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Peer-reviewedCC BY 4.0The Astrophysical Journal

Testing ΛCDM versus Dynamical Dark Energy in 1 Yr: A DESI Spectroscopic Follow-up Program for Rubin Supernovae

  • Jannik Truong1
  • Greg Aldering2
  • Saul Perlmutter1,2
  • David Rubin3
  • David Schlegel2
  1. 1University of California
  2. 2E. O. Lawrence Berkeley National Laboratory
  3. 3University of Hawaií at Mānoa
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Abstract

Combined cosmological probes currently indicate that best-fit values in the w ₀ − w a parameterization of dynamical dark energy deviate from ΛCDM by ∼3 σ . In this work, we present a supernova (SN) survey capable of measuring dynamical dark energy at the >5 σ level with just 1 yr of data, starting in 2027. We first show that with the present values of w ₀ and w a , new Type Ia supernovae (SNe Ia) at redshifts of z ≲ 0.6 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 reprioritize the scheduling of already-planned DESI tile visits. This would yield 7500 near-peak transient spectra in 1 yr 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 2300 new SNe Ia at z < 0.3 with current SN, baryon acoustic oscillation, and cosmic microwave background data would push the tension with ΛCDM beyond 5 σ . 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.

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Cite

BibTeXRIS
BibTeX
@article{truong2026testing,
  title = {{Testing ΛCDM versus Dynamical Dark Energy in 1 Yr: A DESI Spectroscopic Follow-up Program for Rubin Supernovae}},
  author = {Jannik Truong and Greg Aldering and Saul Perlmutter and David Rubin and David Schlegel},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = sep,
  doi = {10.3847/1538-4357/ae9a98},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/ae9a98},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Testing ΛCDM versus Dynamical Dark Energy in 1 Yr: A DESI Spectroscopic Follow-up Program for Rubin Supernovae
AU  - Jannik Truong
AU  - Greg Aldering
AU  - Saul Perlmutter
AU  - David Rubin
AU  - David Schlegel
PY  - 2026
DA  - 2026/09/30
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/ae9a98
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/ae9a98
AB  - Combined cosmological probes currently indicate that best-fit values in the w ₀ − w a parameterization of dynamical dark energy deviate from ΛCDM by ∼3 σ . In this work, we present a supernova (SN) survey capable of measuring dynamical dark energy at the >5 σ level with just 1 yr of data, starting in 2027. We first show that with the present values of w ₀ and w a , new Type Ia supernovae (SNe Ia) at redshifts of z ≲ 0.6 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 reprioritize the scheduling of already-planned DESI tile visits. This would yield 7500 near-peak transient spectra in 1 yr 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 2300 new SNe Ia at z < 0.3 with current SN, baryon acoustic oscillation, and cosmic microwave background data would push the tension with ΛCDM beyond 5 σ . 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.
SN  - 0004-637X
SN  - 1538-4357
ER  -