Dark energy

6 papers

About 70% of the energy content of the Universe drives its accelerated expansion, yet its nature is unknown. In ΛCDM it is a cosmological constant; it could also be a dynamical field, or a sign that General Relativity breaks down on cosmological scales.

My approach is to let the data speak: reconstruct the expansion history without assuming any dark energy model, then ask which models, including Λ, remain consistent with it. I also use N-body simulations to understand how a dark energy that clusters would change the formation of structure.

Joint reconstructions of the effective gravitational coupling, H(z) and fsigma8(z) for three fiducial cosmologies; dashed lines show the truth. — Joint reconstructions of the effective gravitational coupling, $H(z)$ and $f\sigma_8(z)$ for three fiducial cosmologies; dashed lines show the truth.

2022 · Phys. Rev. D 106 (2022) 083513

Joint reconstructions of growth and expansion histories from stage-IV surveys with minimal assumptions I: dark energy beyond $\Lambda$

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

Gaussian processes reconstruct the dark energy density from forecast stage-IV supernova, BAO and redshift-space-distortion data, assuming only a flat FLRW universe that becomes matter-dominated at high redshift, which also yields the growth history. Several dark energy models can be distinguished from ΛCDM at $2\sigma$ or more.

DOI · arXiv:2206.13820

Dark energy Type Ia supernovae BAO Growth of structure (RSD)Gaussian processes

Deltachi2 distributions for ΛCDM and PEDE over Roman-like mocks from a third model; vertical lines mark the 95% and 99% limits. — $\Delta\chi^2$ distributions for ΛCDM and PEDE over Roman-like mocks from a third model; vertical lines mark the 95% and 99% limits.

2022 · JCAP 03 (2022) 047

Bayesian vs frequentist: comparing Bayesian model selection with a frequentist approach using the iterative smoothing method

Koo, H., Keeley, R. E., Shafieloo, A., L'Huillier, B.

On simulated Roman supernova data, Bayesian model selection finds the true model when it is among the candidates, but otherwise only picks the least wrong one. A frequentist test based on iterative smoothing can instead conclude that all tested models are false.

DOI · arXiv:2110.10977

Dark energy Type Ia supernovae Iterative smoothing Model selection

Distributions of Deltachi2 between the smoothed and best-fit models over WFIRST-like ΛCDM mocks, for ΛCDM, PEDE and Kink. — Distributions of $\Delta\chi^2$ between the smoothed and best-fit models over WFIRST-like ΛCDM mocks, for ΛCDM, PEDE and Kink.

2021 · JCAP 03 (2021) 034

Model selection and parameter estimation using the iterative smoothing method

Koo, H., Shafieloo, A., Keeley, R. E., L'Huillier, B.

Likelihood distributions derived from the non-parametric iterative smoothing method let us test a dark energy model and estimate its parameters without comparing it to an alternative. On WFIRST-like mocks we quantify how confidently different dark energy models can be distinguished.

DOI · arXiv:2009.12045

Dark energy Type Ia supernovae Iterative smoothing Model selection

Where a universe with a negative cosmological constant still accelerates today (white), accelerated only in the past (dark grey), or never accelerated (light grey), for Omegam = 0.3. — Where a universe with a negative cosmological constant still accelerates today (white), accelerated only in the past (dark grey), or never accelerated (light grey), for $\Omega_\mathrm{m} = 0.3$ .

2021 · Phys. Rev. D 103 (2021) 023526

Negative cosmological constant in the dark sector?

Calderón, R., Gannouji, R., L'Huillier, B.*, Polarski, D.

We study dark sectors made of a negative cosmological constant plus a late-time accelerating component. The acceleration is often transient and some models eventually contract; current data show no decisive evidence for a negative $\Lambda$ , but the best fits are phantom at $z \gtrsim 1$ .

DOI · arXiv:2008.10237

Key papers Dark energy

Ratio mu(k,z) of the k-essence to ΛCDM gravitational potential for sound speed cs2 = 10-4, non-linear (points) versus linear (dashed). — Ratio $\mu(k,z)$ of the k-essence to ΛCDM gravitational potential for sound speed $c_s^2 = 10^{-4}$ , non-linear (points) versus linear (dashed).

2020 · JCAP 04 (2020) 039

Parametrising non-linear dark energy perturbations

Hassani, F., L'Huillier, B., Shafieloo, A., Kunz, M., Adamek, J.

Using k-evolution N-body simulations, we quantify non-linear k-essence dark energy perturbations through an effective modification $\mu$ of the Poisson equation, show that linear theory is accurate at large sound speeds, and propose a simulation-calibrated parametrisation of $\mu$ .

DOI · arXiv:1910.01105

Dark energy Large-scale structure Simulations

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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