arXiv subjects

Jannik Truong

Publications and source records attributed to Jannik Truong.

4 recordsLinked to original sources

arXiv2026

Testing $Λ$CDM versus dynamical dark energy in one year: A DESI spectroscopic follow-up program for Rubin supernovae

Combined cosmological probes currently indicate that best-fit values in the $w_0-w_a$ parametrization of dynamical dark energy deviate from $Λ$CDM by $\sim3σ$. In this work, we present a supernova survey capable of measuring dynamical dark energy at the $>5σ$ level with just one year of data, starting in 2027. We first show that with the present values of $w_0$ and $w_a$, new SNe Ia at redshifts $z\lesssim0.6$ near dark energy-matter equality would add the most constraining power. This is well within reach of the Vera C. Rubin Observatory and the Dark Energy Spectroscopic Instrument (DESI). Because cosmology measurements with SNe Ia quickly become systematics-limited, we focus on eliminating key systematics by using only a spectroscopically confirmed and volume-limited sample. In our proposed survey, SN alerts from Rubin would actively re-prioritize the scheduling of already-planned DESI tile visits. This would yield 7 500 near-peak transient spectra in one year without delaying DESI's primary survey. We forecast that if current best-fit $w_0-w_a$ values persist, combining just our volume-limited subset of 2 300 new SNe Ia at $z<0.3$ with current SN, BAO, and CMB data would push the tension with $Λ$CDM beyond $5σ$. This applies across a wide range of assumed uncertainties. To further circumvent systematics, we explore how DESI enables spectroscopic standardization via machine learning, offering a path toward a cosmology measurement independent of light-curve-based standardization. Finally, we discuss how early results from this program could inform future dark energy experiments.

astro-ph.CO↗

arXiv2026

The Carousel Lens II: Cosmological Constraints with GIGA-Lens

The nature of dark matter and dark energy are among the central questions in cosmology. Strong gravitational lenses with multiple source planes provide a geometric probe of cosmology: the ratio of deflection angles at different redshifts depends only on angular-diameter distances, constraining the matter density $Ω_m$ and the dark energy equation of state $w$. However, constraints from this technique have historically lagged behind those from the CMB, SNe Ia, and BAO. In this work, we present new cosmological constraints from the Carousel Lens, a cluster-scale lens with more than 40 extended images from 11 spectroscopically confirmed sources. Its relaxed core and rich set of extended images behind the main halo make it particularly suitable for cosmological inference. Using the GIGA-Lens pipeline, we construct a pixel-level lens model including six HST-detected sources and four mass components. From this model, we obtain $w$CDM constraints of $Ω_m = 0.34^{+0.16}_{-0.13}$ and $w = -1.31^{+0.35}_{-0.32}$ from the Carousel Lens alone, accounting for both statistical and systematic uncertainties. We further project that including four additional known higher-redshift sources, assuming similar fractional uncertainties, could improve the constraining power by ~80%, bringing the precision close to that of the CMB and SNe Ia. For an evolving dark energy model ($w_0w_a$CDM), the Carousel Lens alone yields constraints comparable to the CMB, providing an independent and complementary probe alongside SN Ia and BAO. While currently systematic uncertainties dominate, which we quantify through simulations, our results demonstrate that relaxed multi-source-plane cluster lenses can deliver competitive cosmological constraints. Further improvements are expected from reductions in systematics and from incorporating higher-redshift sources (known and new) with high-resolution imaging.

astro-ph.CO↗

arXiv2025

Fishing for the Optimal Roman High Latitude Time Domain Survey: Cosmological Constraints for 1,000 Possible Surveys

The upcoming Nancy Grace Roman Space Telescope is set to conduct a generation-defining SN Ia cosmology measurement with its High Latitude Time Domain Survey (HLTDS). However, between optical elements, exposure times, cadences, and survey areas, there are many survey parameters to consider. This work was part of a Roman Project Infrastructure Team effort to help the Core Community Survey (CCS) Committee finalize the HLTDS recommendation to the Roman Observations Time Allocation Committee. We simulate 1,000 surveys, with and without a conservative (volume-limited) version of the Vera C. Rubin Observatory Deep Drilling Field SNe Ia, and compute Fisher-matrix-analysis Dark Energy Task Force Figures of Merit (FoM, based on w0-wa constraints) for each. We investigate which survey parameters correlate with FoM, as well as the dependence of the FoM values on calibration uncertainties and the SN dispersion model. The exact optimum depends on the assumed dispersion model and whether Rubin DDF SNe Ia are also considered, but ~20% time in prism, ~30--40% time in Wide imaging and the remainder in Deep imaging seems most promising. We also advocate for "interlaced" cadences where not every filter is used in every cadence step to reduce overheads while maintaining a good cadence and increasing the number of filters compared to the Rose et al. (2021) reference survey (the prism has proportionately lower overheads and can be used for each cadence step). We show simulated light curves and spectra for the baseline HLTDS CCS recommendation and release distance-modulus covariance matrices for all surveys to the community.

astro-ph.CO↗

arXiv2025

DESI forecast for Dark Matter-Neutrino interactions using EFTofLSS

We apply the Effective Field Theory of Large Scale Structure (EFTofLSS) to non-standard models of dark matter with suppressed small-scale structure imprinted by early-time physics, here exemplified by interacting dark matter (IDM) coupled to standard model neutrinos, and cross-check that the EFTofLSS has no trouble replicating the real-space halo-halo power spectrum from N-body simulations. We perform forecasts for a DESI ELG-like experiment using the redshift-space power spectrum and find that, under very conservative priors on these parameters, the EFTofLSS is not expected to yield strong constraints on dark matter interactions. However, with a better understanding of the evolution of counterterms and stochastic terms with redshift, realistic IDM models could in principle be detected using the full-shape power spectrum analysis of such a spectroscopic galaxy survey.

astro-ph.CO↗