Where the Dark Things Are Astrophysical uncertainties in dark-matter detection

Annika Peter

McCue Fellow

UC Irvine

Dark-matter searches

Signal Particle physics Astrophysics

Mass Spin Cross sections Family

Where is it? How fast is it?

(NB: Sometimes the “particle” properties can imprint themselves here)

Nuclear recoils Gammas Neutrinos

Dark-matter searches

Goal # 2:

Invert this equation

Signal Particle physics Astrophysics

Goal # 1: DETECT SOMETHING!

Dark-matter astrophysics

•  What do we know?

•  What don’t we know?

•  How can we find out what we don’t know?

•  Local neighborhood –  Direct detection

–  Neutrinos from solar/Earth WIMPs

•  Milky Way substructure –  Indirect detection

(NB: small slice of interesting topics)

Local Neighborhood

Direct detection

WIMP Mass mΧ

Nucleus Mass mA

v

Energy Q

Who’s the wimp now, sucker?

©Annika Peter

Direct detection

Energy Q

Q

dR/

dQ

Norm ~ σρ/mχ

Direct detection

Energy Q

Q

dR/

dQ

High mχ

Low mχ

Direct detection

Energy Q

Q

dR/

dQ

High speed

Low speed

WIMPs in the Sun and Earth

from Antares website

(Press & Spergel 1985, Krauss et al. 1985, Silk et al. 1985, Gould 1987, Griest & Seckel 1987, Kamionkowski 1991)

Γ ~ Cα

Flux big: Smallish mass High cross section High local density Speeds low so WIMPs scatter below escape velocity

Flux small: High mass Low cross section Low local density High speeds

Spectrum: More high-E neutrinos for high mass

Local density, or, where does 0.3 GeV/cc come from?

Dark matter Data we have:

• Density profiles of stellar populations. • Stellar motions.

Data ρ 1.  Assume equilibrium (or else things become MUCH harder) 2.  Stellar motions + density profilegravitational force F or Φ

1.  Jeans equations 2.  Distribution function

3.  Poisson equation: Φ ρ

This year

1. 1204.3924

Moni Bidin+ claim there is

NO

dark matter in the disk.

2. 1205.4033

Message (my paraphrase): “Maybe you should read Ch. 4 of Binney & Tremaine BEFORE making big claims about dark matter using disk stars.”

ρ=0 ρ=0.3±0.1 GeV/cc

3. 1206.0015 Garbari, Liu, Read & Lake Reanalysis of classic K dwarf data set.

Message: Use simulations to test your density-extraction method and assumptions.

ρ=0.85±0.5 GeV/cc

Velocity distribution

1.  Galactocentric energy scale: Smooth Milky Way halo properties? –  vRMS ~ (M/R)1/2

–  R ~ M1/3

  vRMS ~ M1/3

Velocity distribution

1.  Galactocentric energy scale

2.  Large-scale features from assembly history? (see also Kuhlen+2010, 2012; Lisanti & Spergel 2011; Read+2008, 2009; Ling+2009)

Vogelsberger+ 2009

Purcell+ 2009

Velocity distribution

1.  Galactocentric energy scale

2.  Large-scale features from assembly history?

3.  Small-scale features (fine- vs. coarse-grained distribution function, and mpc scales; Schneider+2010)

Image credit: V. Springel

Velocity distribution

1.  Galactocentric energy scale

2.  Large-scale features from assembly history?

3.  Small-scale features

4.  How much gets bound to the Solar System? (Gould 1991; Peter 2009; Bruch, Peter+ 2009; Sivertsson & Edsjö 2012)

Parameter estimation gone bad

Halo hypothesis

•  Mock data sets for 4 future experiments.

•  Fit to the energy spectrum of events.

•  Several hundred events total!

! "!! #!! $!! %!! &!!!

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Peter (2011), Phys. Rev. D 83, 125029

Parameter estimation gone better

(Shan+2008-2012; Alves, El Hedri & Wacker 2012; Kavanaugh & Green 2012)

(See Lee & Peter 2012 for the awesomeness of directional detection)

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Peter (2011), Phys. Rev. D 83, 125029

What we can and can’t do

•  Velocity distribution: we can get a handle on this if detection.

•  Density: cross sections totally degenerate with the local density. – We MUST have additional information to

distinguish the two.

Milky Way dwarf galaxies

Milky Way dwarf galaxies

Image credit: James Bullock

Segue I

L ≈ 300 L'

(M/L)1/2 ≈ 3500Υ!

Image credit: Marla Geha

Why Milky Way dwarfs are awesome

•  They are close.

•  There are few foregrounds (e.g., Υhuge).

•  Assuming equilibrium, can get a good estimate of mass within r1/2 with stellar kinematics (Walker+2009, Wolf+2010). ⇒ They have a ton of dark matter (Strigari+

2007,2008; Martinez+2009,2011).

Flux ! J(!") =!

!"

!!2dld"

Possible issues

•  TIDES (questions equilibrium assumptions): – Read+2006, Peñarrubia+2008, Muñoz+2010,

Deason+2012

•  Cusp/core (Walker & Peñarrubia 2011)

Some issues can be dealt with

Walker+ 2011 Carina

Possible issues

•  TIDES (questions equilibrium assumptions): – Read+2006, Peñarrubia+2008, Muñoz+2010,

Deason+2012

•  Cusp/core (Walker & Peñarrubia 2011)

•  Binary stars

•  Boost factors

•  …

Some issues can be dealt with

Draco Segue I (Martinez et al. 2009)

Fermi limits

Fermi-LAT, Martinez & Kaplinghat, 1108.3546

Geringer-Sameth & Koushiappas, 1108.2914

Summary Signal

Particle physics Astrophysics

Energy Q

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