Probing Self-Interacting Warm via Matter Power Spectrum

Daniel Gift [email protected] Yang Institute for Theoretical Physics Stony Brook University

With Daniel Egana-Ugrinovic (Perimeter Institute) and Rouven Essig (YITP, SBU) Dark Matter: “Nightmare Scenario”

● Lots of efforts to measure: directly, indirectly, collider

● If it doesn’t interact with the Standard Model: How and what can we learn about Dark Matter (DM)? ● Dynamics of dark sector can be probed by measurements of

2 Daniel Gift Phenomenology 2020 [email protected] Structure in the

● Universe expands, size is measured by scale factor a;

a {

● Energy density dominated initially by radiation, later by matter

● Primordial fluctuations in otherwise homogeneous universe evolve ○ Overdensities draw in more matter, interactions, etc.

3 Daniel Gift Phenomenology 2020 [email protected] Matter Power Spectrum

● How big are the perturbations of various sizes today? ● Smallest sizes → biggest k values ● Shape tells us something about DM dynamics

4 Daniel Gift Phenomenology 2020 [email protected] Self-interacting Dark Matter

● Free streaming: any particle with a velocity will travel unless interrupted ● Self-scattering interrupts free-streaming

● Decouples when interaction rate (횪2→2) drops below Hubble expansion rate:

Happens at scale factor a = a dec

5 Daniel Gift Phenomenology 2020 [email protected] Self-interacting Dark Matter

● Free streaming: any particle with a velocity will travel unless interrupted ● Self-scattering interrupts free-streaming

● Decouples when interaction rate (횪2→2) drops below Hubble expansion rate:

Happens at scale factor a = a dec

6 Daniel Gift Phenomenology 2020 [email protected] Self-interactions and Acoustic Oscillations

● Self interactions → pressure

● Pressure waves drive out matter from overdensity at speed of sound

● Distance travelled by pressure wave = sound horizon (rs)

○ Perturbations suppressed at scales < rs

7 Daniel Gift Phenomenology 2020 [email protected] Suppression scales

● aNR: Scale factor when DM becomes non-relativistic

● Sound horizon depends mostly on aNR, but also partly on interaction strength

(through adec)

8 Daniel Gift Phenomenology 2020 [email protected] Excluded by halo shape/Bullet Cluster

1

/g) 2

Earlier decoupling means smaller sound horizon→ less suppression compared σ/m (cm Free to CDM streaming

~keV mass 9 Daniel Gift Phenomenology 2020 [email protected] KeV-scale Warm Dark Matter (WDM)

● All particles with velocity will free-stream ○ Travel furthest when relativistic

10 Daniel Gift Phenomenology 2020 [email protected] KeV-scale Warm Dark Matter (WDM)

● All particles with velocity will free-stream ○ Travel furthest when relativistic ● Small overdensities smooth out

11 Daniel Gift Phenomenology 2020 [email protected] KeV-scale Warm Dark Matter (WDM)

● All particles with velocity will free-stream ○ Travel furthest when relativistic ● Small overdensities smooth out

12 Daniel Gift Phenomenology 2020 [email protected] KeV-scale Warm Dark Matter (WDM)

● All particles with velocity will free-stream ○ Travel furthest when relativistic ● Small overdensities smooth out ● DM won’t have overdensities on scales below free streaming length

13 Daniel Gift Phenomenology 2020 [email protected] Free Streaming Suppression

14 Daniel Gift Phenomenology 2020 [email protected] High-k Power Spectrum

15 Daniel Gift Phenomenology 2020 [email protected] Big Picture

DM acoustic DM scattering freezes DM free-streams oscillations out, DM begins free-streaming

? DM becomes ? non-relativistic

16 Daniel Gift Phenomenology 2020 [email protected] Excluded by halo shape/Bullet Cluster

1 Acoustic

oscillations /g) 2 σ/m (cm Free streaming

mass 17 Daniel Gift Phenomenology 2020 [email protected] Preliminary Results

Excluded by halo shape/Bullet Cluster

Preliminary

18 Daniel Gift Phenomenology 2020 [email protected] Conclusions

● Self-Interactions affect WDM bounds ● Acoustic Oscillations and Free Streaming suppress structure formation ● Understanding the interplay of the two will help set more robust bounds ● Current work is making more precise the bounds given by Boltzmann evolver code

19 Daniel Gift Phenomenology 2020 [email protected] Thank You!

Daniel Gift Phenomenology 2020 [email protected] Backups aNR

● at which DM becomes non-relativistic: TDM = m

● Relationship between aNR and m depends on specific model

● ξ = TSM/TDM at TDM > m

22 Daniel Gift Phenomenology 2020 [email protected] Evolution of Perturbations

● During radiation domination:

● During matter domination:

● If perturbations suppressed during matter domination, will affect what we see

today

23 Daniel Gift Phenomenology 2020 [email protected] Sample model

● Scalar:

DM DM

DM DM 24 Daniel Gift Phenomenology 2020 [email protected] Excluded by halo shape/Bullet Cluster

1

Structure suppressed mostly by acoustic oscillations /g) 2

Structure suppressed first by acoustic oscillations and later by free streaming σ/m (cm

Structure suppressed mostly by free streaming a NR 25 Daniel Gift Phenomenology 2020 [email protected] Preliminary Results

Excluded by halo shape/Bullet Cluster

Preliminary

26 Daniel Gift Phenomenology 2020 [email protected]