Research & Motivation

With respect to astrophysics and cosmology, we live in truly fascinating times. Upcoming galaxy surveys will allow us to map a large part of our Universe, looking far back in time, with unprecedented precision. Moreover, the observation of gravitational waves offers an exiting alternative window into our Universe. In particular, recent observations of pulsar timing arrays have found evidence for the existence of a stochastic gravitational wave background. With these observational advances, we will have the opportunity to learn more about the Universe than ever before, which will help us to address long-standing questions in cosmology: What is the nature of dark energy, this mysterious component causing the accelerated expansion of space? Does Einstein's theory of general relativity work well on cosmological scales, or do we need to include new physics described by a modified theory of gravity? Moreover, what is the origin of the stochastic gravitational wave backgroud that seems to permeate spacetime?

As we will gain an enormous amount of high-precision cosmological data in the next two decades, we have a good chance to solve these mysteries – or at least come a great step closer to doing so! However, this goal cannot be achieved without overcoming a number of observational and theoretical challenges. In fact, determining which gravity theory is best compatible with cosmological data is a highly non-trivial task. Given the plethora of modified gravity theories and the high computational cost of cosmological data analysis, testing each theory individually is infeasible. Alternatively, by first identifying model-independent observables, gravity modification can be detected robustly and independently from the governing theory of gravity. For this reason, one focus of my research lies on developing such model-independent tests of gravity. Moreover, I aim to explore synergies between pulsar timing arrays and other probes of our Universe, as this can give us novel insights into the origin of the stochastic gravitational wave background.

My complete list of publications can be find below. If you have some more specific questions about my research, or ideas for collaborations, feel free to contact me – I'd be happy to hear from you!

List of Publications

  1. Beyond ΛCDM with the SKA Observatory – I: Probing Gravity on Cosmological Scales, S. Camera et al. (including N. Grimm),
    published in Advancing Astrophysics with the SKA II (2026), Report-no: AASKAII/Camera01 arXiv:2607.11917.

  2. A novel test of gravity: Does spacetime geometry track matter density?, C. Bonvin, N. Grimm and I. Tutusaus,
    A&A 711 (2026) A77, arXiv:2506.04387

  3. cloelib: A Flexible Python Library for Computing Cosmological Observables in the Euclid Era, M. Bonici et al. (including N. Grimm), on behalf of the Euclid Consortium,
    prepared for submission to JOSS, arXiv:2605.23839.

  4. cloelike: A Python Library for Cosmological Likelihood Inference in the Euclid Era, M. Bonici et al. (including N. Grimm), on behalf of the Euclid Consortium,
    prepared for submission to JOSS, arXiv:2605.23841.

  5. The impact of evolving dark energy on the Weyl potential measured from the Dark Energy Survey Year 3 data, B. Rosatello, G. Ye, M. Berti, I. Tutusaus, N. Grimm and C. Bonvin
    undergoing peer review, arXiv:2605.22599

  6. Comparing the motion of dark matter and standard model particles on cosmological scales, N. Grimm, C. Bonvin and I. Tutusaus,
    Nature Communications 16 (2025) 1, 9399, arXiv:2502.12843

  7. The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics, CosmoVerse Network Collaboration, Eleonora Di Valentino et al. (including N. Grimm),
    Phys. Dark Univ. 49 (2025) 101965, arXiv:2504.01669

  8. The impact of large-scale galaxy clustering on the variance of the Hellings-Downs correlation: theoretical framework, N. Grimm, M. Pijnenburg, G. Cusin and C. Bonvin,
    JCAP 03 (2025) 011, arXiv:2404.05670

  9. New measurements of EG: Testing General Relativity with the Weyl potential and galaxy velocities, N. Grimm, C. Bonvin and I. Tutusaus,
    Phys. Rev. Lett. 133 (2024) 211004 , arXiv:2403.13709

  10. The impact of large-scale galaxy clustering on the variance of the Hellings-Downs correlation: numerical results, N. Grimm, M. Pijnenburg, G. Cusin and C. Bonvin,
    JCAP 04 (2025) 047, arXiv:2411.08744

  11. Measurement of the Weyl potential evolution from the first three years of dark energy survey data, I. Tutusaus, C. Bonvin and N. Grimm,
    Nature Communications 15 (2024) 9295, arXiv:2312.06434

  12. Gravitational Redshift Constraints on the Effective Theory of Interacting Dark Energy, S. Castello, M. Mancarella, N. Grimm, D. Sobral-Blanco, I. Tutusaus and C. Bonvin,
    JCAP 05 (2024) 003, arXiv:2311.14425

  13. Combining chirp mass, luminosity distance and sky localisation from gravitational wave events to detect the cosmic dipole, N. Grimm, M. Pijnenburg, S. Mastrogiovanni, C. Bonvin, S. Foffa and G. Cusin,
    MNRAS 526 (2023) 3, 4673–4689, arXiv:2309.00336

  14. Rescuing constraints on modified gravity using gravitational redshift in large-scale structure, S. Castello, N. Grimm and C. Bonvin,
    Phys. Rev. D 106 (2022) 8, 083511, arXiv:2204.11507

  15. Non-Gaussianity in the squeezed three-point correlation from the relativistic effects, J. Yoo, N. Grimm and E. Mitsou,
    JCAP 08 (2022) 050, arXiv:2204.03002

  16. General relativistic effects in weak lensing angular power spectra, N. Grimm and J. Yoo,
    Phys. Rev. D 104 (2021) 8, 083548 , arXiv:2012.06368

  17. Cutting out the cosmological middle man: General Relativity in the light-cone coordinates, E. Mitsou, G. Fanizza, N. Grimm and J. Yoo,
    Class. Quant. Grav. 38 (2021) 5, 055011 , arXiv:2009.14687

  18. Galaxy Power Spectrum in General Relativity, N. Grimm, F. Scaccabarozzi, J. Yoo, S. G. Biern and J.-O. Gong,
    JCAP 11 (2020) 064, arXiv:2005.06484

  19. Cosmological Information Contents on the Light-Cone, J. Yoo, E. Mitsou, N. Grimm, R. Durrer and A. Refregier,
    JCAP 12 (2019) 015, arXiv:1905.08262

  20. Jacobi Mapping Approach for a Precise Cosmological Weak Lensing Formalism, N. Grimm and J. Yoo,
    JCAP 07 (2018) 067, arXiv:1806.00017

  21. Gauge-Invariant Formalism of Cosmological Weak Lensing, J. Yoo, N. Grimm, E. Mitsou, A. Amara and A. Refregier,
    JCAP 04 (2018) 029, arXiv:1802.03403