Dr. Miguel Zumalacarregui

Gravitational-wave cosmology, lensing, and fundamental physics
I am a theoretical physicist working at the interface of cosmology, gravitational-wave (GW) astronomy, and fundamental physics. My research uses gravitational and cosmological observations to study astrophysical compact objects, illuminate the nature of dark matter and dark energy, and develop new tests of gravity.

While the standard cosmological model provides an excellent description of a wide range of observations, it relies on ingredients whose physical nature remains unknown—most notably dark matter and dark energy, which together account for about 95% of the energy content of the Universe. Gravitational interactions are currently our primary window into these components. A central goal of my work is to develop theoretical frameworks and data-analysis tools that allow us to extract fundamental-physics information from gravitational-wave and cosmological data in a consistent and optimal way. Over the years, my research has increasingly focused on the synergies between gravitational waves and traditional cosmological probes (such as large-scale structure and supernovae), with particular emphasis on wave propagation, lensing, and beyond–general relativity effects.

Gravitational-wave lensing and wave optics
A major focus of my current work is gravitational-wave lensing, including wave-optics and diffraction effects that arise when gravitational waves interact with compact or complex matter distributions. These phenomena open a new observational window on dark matter substructure, compact objects, and strong-gravity environments. I develop theoretical models and numerical tools to predict lensing signatures in GW signals and to assess their detectability with current and future observatories, including space-based detectors. This line of work connects GW astronomy with strong and weak lensing, astrophysical populations, and fundamental physics. My team developed GLoW, a fast, flexible, and accurate software package for wave-optics lensing computations.

Dark matter and compact objects
Gravitational lensing provides a powerful probe of dark matter and compact objects that is largely insensitive to their non-gravitational interactions. A central theme of my work is the use of GWs as precision probes of dark objects, ranging from dark-matter halos to stellar-mass and supermassive black holes. I have developed new methods to identify and characterize dark matter structures through diffraction and stochastic lensing signatures imprinted on GW signals, allowing us to probe mass scales and internal properties that are inaccessible to electromagnetic observations. In parallel, I study how compact objects themselves can act as gravitational “telescopes,” producing distinctive lensing phenomena—such as highly magnified or quasi-periodic signals—that enable the discovery and characterization of otherwise unresolved systems, including supermassive black hole binaries. Together, these approaches establish gravitational-wave lensing as a novel and versatile tool to explore both the dark matter sector and compact astrophysical populations.

Gravitational waves as probes of fundamental physics
Gravitational waves provide a powerful and largely unexplored arena to test gravity and dark energy. I study how GW propagation is modified in theories beyond general relativity, including effects such as modified amplitudes and phases, dispersion, birefringence, and additional polarizations. The multi-messenger detection of GW170817 placed extremely strong constraints on many alternative gravity theories, reshaping the viable theory landscape. More recently, my work has shown that frequency- and polarization-dependent propagation effects are generic in strong gravitational fields and in broad classes of modified-gravity theories, opening new avenues for testing fundamental physics with GW observations.

Cosmology and modified gravity
Understanding the physics driving cosmic acceleration and the growth of structure remains a central challenge in cosmology. I have worked extensively on testing dark energy and modified-gravity models against cosmological data, including large-scale structure and cosmic microwave background observations. I am a main developer of hi_class, a publicly available Einstein–Boltzmann solver for general dark energy and gravity theories that is widely used by the community. My interests include addressing cosmological tensions and developing theoretically consistent extensions of the standard model that can be robustly confronted with data. On the theoretical side, I explore the structure and consistency of gravity theories beyond Einstein’s general relativity, including the use of field redefinitions and effective descriptions to uncover new viable frameworks and clarify their physical interpretation.

Selected Publications
[1] “Black Holes as Telescopes: Discovering Supermassive Binaries through Quasiperiodic Lensed Starlight”, H. Wang, M. Zumalacárregui, B. Kocsis, arXiv:2506.16544 Phys.Rev.Lett. 136 (2026) 6, 061403
[2] “Across the Universe: GW231123 as a magnified and diffracted black hole merger”, S. Goyal, H. Villarrubia-Rojo, M. Zumalacarregui, arXiv:2512.17631
[3] “Gravitational lensing of waves: Novel methods for wave-optics phenomena” , H. Villarrubia-Rojo, S. Savastano, M. Zumalacárregui, L. Choi, S. Goyal et al, arXiv:2409.04606 Phys.Rev.D 111 (2025) 10, 103539
[4] “Gravitational wave lensing as a probe of halo properties and dark matter”, G. Tambalo, M. Zumalacárregui, L. Dai, M. Cheung, arXiv: 2212.11960 Phys.Rev.D 108 (2023) 10, 103529
[5] “Limits on stellar-mass compact objects as dark matter from gravitational lensing of type Ia
supernovae”, M. Zumalacárregui and U. Seljak, arXiv:1712.02240 Phys. Rev. Lett. 121 (2018) 141101
[6] “Dark Energy after GW170817: dead ends and the road ahead” J. M. Ezquiaga and M. Zumalacárregui, arXiv:1710.05901 Phys.Rev.Lett. 119 (2017) 251304
[7] “hi class: Horndeski in the Cosmic Linear Anisotropy Solving System” M. Zumalacárregui, E. Bellini, I. Sawicki, J. Lesgourgues and P. Ferreira arXiv:1605.06102 JCAP08 (2017) 019
[8] “Transforming gravity: from derivative couplings to matter to second-order scalar-tensor theories
beyond the Horndeski Lagrangian” M. Zumalacarregui, J. Garcia-Bellido, arXiv:1308.4685. Phys.Rev. D89 (2014) 064046
[9] “Screening Modifications of Gravity through Disformally Coupled Fields” T. Koivisto, D. Mota, and M. Zumalacarregui, arXiv:1205.3167, Phys.Rev.Lett. 109 (2012) 241102.

All Publications
Here are links to all my publications: from INSPIRE, from the ADS database and on the Arxiv.