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Understanding Orbifold TQFTs and Their Significance

A look into orbifolds and defect TQFTs in mathematics and physics.

― 6 min read


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In the world of mathematics, particularly in the study of topology and geometry, scientists explore the structure and properties of spaces. A significant area of focus is on understanding what happens when spaces exhibit symmetries or when they are constructed from simpler pieces. One concept that comes into play is that of an "orbifold," which can be thought of as a kind of space that has certain types of singularities or "corners." These spaces can arise naturally when considering the action of a group on a manifold.

Defect Topological Quantum Field Theories (TQFTS) are mathematical frameworks used to study quantum field theories with Defects, such as points or lines where the usual rules of the theory might break down or change. In simpler terms, these theories help us understand how quantum systems behave when they have imperfections or interruptions in their structure.

The Basics of TQFTs

At their core, TQFTs relate geometry and physics. They assign algebraic structures to topological spaces, which can help in calculating invariants-properties that remain unchanged under continuous deformations. For instance, in two-dimensional TQFTs, surfaces can be classified based on their shapes and characteristics, leading to powerful insights into the nature of these surfaces.

TQFTs can be thought of as functors, which are mathematical mappings that preserve certain structures, from a category of manifolds to a category of vector spaces. Essentially, they translate geometric questions into algebraic ones, allowing for computations that can reveal deep truths about the physical world.

What are Orbifolds?

Orbifolds are a type of space that generalizes the concept of a manifold. While a manifold is a space that looks "smooth" locally, an orbifold can have points that are not smooth, like a cone point, where the structure resembles a cone around that point. These singular points are essential when considering symmetries and can be useful in various applications, from string theory to algebraic geometry.

Orbifolds capture the idea of symmetry in a structured way. They are formed by taking a manifold and allowing a group of symmetries to act on it, leading to a more intricate structure that retains information about these symmetries. This makes orbifolds a valuable tool in modern mathematics and physics, particularly in understanding how spaces can be built from simpler parts.

The Role of Defects in TQFTs

In TQFTs, defects represent interruptions or alterations within a quantum field theory. They can take various forms, such as points (point defects), lines (line defects), or surfaces (surface defects). Each type of defect can impact the way the theory operates and yields new insights into the interactions and structures present in the quantum system.

Defect TQFTs extend the classical TQFT framework by incorporating these defects, providing a richer structure that reflects the complexities of real-world systems. By studying defect TQFTs, researchers can gain a better understanding of how defects influence physical systems, especially in high-energy physics and condensed matter systems.

Orbifold Completion in TQFTs

The process of orbifold completion can be seen as a way to lift a TQFT’s structure to include defects. This involves embedding the original theory into a more extensive framework that accounts for the presence of defects, leading to a new and enhanced theory.

In practical terms, this means that scientists can take a defect TQFT and understand it better by translating its properties into the language of orbifolds. This correspondence between orbifolds and defect TQFTs allows for a more profound investigation into the mathematical structures underpinning these theories.

Constructing Orbifold Data

To study orbifolds in the context of TQFTs, we need to construct what is known as orbifold data. This involves defining algebraic structures that encapsulate the properties of the orbifold and the interactions arising from the defects.

The construction of orbifold data typically requires understanding how different mathematical objects relate to one another within the orbifold structure. This includes defining Morphisms-maps between objects-that respect the orbifold's symmetries and properties.

These orbifold data serve as the building blocks for creating new TQFTs, providing a systematic way to incorporate defects and explore their consequences. When successful, this process leads to a better understanding of how quantum systems behave in the presence of various types of defects.

The Role of Categories in TQFTs

Categories are foundational structures in mathematics that help organize objects and their relationships systematically. In TQFTs and orbifold studies, categories serve a crucial role, enabling the formulation of advanced concepts and relationships between different mathematical entities.

The categorical framework allows for a clear representation of how morphisms behave between various spaces, including orbifolds and defects. This organization is essential for understanding the more complex interactions that occur within TQFTs, particularly as they relate to orbifolds.

Evaluating Orbifold TQFTs

When it comes to evaluating orbifold TQFTs, the process typically involves understanding how the theories interact with different geometric structures, including manifolds and stratified spaces. This evaluation helps determine how specific configurations influence the properties of the field theory.

One approach is to use triangulations of the spaces involved, breaking them down into simpler components that can be analyzed more easily. By labeling these components according to the orbifold data and evaluating how they interact, researchers can deduce important properties about the overall theory.

Applications of Orbifold TQFTs

Orbifold TQFTs have a wide range of applications in both mathematics and theoretical physics. They can help researchers understand complex phenomena in quantum physics, such as quantum gravity and string theory, by providing a structured way to analyze the properties of different systems.

Moreover, these theories can offer insights into topology, allowing mathematicians to classify and understand different types of spaces based on their structural features. The interplay between geometry and algebra in orbifold TQFTs leads to innovations in both fields.

Conclusion: The Future of Orbifold TQFTs

As the fields of mathematics and physics continue to evolve, the study of orbifolds and defect TQFTs remains a vibrant area of research. The interplay between geometry, algebra, and quantum theory presents numerous opportunities for discovery and exploration.

Researchers are likely to continue developing new techniques for understanding these complex structures, leading to advances in both theoretical frameworks and practical applications. The future promises to unveil new relationships and insights that can arise from the rich interplay between orbifolds and defect TQFTs.

As we continue to unravel the intricacies of these subjects, we may find new ways to apply their principles to real-world problems and deepen our understanding of the universe's fundamental nature. The journey through the fascinating landscape of orbifolds and defect TQFTs is just beginning, and their full potential has yet to be realized.

Original Source

Title: Orbifold completion of 3-categories

Abstract: We develop a general theory of 3-dimensional ``orbifold completion'', to describe (generalised) orbifolds of topological quantum field theories as well as all their defects. Given a semistrict 3-category $\mathcal{T}$ with adjoints for all 1- and 2-morphisms (more precisely, a Gray category with duals), we construct the 3-category $\mathcal{T}_{\textrm{orb}}$ as a Morita category of certain $E_1$-algebras in $\mathcal{T}$ which encode triangulation invariance. We prove that in $\mathcal{T}_{\textrm{orb}}$ again all 1- and 2-morphisms have adjoints, that it contains $\mathcal{T}$ as a full subcategory, and we argue, but do not prove, that it satisfies a universal property which implies $(\mathcal{T}_{\textrm{orb}})_{\textrm{orb}} \cong \mathcal{T}_{\textrm{orb}}$. This is a categorification of the work in [CR]. Orbifold completion by design allows us to lift the orbifold construction from closed TQFT to the much richer world of defect TQFTs. We illustrate this by constructing a universal 3-dimensional state sum model with all defects from first principles, and we explain how recent work on defects between Witt equivalent Reshetikhin--Turaev theories naturally appears as a special case of orbifold completion.

Authors: Nils Carqueville, Lukas Müller

Last Update: 2024-02-25 00:00:00

Language: English

Source URL: https://arxiv.org/abs/2307.06485

Source PDF: https://arxiv.org/pdf/2307.06485

Licence: https://creativecommons.org/licenses/by/4.0/

Changes: This summary was created with assistance from AI and may have inaccuracies. For accurate information, please refer to the original source documents linked here.

Thank you to arxiv for use of its open access interoperability.

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