Speaker
Description
Current and anticipated large-scale structure surveys are mapping the Lyman-alpha forest on growing cosmological scales, enabling measurements of the Baryon Acoustic Oscillation (BAO) peak and motivating a careful accounting of theoretical systematics at sub-percent precision. Among these systematics, the inhomogeneous Ultra-Violet Background (UVB) has received growing attention, yet its large-scale fluctuations are rarely treated within a relativistic framework. We present a linear-theory description of large-scale UVB fluctuations, connecting ionising source phenomenology directly to large-scale structure observables. Our approach incorporates general relativistic radiative transfer corrections — of the same order as those identified in existing analysis of the relativistic Lyman-Alpha forest (Iršič et al., 2016) — and allows us to quantify their impact on clustering signatures in the cosmic ionising radiation field. The inclusion of GR radiative transfer corrections introduces sub-percent-level corrections to the UVB contribution to the clustering of the Lyman-alpha forest at ultra-large scales.