Simulating Structure Formation in SIDM
Mark Vogelsberger

Cosmic Controversies Conference,Chicago, October 2019

MV, Marinacci,Torrey, Puchwein
Nature Reviews Physics 2019

MV, Marinacci, Torrey, Puchwein
Nature Reviews Physics 2019

The IllustrisTNG Simulations
Illustris galaxy formation model (MV+ 2013, 2014 Nature)+novel low accretion rate SMBH model (Weinberger+ w/ MV 2017)

dwarfsL* galaxies

galaxy clusters

Galaxy Clustering: Simulation vs. Observations

two-pointcorrelation
function

Springel+ w/ MV 2018

Impact of Baryons on Matter Power Spectrum
baryon physics
modifies matterpower spectrum

inclusion ofbaryonic physics
is crucial

matter powerspectra

Springel+ w/ MV 2018

Cold Dark Matter Alternatives●

missing satellites problem●core/cusp problem●

too-big-to-fail problem●

diversity problem●

plane of satellites problem

small-scale
CDM problems

Cold Dark Matter Alternatives

Solutions:●baryonic physics (most small-scale problems have been identified in DM only simulations)?

●

uncertainties in observations / measurements / modeling?

●

DM is not exactly CDM?

Cold Dark Matter Alternatives●

missing satellites problem●

core/cusp problem●

too-big-to-fail problem●

diversity problem●

plane of satellites problem

small-scale
CDM problems?

Cold Dark Matter Alternatives●

missing satellites problem●

core/cusp problem●

too-big-to-fail problem●

diversity problem●

plane of satellites problem●

generic WIMP not detected so far

small-scale
CDM problems?

‘fundamental’problem

Going beyond CDM: Some Candidates

Warm Dark Matter?

Self-Interacting Dark Matter?

BECDM?

...?

Going beyond CDM: Some Candidates

Warm Dark Matter?

Self-Interacting Dark Matter?

BECDM?

...?

Self-Interacting Dark Matter

The Outcome of SIDM Simulations

impact of SIDM on dark matter
density field of MW-like halos

MV+ 2012

Self-Interacting Dark Matter: Implications for Subhalos

circularvelocities

crosssection

constantve
loc
deen
nt

can be achieved with constant andvelocity-dependent cross sections

ep-d

Zavala, MV, Walker 2013

ityMV, Zavala, Loeb 2012

SIDM simulations alleviate thetension with TBTF problem

Self-Interacting Dark Matter: Implications for Subhalos

circularvelocities

crosssection

constantve
loc
deen
nt

can be achieved with constant andvelocity-dependent cross sections

ep-dZavala, MV, Walker 2013

ityMV, Zavala, Loeb 2012

SIDM simulations alleviate thetension with TBTF problem

How often do SIDM particles scatter on average?

large cross section

tions

typically only a few scattering
events per Hubble time aresufficient to create cores

io nectro sgec
la rsma llscatterings

sscrossersmaller cross sections

sec

mean free path~100 kpc mean freepath in inner haloMV, Zavala, Loeb 2012

CDM: The Diversity Problem

OBSERVATIONS“The severity of the problem … with the apparent failure of‘baryon physics’ to solve it begs for the consideration ofvarious alternatives [like] ‘self-interacting’ dark matter,...”

THEORY

Oman+ 2015

spread at fixed Vmax

Diversity in SIDM?

increased diversity
in SIDM simulations

self-interactions allow lower Vcirc(2kpc) [lowcentral densities in both baryons and darkmatter]; high values of Vcirc(2kpc) stillachieved with compact baryonic disks

Creasey+ w/ MV 2017[see also Ren+ 2018]

ETHOS – Effective Theory of Structure Formation: Ingredients

Basic Idea:I) Effective theory of structure formation (ETHOS) enables cosmological structure formation to becomputed in almost any microphysical model of dark matter physics.

II) Framework maps detailed microphysical theories of particle dark matter interactions into physicaleffective parameters that shape linear matter power spectrum and self-interaction transfer crosssection of nonrelativistic dark matter.

ETHOS – Effective Theory of Structure Formation: Ingredients
Initial Conditions

initial powerspectrum

damping+
DAO

self-interactions affect evolutionof early and late universe=self-consistent SIDM model

Self-Interactions

dwarfscrosssection

MV+ 2016
Cyr-Racine+ 2016

clusterETHOS: A Milky Way-like Halo Simulation

MV+ 2016

ETHOS: Impact on Milky Way Subhalos

circular velocity
profilessubhaloabundanceboth CDM abundance and structuralproperties altered simultaneously

MV+ 2016

ETHOS: Damping vs. SIDM

disentangling theimpact of SIDM andpower spectrum
modifications

self-interactions do
not change thesubhalo abundanceMV+ 2016

ETHOS: The High-Redshift UniversezLovell, Zavala, MV+ 2018

Inelastic SIDM: Two-State SIDM Model

How does structure formation change
if we allow for inelastic collisions?

specific model allows
exothermic, but noendothermic reactions

crosssections

MV, Zavala, Schutz, Slatyer 2019[see also Todoroki & Medvedev 2018]total DM density

Elastic SIDM
vs.
Inelastic SIDM

Inelastic SIDM

Elastic SIDM

ground state DM density

excited state DM density

exothermic reactions‘evaporate’ halo cores

MV, Zavala, Schutz, Slatyer 2019

Evaporation: Unbinding Dark Matter Particles From Halounbound particles
due to de-excitationenergydistribution

dimensionless energy distribution ofgravitationally unbound particles
MV, Zavala, Schutz, Slatyer 2019

Inelastic SIDM: Halo Dark Matter Density Profiles

more efficient coreformation withininelastic SIDM

halo DM dMV, Zavala, Schutz, Slatyer 2019

Inelastic SIDM: Injected Energy

energy injection isequivalent to a few 100
million supernovae type II

injected energy into halo
due to level de-excitation

MV, Zavala, Schutz, Slatyer 2019

Subhalo Properties

inelastic SIDM creates larger subhalo cores thanelastic SIDM for the same cross section normalization

MV, Zavala, Schutz, Slatyer 2019

Comparison to Elastic Models: Implications for Cross Section Constraints

an elastic model with a ~5 times
larger cross section leads to acentral density reduction similar
to the inelastic model

implications for crosssection constraints?

MV, Zavala, Schutz, Slatyer 2019

Summary●●●●CDM galaxy formation simulations reproduce observed galaxy population on large scales(e.g., clustering, luminosity functions, etc.)

SIDM can alleviate outstanding small-scale CDM problems(e.g., too-big-to-fail problem, diversity problem, etc.)

ETHOS: self-consistent SIDM models with modified initial conditions(i.e. early and late self interactions)inelastic SIDM creates larger density cores for the same cross section normalization(i.e. can create same core sizes as elastic models with smaller cross section normalization)

Summary
●

●

●

●

CDM galaxy formation simulations reproduce observed galaxy population on large scales(e.g., clustering, luminosity functions, etc.)

SIDM can alleviate outstanding small-scale CDM problems(e.g., too-big-to-fail problem, diversity problem, etc.)

ETHOS: self-consistent SIDM models with modified initial conditions(i.e. early and late self interactions)inelastic SIDM creates larger density cores for the same cross section normalization(i.e. can create same core sizes as elastic models with smaller cross section normalization)

Future?
●More SIDM simulations with baryonic physics and better understanding of their interplay.

●

Retuning of feedback physics?

●How to distinguish baryonic feedback effects from alternative DM?

SIDM: DM + Baryons

dwarf galaxy within CDM and different SIDM
models with baryons using Illustris(~IllustrisTNG) galaxy formation modelMV+ 2014

density
profilesstellar massstellar density profile correlates withcentral cross section leading tolower central densities for models
with larger central cross sections

SIDM: DM + Baryons

dwarf galaxy within CDM and different SIDM
models with baryons using Illustris(~IllustrisTNG) galaxy formation modelMV+ 2014

density
profilesstellar mass

Robles+ 2017 [SIDM + FIRE]