Dat Tan Nguyen

No causal-set everpresent-Lambda Model 1 history among 83,760 noise sequences fits DESI DR2 BAO and Pantheon+ supernovae together

Version 3. Causal set theory heuristically predicts a cosmological constant that fluctuates over cosmic history (everpresent Λ). Three independent preprints have compared its stochastic Model 1 with DESI: with DR1 through fitted w0, wa; with DR2 for six supernova-selected histori...

Everpresent Lambda Model 2 and DESI DR2: rare fits and a Bayes factor favouring LambdaCDM

In Model 2 of everpresent Λ (Zwane, Afshordi and Sorkin, ZAS) the dark energy fraction is Ωde = tanh Ω̂, with Ω̂ a Gaussian random function of ln a with amplitude α and coherence parameter μ. We found no test of it by other authors against BAO data since ZAS's own in 2018 (an exp...

Two corrected potential coefficients in SL(2) x R+ exceptional field theory, and the sign of its squared topological coupling

We test the SL(2) x R+ exceptional field theory of Berman, Blair, Malek and Rudolph at nonlinear order in the fields and in sign sectors other than the standard one. For the metric sector we compare the integrated exceptional field theory action with the integrated Einstein-Hilbe...

Everpresent Lambda Model 2 and DESI DR2: rare fits and a Bayes factor favouring LambdaCDM

In Model 2 of everpresent Λ (Zwane, Afshordi and Sorkin, ZAS) the dark energy fraction is Ωde = tanh Ω̂, with Ω̂ a Gaussian random function of ln a with amplitude α and coherence parameter μ. We found no test of it by other authors against BAO data since ZAS's own in 2018 (an exp...

The lattice offset of loop quantum cosmology is the Wheeler-DeWitt extension angle of each orientation branch: closed-form sLQC phase and unimodular tower for negative cosmological constant

In Wheeler-DeWitt (WDW) quantum cosmology with a massless scalar and a dynamical cosmological constant, the unimodular-time Hamiltonian at fixed scalar momentum has, for Lambda<0, a geometric (Efimov-like) tower of Lambda levels whose position is set by a self-adjoint extension a...

Signs and signatures in SL(2) x R+ exceptional field theory: Hull's starred theories from a non-Euclidean generalised metric

We determine, with every sign kept, which eleven- and ten-dimensional theories the SL(2) x R+ exceptional field theory of Berman, Blair, Malek and Rudolph describes when its generalised metric is not positive definite, for external signatures (8,1) and (9,0). For all twelve sign...

Two corrected potential coefficients in SL(2) x R+ exceptional field theory, and the sign of its squared topological coupling

We test the SL(2) x R+ exceptional field theory of Berman, Blair, Malek and Rudolph at nonlinear order in the fields and in sign sectors other than the standard one. For the metric sector we compare the integrated exceptional field theory action with the integrated Einstein-Hilbe...

A closed quantum universe with a massless scalar in unimodular time: a truncated Efimov tower for negative Lambda, and an exploratory Gamow-law check for small positive Lambda

For a closed Friedmann universe with a massless scalar field and a unimodular (dynamical) cosmological constant, we compare with the known flat-space results in unimodular time. (i) At Lambda = 0 the Wheeler-DeWitt equation is a Bessel equation, giving the threshold phase delta0(...

Tunnelling of a closed quantum universe in unimodular and scalar-field time: identical barrier transmission and, assuming absolutely continuous spectra, opposite eventual fates

We study a closed Friedmann universe with a massless scalar field φ and a unimodular cosmological constant λ in canonical quantum cosmology, and compare two of the three clocks used in the flat case by Gielen and Menéndez-Pidal, the two that remain global in the closed model: uni...

Three tomographic redshift-dipole estimators barely respond to the observer's velocity in DESI-like quasar samples cut on observed redshift

The Doppler dipole in spectroscopic redshifts has been used to test, independently of source counts, whether the excess quasar and radio-source number-count dipole reflects our motion. Recent measurements with the tomographic redshift-dipole estimator report 196 km/s (combined eB...

Timescape versus ΛCDM with the Seifert et al. supernova method: a replication, an application to DES-Dovekie and a measurement-error test

Seifert et al. (2025) reported very strong evidence for the timescape cosmology over flat ΛCDM from Pantheon+ supernovae (ln B > 5 on the full sample) and moderate evidence (ln B > 1) when every supernova below z = 0.075 is removed. An independent implementation reproduces their...

The crossover of parametrized Schwarzschild quasinormal-mode overtones: a one-parameter local connection problem, tested numerically

Miyachi, Namba, Omiya and Oshita (arXiv:2512.18631) showed with exact WKB that parametrized corrections δV = f Σj αj r−j to the Regge–Wheeler potential change the high-overtone asymptotics of Schwarzschild quasinormal modes. For j = 4, Re ωN grows as N1/5 once α42|ω| ≫ 1, and the...

A negative Delta-BIC is not a detection: calibrating an orbit-versus-noise test on 87 RR Lyrae binary candidates

Binary companions to RR Lyrae stars are sought through the light-travel-time effect (LTTE) in O−C pulsation timing. The same stars show stochastic period fluctuations, which produce O−C excursions of similar size and timescale. This note measures what an information-criterion com...

The crossover of parametrized Schwarzschild quasinormal-mode overtones: a one-parameter local connection problem, tested numerically

Miyachi, Namba, Omiya and Oshita (arXiv:2512.18631) showed with exact WKB that parametrized corrections δV = f Σj αj r−j to the Regge–Wheeler potential change the high-overtone asymptotics of Schwarzschild quasinormal modes. For j = 4, Re ωN grows as N1/5 instead of approaching l...

Stochastic period fluctuation as a null hypothesis for RR Lyrae binary candidates identified from O−C timing

Searches for binary companions to RR Lyrae stars using the light-travel-time effect (LTTE) in observed-minus-calculated (O−C) pulsation timing have produced candidate lists numbering in the dozens, the largest containing 87 objects from OGLE bulge photometry. Independently, it is...

Stochastic period fluctuation as a null hypothesis for RR Lyrae binary candidates identified from O−C timing

Searches for binary companions to RR Lyrae stars using the light-travel-time effect (LTTE) in observed-minus-calculated (O−C) pulsation timing have produced candidate lists numbering in the dozens, the largest containing 87 objects from OGLE bulge photometry. Independently, it is...

How sharp is the radial acceleration relation's transition? A calibration-limited measurement of the interpolating-function index, and the exclusion of a C0 onset to weak gravity

Version 4. This version corrects twelve errors found over three rounds of adversarial pre-publication review; versions 1–3 are withdrawn. The measurement itself is unchanged and has been reproduced independently, from the printed equations and the public SPARC release, by three r...

The unit of analysis in two claimed detections of open-cluster tidal-tail asymmetry

Two recent results are read as evidence that the tidal tails of nearby open clusters are asymmetrically populated, with more stars in the leading tail than in the trailing one. Kroupa et al. (2024) combine six teams' member catalogues for four clusters and report an 8.99σ falsifi...

How sharp is the radial acceleration relation's transition? A calibration-limited measurement of the interpolating-function index, and the exclusion of a C0 onset to weak gravity

Version 3. Attributes the interpolating-function family to Milgrom's n-family (Famaey & McGaugh 2012; Desmond, Hees & Famaey 2024, Eq. 7a) — the family is standard, the measurement with a systematic budget is what is new. Adds a §4 comparison with Desmond et al.'s n = 0.78 ± 0.03...

How sharp is the radial acceleration relation's transition? A calibration-limited measurement of the interpolating-function index, and the exclusion of a C0 onset to weak gravity

Version 2. Adds a comparison with the published SPARC MOND fits of Li, Lelli, McGaugh & Schombert (2018, A&A 615, A3), which reported the same α–mass-to-light degeneracy from the opposite side and closed it with a 1.7% prior on a_0. That reference was missing from v1 and its omis...