Confronting Everpresent Λ with DESI DR2 Baryon Acoustic Oscillations

Everpresent Λ is a causal-set-motivated proposal in which the cosmological constant fluctuates with an amplitude δΛ ~ V^(-1/2), V being the four-volume of the past light cone. Following a recent suggestion to revisit this model in light of the DESI results, we confront its stochastic "Model 1" with the DESI Data Release 2 (DR2) baryon acoustic oscillation (BAO) measurements. We first reproduce the published behaviour of the model: the fraction of realizations that recollapse before today ("crashes") is 0.04% and 68% for α = 0.005 and 0.01, compared with the published 0.1% and 67.7%. We then evaluate 3×10^6 realizations on a grid of the model parameter α ∈ [0.005, 0.01] and the cold dark matter density ω_c ∈ [0.11, 0.13]. The best realization reaches χ²_min = 22.8 for the 13 DESI DR2 BAO points, compared with χ²_min = 10.3 for flat ΛCDM fitted with the same pipeline. The rare realizations that approach the data require h ≈ 0.49–0.64 and low ω_c, in tension with independent determinations. Within the stated assumptions, DESI DR2 BAO data therefore place Everpresent Λ (Model 1) under strong pressure. We state the limitations of this preliminary analysis.