The ETHOS project provides a framework to map different dark matter models into effective structure formation models.
Paper I: From Dark particle physics to the matter distribution of the Universe
Francis-Yan Cyr-Racine, Kris Sigurdson, Jesus Zavala, Torsten Bringmann, Mark Vogelsberger, and Christoph Pfrommer:
We formulate an effective theory of structure formation (ETHOS) that enables cosmological structure formation to be computed in almost any microphysical model of dark matter physics. This
framework maps the detailed microphysical theories of particle dark matter interactions into the
physical effective parameters that shape the linear matter power spectrum and the self-interaction
transfer cross section of non-relativistic dark matter. These are the input to structure formation
simulations, which follow the evolution of the cosmological and galactic dark matter distributions.
Models with similar effective parameters in ETHOS but with different dark particle physics would
nevertheless result in similar dark matter distributions. We present a general method to map an
ultraviolet complete or effective field theory of low energy dark matter physics into parameters
that affect the linear matter power spectrum and carry out this mapping for several representa-
tive particle models. We further propose a simple but useful choice for characterizing the dark
matter self-interaction transfer cross section that parametrizes self-scattering in structure formation
simulations. Taken together, these effective parameters in ETHOS allow the classification of dark
matter theories according to their structure formation properties rather than their intrinsic particle
properties, paving the way for future simulations to span the space of viable dark matter physics
relevant for structure formation.
Paper II: Dark matter
physics as a possible explanation of the small-scale CDM problems
Mark Vogelsberger, Jesus Zavala, Francis-Yan Cyr-Racine, Christoph Pfrommer,
Torsten Bringmann, and Kris Sigurdson:
We present the first simulations within an effective theory of structure formation (ETHOS),
which includes the effect of interactions between dark matter and dark radiation on the linear
initial power spectrum and dark matter self-interactions during non-linear structure formation.
We simulate a Milky Way-like halo in four different dark matter models in addition to the cold
dark matter case. Our highest resolution simulation has a particle mass of 2.8 × 10 4 M and a
softening length of 72.4 pc. We demonstrate that all alternative models have only a negligible
impact on large scale structure formation and behave on those scales like cold dark matter.
On galactic scales, however, the models significantly affect the structure and abundance of
subhaloes due to the combined effects of small scale primordial damping in the power spectrum and the late time self-interaction rate in the center of subhaloes. We derive an analytic
mapping from the primordial damping scale in the power spectrum to the cutoff scale in the
halo mass function and the kinetic decoupling temperature. We demonstrate that it is possible
to find models within this extended effective framework that can alleviate the too-big-to-fail
and missing satellite problems simultaneously, and possibly the core-cusp problem. Furthermore, the primordial power spectrum cutoff of our models naturally creates a diversity in the
circular velocity profiles of haloes, which is larger than that found for cold dark matter simulations. We also show that the parameter space of models can be constrained by contrasting
model predictions to astrophysical observations. For example, some of our models may be
challenged by the missing satellite problem if baryonic processes were to be included and
even over-solve the too-big-to-fail problem; thus ruling them out.