The Dark Energy Spectroscopic Instrument: HOD-dependent systematics in modelling Baryon Acoustic Oscillations for Emission Line Galaxy and Modified Gravity analysis using overlapping photometric surveys.

The Dark Energy Spectroscopic Instrument (DESI) is designed to conduct a survey of 14000 square degrees over a five years period to constrain the expansion history of the Universe. DESI will produce precise measurements of Baryon Acoustic Oscillations (BAO) using four tracers spanning different redshift ranges. Therefore, a precise knowledge of the global error budget due to several systematics is required. Hence it is important to quantify the error of potential systematics and assure that the analysis pipeline is robust against them. In particular, we focus on the robustness of the BAO measurements against the Halo Occupation Distribution (HOD) model. We consider several HOD models for the Emission Line Galaxy (ELG) tracer and develop mocks using a common underlying dark matter simulation. We use the DESI official pipeline to apply the reconstruction procedure to enhance the BAO feature in our mocks and perform clustering measurements. Finally we perform BAO fits to quantify the systematics error due to the assumed HOD prescription and assess that our analysis pipeline is robust against HOD dependence for the DESI year 1 analysis. Additionally, we use the Integrated Software in Testing General Relativity (ISiTGR) within the context of the DESI lensing mock challenge to perform a modified gravity analysis between DESI and overlapping photometric surveys.