The LS4 cosmology program seeks to use Type Ia supernovae and gravitationally-lensed supernovae to make advances in the measurement of the dark energy equation of state, tests of General Relativity through the growth rate of structure, and the Hubble constant. We advocate an LS4 survey in the ~20,000 sq. deg. of sky having low dust extinction between -80o < Dec < +20o. Interleaving the LS4 filters will allow for a 2 day cadence in i band and a 4 day cadence in g and z. This allows about half of the survey area to be monitored, with the window advancing eastward during the year. An unusually strong effort will be made to calibrate the supernova survey to a precision similar to that of the Roman Space Mission. For this purpose we have an NASA gramt and a collaboration with a group from NIST and a group working with Chris Stubbs to carry out this calibration.
Scientific Goals:
1. A minimum of 800 unbiased SNe Ia with LS4 light curves, spectroscopically-typed, with host redshifts, and minimal Malmquist bias. These will serve to “anchor” the SN Ia Hubble diagram, and in combination with Rubin and Roman, constrain the time-evolution of the dark energy equation of state.
2. 5000 SNe Ia with LS4 light curves with minimal Malmquist bias over a solid angle of 20,000 sq deg. in the combined footprint of the DESI + 4MOST galaxy redshift surveys. Spectroscopic classification is desired for these. Host galaxy redshifts – primarily from DESI and 4MOST will be needed. Cross-correlation of the SN velocity field with the DESI and 4MOST galaxy density field will constrain the growth of structure to twice the accuracy of DESI or 4MOST alone.
3. SNe experiencing strong-lensing, such that the time delay between the lensed images and the brightness (for SNe Ia and II) can be used to improve the measure of the Hubble constant using a technique independent of the existing distance ladder.
4. Obtain the best light curves for nearby SNe Ia that could be used, along with techniques like Cepheids and TRGB, to measure the Hubble constant.
5. Improve the dynamic range and temporal sampling of the Rubin wide-fast-deep survey.
