# Quadratic genetic modifications: a streamlined route to cosmological simulations with controlled merger history

## TL;DR

This paper introduces quadratic genetic modifications for cosmological simulations, enabling controlled variation of merger histories by adjusting local variance, which enhances the study of galaxy evolution.

## Contribution

It extends existing genetic modification techniques to include quadratic features like local variance, providing a new method for controlling galaxy merger histories in simulations.

## Key findings

- Developed an efficient algorithm for quadratic modifications.
- Demonstrated control of variance in a toy model.
- Clarified the formulation of genetic modifications.

## Abstract

Recent work has studied the interplay between a galaxy's history and its observable properties using "genetically modified" cosmological zoom simulations. The approach systematically generates alternative histories for a halo, while keeping its cosmological environment fixed. Applications to date altered linear properties of the initial conditions such as the mean overdensity of specified regions; we extend the formulation to include quadratic features such as local variance, which determines the overall importance of smooth accretion relative to mergers in a galaxy's history. We introduce an efficient algorithm for this new class of modification and demonstrate its ability to control the variance of a region in a one-dimensional toy model. Outcomes of this work are two-fold: (i) a clarification of the formulation of genetic modifications and (ii) a proof of concept for quadratic modifications leading the way to a forthcoming implementation in cosmological simulations.