Speaker
Description
deviations in the dark energy sector. We systematically compare $\Lambda$CDM with phenomenological extensions inspired by Scalar–Vector–Tensor (SVT) modified gravity, collectively denoted as poly$\Lambda$CDM. These models introduce exotic components with constant equations of state, parametrised by their present‑day density parameters $\Omega_v$, $\Omega_x$, $\Omega_z$ and a fixed exponent $\alpha = 0.5$ for the SVT sector. We use Pantheon+SH0ES Type Ia supernovae (1701 objects), DESI early data release baryon acoustic oscillations (12 correlated measurements), and the Planck 2018 compressed likelihood for the CMB angular scale $\ell_a$. For the CMB we employ the exact sound horizon expression, relating $r_s(z_*)$ to the drag‑epoch scale $r_d$ via the integral correction, with baryon and photon densities scaled consistently with $H_0$. Model comparison uses the Akaike Information Criterion corrected for small samples (AICc). We study a subset of poly$\Lambda$CDM models. Single‑component extensions ($v\Lambda$CDM and $x\Lambda$CDM) yield $\Delta\mathrm{AICc} = 1.07$ and $0.90$ respectively, indicating statistical equivalence with $\Lambda$CDM. Two‑component models ($xz\Lambda$CDM and $vx\Lambda$CDM) are disfavoured ($\Delta\mathrm{AICc} = -1.13$ and $-0.11$). Constraints on exotic densities – e.g. $\Omega_v = 0.37 \pm 0.21$ from $v\Lambda$CDM – provide useful bounds on modified gravity effects across cosmic history. Although $\Lambda$CDM remains the most parsimonious description of current data, the extended models are not ruled out and serve as valuable phenomenological tools to test fundamental physics, particularly in quantifying deviations from a cosmological constant. Current, and upcoming surveys, with advanced data analysis, will sharpen these constraints. This work can be considered as an novel observational test a complementary to gravitational waves potentially testing novel cosmological theories that rise from advanced tensor theories (ATT), advanced manifold metric pairs (AMMP), functors of actions theories (FAT).