# Noncommutative Geometry

## Friday, October 11, 2019

### Sir Michael Atiyah, a Knight Mathematician. A Tribute to Michael Atiyah, an Inspiration and a Friend. By Alain Connes and Joseph Kouneiher

Sir Michael Atiyah was considered one of the world’s foremost mathematicians. He is best known for his work in
algebraic topology and the codevelopment of a branch of
mathematics called topological 𝐾-theory, together with
the Atiyah–Singer index theorem, for which he received
the Fields Medal (1966). He also received the Abel Prize
(2004) along with Isadore M. Singer for their discovery and
proof of the index theorem, bringing together topology,
geometry, and analysis, and for their outstanding role in
building new bridges between mathematics and theoretical physics. Indeed, his work has helped theoretical physicists to advance their understanding of quantum field theory and general relativity. (Continued here.)

## Monday, September 16, 2019

### Jami Workshop: Riemann-Roch in characteristic one and related topics

The Johns Hopkins Mathematics Department jointly with the Japan-U.S. Mathematics

Institute (JAMI) plan to organize a workshop on the weekend of October 18-20 2019.

The interactions between the fields of noncommutative arithmetic geometry, tropical geometry, the theory of toposes and mathematical logic, optimization and game theory have matured quite rapidly in the last few years and have produced very exciting results.

The goal of the workshop is thus that of coordinating these diverse research areas and with a common aim that is deeply related to the Riemann Hypothesis (RH).

The Noncommutative Geometry approach to RH has unveiled the exotic nature of the adele class space of the rationals, based on the theory of Grothendieck toposes on one hand and tropical geometry on the other. The search of a suitable Riemann-Roch formula on the square of the Scaling Site seems to require the development of algebraic geometry in characteristic one and of refinements of the tropical Riemann-Roch theory as developed so far and its connections to game and potential theory.

On the other hand, the theory of Segal's Gamma-rings provides a natural extension of the theory of rings and of semirings: the clear advantage of working with Gamma-rings is that this category forms the natural groundwork where cyclic homology is rooted (this means that de Rham theory is here naturally available). In fact, much more holds, since the simplicial version of modules over Gamma-rings (ie the natural set-up for homological algebra in this context) forms the core of the local structure of algebraic K-theory. In arithmetic geometry, the new Gamma-ring arising as the stalk of the structure sheaf of the Arakelov compactification of Spec

The goal of the workshop is thus that of coordinating these diverse research areas and with a common aim that is deeply related to the Riemann Hypothesis (RH).

The Noncommutative Geometry approach to RH has unveiled the exotic nature of the adele class space of the rationals, based on the theory of Grothendieck toposes on one hand and tropical geometry on the other. The search of a suitable Riemann-Roch formula on the square of the Scaling Site seems to require the development of algebraic geometry in characteristic one and of refinements of the tropical Riemann-Roch theory as developed so far and its connections to game and potential theory.

On the other hand, the theory of Segal's Gamma-rings provides a natural extension of the theory of rings and of semirings: the clear advantage of working with Gamma-rings is that this category forms the natural groundwork where cyclic homology is rooted (this means that de Rham theory is here naturally available). In fact, much more holds, since the simplicial version of modules over Gamma-rings (ie the natural set-up for homological algebra in this context) forms the core of the local structure of algebraic K-theory. In arithmetic geometry, the new Gamma-ring arising as the stalk of the structure sheaf of the Arakelov compactification of Spec

**Z**at the archimedean place, is intimately related to hyperbolic geometry and the Gromov norm. The theory of Gamma-rings in fact culminates with the development of a new theory of**ABSOLUTE ALGEBRAIC GEOMETRY**
All these developments are thus part of a general program for a workshop that brings together researchers from these different fields.

K. Consani

## Tuesday, April 9, 2019

## Monday, April 8, 2019

## Tuesday, January 22, 2019

## Friday, January 18, 2019

### for a dead friend

It is not surprising that all the honourable men who are manning (what else) this blog did not find it proper to comment on the passing of Sir Michael Atiyah, so I am offering a link to my own:

https://listeningtogolem.blogspot.com/2019/01/the-polar-star-and-life-endgame-elegy.html

https://listeningtogolem.blogspot.com/2019/01/the-polar-star-and-life-endgame-elegy.html

## Friday, August 3, 2018

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