About Scientific Rationale

In the cosmological concordance model, ΛCDM, dark matter (DM) makes up the majority of the matter content of the Universe. But its nature is little known. It must interact gravitationally, but whether it has further interactions is unknown. In ΛCDM, one assumes that DM is collisionless. But it could be that DM has additional self-interactions beyond gravity. Such models of self-interacting dark matter (SIDM) show a different phenomenology on small scales (galactic scales) but keep the success of ΛCDM on large scales. Thus SIDM can mitigate problems or curiosities of the small-scale crisis. Moreover, SIDM is well motivated from the particle physics side and a variety of DM candidates that differ qualitatively in their phenomenology exist.

We study SIDM with the help of N-body simulations. Therefore we employ the cosmological simulation code OpenGadget-3. Our simulations include various setups, such as idealized mergers of galaxy clusters or full cosmological boxes. Besides our efforts, there exist further projects that investigate SIDM, e.g. ETHOS, TangoSIDM or Symphony. However, until today we are the only ones able to faithfully simulate DM models that typically scatter about tiny angels and hence must interact frequently to alter the distribution of DM significantly. We call these models frequently self-interacting dark matter (fSIDM), in contrast to rarely self-interacting dark matter (rSIDM) with large scattering angles. In the paper by Fischer et al. 2021a, we have introduced the first numerical scheme that allows simulating such models from first principles. Frequent self-interactions are well motivated by particle physics, e.g. light mediator models fall into this class. Their phenomenology is particularly interesting as they can explain larger offsets between galaxies and DM in cluster mergers and suppress the abundance of satellites at late times more strongly than rSIDM.

A lot more is waiting to be explored, and we continue studying the differences between DM candidates through simulations. Several projects concerning various aspects of SIDM are underway.

Data Simulations

Merger simulations

We have simulated mergers of NFW haloes in different configurations, with and without intracluster medium.

NFW haloes:

Mvir rs ρ0
[M] [kpc] [M kpc-3]
1015 389.31 1.33 x 106
2 x 1014 194.76 1.91 x 106
1014 144.53 2.24 x 106
The first column gives the virial mass of the halo, the second column shows the scale radius, and the third one displays the density parameter.

Merger configurations:

Mvir, main MMR dini Δvini σT/mχ
[M] [kpc] [km s-1] [cm2 g-1]
1015 1:1 4000 1000 0.0, 0.1, 0.3, 0.5
1015 1:5 4000 1000 0.0, 0.1, 0.3, 0.5
1015 1:10 4000 1000 0.0, 0.1, 0.3, 0.5
The first column gives the virial mass of the main halo, and the second column shows the merger mass ratio. It follows the initial distance between the haloes and their relative velocity. Lastly, the simulated momentum-transfer cross-sections are shown.

Further information on the simulations can be found in the paper by Fischer et al. 2021b and Fischer et al. 2023.

Cosmological simulations

Our full box cosmological simulations are based on Box 4 of the Magneticum simulations and are DM-only. You can download the snapshots and halo catalogues for z=0 by clicking on the corresponding cross-section.

Name lbox NDM mDM σT/mχ
[cMpc h-1] [M h-1] [cm2 g-1]
hr 48 2163 8.26 x 108 0.0, 0.1 (freq., rare), 1.0 (freq., rare)
uhr 48 5763 4.37 x 107 0.0, 0.1 (freq., rare), 1.0 (freq., rare)
The first column gives the resolution name of the simulation, the second column shows the cubic side length of the box, and the third one displays the number of numerical particles. It follows the numerical particle mass and the simulated momentum-transfer cross-sections.

Further information on the simulations can be found in the paper by Fischer et al. 2022 and Fischer et al. 2024a.

Access and use

If you are interested in our data, feel free to contact us.

Tools to read the simulation data are available in various languages such as Julia and Python.

Publications Based on our SIDM implementation

Dianoga SIDM: galaxy cluster self-interacting dark matter simulations

Numerical challenges for energy conservation in N-body simulations of collapsing self-interacting dark matter haloes

Simulations of galaxy cluster mergers with velocity-dependent, rare and frequent self-interactions

Cosmological and idealised simulations of dark matter haloes with velocity-dependent, rare and frequent self-interactions

Sensitivity of halo shape measurements

Unequal-mass mergers of dark matter haloes with rare and frequent self-interactions

Team Who is involved

Core Team

Moritz S. Fischer

Moritz S. Fischer

Postdoctoral researcher at the Ludwig Maximilian University Munich

Marcus Brüggen

Marcus Brüggen

Professor at the University Hamburg

Klaus Dolag

Klaus Dolag

Staff scientist at the Ludwig Maximilian University Munich

Felix Kahlhöfer

Felix Kahlhöfer

Junior Professor at Karlsruhe Institute of Technology

Antonio Ragagnin

Antonio Ragagnin

Postdoctoral researcher at the University of Bologna

AndrewRobertson

Andrew Robertson

Postdoctoral researcher at the Jet Propulsion Laboratory

Kai Schmidt-Hoberg

Kai Schmidt-Hoberg

Staff scientist at DESY

Sabarish Venkataramani

Sabarish Venkataramani

PhD student at the University Hamburg

Collaborators

Mathias Garny

Staff scientist at Technical University Munich

Tobias Binder

Postdoctoral researcher at Technical University Munich

Lucas Valenzuela

PhD student at the Ludwig Maximilian University Munich

Hai-Bo Yu

Professor at University of California, Riverside

Master & Bachelor students

Cenanda Arido

Master student at Technical University Munich

Lenard Kasselmann

Master student at University Hamburg

Yashraj Patil

Master student at Birla Institute of Technology & Science, Pilani

Marc Wiertel

Master student at Karlsruhe Institute of Technology

Alumni

Nils-Henrik Durke

Involved as a master student at University Hamburg

Claudius Hammer

Involved as an intern at University Hamburg

Katharina Hollingshausen

Involved as an intern at University Hamburg

Contact Get in touch with us

If you are interested in our research, don't hesitate to get in touch with us by sending an email to mfischer@usm.lmu.de.