Image: Navarro et al.

The Physics of Fine TuningJune, 2017

Rocky KolbUniversity of Chicago

Dark Matter Shapes the Universe

Dark Matter: 25%

Dark Energy: 70%

Stars:0.8%

H & He:gas 4%

Chemical Elements: (other than H & He) 0.025%

Neutrinos:0.17%

Radiation: 0.005%

νe νμ ντ

??

• What is origin of normal-matter (baryon) density?

• Baryon density determined by baryon asymmetry of yet unknown origin:

• Asymmetric dark matter: same (yet unknown) mechanism generates DM asymmetry.

• Is ratio 6:1 because DM particle mass: baryon mass = 6:1?

• For most DM scenarios 6:1 is input, not output.

• Sensitivity of 6:1 on input parameters.

Why 6:1 in the cosmic recipe?

910b bn n

nγ

−−

• Dark matter drives structure formationo Do we “need” dark matter?o Structures would still form (probably top-down)

• Baryon only halos?

• Tuesday talk by Joe Silk, “Fine-tuning from stars to galaxies to supermassive black holes”, and Debora Aijacki, “Fine tuning or not in structure formation simulations”

• Why so many components?o Why is neutrino contribution 0.17%?

Why 6:1 in the cosmic recipe?

Dark Matter: goals and questions• Particle Physics:

Understand the nature of dark matter (DM) and how it is embedded within a deeper theoretical framework:

o If DM is a particle, want to know more than just mass, spin, o and couplings, want to know how it fits into a model or theory

o Want to know why DM exists

o Want to understand its contribution to the mass budget (why 6:1)

• Astrophysics:

Understand the role of DM in the evolution of the universe and structure formation:

o Is the DM completely cold?

o Is there only one DM component?

o Does DM have interactions that affect structure formation?

cluster dynamics

cluster gas in x-raysgravitational lensing

structure formation cluster collisionsbackground radiation

dwarf galaxies

observed

luminous disk

galactic rotation curves

nucleosynthesis

For 85 years dark matter has been a beast of a problem.

Where is Theseus when we need him?

Which experiment will serve as the sword of Aegeus?

Known particle speciesAntiquarksQuarks

AntileptonsLeptons

Images: CERN

and now the HIGGS!top bottom

strange charm

electron electron neutrino

muon muon neutrino

up down

tau tau neutrino

Force Carriers

photon gluon W Z graviton

Dark particle must be “A New Particle Species”Dark particle must be stable and massive and interact weakly

Particle dark-matter bestiary• (sub-) eV mass neutrinos (WIMPs exist!)

• sterile neutrinos, gravitini

• lightest supersymmetric particle

• lightest Kaluza-Klein particle

thermal relics, or decay of or oscillation from thermal relics

(hot)

(warm)

(cold)

(cold)

• Bose-Einstein condensates

• axions, axion miniclusters

• solitons (Q-balls, B-balls, …)

• supermassive WIMPZILLAs from inflation

nonthermal relics

from phase transitions

Interaction Strengthonly gravitational: WIMPZILLAsstrongly interacting: B balls

Mass10−22 eV (10−56 g) Bose-Einstein 10−8 Mʘ (10+25 g) axion miniclusters

Cold thermal relics*

* An object of particular veneration.

• DM species in thermal equilibrium at T > M with standard-model particles

• Equilibrium abundance of DM determined by M / T (no asymmetry)

• As universe expanded and cooled, DM species “froze-out”

• Present abundance determined by freeze-out

• Freeze-out: interplay between

DM—SM interaction strength (particle physics),

and expansion rate of the Universe (gravity).

Rel

ativ

e ab

unda

nce

M / T

equilibrium e−M / Tequilibrium e−M / Tequilibrium e−M / Tequilibrium e−M / T

101 102 103110−20

10−15

10−10

10−5

1

increasing σA

decreasing abundance

Cold thermal relics

á ñNR annihilation cross section × Møller flux …thermal average…

Ωh2 ≈ 0.12 ×áσAvñ

3×10−26 cm3 s−1

σ = 10−36 cm2 = α 2(150 GeV) 2

weak scale!

• velocity dependence• resonances• co-annihilation• log dependence on M• decay production• spin-dependence• asymmetries• …

Not quite so clean:

Final freeze-out abundance:

σ = 10 −36 cm2: the WIMP “Miracle”

mir·a·cle\ˈmir-i-kəl \

noun

1 : an extraordinary event manifestingdivine intervention in human affairs

I think you should be more explicit here in step two

WIMP hypothesis predicts DM mass range, and DM—SM interaction strength(But not 6:1)

WIMP hypothesis relatesDM mass and DM interactions to a “known” scale

WIMPs and Cold Dark Matter (CDM)• Cold Dark Matter

o Cold: have a negligible velocity during structure formationo Dark: can’t “see” them in any wavelengtho Matter: are massive

• WIMPs are cold thermal relicso Part of the thermal bath in the early universeo Present abundance determined by freeze-outo Froze out when nonrelativistic (at least semi-relativistic)

• Cold Dark Matter need not be a WIMPo Axions are CDM but not a thermal relico Asymmetric relics are CDM

• WIMPS need not be Cold Thermal Relic o GUTzillas

Follow the WIMP thread

through the dark-matter labyrinth

In the early universeIn the early universe

WIMPWIMP

áσAvñ= 3×10−26 cm3 s−1

quark quark

WIMP annihilation áσAvñ= 3×10 −26 cm3 s−1

• Galactic Centerknow where to looklargest signallargest backgrounds

• Nearby subclumpsclean: no baryonsdon’t know where to looksignal down 10−3

• Dwarf spheroidals (/) > 3000know where to look (about 20)clean: very few baryonssignal down another 10−3

Where to look for it

• Charged particles: p, high-energy e−e+

easy to detectastronomical backgroundsbent by magnetic field

• Continuum photons, neutrinosγ easy to detectastronomical backgroundsν hard to detect/often not dominant

• Monoenergetic photon line (χχ → γγ )low background(probably) low signal“golden” detection channel

What to look for

( ) ( )2,

2WIMPline of region of

sight interest

, ,vcos

4 2A

r s l bdNd Eds b db dl

dE dE Mg n rs

p

é ùF ë û= ò

Diffuse γ - rays from the galactic centerGoodenough, Hooper, Dalyan, Portillo, Rood, Boyarsky, Malyshev, Ruchayskiy, Linden, Abazajian, Kaplinghat, Gordon, Macias, Canac, Horiuchi, Slayter, Berlin, Cholis, McDermott, Lin, Finkbeiner, Calore, Cholis, Weniger, …

• Start with FERMI public data and tools• Pick search region of interest (around galactic center)• Remove point sources and model and remove every non-DM astrophysical source• Fit excess (if any) to cross section & annihilation channel(s)

Dalyan, et al. 1402.6703

M = 32.25 GeVannihilation to bb σ v = 1.7×10−26 cm3/s

Calore, Cholis, Weniger JCAP 2015

2

0.22 0.13 0.231 0.31 1 0.095 0.17

Model Parameters dof -valueBPL 1.42 2.63 2.06 GeV 1.06 0.39

B

p

E

bb

c

a a+ + +- - -= = =

6.4 0.28 26 25.4 0.27

4.6 0.2 26 23.9 0.18

3.9

49 GeV v 1.76 10 cm 1.08 0.36 38.2 GeV v 1.25 10 cm 1.07 0.37 0.337

M

cc M

M

s

s

tt

+ + -- -

+ + -- -

+-

= = ´

= = ´

= 0.047 0.2 26 20.18GeV v 1.25 10 cm 1.52 0.06s + -

-= ´

The Fermi-LAT collaboration

1705.00009

Better fit to (large ∼ few thousand) number of Pulsars

In the early universeIn the early universe

WIMPWIMP

quark quark

áσAvñ= 3×10−26 cm3 s−1

WIMPWIMP

quark quark

Quarks make WIMPsQuarks make WIMPs

protonproton

Protons make WIMPsProtons make WIMPs

WIMPWIMP

quark quark

Accelerator production

Large Hadron Collider

WIMPs at the LHCWIMPs at the LHC

Looking for aninvisible

needle in a haystack

WIMPs: social or maverick species?

Not friended by new like-mass particlesAny un-WIMPy pals beyond reachTheory framework: Don’t ask/Don’t tellBottom upNot UV complete: Effective Field TheoryFind the WIMP through what is not seenExample: Neutrinos before late 1960s

Friended by many like-mass particlesPals around with new un-WIMPy particlesPart of a larger theoretical frameworkTop downGenerally UV completeFind the WIMP by finding its friendsExample: SUSY

Social WIMP Maverick WIMP

Supersymmetry & social WIMPs

Developed in the early 70’s

Every known particle has an undiscovered superpartner.

Superpartners are massive.

Lightest superpartner should be stable!

In many realizations, lightest superpartner is weakly interacting.

Superpartners

squarkssleptons

u d s

e m t

h H A H + Higgsinos

g

photino g

Ggravitinogluonino

W Zwino, zino

Particles

Higgs h H A H +

quarksleptons

u d s

e m t

photon g

Ggravitongluon

W ZW, Zg

Lightest Supersymmetric Particle is a candidate WIMP

Supersymmetry, supergravity, grand unification, string theory, M theory,

multiverse, landscape, etc.

Theory of Everything (ToE)

*ToE—a Theory omitting Evidence which solves yuge problems without making boring testable predictions. Who needs observational verification? Losers! Sad. #MakeAstronomyGreekAgain

Heroic effort—but SUSY not seen at LHC

Missing-energy signals and dark matter

In the early universeIn the early universe

WIMPWIMP

quark quark

áσAvñ= 3×10−26 cm3 s−1

WIMPs scatter with quarksWIMPs scatter with quarks

WIMPWIMP

quark quark

nucleusnucleus

WIMPs scatter with nucleiWIMPs scatter with nuclei

WIMPWIMP

ultrapure, ultracold,ultraradiopure,

solid, liquid, or gas

Relic WIMP (1,00,000 kph)

ionization, heat, light, vibrations,

bubble nucleation

deep underground shielded from cosmic rays

Direct detectionWIMP

WIMP

NUCLEUS

Direct detection

( )( )( )

MIN

3WIMP

Nucleus WIMP v

v1 v v vvR R

ddRd f

dE M M dE

sr= ò

Recoil energies few to few dozen keV

WIMP

nuclear

recoil

WIMP

Experiment:

Detector Mass

Nuclear Target(s) (MNucleus and JNucleus)

EThreshold = 2μχN vMIN / MNucleus/ 2

Particle physics: MWIMP/Astrophysics:ρ WIMPf (v)

2

Direct detection

M. Fedderke

Spin-Independent Scattering

10−45 cm2 = 1 zeptobarn!

10−42 cm2 = 1 attobarn

10−48 cm2 = 1 yoctobarn

10−39 cm2 = 1 femtobarn

10−36 cm2 = 1 picobarn

Direct detection

M. Fedderke

Spin-Dependent Scattering

Dark Matter: if not a WIMP

• If DM not a WIMP, many other possibilities:− Axions− Asymmetric DM− Sterile neutrino DM (e.g., 7 keV sterile neutrino producing 3.5 keV X-ray

line which may, or may not, be observed)− Axino (7 keV axino) DM− Self-interacting DM− Inelastic DM− Q-balls or other solitonic DM− Quark nuggets− Hidden-sector DM− WIMPZILLA

Dark Matter: the future• We are in the eighth decade of Dark Matter!

• 2010s is the Decade of the WIMP− LHC− Direct detection− Indirect detection

Have to run to ground the WIMP (cold thermal relic) hypothesis.

• Indirect/Direct/LHC confusion not an issue

• WIMPs may be more complicated than discussed: Leptophilic, Leptophobic, Flavorful, Self-Interacting, Dynamical, Inelastic, …

• My predictions:− Dark matter identity will be known before a century of dark matter− Dark matter discovery will be unanticipated− Dark matter will be “none of the above”− Dark matter will be multicomponent− Dark matter will be part of a dark sector

Thank You !

The Physics of Fine TuningJune, 2017

Rocky KolbUniversity of Chicago

Dark Matter Shapes the Universe