Modified gravity

5 papers

Model-independent test of GR

With Arman Shafieloo and Hyungjin Kim (University of Waterloo), we combined model-independent reconstructions of the expansion history from supernovae and BAO with growth measurements from redshift-space distortions, and put model-independent constraints on the matter density $\Omega_\mathrm{m}$ , the rms fluctuation $\sigma_8$ , and the growth index $\gamma$ , defined by

f(z) \equiv \frac{\mathrm{d}\ln\delta}{\mathrm{d}\ln a} \simeq \Omega_\mathrm{m}(z)^{\gamma},

with $\gamma \simeq 0.55$ in GR. Our results are consistent with $\Lambda$ CDM + GR (L'Huillier, Shafieloo & Kim 2018, MNRAS 476, 3263).

With Arman Shafieloo and Alexei Starobinsky, we then combined the latest type Ia supernova data (Pantheon) with growth measurements (including eBOSS DR14Q) and obtained more stringent constraints, still consistent with $\Lambda$ CDM + GR (Shafieloo, L'Huillier & Starobinsky 2018, PRD 98, 083526).

Constraints on the growth index gamma and sigma_8 from model-independent tests of ΛCDM — Tests of the ΛCDM model — Shafieloo, L'Huillier & Starobinsky (2018), Physical Review D.

Realistic forecast: reconstructed Geff/G and fsigma8 for two modified-gravity scenarios (bump and dip). Both rule out GR at more than 2sigma around z approx 1. — Realistic forecast: reconstructed $G_\mathrm{eff}/G$ and $f\sigma_8$ for two modified-gravity scenarios (bump and dip). Both rule out GR at more than $2\sigma$ around $z \approx 1$ .

2023 · Phys. Rev. D 108 (2023) 023504

Joint reconstructions of growth and expansion histories from stage-IV surveys with minimal assumptions. II. Modified gravity and massive neutrinos

Calderón, R., L'Huillier, B., Polarski, D., Shafieloo, A., Starobinsky, A. A.

We reconstruct the effective gravitational coupling $G_\mathrm{eff}(z)$ as a Gaussian process from forecast stage-IV growth data. DESI-like surveys could detect departures from General Relativity if dark energy is well determined; massive neutrinos do not change this, but assuming a ΛCDM expansion biases the inferred $\Omega_\mathrm{m}$ and $\sigma_8$ .

DOI · arXiv:2301.00640

Modified gravity Growth of structure (RSD)Gaussian processes

Reconstructions of Omegade(z) (left) and the growth index gamma(z) (right) that fit the growth data better than ΛCDM, for three cases. — Reconstructions of $\Omega_\mathrm{de}(z)$ (left) and the growth index $\gamma(z)$ (right) that fit the growth data better than ΛCDM, for three cases.

2020 · MNRAS 494 (2020) 819

Defying the laws of Gravity I: model-independent reconstruction of the Universe expansion from growth data

L'Huillier, B., Shafieloo, A., Polarski, D., Starobinsky, A. A.

From redshift-space distortion data alone, we reconstruct the growth history with crossing statistics and Gaussian processes, derive the expansion history from it, and fit supernovae to constrain $\Omega_{\mathrm{m},0}$ and $\sigma_{8,0}$ . The results are consistent with flat ΛCDM and General Relativity.

DOI · arXiv:1906.05991

Modified gravity Growth of structure (RSD)Type Ia supernovae Gaussian processes First author

Theta(z) (top) and Ok(z) (bottom) from supernovae and BOSS/eBOSS BAO. A flat FLRW universe gives Theta = 1. — $\Theta(z)$ (top) and $\mathcal{O}_k(z)$ (bottom) from supernovae and BOSS/eBOSS BAO. A flat FLRW universe gives $\Theta = 1$ .

2018 · Phys. Rev. D 98 (2018) 083526

Falsifying ΛCDM: model-independent tests of the concordance model with eBOSS DR14Q and Pantheon

Shafieloo, A., L'Huillier, B.*, Starobinsky, A. A.

Combining model-independent expansion reconstructions from Pantheon supernovae and BAO, we test the FLRW metric and flatness, and use eBOSS DR14Q growth data to constrain $\Omega_\mathrm{m}$ , $\gamma$ and $\sigma_8$ . Everything is consistent with a flat FLRW universe, General Relativity and $\Lambda$ , with some tension at $z > 1$ .

DOI · arXiv:1804.04320

Key papers Curvature & FLRW Modified gravity Type Ia supernovae BAO Growth of structure (RSD)Iterative smoothing

Model-independent regions allowed by growth data (blue) compared with ΛCDM (red), at fixed gamma = 0.55 (left) and fixed sigma8 = 0.8 (right). — Model-independent regions allowed by growth data (blue) compared with ΛCDM (red), at fixed $\gamma = 0.55$ (left) and fixed $\sigma_8 = 0.8$ (right).

2018 · MNRAS 476 (2018) 3263

Model-independent cosmological constraints from growth and expansion

L'Huillier, B., Shafieloo, A., Kim, H.†

We reconstruct the expansion history from supernovae and fit growth-rate data to constrain $\Omega_\mathrm{m}$ , the growth index $\gamma$ and $\sigma_8$ without a dark energy model. The results agree with ΛCDM in General Relativity, and requiring a positive dark energy density tightens them further.

DOI · arXiv:1712.04865

Key papers Modified gravity Type Ia supernovae Growth of structure (RSD)First author With my students

Halo interaction rate versus mass in ΛCDM and in f(R), DGP and coupled dark energy simulations. — Halo interaction rate versus mass in ΛCDM and in $f(R)$ , DGP and coupled dark energy simulations.

Haloes beyond General Relativity

2017 · MNRAS 468 (2017) 3174

Dark matter haloes in modified gravity and dark energy: interaction rate, small- and large-scale alignment

L'Huillier, B., Winther, H. A., Mota, D. F., Park, C., Kim, J.

In N-body simulations of $f(R)$ gravity, DGP and coupled dark energy, $f(R)$ raises halo spin and weakens the spin alignment of interacting pairs, while only strongly coupled dark energy increases the halo interaction rate and the alignment of halo shapes with the large-scale structure.

DOI · arXiv:1703.07357

Key papers Modified gravity Dark energy Dark matter haloes Simulations First author

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