Modified Gravity Cosmologies and Structure Formation

Extensions to general relativity have been proposed to account for the accelerated expansion of the Universe without invoking a cosmological constant. Such modified gravity models introduce additional scalar or tensor degrees of freedom that alter both the background expansion and the growth of cosmic structure. Prominent examples include f(R) theories, scalar–tensor and Horndeski frameworks, braneworld scenarios such as the Dvali–Gabadadze–Porrati (DGP) model, and Galileon fields. In each case, screening mechanisms—such as the chameleon or Vainshtein effect—suppress deviations from general relativity in high-density environments while allowing modifications on large scales. Theoretical predictions rely on linear perturbation theory at early times and on a combination of halo models, semi-analytic “reaction” approaches and cosmological N-body simulations to capture the non-linear regime. Observable signatures include changes to the matter power spectrum, redshift-space distortions, gravitational lensing (weak and CMB), galaxy cluster abundances and velocity fields within the cosmic web. By confronting these signatures with data from current and forthcoming surveys, researchers aim to distinguish between general relativity plus dark energy and alternative gravity scenarios, shedding light on the fundamental origin of cosmic acceleration.

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Modified Gravity Cosmologies and Structure Formation publication trend

The graph below shows the total number of articles in modified gravity cosmologies and structure formation across all publications each year (not limited to Nature Index journals).

Technical terms

f(R) gravity: A class of theories in which the Einstein–Hilbert action is generalised by replacing the Ricci scalar R with an arbitrary function f(R), introducing an extra scalar degree of freedom that modifies gravitational forces on cosmological scales.

Dvali–Gabadadze–Porrati (DGP) model: A braneworld scenario in which our four-dimensional Universe is embedded in a higher-dimensional bulk, leading to a modification of gravity at large distances and an apparent self-acceleration.

Matter power spectrum: The Fourier transform of the two-point correlation function of density fluctuations, describing the distribution of matter as a function of spatial scale and serving as a key statistic for structure formation.

Halo model: A semi-analytic framework that represents all matter as residing within dark-matter haloes, enabling calculations of non-linear clustering by summing contributions from halo profiles and their spatial correlations.

Screening mechanism: A non-linear process present in many modified gravity theories that restores general relativity in high-density or high-curvature regions—such as galaxies and clusters—while allowing deviations on larger cosmological scales.

References

1. Constraining f(R) gravity with cross-correlation of galaxies and cosmic microwave background lensing. Astronomy & Astrophysics (2024).
2. On the road to percent accuracy: non-linear reaction of the matter power spectrum to dark energy and modified gravity. Monthly Notices of the Royal Astronomical Society (2019).
3. Fast production of cosmological emulators in modified gravity: the matter power spectrum. Journal of Cosmology and Astroparticle Physics (2023).