A Note on Derived Geometric Interpretation of Classical Field Theories

In this note, we would like to provide a conceptional introduction to the interaction between derived geometry and physics based on the formalism that has been heavily studied by Kevin Costello. Main motivations of our current attempt are as follows: (i) to provide a brief introduction to derived algebraic geometry, which can be, roughly speaking, thought of as a higher categorical refinement of an ordinary algebraic geometry, (ii) to understand how certain derived objects naturally appear in a theory describing a particular physical phenomenon and give rise to a formal mathematical treatment, such as redefining a perturbative classical field theory (or its quantum counterpart) by using the language of derived algebraic geometry, and (iii) how the notion of factorization algebra together with certain higher categorical structures come into play to encode the structure of so-called observables in those theories by employing certain cohomological/homotopical methods. Adopting such a heavy and relatively enriched language allows us to formalize the notion of quantization and observables in quantum field theory as well.Comment: 14 pages. This note serves as an introductory survey on certain mathematical structures encoding the essence of Costello's approach to derived-geometric formulation of field theories and the structure of observables in an expository manne

Sheaves and schemes: an introduction to algebraic geometry

Master of ScienceDepartment of MathematicsRoman FedorovThe purpose of this report is to serve as an introduction to the language of sheaves and schemes via algebraic geometry. The main objective is to use examples from algebraic geometry to motivate the utility of the perspective from sheaf and scheme theory. Basic facts and definitions will be provided, and a categorical approach will be frequently incorporated when appropriate

A Higher-Order Calculus for Categories

A calculus for a fragment of category theory is presented. The types in the language denote categories and the expressions functors. The judgements of the calculus systematise categorical arguments such as: an expression is functorial in its free variables; two expressions are naturally isomorphic in their free variables. There are special binders for limits and more general ends. The rules for limits and ends support an algebraic manipulation of universal constructions as opposed to a more traditional diagrammatic approach. Duality within the calculus and applications in proving continuity are discussed with examples. The calculus gives a basis for mechanising a theory of categories in a generic theorem prover like Isabelle

Algebraic groups in non-commutative probability theory revisited

The role of coalgebras as well as algebraic groups in non-commutative probability has long been advocated by the school of von Waldenfels and Sch\"urmann. Another algebraic approach was introduced more recently, based on shuffle and pre-Lie calculus, and resulting in another construction of groups of characters encoding the behaviour of states. Comparing the two, the first approach, recast recently in a general categorical language by Manzel and Sch\"urmann, can be seen as largely driven by the theory of universal products, whereas the second construction builds on Hopf algebras and a suitable algebraization of the combinatorics of noncrossing set partitions. Although both address the same phenomena, moving between the two viewpoints is not obvious. We present here an attempt to unify the two approaches by making explicit the Hopf algebraic connections between them. Our presentation, although relying largely on classical ideas as well as results closely related to Manzel and Sch\"urmann's aforementioned work, is nevertheless original on several points and fills a gap in the free probability literature. In particular, we systematically use the language and techniques of algebraic groups together with shuffle group techniques to prove that two notions of algebraic groups naturally associated with free, respectively Boolean and monotone, probability theories identify. We also obtain explicit formulas for various Hopf algebraic structures and detail arguments that had been left implicit in the literature.Comment: 24 page

On Multi-Language Semantics: Semantic Models, Equational Logic, and Abstract Interpretation of Multi-Language Code

Modern software development rarely takes place within a single programming language. Often, programmers appeal to cross-language interoperability. Benefits are two-fold: exploitation of novel features of one language within another, and cross-language code reuse. For instance, HTML, CSS, and JavaScript yield a form of interoperability, working in conjunction to render webpages. Some object oriented languages have interoperability via a virtual machine host (.NET CLI compliant languages in the Common Language Runtime, and JVM compliant languages in the Java Virtual Machine). A high-level language can interact with a lower level one (Apple's Swift and Objective-C). Whilst this approach enables developers to benefit from the strengths of each base language, it comes at the price of a lack of clarity of formal properties of the new multi-language, mainly semantic specifications. Developing such properties is a key focus of this thesis. Indeed, while there has been some research exploring the interoperability mechanisms, there is little development of theoretical foundations. In this thesis, we broaden the boundary functions-based approach à la Matthews and Findler to propose an algebraic framework that provides systematic and more general ways to define multi-languages, regardless of the inherent nature of the underlying languages. The aim of this strand of research is to overcome the lack of a formal model in which to design the combination of languages. Main contributions are an initial algebra semantics and a categorical semantics for multi-languages. We then give ways in which interoperability can be reasoned about using equations over the blended language. Formally, multi-language equational logic is defined, within which one may deduce valid equations starting from a collection of axioms that postulate properties of the combined language. Thus, we have the notion of a multi-language theory and part of the thesis is devoted to exploring the properties of these theories. This is accomplished by way of both universal algebra and category theory, giving us a very general and flexible semantics, and hence a wide collection of models. Classifying categories are constructed, and hence equational theories furnish each categorical model with an internal language. From this we establish soundness and completeness of the multi-language equational logic. As regards static analysis, the heterogeneity of the multi-language context opens up new and unexplored scenarios. In this thesis, we provide a general theory for the combination of abstract interpretations of existing languages in order to gain an abstract semantics of multi-language programs. As a part of this general theory, we show that formal properties of interest of multi-language abstractions (e.g., soundness and completeness) boil down to the features of the interoperability mechanism that binds the underlying languages together. We extend many of the standard concepts of abstract interpretation to the framework of multi-languages. Finally, a minor contribution of the thesis concerns language specification formalisms. We prove that longstanding syntactical transformations between context-free grammars and algebraic signatures give rise to adjoint equivalences that preserve the abstract syntax of the generated terms. Thus, we have methods to move from context-free languages to the algebraic signature formalisms employed in the thesis