Forecasts for decaying dark matter from cross-correlation between line intensity mapping and large scale structures surveys

Axion-like particles (ALPs) are compelling candidates for dark matter with a broad range of possible masses and coupling strengths. These particles decay into two photons, contributing to cosmic background radiation, which may correlate with large-scale structure (LSS). ALPs with a mass around 1 eV decay into monochromatic photons in the near-infrared spectrum, which can be detected by the upcoming SPHEREx mission using line intensity mapping (LIM) technology. To search for ALP signals in SPHEREx, we calculate the cross angular power spectrum between the intensity maps and LSS probes. We employ several LSS probes, including galaxy clustering and weak lensing surveys conducted by the China Space Station Telescope (CSST), as well as CMB lensing performed by CMB-S4. Using a Fisher analysis, we place constraints on the ALP parameters, with uncertainties of \(\sigma (m_a) = 0.062\) and \(\sigma (g_{a\gamma \gamma }) = 0.19\) from the joint surveys. Our results suggest that the current bounds on \(g_{a\gamma \gamma }\) could be improved by an order of magnitude for ALPs in the mass range around 1 eV. The cross-correlation also allows for detection of star formation lines observed by SPHEREx, providing constraints on the amplitude and redshift exponent of their power spectrum with uncertainties of \(\sigma (A_\text {astro}) = 0.004\) and \(\sigma (\eta _\text {astro}) = 0.004\), respectively. Additionally, we consider intrinsic alignment (IA) as a systematic effect in the weak lensing survey. The IA amplitude and exponent are well constrained by the LIM-WL cross-correlation, yielding results of \(\sigma (A_{\text {IA}}) = 0.016\) and \(\sigma (\eta _{\text {IA}}) = 0.025\), which offer significant improvements over previous works related to CSST.