# Achim Schwenk
**Achim Schwenk** (A. Schwenk) is a theoretical nuclear physicist, EMMI Professor of Physics at the Institute for Nuclear Physics (IKP) Theory center of the Technische Universität Darmstadt.[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) His research concerns strong-interaction matter in the laboratory and the cosmos: nuclear forces and nuclei at the extremes, neutron stars, supernovae and mergers, electroweak interactions, dark-matter detection, and ultracold atoms, all treated with effective field theories of quantum chromodynamics (QCD).[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) • [2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp) He is known for renormalization group methods for nuclear forces, the in-medium similarity renormalization group (IMSRG) ab initio method, and calculations of neutron matter and neutron-star dense matter from chiral [three-nucleon forces](https://www.edgepedia.org/three-nucleon-force).[2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp)
| Key facts | |
|---|---|
| Position | Professor (W3) at TU Darmstadt and the ExtreMe Matter Institute EMMI since 2009[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) |
| Training | Physics at Heidelberg (Vordiplom 1997); Ph.D. at SUNY Stony Brook with Gerald Brown, 2002[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) • [3](https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/archiv_2/2023/2023quartal3/neuesausdertueinzelansichtbreitespalte_419456.en.jsp) |
| Signature work | "Chiral three-nucleon forces and neutron matter" (Phys. Rev. C, 2010); "Improved nuclear matter calculations from chiral low-momentum interactions" (Phys. Rev. C, 2011); "The nuclear charge radius of 13C" (Nature Communications, 2025) |[4](https://journals.aps.org/prc/abstract/10.1103/PhysRevC.82.014314) • [5](https://link.aps.org/doi/10.1103/PhysRevC.83.031301) • [6](https://link.springer.com/article/10.1038/s41467-025-60280-9)
| Ab initio reach | IMSRG calculations of nuclei reaching up to 200 nucleons[2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp) |
| Astrophysical link | Neutron-matter calculations predicting neutron-star radii consistent with LIGO/Virgo constraints from GW170817 and NICER observations[2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp) |
| ERC funding | Starting Grant 2012; second ERC grant EUSTRONG, about 2.3 million euros over five years, according to his TU Darmstadt profile |[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) • [3](https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/archiv_2/2023/2023quartal3/neuesausdertueinzelansichtbreitespalte_419456.en.jsp)
| Recent honors | LOEWE Top Professorship 2023, approximately 1.9 million euros over five years[7](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/projects_rg_achim_schwenk/projects_rg_a_s.en.jsp) |
## Education and career
Schwenk studied physics at the University of Heidelberg from 1995 to 1998, receiving his Vordiplom in 1997.[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) According to his TU Darmstadt profile, after a Fulbright Fellowship he moved to the [State University of New York](https://www.edgepedia.org/state-university-of-new-york) at Stony Brook (1998–2002), earning an M.A. in 1999 and a Ph.D. in physics in 2002 under Gerald Brown.[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) • [3](https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/archiv_2/2023/2023quartal3/neuesausdertueinzelansichtbreitespalte_419456.en.jsp) His doctoral thesis received the Max Dresden Prize for Outstanding Theoretical Thesis at Stony Brook in 2003.[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html)
His postdoctoral and early research career moved through several North American institutions: Postdoctoral Fellow at The Ohio State University (2002–2004), Assistant Research Scientist at the Nuclear Theory Center of Indiana University (2004–2005), and Senior Fellow at the University of Washington (2005–2006).[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) In 2009 he was appointed Professor of Theoretical Nuclear Physics at TU Darmstadt, a W3 professorship held jointly with the ExtreMe Matter Institute EMMI.[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) • [8](https://www.physik.tu-darmstadt.de/aktuelles_physik/news_details_122112.en.jsp) He has been Affiliate Faculty at the University of Washington since 2007 and was an affiliate member of the Perimeter Institute from 2009 to 2015.[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html)
## Research
Schwenk's program builds nuclear interactions from QCD through chiral effective field theory, in which the strong interaction between nucleons is organized by powers of a momentum scale, and then applies renormalization group methods to soften these forces for many-body use.[2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp) The group developed the in-medium similarity renormalization group, an ab initio method that solves nuclei systematically from the underlying interactions and reaches systems of up to 200 nucleons.[2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp) In the wider ab initio landscape, approximate methods such as coupled-cluster theory, Gorkov-Green's functions, the IMSRG, and nuclear lattice effective field theory carry a computational cost that grows polynomially with system size, unlike exponentially scaling exact methods, and have moved the ab initio frontier from light nuclei up to 208Pb.[9](https://arxiv.org/pdf/2410.00843)
Three-nucleon forces are central to this work. The 2010 Physical Review C paper on chiral three-nucleon forces and neutron matter showed that for neutrons only the long-range two-pion-exchange part of the leading chiral three-nucleon force contributes, and derived density-dependent two-body interactions by summing the third particle over occupied Fermi-sea states; the results suggest neutron matter is perturbative at nuclear densities and provide constraints on the symmetry energy and its density dependence.[4](https://journals.aps.org/prc/abstract/10.1103/PhysRevC.82.014314) The group's work has also elucidated the role of three-body forces for the limits of bound nuclei and the emergence of shell structure.[2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp) On the astrophysical side, chiral EFT neutron-matter calculations with two-, three-, and four-nucleon interactions, combined with quantum [Monte Carlo](https://www.edgepedia.org/monte-carlo) simulations, predicted neutron-star radii consistent with the LIGO/Virgo gravitational-wave constraints from GW170817 and with NICER observations.[2](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp)
## Representative work
The 2011 Physical Review C Rapid Communication "Improved nuclear matter calculations from chiral low-momentum interactions" ([DOI: 10.1103/PhysRevC.83.031301](https://doi.org/10.1103/physrevc.83.031301)) used low-momentum interactions derived from chiral EFT potentials with an improved three-nucleon-force treatment, including a corrected combinatorial factor beyond Hartree-Fock. It found realistic nuclear-matter saturation properties using parameters fit only to few-body data, while giving larger uncertainty estimates from cutoff dependence and three-nucleon-force parametrization than previous calculations.[5](https://link.aps.org/doi/10.1103/PhysRevC.83.031301)
The 2025 [Nature Communications](https://www.edgepedia.org/nature-communications) paper "The nuclear charge radius of 13C" ([DOI: 10.1038/s41467-025-60280-9](https://doi.org/10.1038/s41467-025-60280-9)) presented a laser spectroscopic measurement of the root-mean-square charge radius of carbon-13 and compared it with ab initio nuclear structure calculations. Measuring all hyperfine components of the 2 ³S → 2 ³P fine-structure triplet in 13C4+ ions, referenced to a frequency comb, determined the center of gravity with accuracy better than 2 MHz even though second-order hyperfine-structure effects shift individual lines by several GHz. The measurement improved the uncertainty of the electron-determined 13C charge radius by a factor of 6 and found a 3σ discrepancy with the muonic-atom result of similar accuracy.[6](https://link.springer.com/article/10.1038/s41467-025-60280-9)
## Honors, funding, and roles
Schwenk received an ERC Starting Grant in 2012.[1](https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html) His second ERC grant funds the project "Exploring the Universe through Strong Interactions" (EUSTRONG) with about 2.3 million euros over five years.[3](https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/archiv_2/2023/2023quartal3/neuesausdertueinzelansichtbreitespalte_419456.en.jsp) In 2023 the state of Hesse awarded him a LOEWE Top Professorship worth approximately 1.9 million euros over five years, supporting research on matter in atomic nuclei and neutron stars described by the strong interaction.[7](https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/projects_rg_achim_schwenk/projects_rg_a_s.en.jsp) • [3](https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/archiv_2/2023/2023quartal3/neuesausdertueinzelansichtbreitespalte_419456.en.jsp)
Since 2015 he has been a Max Planck Fellow at the Max Planck Institute for Nuclear Physics (MPIK) in [Heidelberg](https://www.edgepedia.org/heidelberg), heading the research group "Strong Interactions and Exotic Nuclei", and he has been appointed an external scientific member of MPIK, according to TU Darmstadt.[3](https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/archiv_2/2023/2023quartal3/neuesausdertueinzelansichtbreitespalte_419456.en.jsp) • [8](https://www.physik.tu-darmstadt.de/aktuelles_physik/news_details_122112.en.jsp) He is spokesperson of the Collaborative Research Centre CRC 1245, "Nuclei: From Fundamental Interactions to Structure and Stars".[8](https://www.physik.tu-darmstadt.de/aktuelles_physik/news_details_122112.en.jsp)
## References
1. Achim Schwenk – IKP Theory – TU Darmstadt. https://theorie.ikp.physik.tu-darmstadt.de/strongint/people_schwenk.html
2. RG A Schwenk – IKP Theory Center – TU Darmstadt. https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/startseite_ag_a_schwenk.en.jsp
3. LOEWE Top Professorship for nuclear physicist Achim Schwenk – TU Darmstadt. https://www.tu-darmstadt.de/universitaet/aktuelles_meldungen/archiv_2/2023/2023quartal3/neuesausdertueinzelansichtbreitespalte_419456.en.jsp
4. Chiral three-nucleon forces and neutron matter, Phys. Rev. C 82, 014314 (2010). https://journals.aps.org/prc/abstract/10.1103/PhysRevC.82.014314
5. Improved nuclear matter calculations from chiral low-momentum interactions, Phys. Rev. C 83, 031301(R) (2011). https://link.aps.org/doi/10.1103/PhysRevC.83.031301
6. The nuclear charge radius of 13C, Nature Communications 16, 6234 (2025). https://link.springer.com/article/10.1038/s41467-025-60280-9
7. Projects RG A S – IKP Theory Center – TU Darmstadt. https://www.ikp.tu-darmstadt.de/theory/theoriezentrum/arbeitsgruppen_theoriezentrum/ag_achim_schwenk/projects_rg_achim_schwenk/projects_rg_a_s.en.jsp
8. Scientific exchange at the highest level – Department of Physics – TU Darmstadt. https://www.physik.tu-darmstadt.de/aktuelles_physik/news_details_122112.en.jsp
9. Lecture notes on ab initio nuclear structure methods (arXiv, 2024). https://arxiv.org/pdf/2410.00843
10. Exploring quark mass dependent three-nucleon forces in medium-mass nuclei (arXiv preprint, 2025). https://arxiv.org/html/2512.20454v1
11. Achim Schwenk – INSPIRE-HEP author record. https://inspirehep.net/authors/1023420
12. Neutron-rich nuclei and neutron skins from chiral low-resolution interactions, EPJ A (2026). https://epja.epj.org/articles/epja/abs/2026/07/10050_2026_Article_1905/10050_2026_Article_1905.html
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*Topic: Encyclopedia › Physical world and mathematics › Physical and mathematical scientists › Physicists and astronomers › Researchers in particle, nuclear, and high-energy theoretical physics › Nuclear structure and few-body theory*
*Initially written Sep 21, 2026 · Reviewed: Sep 25, 2026 · Edited: Sep 25, 2026; Oct 11, 2026; Oct 15, 2026 · Last review: Sep 25, 2026*
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