Exploring Beyond {\Lambda}CDM with the Weak Lensing Power Spectrum and Bispectrum

In this work, we present Fisher matrix forecast of the tomographic weak lensing power spectrum and bispectrum for three physically distinct types of models of beyond-$\Lambda$CDM: the CPL parametrisation of dynamical dark energy, interacting dark energy (IDE) with a dark sector energy-momentum exchange, and Hu-Sawicki models of $f(R)$ gravity. We find that for all three models, including the bispectrum significantly tightens the Fisher constraints: the bispectrum reduces the marginalised $1\sigma$ error on the CPL equation of state parameter from $\sigma(w_0) = 0.2511$ (power spectrum only) to $\sigma(w_0) = 0.1557$, on the IDE coupling from $\sigma(\alpha) = 2.6895$ to $\sigma(\alpha) = 0.2944$, and on the scalaron amplitude from $\sigma(\ln|f_{R0}|) = 2.236$ to $\sigma(\ln|f_{R0}|) = 2.237$ after full marginalisation over nuisance parameters e.g., photo-z error $\sigma_z$ and intrinsic alignment amplitude $\mathcal{A}_{\rm IA}$. We find that $f(R)$ models are the most sensitive to systematics and especially in bispectrum. The results also demonstrates the importance of higher order weak lensing statistics as a practical necessity to maximise the scientific return of Stage IV surveys.