Everpresent Lambda Model 2 and DESI DR2: rare fits and a Bayes factor favouring LambdaCDM
Year: 2026
Type: preprint
Abstract: In Model 2 of everpresent Lambda (Zwane, Afshordi and Sorkin, ZAS) the dark energy fraction is Omega_de = tanh(Omega_hat), with Omega_hat a Gaussian random function of ln a with amplitude alpha and coherence parameter mu. We found no test of it by other authors against BAO data since ZAS's own in 2018. We draw 40,000 histories at each of 25 points of an (alpha, mu) grid and confront them with DESI DR2 BAO and Pantheon+ supernovae, refitting omega_m and omega_b (BBN prior) for each history, with z* and z_d from a recombination solver run on each history's own expansion. The protocol was committed before the formal runs (our own time stamps) and reviewed by a separate AI instance; changes made after the first results (the sound horizon, the omega_m range, the Bayes-factor computation and the final optimiser) are disclosed. Results. Model 2 is excluded by our pre-set rule at 6 grid points. At 15 points some histories come within Delta chi^2 of 4 of LambdaCDM, at most 21 of 40,000. At ZAS's best-fit point, 178 of 400,000 histories do (4.4e-4); adding the CMB acoustic scale leaves 7. The fitting histories have H0 from 37 to 168 km/s/Mpc (median 56). Averaged over histories, the Bayes factor favours LambdaCDM at every grid point, by about 37:1 at the least unfavourable one (a point estimate uncertain by about a factor of two, flagged unreliable because its effective sample size is below 10); a wider h prior for LambdaCDM would lower these odds. A 2018 statement. ZAS wrote that at their best fit there is a 78% chance that Omega_de is negative somewhere in 1.5 < z < 3. Under their printed model we find 57% (35% given Omega_de of about 0.7 today). Of the readings we tried, only a process in redshift with mu doubled gives about 78%; their Fourier-space formula implies the doubled mu. Caveats. The CMB enters only through theta*. One registered control failed. This is a short data note. The archive contains the code, protocol with amendments, plan review, literature-search log, red-team findings, all run outputs and a script that fetches the public data.
Author: Nguyen, Danny
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7215065545