No Non-Susy Stable AdS Conjecture
One of the innovative discussions is on the instability of non-supersymmetric AdS vacua, which postulates that these vacua are inherently unstable in quantum gravity. This conjecture ties into the Weak Gravity Conjecture, offering decay channels that potentially destabilize such vacua, harking at broader ramifications for non-supersymmetric constructions in string theory.
The authors encapsulate the essence of the Swampland program as a series of interrelated conjectures that collectively challenge the conventional lore in effective field theory by incorporating quantum gravitational effects. These conjectures influence theoretical constructs significantly, presenting constraints that refine the landscape of plausible effective theories in string theory.
This pedagogical review functions not only as a primer into the Swampland program but as a springboard for ongoing research endeavors aimed at resolving outstanding conjectures through a quantum gravity lens. As such, "Lectures on the Swampland Program in String Compactifications" serves as an essential contribution to the literature, providing both a comprehensive overview and a launchpad for further inquiry.