Biannual Report Department of Mathematics 2017 and 2018 On the cover page the velocity and pressure profile in the vicinity of one opening of a perfo- rated wall within a visco-acoustic model is illustrated. It is obtained in the project "Impedance conditions for visco-acoustic models" (see page 65). Dear reader, this biannual report provides a comprehensive overview of the research and teaching ac- tivities at the Department of Mathematics at TU Darmstadt during the years 2017 and 2018. A characteristic of our department is the broad area of topics that are covered both in re- search and teaching. This is, for instance, reflected by the organization into eight diverse working groups: Algebra, Analysis, Applied Geometry, Didactics and Pedagogics of Mathe- matics, Logic, Numerical Analysis and Scientific Computing, Optimization and Stochastics. The research activities are demonstrated by several joint research endeavors like Collabo- rative Research Centers, Graduate Schools, LOEWE centers, and, last but not least, a large number of personal contacts. In particular, inter-disciplinary work, for instance in coop- eration with mechanical and electrical engineering, is one of the main pillars of research at our department. We are also very well connected to other research groups – at the TU Darmstadt, in the Rhein-Main-Neckar area, within Germany, and far beyond. As such, our department is one of the largest and strongest departments of mathematics in Germany. The wealth of research areas is also represented in the different teaching activities. On the one hand, we provide several well established degrees in mathematics and additionally the new English master in mathematics. On the other hand, our department offers a significant number of courses for thousands of students in each semester, mostly coming from other departments at the TU Darmstadt. In all of the these courses, we are dedicated to excellent and innovative teaching. The present report is meant to provide information about all research and teaching activi- ties, about publications and prizes, presentations and events, from every single graduation thesis to our activities for high schools, and many other details that taken together rep- resent our work in the last two years. We hope that this report forms an interesting and enjoyable reading experience. With kind regards, Prof. Dr. Marc Pfetsch (Dean of the department) Contents 1 Research Groups 4 1.1 Algebra . .4 1.2 Analysis . .9 1.3 Applied Geometry . 30 1.4 Didactics and Pedagogics of Mathematics . 33 1.5 Logic . 47 1.6 Numerical Analysis and Scientific Computing . 50 1.7 Optimization . 73 1.8 Stochastics . 95 2 Collaborative Research Projects and Cooperations 104 2.1 Collaborative Research Centre SFB 666 . 104 2.2 Collaborative Research Centre SFB 805 . 105 2.3 Collaborative Research Centre SFB 1194 . 105 2.4 Collaborative Research Centre Transregio TRR 146 . 106 2.5 Collaborative Research Centre Transregio TRR 154 . 107 2.6 Graduate School of Computational Engineering . 107 2.7 Graduate School of Energy Science and Engineering . 108 2.8 International Research Training Group IRTG 1529 . 109 2.9 Priority Programme SPP 1740 . 109 2.10 Priority Programme SPP 1962 . 110 2.11 Research Unit Symmetry, Geometry, and Arithmetic . 110 2.12 LOEWE Research Unit USAG: Uniformized Structures in Arithmetic and Ge- ometry . 111 2.13 Scientific and Industrial Cooperations . 111 3 Teaching 124 3.1 Degree Programmes in Mathematics . 124 3.2 Teaching for Other Departments . 127 3.3 Characteristics in Teaching . 128 3.4 E-Learning/E-Teaching in Academic Training . 129 3.5 Career-related Activities . 131 4 Publications 133 4.1 Co-Editors of Publications . 133 4.1.1 Editors of Journals . 133 4.1.2 Editors of Proceedings . 135 4.2 Monographs and Books . 136 4.3 Publications in Journals and Proceedings . 136 4.3.1 Journals . 136 4.3.2 Proceedings and Chapters in Collections . 148 4.4 Preprints . 154 4.5 Reviewing and Refereeing . 161 2 Contents 4.6 Software . 166 5 Theses 169 5.1 Habilitations . 169 5.2 PhD Dissertations . 169 5.3 Master Theses . 171 5.4 Staatsexamen Theses . 179 5.5 Bachelor Theses . 180 6 Presentations 188 6.1 Talks and Visits . 188 6.1.1 Invited Talks and Addresses . 188 6.1.2 Contributed Talks . 210 6.1.3 Visits . 232 6.2 Organization and Program Commitees of Conferences and Workshops . 237 7 Workshops and Visitors at the Department 241 7.1 The Colloquium . 241 7.2 Guest Talks at the Department . 245 7.3 Visitors at the Department . 254 7.4 Workshops and Conferences at the Department . 259 8 Other scientific and organisational activities 262 8.1 Memberships in Scientific Boards and Committees . 262 8.2 Awards and Offers . 264 8.3 Secondary Schools and Public Relations . 264 8.4 Student Body (Fachschaft) . 267 9 Contact 269 Contents 3 1 Research Groups This section gives a brief overview of the research done in the eight research groups. 1.1 Algebra The main research areas of this group are algebraic geometry, number theory and confor- mal field theory. We are interested in Shimura varieties and automorphic forms and their applications in geometry and arithmetic. For example we investigate intersection and height pairings of special algebraic cycles on Shimura varieties and their connection to automorphic L- functions. We also study the relation between the representation theory of conformal field theories and automorphic forms. Members of the research group Professors Jan Hendrik Bruinier, Yingkun Li, Anna von Pippich, Nils Scheithauer, Torsten Wed- horn Retired professors Karl-Heinrich Hofmann Postdocs Moritz Dittmann, Jolanta Marzec, Michalis Neururer, Brandon Williams Research Associates Patrick Bieker, Johannes Buck, Timo Henkel, Jens Hesse, Patrick Holzer, Paul Kiefer, David Klein, Jennifer Kupka, Priyanka Majumder, Sebastian Opitz, Maxim- ilian Rössler, Thomas Spittler, Fabian Völz Secretaries Ute Fahrholz, Anja Spangenberg Project: Regularized theta lifts In this project we study regularized theta lifts of harmonic Maass forms and meromorphic modular forms. The Shimura correspondence connects modular forms of integral weights and half-integral weights. One of the directions is realized by the Shintani lift, where the inputs are holo- morphic differentials and the outputs are holomorphic modular forms of half-integral weight. In joint work with Funke, Imamoglu and Li, we generalize this lift to meromor- phic differentials of the third kind on modular and Shimura curves. As an application we obtain a modularity result concerning the generating series of winding numbers of closed geodesics on modular curves. In joint work with M. Schwagenscheidt we express the coefficients of mock theta functions of weight 1=2 and 3=2 in terms of traces of certain weakly holomorphic modular forms of weight 0 for Γ0(N). As an application we obtain rationality results for these coefficients and explicit formulas for Weyl vectors of Borcherds products. Partner: J. Funke, Durham University; O. Imamoglu, ETH Zürich; Y. Li, TU Darmstadt Support: DFG 4 1 Research Groups Contact: J. H. Bruinier, Y. Li, M. Schwagenscheidt References [1] C. Alfes-Neumann and M. Schwagenscheidt. On a theta lift related to the Shintani lift. Ad- vances in Mathematics, 328:858–889, 2018. [2] J. H. Bruinier, J. Funke, and O. Imamoglu. Regularized theta liftings and periods of modular functions. Journal für die reine und angewandte Mathematik, 703:43–93, 2015. [3] J. H. Bruinier, J. Funke, O. Imamoglu,¯ and Y. Li. Modularity of generating series of winding numbers. Research in the Mathematical Sciences, 5:23pp., 2018. [4] J. H. Bruinier and M. Schwagenscheidt. Algebraic formulas for the coefficients of mock theta functions and Weyl vectors of Borcherds products. Journal of Algebra, 478:38–57, 2017. Project: Arithmetic intersection theory on Shimura varieties We study special cycles on integral models of Shimura varieties associated with unitary similitude groups of signature (n 1, 1). In joint work with Howard and Yang we construct an arithmetic theta lift from harmonic− Maass forms of weight 2 n to the first arithmetic Chow group of a toroidal compactification of the integral model− of the unitary Shimura variety, by associating to a harmonic Maass form f a suitable linear combination of Kudla- Rapoport divisors, equipped with the Green function given by the regularized theta lift of f . Our main result expresses the height pairing of this arithmetic Kudla-Rapoport divisor with a CM cycle in terms of a Rankin-Selberg convolution L-function of the cusp form of weight n corresponding to f and the theta function of a positive definite hermitian lattice of rank n 1. The proof relies on a new method for computing improper arithmetic inter- sections (among− other things). In more recent work with Howard, Kudla, Rapoport, and Yang we prove that the gener- ating series of arithmetic Kudla Rapoport divisors is an elliptic modular form of weight n with values in the arithmetic Chow group. This can be used to define an arithmetic theta lift from weight n cusp forms to the arithmetic Chow group. As applications, one obtains Gross-Zagier type formulas for heights of CM cycles in this setting as well as a proof of the Colmez conjecture in cases where the CM field is the compositum of a totally real field and an imaginary quadratic field. Partner: B. Howard, Boston College; S. Kudla, University of Toronto; M. Rapoport, Uni- versität Bonn; T. Yang, University of Wisconsin at Madison Support: DFG, NSF, AIM Contact: J. H. Bruinier, Y. Li References [1] J. H. Bruinier, B. Howard, S. Kudla, M. Rapoport, and T. Yang. Modularity of generating series of divisors on unitary Shimura varieties. Preprint, 2017. [2] J. H. Bruinier, B. Howard, S. Kudla, M. Rapoport, and T. Yang. Modularity of generating series of divisors on unitary Shimura varieties II: arithmetic applications. Preprint, 2017. [3] J.