Overview

Welcome! This is the page of the Particle Cosmology Münster research group at the Institute for Theoretical Physics. The research group was established in May 2022 and is headed by Kai Schmitz, a newly appointed junior professor in the Physics Department at the University of Münster. The group deals with research topics at the interface of particle physics and cosmology, notably gravitational waves from the early Universe, and is involved in the activities of the NANOGrav Pulsar Timing Array Collaboration. On this page, you will find more information on the following topics ...

• Contents

  • Contact
  • Members
  • Research
  • Teaching
  • Publications

Contact

Prof. Dr. Kai Schmitz
Research group leader
University of Münster
Institute for Theoretical Physics

Room 314
Wilhelm-Klemm-Str. 9
48149 Münster
Germany

T: +49-251-83-34911
kai.schmitz@uni-muenster.de
Consultation hours: on appointment

External Profiles:

• ORCID

Members

Current group members and guests more

Former PhD students

Former MSc students

Former BSc students

Former guests

Research

New physics at the PTA frontier more
Topics: Exotic sources in the nHz band

Primordial gravitational waves more
Topics: Cosmic strings, cosmological phase transitions

Axion cosmology more
Topics: Dark matter, magnetic fields, black holes, hierarchy problem

Early Universe more
Topics: Inflation, reheating, baryogenesis, leptogenesis

Teaching

Courses

• Summer 26 more
  [114646] General relativity (course)
  [114647] General relativity (tutorial)
  Learnweb:
• Winter 25/26 more
  [112694] Quantum field theory (course)
  [112695] Quantum field theory (tutorial)
  Learnweb: [QFT-2025_2]
• Summer 25 more
  [110617] Standard model (course)
  [110618] Standard model (tutorial)
  Learnweb: [Standard-Model-2025_1]
• Winter 24/25 more
  [118687] Gravitational waves (course)
  [118688] Gravitational waves (tutorial)
  Learnweb: [GW-2024_2]
• Sommer 24 more
  [116544] General relativity (course)
  [116545] General relativity (tutorial)
  Learnweb: [GRC-2024_1]
• Winter 23/24 more
  [114658] Quantum field theory (course)
  [114659] Quantum field theory (tutorial)
  Learnweb: [QFT-2023_2]
• Sommer 23 more
  [112525] General relativity (course)
  [112545] General relativity (tutorial)
  Learnweb: [GR-2023_1]
• Winter 22/23 more
  [110636] Gravitational waves (course)
  [110637] Gravitational waves (tutorial)
  Learnweb: [GW-2022_2]
• Summer 22 more
  [118669] Standard model (course)
  [118670] Standard model (tutorial)
  Learnweb: [EIDSDT-2022_1]

Seminars

• Winter 25/26
  [112700] BSc theory seminar: Seminar on the theory of atoms, nuclei and condensed matter
  Learnweb: [BScTh-Seminar-2025_2]
• Winter 24/25
  [118686] BSc theory seminar: Seminar on the theory of atoms, nuclei and condensed matter
  Learnweb: [BScTh-Seminar-2024_2]
• Winter 23/24
  [114666] BSc theory seminar: Seminar on the theory of atoms, nuclei and condensed matter
  Learnweb: [BScTh-Seminar-2023_2]
• Winter 22/23
  [110281] BSc theory seminar: Seminar on the theory of atoms, nuclei and condensed matter
  Learnweb: [BScTh-Seminar-2022_2]

Publications

Names of group members are printed in boldface.

2026

• [MS-TP-26-03] NANOGrav Collaboration (incl. Kai Schmitz)
  The NANOGrav 15 yr data set: Piecewise power-law reconstruction of the gravitational-wave background
  arXiv:2601.09481

2025

• [MS-TP-25-39] Deepali Agarwal, Maximilian Blümke, Joseph D. Romano, Kai Schmitz, Tobias Schröder
  Kinematic Anisotropies in PTA Observations: Analytical Toolkit
  Symmetry 18 (2026) 355 arXiv:2512.24055
• [MS-TP-25-37] Richard von Eckardstein
  GEFF: The Gradient Expansion Formalism Factory - A tool for inflationary gauge-field production
  arXiv:2510.12644
• [MS-TP-25-28] Anastasia Lysenko, Oleksandr Sobol, Stanislav Vilchinskii
  Vector dark matter production during inflation in the gradient-expansion formalism
  arXiv:2509.24963
• [MS-TP-25-27] Richard von Eckardstein, Kai Schmitz, Oleksandr Sobol
  Gravitational waves from axion inflation in the gradient expansion formalism. Part II. Fermionic axion inflation
  arXiv:2509.25013
• [MS-TP-25-23] Richard von Eckardstein, Kai Schmitz, Oleksandr Sobol
  Gravitational waves from axion inflation in the gradient expansion formalism. Part I. Pure axion inflation
  JHEP 01 (2026) 018 arXiv:2508.00798
• [MS-TP-25-20] David Esmyol, A. J. Iovino, Kai Schmitz
  From new physics to a running power law and back again: Minimal refitting techniques for the reconstruction of the gravitational-wave background signal in pulsar timing array data
  arXiv:2506.23574
• [MS-TP-25-16] Kai Schmitz, Tobias Schröder
  Gravitational waves from low-scale cosmic strings without scaling
  Phys. Rev. D 112 (2025) 8, 083517 arXiv:2505.04537
• [MS-TP-25-15] Dima Zharov, Oleksandr Sobol, Stanislav Vilchinskii
  ACT observations, reheating, and Starobinsky and Higgs inflation
  Phys. Rev. D 112 (2025) 2, 023544 arXiv:2505.01129
• [MS-TP-25-09] Christian Dioguardi, Antonio J. Iovino, Antonio Racioppi
  Fractional attractors in light of the latest ACT observations
  Phys. Lett. B 868 (2025) 139664 arXiv:2504.02809
• [MS-TP-25-01] Martin A. Mojahed, Kai Schmitz, Dominik Wilken
  A lower bound on the right-handed neutrino mass from wash-in leptogenesis
  Phys. Lett. B 871 (2025) 139997 arXiv:2501.07634

2024

• [MS-TP-24-58] NANOGrav Collaboration (incl. Richard von Eckardstein, David Esmyol, Kai Schmitz, Tobias Schröder)
  The NANOGrav 15 yr data set: Running of the spectral index
  Astrophys. J. Lett. 978 (2025) 2, L29 arXiv:2408.10166
• [MS-TP-24-38] Kai Schmitz, Tobias Schröder
  Gravitational waves from cosmic strings for pedestrians
  JCAP 01 (2026) 025 arXiv:2412.20907
• [MS-TP-24-25] Martin A. Mojahed, Kai Schmitz, Xunjie Xu
  Gravitational charge production
  Phys. Rev. D 111 (2025) 5, 055005 arXiv:2409.10605
• [MS-TP-24-20] Richard von Eckardstein, Kai Schmitz, Oleksandr Sobol
  On the Schwinger effect during axion inflation
  JHEP 02 (2025) 096 arXiv:2408.16538
• [MS-TP-24-13] Nina Cordes, Andrea Mitridate, Kai Schmitz, Tobias Schröder, Kim Wassner
  On the overlap reduction function of pulsar timing array searches for gravitational waves in modified gravity
  Class. Quant. Grav. 42 (2025) 1, 015003 arXiv:2407.04464
• [MS-TP-24-11] Kai Schmitz, Tobias Schröder
  Gravitational waves from low-scale cosmic strings
  Phys. Rev. D 110 (2024) 6, 063549 arXiv:2405.10937 YouTube video abstract
• [MS-TP-24-10] Ruth Durrer, Richard von Eckardstein, Deepen Garg, Kai Schmitz, Oleksandr Sobol, Stanislav Vilchinskii
  Scalar perturbations from inflation in the presence of gauge fields
  Phys. Rev. D 110 (2024) 4, 043533 arXiv:2404.19694
• [MS-TP-24-07] Tobias Schröder, Robert Brandenberger
  Embedded domain walls and electroweak baryogenesis
  Phys. Rev. D 110 (2024) 4, 043516 arXiv:2404.13035 YouTube video abstract

2023

• [MS-TP-23-50] Anastasia Lysenko, Oleksandr Sobol
  Quantum kinetic approach to the Schwinger production of scalar particles in an expanding universe
  Gen. Rel. Grav. 56 (2024) 4, 39 arXiv:2311.15981
• [MS-TP-23-46] Kai Schmitz, Xunjie Xu
  Wash-in leptogenesis after the evaporation of primordial black holes
  Phys. Lett. B 849 (2024) 138473 arXiv:2311.01089
• [MS-TP-23-38] Richard von Eckardstein, Marco Peloso, Kai Schmitz, Oleksandr Sobol, Lorenzo Sorbo
  Axion inflation in the strong-backreaction regime: decay of the Anber-Sorbo solution
  JHEP 11 (2023) 183 arXiv:2309.04254
• [MS-TP-23-37] Wilfried Buchmüller, Valerie Domcke, Kai Schmitz
  Metastable cosmic strings
  JCAP 11 (2023) 020 arXiv:2307.04691
• [MS-TP-23-36] Richard von Eckardstein, Andrea Mitridate, Jonathan Nay, Ken Olum, Kai Schmitz, Tobias Schröder, Tanner Trickle, David Wright
  PTArcade
  arXiv:2306.16377
• [MS-TP-23-31] NANOGrav Collaboration (incl. Adeela Afzal, Richard von Eckardstein, Rafael R. Lino dos Santos, Kai Schmitz, Tobias Schröder, Peter Stratmann)
  The NANOGrav 15 yr data set: Search for signals from new physics
  Astrophys. J. Lett. 951 (2023) 1, L11 arXiv:2306.16219
• [MS-TP-23-27] Astrid Eichhorn, Rafael R. Lino dos Santos, João Lucas Miqueleto
  From quantum gravity to gravitational waves through cosmic strings
  Phys. Rev. D 109 (2024) 2, 026013 arXiv:2306.17718
• [MS-TP-23-13] Axel Brandenburg, Kohei Kamada, Kyohei Mukaida, Kai Schmitz, Jennifer Schober
  Chiral magnetohydrodynamics with zero total chirality
  Phys. Rev. D 108 (2023) 6, 063529 arXiv:2304.06612
• [MS-TP-23-12] Gilles Weymann-Despres, Sophie Henrot-Versillé, Gilbert Moultaka, Vincent Vennin, Laurent Duflot, Richard von Eckardstein
  MSSM-inflation revisited: Towards a coherent description of high-energy physics and cosmology
  Phys. Rev. D 108 (2023) 2, 023511 arXiv:2304.04534
• [MS-TP-23-06] Ruth Durrer, Oleksandr Sobol, Stanislav Vilchinskii
  Backreaction from gauge fields produced during inflation
  Phys. Rev. D 108 (2023) 4, 043540 arXiv:2303.04583

2022

• [MS-TP-22-57] Rafael R. Lino dos Santos, Linda van Manen
  Gravitational waves from the early universe
  arXiv:2212.05594
• [MS-TP-22-37] Valerie Domcke, Kohei Kamada, Kyohei Mukaida, Kai Schmitz, Masaki Yamada
  Wash-in leptogenesis after axion inflation
  JHEP 01 (2023) 053 arXiv:2210.06412
• [MS-TP-22-23] Valerie Domcke, Kohei Kamada, Kyohei Mukaida, Kai Schmitz, Masaki Yamada
  New constraint on primordial lepton flavour asymmetries
  Phys. Rev. Lett. 130 (2023) 26, 261803 arXiv:2208.03237
• [MS-TP-22-22] Martin Enriquez-Rojo, Tobias Schröder
  Asymptotic symmetries and memories of gauge theories in FLRW spacetimes
  JHEP 01 (2023) 011 arXiv:2207.13726
• [MS-TP-22-19] Pierre Auclair, Simone Blasi, Vedran Brdar, Kai Schmitz
  Gravitational waves from current-carrying cosmic strings
  JCAP 04 (2023) 009 arXiv:2207.03510 YouTube video abstract
• [MS-TP-22-17] Alexandros Papageorgiou, Pablo Quílez, Kai Schmitz
  Axion dark matter from frictional misalignment
  JHEP 01 (2023) 169 arXiv:2206.01129 YouTube video abstract