Noncommutative differential geometry has many actual and potential applications to several domains in physics ranging from solid state to quantization of gravity. The strategy is to formulate usual differential geometry in a somewhat unusual manner, using in particular operator algebras and related concepts, so as to be able to plug in noncommutativity in a natural way. Algebraic tools such as K-theory and cyclic cohomology and homology play an important role in this field.

Noncommutative differential geometry is a novel approach to geometry, aimed in part at applications in physics. It was founded in the early eighties by the 1982 Fields Medalist Alain Connes on the basis of his fundamental works in operator algebras. It is now a very active branch of mathematics with actual and potential applications to a variety of domains in physics ranging from solid state to quantization of gravity. The strategy is to formulate usual differential geometry in a somewhat unusual manner, using in particular operator algebras and related concepts, so as to be able to plug in noncommutativity in a natural way. Algebraic tools such as K-theory and cyclic cohomology and homology play an important role in this field. It is an important topic both for mathematics and physics.

Noncommutative differential geometry is a novel approach to geometry, aimed in part at applications in physics. It was founded in the early eighties by the 1982 Fields Medalist Alain Connes on the basis of his fundamental works in operator algebras. It is now a very active branch of mathematics with actual and potential applications to a variety of domains in physics ranging from solid state to quantization of gravity. The strategy is to formulate usual differential geometry in a somewhat unusual manner, using in particular operator algebras and related concepts, so as to be able to plug in noncommutativity in a natural way. Algebraic tools such as K-theory and cyclic cohomology and homology play an important role in this field. It is an important topic both for mathematics and physics.

In this work the question whether noncommutative geometry allows for supersymmetric theories is addressed. Noncommutative geometry has seen remarkable applications in high energy physics, viz. the geometrical interpretation of the Standard Model, however such a question has not been answered in a conclusive way so far.The book starts with a systematic analysis of the possibilities for so-called almost-commutative geometries on a 4-dimensional, flat background to exhibit not only a particle content that is eligible for supersymmetry, but also have a supersymmetric action. An approach is proposed in which the basic `building blocks' of potentially supersymmetric theories and the demands for their action to be supersymmetric are identified. It is then described how a novel kind of soft supersymmetry breaking Lagrangian arises naturally from the spectral action. Finally, the above formalism is applied to explore the existence of a noncommutative version of the minimal supersymmetric Standard Model.This book is intended for mathematical/theoretical physicists with an interest in the applications of noncommutative geometry to supersymmetric field theories.

The work of Alain Connes has cut a wide swath across several areas of mathematics and physics. Reflecting its broad spectrum and profound impact on the contemporary mathematical landscape, this collection of articles covers a wealth of topics at the forefront of research in operator algebras, analysis, noncommutative geometry, topology, number theory and physics. Specific themes covered by the articles are as follows: entropy in operator algebras, regular $C^*$-algebras of integral domains, properly infinite $C^*$-algebras, representations of free groups and 1-cohomology, Leibniz seminorms and quantum metric spaces; von Neumann algebras, fundamental Group of $\mathrm{II}_1$ factors, subfactors and planar algebras; Baum-Connes conjecture and property T, equivariant K-homology, Hermitian K-theory; cyclic cohomology, local index formula and twisted spectral triples, tangent groupoid and the index theorem; noncommutative geometry and space-time, spectral action principle, quantum gravity, noncommutative ADHM and instantons, non-compact spectral triples of finite volume, noncommutative coordinate algebras; Hopf algebras, Vinberg algebras, renormalization and combinatorics, motivic renormalization and singularities; cyclotomy and analytic geometry over $F_1$, quantum modular forms; differential K-theory, cyclic theory and S-cohomology.

Alain Connes a découvert une approche algébrique à la géométrie en remplaçant la géométrie Riemannienne de spin ordinaire par des triplets spectraux. Un triplet spectral est un ensemble avec trois membres : une algèbre, un opérateur de Dirac et un espace de Hilbert. Toutes les informations géométriques de la variété sont codées dans les triplets spectraux. Une qualité nouvelle de cette reformulation est la possibilité d'inclure des espaces non commutatifs. Ils sont représentés par des algèbres non commutatives, alors que les espaces ordinaires sont codés par des algèbres commutatives. Il est maintenant possible de rendre les algèbres commutatives, qui représentent l'espace-temps, un petit peu non commutatives, en prenant le produit tensoriel avec une somme d'algèbres matricielles. Alain Connes et Ali Chamseddine ont découvert que, pour un certain choix d'algèbre matricielle, on obtient la relativité générale et la théorie de champ classique du modèle standard de la physique des particules. Les géométries presque-commutatifs offrent aussi une interprétation naturelle pour le boson de Higgs comme connexion dans la partie non commutative de la géométrie. Chaque triplet spectral presque-commutatif représente un modèle de Yang-Mills-Higgs et peut être un canditat potentiel pour une théorie physique. Dans cette thèse doctorale des restrictions physiques supplémentaires seront imposées sur les triplets spectraux, par exemple que les masses des fermions soient non-dégénérées et que la théorie soir renormalisable. A partir de ces principes fondamentaux tous les triplets spectraux presque-commutatifs ont été classifiés en collaboration avec les professeurs Thomas Schücker et Bruno Iochum, et avec Jan-Hendrik Jureit. Il est surprenant que le modèle standard de la physique des particules occupe une position proéminente dans cette classification. La question de savoir s'il y a des modèles physiques avec plus de quatre algèbres reste ouverte.