I am a postdoc in the topology group of the Institute for Algebra and Geometry at KIT. My mathematical interests range around algebraic topology and L²invariants in geometry and group theory. I am member of the Priority Program 2026 "Geometry at Infinity" and of the RTG 2229 "Asymptotic Invariants and Limits of Groups and Spaces". Here you can find slides of a talk on "The construction of the regular 65.537gon with compass and straightedge" at the Day of Mathematics 2019 (in German).
Dr. Holger Kammeyer 

Office Hours: nach Vereinbarung Room: 1.007 Phone: +49 (0) 721 60843707 Fax: +49 (0) 721 60842148 holger kammeyer ∂kit edu 
Karlsruher Institut für Technologie MATH  IAG  AG Topologie Englerstr. 2  Mathebau (20.30) 76131 Karlsruhe 
Introduction to ℓ²invariants
An uptodate and userfriendly introduction to the rapidly developing field of ℓ ²invariants.
Title  Publisher  Year 

Algebraic Topology I  2016 
Title  Coauthors  Year 

Products of free groups in Lie groups  Caterina Campagnolo 
2020 
Profinite invariants of arithmetic groups  Steffen Kionke, Jean Raimbault, Roman Sauer 
2019 
Profinite commensurability of Sarithmetic groups   
2018 
A remark on torsion growth in homology and volume of 3manifolds   
2018 
Title  Coauthors  Journal 

Sarithmetic spinor groups with the same finite quotients and distinct L²cohomology  Roman Sauer 
to appear in Groups, Geometry, and Dynamics. 
The shrinkage type of knots   
Bull. Lond. Math. Soc., 493 (2017), 428–442 
Approximating NovikovShubin numbers of virtually cyclic coverings   
Groups, Geometry, and Dynamics, 114 (2017), 1231–1251 
The FarrellJones conjecture for arbitrary lattices in virtually connected Lie groups  Wolfgang Lück, Henrik Rüping 
Geometry & Topology,
203 (2016), 12751287 
L²invariants of nonuniform lattices in semisimple Lie groups   
Algebraic & Geometric Topology, 14 (2014), 24752509 
An explicit rational structure for real semisimple Lie algebras   
Journal of Lie Theory, 24, No. 2 (2014), 307319 
Title  Coauthors  Journal 

From Betti numbers to L²Betti numbers  Roman Sauer 
to appear in Oberwolfach Snapshots of Modern Mathematics 
The HestonHullWhite Model I: Finance and Analytics  Jörg Kienitz 
Wilmott Magazine, 
Title  Type, University 

L²invariants of nonuniform lattices in semisimple Lie groups  doctoral thesis, University of Göttingen 
On Exotic Manifolds  diploma thesis, University of Göttingen 
Upcoming
 RTGColloquium
Talk: "Profinite properties of lattices in Lie groups"
February 2020, Göttingen  Manifolds and groups
February 2020, Oberwolfach  Arithmetic groups and 3manifolds
March 2020, Hagen
Past
 L2torsion and symmetric spaces
October 2019, Göttingen  Workshop: Riemannian and Simplicial Volume
April 2019, Karlsruhe  SPP Conference "Geometry at Infinity"
April 2019, Münster  SFB Vorlesung
Talk: "Profinite invariants of arithmetic groups"
November 2018, Regensburg  Growth in Topology and Number Theory: Volume, Entropy, and L2torsion
Talk: "Profiniteness questions for L2Betti numbers of Sarithmetic groups"
July 2018, Bonn  L2invariants and their analogues in positive characteristic
Talk: "Profiniteness questions for L2Betti numbers of Sarithmetic groups"
June 2018, Madrid, Spain  Joint annual convention GDMV 2018
Talk: "Profinite commensurability of Sarithmetic groups"
March 2018, Paderborn  Nacht der Wissenschaft (Night of Science)
Talk: "Die Konstruktion des regelmäßigen 65.537Ecks mit Zirkel und Lineal"
November 2017, Karlsruhe  Manifolds and groups
Talk: "Cyclic knot coverings and transcendental numbers"
September 2017, Regensburg  Summer school on "Growth in geometry and topology"
Mini course: "Intro to L2Betti numbers / L2torsion and torsion growth in homology"
August 2017, Les Diablerets, Switzerland  Group actions and cohomology in nonpositive curvature
June 2017, Cambridge, UK  Groups, manifolds and Ktheory
June 2017, Münster  Oberseminar Topologie
Talk: "Secondary L2invariants of groups and knots"
May 2017, Münster  Compactifications of Buildings and Symmetric Spaces
May 2017, Heidelberg  School on Arithmetic groups
March 2017, Ein Gedi, Israel  Asymptotic geometry of groups and spaces
February 2017, Heidelberg  New directions in L2invariants
October 2016, Bonn  Oberseminar Topologie
Talk:"L²invariants of groups and knots"
September 2016, Bonn  Geometry Day
April 2016, Strasbourg, France  Young Geometric Group Theory
February 2016, Karlsruhe  Oberseminar Global Anlaysis
Talk: "Approximating NovikovShubin numbers along finite coverings"
January 2016, Regensburg  Geometry day
Talk: "The FarrellJones conjecture and lattices in Lie groups"
October 2015, Heidelberg  Topology Retreat
Talk: "Introduction to L²torsion"
September 2015, Bedlewo, Poland  Manifolds and Groups
September 2015, Ventotene, Italy  Oberseminar Topologie
Talk: "L²invariants and approximation along finite coverings"
June 2015, Münster  Followup workshop to trimester program "Rigidity"
April 2015, Bonn  AGSeminar Topologie
Talk: "Local rigidity and the FarrellJones conjecture"
February 2015, Karlsruhe  Workshop "Geometric Topology"
January 2015, Oberwolfach  Workshop "Topologie"
Short talk: "The FarrellJones conjecture for lattices in Lie groups"
September 2014, Oberwolfach  Oberseminar Differentialgeometrie
Talk: "Local rigidity and the FarrellJones conjecture"
June 2014, Augsburg  Seminario de Topología Algebraica
Talk: "Rigidez local y la conjetura de FarrellJones"
May 2014, Morelia, Mexico  Arbeitsgemeinschaft "Superrigidity"
Talk: "Factor theorems for lattices in products of groups (BaderShalom)"
March/April 2014, Oberwolfach  GKKolloquium Regensburg
Talk: "L²invariants and groups"
October 2013, Regensburg  Oberseminar Regensburg
Talk: "NovikovShubin numbers of arithmetic groups"
October 2013, Regensburg  Oberseminar Topologie
Talk: "L²invariants of nonuniform lattices in semisimple Lie groups"
October 2013, Bonn  Geometry, Groups and Topology
October 2013, Karlsruhe  Summer School: Topology of highdimensional manifolds
August 2013, Bonn  Von Neumann Algebras and Measurable Group Theory
July 2013, Leuven, Belgium  Operator Algebra Seminar
Talk: "On L²invariants of lattices in semisimple Lie groups"
January 2013, Copenhagen, Denmark  Topology Seminar
Talk: "On L²invariants of lattices in semisimple Lie groups"
October 2012, Karlsruhe  Workshop "Topologie"
Short talk: "On L²invariants of lattices in semisimple Lie groups"
September 2012, Oberwolfach  Topology and Groups
June 2012, Berlin  Young Topologists Meeting
Talk: "Compactifications of locally symmetric spaces"
June 2011, Lausanne, Switzerland  Von Neumann algebras and ergodic theory of group actions
April 2011, CIRM Marseille, France  Symplectic and Poisson Geometry in interaction with Algebra, Analysis and Topology
May 2010, MSRI Berkeley, California  Many cheerful facts
Talk: "Fair and unfair prices of financial derivatives"
April 2010, Berkeley, California  Eighth Annual Graduate Student Topology and Geometry Conference
February 2010, Ann Arbor, Michigan  First National Forum of Young Topologists
November 2009, New Orleans, Louisiana  Young Topologists Meeting
Talk: "Classification of 3sphere bundles over the 4sphere (CrowleyEscher)"
May 2009, Le Châtelard, Switzerland
Conference: Arithmetic groups and 3manifolds
Venue:  In:  Hagen, Germany 


Date:  March, 23rd  27th, 2020 
Links:  website 
Workshop "New directions in L2invariants"
Venue:  Hausdorff Research Institute for Mathematics 
Place:  Bonn 

Date:  10/04  10/07/2016 
Links:  website 
Junior Trimester Program "Topology"
Name:  Working group "L2Invariants" Joint with G. Herrmann, A. Kar, S. Kionke und J. Raimbault. 
Links:  website 

Venue:  
Summer term 2020
 Lecture "Algebraic Topology" Thu 02:0003:30 pm, 1.012 UG, Fr 09:4511:15 am, 1.025 UG
 Seminar "Representation theory of finite groups" block seminar
 RG Seminar "Topology" Thu 03:4505:15 pm, SR 2.059 (20.30)
Winter term 2019/2020
RGSeminar "Topology" Thu 03:4505:15 pm, SR 2.059 (20.30)
Summer term 2019
 Exercise class for Linear Algebra II Fr 02:00  03:30 pm, FritzHallerHörsaal
 RGSeminar "Topology" Fr 09:4511:15 am, Raum 2.059 (20.30)
Winter term 2018/2019
 Exercise class for Linear Algebra and Analytic Geometry I Mon 03:45  05:15 pm, CarlBenzHörsaal
 RGSeminar "Topology" Thu 03:4505:15 pm, 2.058 (20.30)
 Workshop on current developments around the Atiyah conjecture 19.11.18  21.11.18
Summer term 2018
 Seminar "Projective Geometry" block course 07/23  07/25/2018, SR 0.016 (20.30) seminar announcement
 RGSeminar "Topology" Thu 03:4505:15 pm, 2.059 (20.30)
Winter term 2017/2018
 Lecture "Mathematics for Natural Sciences" Tue 08:0009:30 am, Fr 08:4509:30 am, 30.46 Chemie Neuer Hörsaal
 RGSeminar "Topology" Thu 03:4505:15 pm, 2.058 (20.30)
Summer term 2017
 Seminar: "Differential topology" Thu 09:4511:15 am, 1.009(UG) (20.30) seminar announcement
 Proseminar: "Proofs from THE BOOK" Thu 02:0003:30 pm, 2.059 (20.30) proseminar announcement
 RGSeminar "Arithmetic hyperbolic 3manifolds" Thu 03:4505:15 pm 2.059 (20.30) seminar announcement
Winter term 2016/2017
No teaching due to scientific stay in Bonn.
Summer term 2016
 Lecture "Algebraic Topology" Tue 11:30 am01:00 pm, 2.058 (20.30), Thu 11:30 am01:00 pm, 0.014 (20.30)
 Tutorial "Algebraic Topology" Wed 05:3007:00 pm, 2.059 (20.30)
tutor: Jakob Albers  RGSeminar "Topology" Thu 02:0003:30pm, 2.058 (20.30)
Winter term 2015/2016
 Lecture "L²invariants" Thu 03:4505:15 pm, room 2.058 (20.30)
 Problem class "L²invariants" Mon 02:0003:30 pm, room 2.059 (20.30)
Teaching assistant: Sabine Braun; Starts 10/26/2015  RG Seminar "Topology" Thu 05:3007:00 pm, room 2.058 (20.30)
More information on the lecture "L²invariants" is given in the course announcement.
Summer term 2015
 Exercise class: "Algebraic Topology" Fri 11:3001:00 pm, room 2.059 (20.30)
 Seminar: "Projektive Geometrie" Thu 05:3007:00 pm, room 3.060 (20.30)
 RG Seminar: "Topology" Thu 02:0003:30 pm, room 2.058 (20.30)
Past teaching
 Oberseminar: Lattices in Semisimple Lie Groups (with JeanFrançois Planchat, winter 2011/2012).
Title  Type  Student 

The Lefschetz fixed point theorem: from simplicial to CW complexes  Masterarbeit  Gotami Heller 
Homologies and elations in the projective and Euclidean plane  Bachelorarbeit  Cédric Dujardin 
L2Betti numbers and profinite completions of groups  Master thesis  Nico Stucki 
Construction of Thom spectra for bordism with Gstructure  Bachelor thesis  Amelie Flatt 
Since April 2015  Postdoc at Institute for Algebra and Geometry (working with Roman Sauer) 
Karlsruhe Institute of Technology 
July 2013  March 2015  Postdoc at Mathematical Institute (working with Wolfgang Lück) 
University of Bonn 
July 2010  May 2013  Doctoral studies at Mathematical Institute (working with Thomas Schick) 
University of Göttingen 
August 2009  June 2010  Fulbright scholar at Department of Mathematics  University of California Berkeley 
July 2008  October 2008  Internship in team "Quantitative Analysis"  Deutsche Postbank, Bonn 
October 2004  July 2009  Diploma studies in mathematics with minor theoretical physics  University of Göttingen 