# Can Assembly Bias Explain the Lensing Amplitude of the BOSS CMASS Sample in a Planck Cosmology?

## TL;DR

This study tests if galaxy assembly bias can resolve the discrepancy between observed galaxy clustering and lensing signals in the BOSS CMASS sample within a Planck cosmology, finding it insufficient to explain the difference.

## Contribution

The paper demonstrates that incorporating galaxy assembly bias into extended HOD models does not reconcile the observed clustering and lensing signals at Planck cosmology.

## Key findings

- Standard HOD models over-predict lensing signal by 20-40%.
- Assembly bias models do not resolve the clustering-lensing discrepancy.
- A persistent 31-34% mismatch remains despite extended models.

## Abstract

In this paper, we investigate whether galaxy assembly bias can reconcile the 20-40% disagreement between the observed galaxy projected clustering signal and the galaxy-galaxy lensing signal in the BOSS CMASS galaxy sample reported in Leauthaud et al. (2017). We use the suite of AbacusCosmos Lamda-CDM simulations at Planck best-fit cosmology and two flexible implementations of extended halo occupation distribution (HOD) models that incorporate galaxy assembly bias to build forward models and produce joint fits of the observed galaxy clustering signal and the galaxy-galaxy lensing signal. We find that our models using the standard HODs without any assembly bias generalizations continue to show a 20-40% over-prediction of the observed galaxy-galaxy lensing signal. We find that our implementations of galaxy assembly bias do not reconcile the two measurements at Planck best-fit cosmology. In fact, despite incorporating galaxy assembly bias, the satellite distribution parameter, and the satellite velocity bias parameter into our extended HOD model, our fits still strongly suggest a 31-34% discrepancy between the observed projected clustering and galaxy-galaxy lensing measurements. It remains to be seen whether a combination of other galaxy assembly bias models, alternative cosmological parameters, or baryonic effects can explain the amplitude difference between the two signals.