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Dark Matter detection (1)Dark Matter detection (1)

CTICS 2012 CTICS 2012 Jan 24th, 2012

Sergio ColafrancescoSergio Colafrancesco Wits UniversityWits University - - DST/NRF SKA Research ChairDST/NRF SKA Research Chair INAF - OARINAF - OAR EmailEmail: Sergio.Colafrancesco@wits.ac.za Sergio.Colafrancesco@oa-roma.inaf.it

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Dark Matter exists !

Dark Matter Proof Found, Scientists Say

A team of researchers has found the first direct proof for the existence of dark matter, the mysterious and almost invisible substance thought to make up almost a quarter of the universe.In this composite image, two clusters of galaxies are seen after a collision. Hot gas, seen in red, was dragged away from the galaxies during the collision. That gas makes up more than 90 percent of the mass of normal, or visible, matter. But most of the mass—and thus matter—is located in the galaxy portions of the clusters, shown in blue, scientists say. In other words, the bulk of visible matter in the clusters has been separated from the majority of mass—which therefore must be dark matter.

[F. Zwicky 1933]

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Dark Matter exists ! … or not !?

Dark Matter Proof Found, Scientists Say

A team of researchers has found the first direct proof for the existence of dark matter, the mysterious and almost invisible substance thought to make up almost a quarter of the universe.In this composite image, two clusters of galaxies are seen after a collision. Hot gas, seen in red, was dragged away from the galaxies during the collision. That gas makes up more than 90 percent of the mass of normal, or visible, matter. But most of the mass—and thus matter—is located in the galaxy portions of the clusters, shown in blue, scientists say. In other words, the bulk of visible matter in the clusters has been separated from the majority of mass—which therefore must be dark matter.

Dark matter does not exist ! Einstein wins again!

J. Moffat suggests that his Modified Gravity (MOG) theory can explain the Bullet Cluster observation. MOG predicts that the force of gravity changes with distance.Moffat thinks that the present day expectation by many that dark matter must exist is similar to the expectation by many leading scientists in the beginning of the 20th century that a "luminiferous ether" should exist. This was a hypothetical substance, in which the waves of light were supposed to propagate

J. Moffat and colleagues suggest that there is a good reason dark matter why has never been directly detected: It doesn't exist .

[F. Zwicky 1933]

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Dark Matter Modified G

Gµν=8πG(TMµν+TDM

µν+ΤDEµν) F(gµν)+Gµν=8pG TM

µν

Fundamental Physics - Astronomy connectionFundamental Physics - Astronomy connection

−+−=Φ

3)/exp(1

43)(

1

LrR

GMa

r

5

Multi-messenger Multi-experiments

Multi-wavelength

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Multi-messenger

Multi-wavelength

Multi-experiments

Multi-scale Multi-epoch

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OutlineMulti-epoch

The Dark Matter TimelineThe present

Multi-Scale + M3

Galactic centerGalactic structuresGalaxy Clusters

The FutureThe DM search challenge

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OutlineMulti-epoch

The Dark Matter TimelineThe present

Multi-Scale + M3

DM search at various astronomical scales• Galactic center• Galactic structures• Galaxy Clusters

The FutureThe DM search challenge

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Dark Matter timeline

Fritz Zwicky[Varna (Bulgaria), 1898 – Pasadena (USA), 1974]

skmV /)3601019( ±≈σ

558400 hLM ⋅≈

Zwicky used the words “dunkle (kalte) Materie” dark (cold) Matterwhich might be regarded as the first reference to Cold Dark Matter… even though not in the modern sense (!?)

Coma02 =+ UT

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Dark Matter timeline

1936 - Smith noticed that also the Virgo cluster exhibited a behavior suggestive of an extremely high mass.

1939 - Babcock noticed that the outer regions of M31 were rotating with an unexpectedly high velocity indicating a missing mass.

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Dark Matter timeline

Local Dark Matter

Öpik (1915)Oort (1932, 1960)Kuzmin (1952, 1955)Eelsalu (1959)Jõeveer (1972, 1974)Bahcall (1985)Gilmore et al (1989)

Global Dark Matter

Zwicky (1933)

Zwicky discovered what so many scientists find when probing the depths of the current and accepted knowledge of the times. What Zwicky uncovered was considered an anomaly. Zwicky, who did not particularly belong to the astronomical community, was making a claim that could overthrow present knowledge of the universe. It was not the right time for the astronomical community to accept such a revolutionary idea.

1910’s Ernst Öpik & wife Grigory Kuzmin

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Dark Matter timeline

1959 - Kahn & Woltjer published their discovery of a missing mass in the Local Group ( hot gas with T ∼ 5·105 K )Interestingly enough, they did not cite Zwicky’s (1933) paper.

1961 - The renaissance of Dark Matter truly began with the Santa Barbara Conference on the Instability of Santa Barbara Conference on the Instability of GalaxiesGalaxies. By this time, enough research was done for the community to see that the missing mass anomaly was not going to go away.

“When... an anomaly comes to seem more than just another puzzle of normal science, the transition to crisis and to extraordinary science has begun” (Kuhn).

Vera Rubin working at the Ford spectrograph (1955)

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Dark Matter timeline

1975 – By this time the majority of astronomers had become convinced that missing mass existed in cosmologically significant amounts.Uncertainty on the Dark Matter nature remained !!!

1980 - Experimental results on the neutrino rest mass were announced.

1977 – Rees speculated that “there are other possibilities of more exotic character – for instance the idea of neutrinos with small (∼few eV) rest mass”

Jim Peebles explains the secrets of galaxy formation to Scott Tremaine (Tallinn 1977)

Zel’dovich & Longair

(Tallinn 1977)

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Dark Matter timeline

1980’s – The Cold Dark Matter model with axions or other weakly interactive particles WIMPwas as an alternative to neutrino models (providing the Hot Dark Matter).

A high-resolution CDM simulation with small-scale structure

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Dark Matter timeline

1990’s – Dark Matter distribution in clusters can explain the gravitational lensing of background galaxies.

J. Soldner 1804

A. Einstein 1911

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False Alarms & Diversionary Manouvres

1987 – One particularly interesting dissenter: M.Milgrom. He believed that the existence of the DMimplied that Newton’s law of gravity must be amended for gravitational accelerations that are very small, such as the gravitational accelerations seen in a galaxy’s outer fringes. Bekenstein followed up Milgrom’s idea in TeVeS model

J. Oort (1960, 1965) believed that he had found some dynamical evidence for the presence of missing mass in the disk of the Galaxy. If true, this would have indicated that some of the DM was dissipative in nature. However, late in his life, Oort confessed that the existence of missing mass in the Galactic plane was never one of his most firmly held scientific beliefs. Detailed observations, (reviewed by Tinney 1999), show that brown dwarfs cannot make a significant contribution to the density of the Galactic disk near the Sun.

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Dark Matter timeline

1992-99 – Dark Matter is a main ingredient of the cosmic fluid and its effect is present in the CMB anisotropy spectrum .

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Dark Matter timeline

1990-2000 – Naissance of Astroparticle – Dark Matter physical connection.

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The Dark Matter Scenario: timeline

2010

Astro

nom

yCo

smol

ogy

Parti

clePh

ysics

Missing massDynamics

Rotation curves

N-body simulations Lensing CMB

ν2m∆

Sterile ν

ν - mass theo. & exp. SUSY

SUSY AXION

Beyond the SM

Astro

Par

ticle

Phys

ics

1977Thermal relics

(Lee & Weinberg)1984

Indirect DM search idea(SIlk & Srednicki)

1985Direct DM experiments

(Goodman & Witten)

Today

!?

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The Present

“The Present and the bubbles of Time" - Oil and acrylic on thin cardboard (B. D’Aleppo)

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Dark Matter Scenario: motivations

WMAP

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DM & CMB

Generic ΛCDM WMAP 7yr

236.0222.0 ≤Ω≤ DM

0035.01123.02 ±=Ω DMh

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DM distribution in cosmic time

Dark Matter grows increasingly 'clumpy' as it collapses under

gravity.

The map stretches halfway back to the beginning of the universe

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DM relic density

AV

scmhσχ

13272 103 −−−⋅≈ΩFreeze-out

WIMPs in thermal equilibrium

HVnx ≈σ

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Formation of DM halos

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DM: the most palpable proof

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DM: the most palpable proof

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DM properties: 5 basic

Dissipationless

Collisionless

Cold

Fluid

Classical

No constraint on the space of possibilities

Upper bound

Lower bound

Very weak e.m. interactionsno radiative cooling

DM self-interaction only athigh ρ and short relative D

MX > 1 keV thermalMX smaller non-thermal

No DM discreteness on galactic scales

eVM X717010 −≤

DM confinedon galactic scales

eVM 2210−≥χ

Dar

k M

atte

r

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DM candidates“Fuzzy” CDM

Axions

Neutrinos

Light (MeV) DM

SUSY DM

Dar

k M

atte

rM

WIM

P

Extra dimension

Branons

Mirror Matter

PBHs

Lower possible end of CDMBosons with M∼10-22 eV

Non-thermal productionµ eV < Maxion < m eVExperimental limits

Warm DM 0.0005 < Ων h2< 0.0076Massive neutrinos acceptableSterile ν with mν ∼ 10-100 keV

Gravitinos

Neutralinos

Sneutrinos

Axinos

Q-balls

Split-SUSY

Kaluza-Klein excitationsL-KK (r-parity) particle: stableMKK ∼1 TeV

String theory brane fluctuationsMbranon > 100 GeV

Ordinary matter in mirror worldDissipative & complex chemics

BHs @ quark-hadron transitionMPBH ∼Mhorizon(T=102MeV) > M

WIMPzillas

Chaplygin Gas

Produced at the end of Inflation M > 1013 GeV

DM-DE common originP = - A / ρ

Spin = 0 supersymmetric particle1 MeV < MLDM < 4 MeVElusive: only e± 511 keV line Neutralinos

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Viable DM candidates Light (MeV) DMNeutralinos Sterile ν’s

Unstable

Radiative decay: line

νs → να + γ

13.009.0 2 ≤Ω≤ hDM

AV

scmhσχ

13272 103 −−−⋅≈Ω

In supersymmetry models, all Standard Model particles have partner particles with the same quantum numbers but spin differing by 1/2. Since the superpartners of the Z boson (zino), the photon (photino) and the neutral higgs (higgsino) have the same quantum numbers, they can mix to form four eigenstates of the mass operator called "neutralinos". In many models the lightest of the four neutralinos turns out to be the lightest supersymmetric particle (LSP).

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Viable DM candidates Light (MeV) DMNeutralinos Sterile ν’s

Unstable

Radiative decay: line

νs → να + γ

13.009.0 2 ≤Ω≤ hDM

AV

scmhσχ

13272 103 −−−⋅≈Ω

Scalar (spin=0) particles may be DM candidates, provided they annihilate sufficiently strongly through new interactions, such as those induced by a new light neutral spin-1 boson U. The corresponding interaction is stronger than weak interactions at lower energies, but weaker at higher energies. Annihilation cross sections of (axially coupled ) spin-1/2 DM particles, induced by a U vectorially coupled to matter, are the same as for spin-0 particles. In both cases, the cross sections (σannVrel/c) into e+e− automatically include a v2

dm suppression factor, needed to avoid an excessive production of γ-rays from residual DM annihilations. Spin-0 DM particles annihilating into e+e− have been claimed to be responsible for the bright 511 keV γ-ray line observed by INTEGRAL from the galactic bulge.

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Viable DM candidates Light (MeV) DMNeutralinos Sterile ν’s

Unstable

Radiative decay: line

νs → να + γ

13.009.0 2 ≤Ω≤ hDM

AV

scmhσχ

13272 103 −−−⋅≈Ω DecayThe term sterile neutrino was coined by Bruno

Pontecorvo who hypothesized the existence of the right-handed neutrinos in a seminal paper (1967), in which he also considered vacuum neutrino oscillations in the laboratory and in astrophysics, the lepton number violation, the neutrinoless double beta decay, some rare processes, such as μ → e γ, and several other questions that have dominated the neutrino physics for the next four decades. Most models of the neutrino masses introduce sterile (or right-handed) neutrinos to generate the masses of the ordinary neutrinos via the seesaw mechanism.

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Viable DM candidates Light (MeV) DMNeutralinos Sterile ν’s

Unstable

Radiative decay: line

νs → να + γ

WMAP (95%)

Excl

uded

by

BB

N

Bremsstrahlung

in-flight annihilation

SNe

e- anomalous magnetic moment

Excl

uded

by

BB

NNo C

osmolo

gical D

M

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Hunt for the DM particle

DM exists: we feel its (gravitational) presence

DM is mostly non-baryonic: we must think of a specific search strategy

DM is very elusive: we must consider un-ambiguous evidence

Crucial Probes are required !

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Dark Matter probesAbove-the-ground

Under-ground

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DM direct search

χ

χ

ER

χχ

~ 10-30 keV

Elastic interaction on nucleus, typical χ velocity ~ 250 km/s

vsun= 230 km/sδ = 30o

vorb = 30 km/s

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DM direct search

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The first hint

There is evidence for a modulation in the DAMA data at 8.2 σ.

Compatible with what would be expected from some dark matter particles in some galactic halo

models.

Gran Sasso (Italy)

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Some of the latest results: CDMS II

Ahmed et al. arXiv:0912.3592v1

2 events in the observed signal region.Based on background estimate, the probability of observing two or more background events is ~23%.

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Some of the latest results: CoGeNT

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Some of the recent results: CRESST-II

[arXiv:1109.0702]

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DM direct search: criticalities

Effect of substructures on the local DM density

[Kamionkowski & Koushiappas 2008]

Experimental techniques Astrophysics

Assume a local DM densityand a DM halo structure

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DM search @ accelerators

“Well, either we’ve found the Higgs boson, or Fred’s just put the kettle on.”

CERN - Geneva

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LHC vs. direct detection experimentsAccelerator searches for DM are particularly promising … but even if WIMPs are found at the Large Hadron Collider (LHC), it will be difficult to prove that they constitute the bulk of the DM in the Universe.

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DM - Astrophysical probes

+

INFERENCE

Virial Theorem

Hydro Equilibrium

Gravitational lensing

PHYSICAL

,...,,0 pXX ±→+ π

ieXX ντµ ,,, ±±±→+

Annihilation Decay

γ+→ ixX

+

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DM - Astrophysical search

+

INFERENCE

Virial Theorem

Hydro Equilibrium

Gravitational lensing

PHYSICAL

,...,,0 pXX ±→+ π

ieXX ντµ ,,, ±±±→+

Annihilation Decay

γ+→ ixX

NOT CRUCIAL

Vulnerable against:

MOND: Modified Newtonian DynamicsTeVeS : Tensor-Vector-Scalar

Ordinary matter feels a transformed metric

CRUCIAL

Testable against:

Electromagnetic signals

DM illuminates thru its interaction

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DM - Astrophysical search

Clean and unbiased location in the sky Best Astrophysical Laboratories

Clear and specific SED in the e.m. spectrum Most specific e.m. signals

NO YES

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Viable DM candidates: signalsLight (MeV) DMNeutralinos

Annihilating MeV DM• Continuum: HXR/γ-rays• Line: e± annihilation

Radiative decay: line

νs → να + γ

511 keVMs

Mχ

Inverse Compton scatteringBremsstrahlung

Synchr.

Bremsstrahlung

π0

Sterile ν’s

No Cosm

ologica

l DM

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Viable DM candidates: signalsNeutralinos

Radiative decay: line

νs → να + γ

Sterile ν’s

Neutralino density profile~ (nχ · nχ)

~ ρ2DM

Sterile ν density profile~ nχ

~ ρDM

Annihilation

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Viable DM candidates: signalsNeutralinos

Radiative decay: line

νs → να + γ

Sterile ν’s

[ ]

×

⟩⟨∝

νχ

σρχ

ddEEf

VM

rD

F

ann

DM

L

);(

)(12

2

2

[ ]

×

⟩Γ⟨∝

ν

ρ

γ ddEME

Mr

DF

v

radv

DM

L

)(

)(12

DM annihilation flux DM decay flux

Astro physics

Particle physics

Annihilation

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Dark Matter halo structure

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[Sand et al. 2002]

MS2137-23

Cluster η1T η2T

A2029 0.5 2

A1689 1.3 1.6

A1835 0.9 1.1

MS1358 1.8 1.8[Bautz & Arabadjis 2002]

η

DM halo profile: constraints

no constraints on η !

[Dalal et al. 2003]

Galaxies Galaxy Clusters

NGC 6822

NFW

• No evidence for a density cusp at r < 0.2 kpc• NGC2976: η =0.27 at r < 1.8 Kpc [Simon et al. 2003]• Inner steeper profile ? [Gnedin & Primack 2003]

[Weldrake et al. 2002]

BH ?

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DM density universal profile

Numerical simulations (CDM)Different groups obtained similar results [Navarro et al. 2003, Reed et al. 2003, …]

Analytical fittingGeneral DM profile

Dwarfs Galaxies Clusters

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DM halo: smooth + clumps + BHsCluster of galaxiesCluster of galaxies

dSph GalaxydSph Galaxy

[CPU 2006]

[Berezinsky et al. 2006]

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Imagine a …

Galaxy Cluster of galaxies

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An astronomer’s view

Galaxy Cluster of galaxies

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A cosmologist’s view

Galaxy Cluster of galaxies

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Galaxy Cluster of galaxies

An Astroparticle Physicist’s view

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Theoretical description [Colafrancesco et al. 2006 A&A 455, 21–43]

60

DM halo profileWe consider the limit in which the mean DM distribution can be regarded as spherically symmetric and represented by the parametric radial density profile

Two schemes are adopted to choose the function g(x) , with x=(r/a)

Assume that g(x) can be directly inferred as the function setting the universal shape of DM halos found in numerical N-body simulations. We are assuming, hence, that the DM profile is essentially unaltered from the stage preceding the baryon collapse, which is – strictly speaking – the picture provided by the simulations for the present-day cluster morphology.

[NFW 2004]

[Diemand 2005]

Scheme 1

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DM halo structure

The other extreme scheme is a picture in which the baryon infall induces a large transfer of angular momentum between the luminous and the dark components of the cosmic structure, with significant modification of the shape of the DM profile in its inner region. Baryons might then sink in the central part of DM halos after getting clumped into dense gas clouds (see El-Zant et al. 2001), with the halo density profile in the final configuration found to be described by a profile with a large core radius (see, e.g., Burkert 1995):

Once the shape of the DM profile is chosen, the radial density profile g(x) is fully specified by two parameters:

i) length-scale a ii) normalization parameter ρ. It is useful to describe the density profile model by other two parameters: the virial mass Mvir and concentration parameter cvir.

Scheme 2

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DM halo structureConcentration parameter

We introduce the virial radius Rvir of a DM halo of mass Mvir as the radius within which the mean density of the halo is equal to the virial overdensity Δvir times the mean background density

We assume that the virial overdensity can be approximated by an expression appropriate for a flat cosmology [Colafrancesco et al.’94,’97; Bryan & Norman ’98, …]

The concentration parameter is then defined as

with r−2 the radius at which the effective logarithmic slope of the DM profile is −2. • x−2 = 1 for the N04 profile • x−2 = 2−γ for D05• x−2 = 1.52 for the Burkert profile

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DM halo structureSince the first numerical results with large statistics became available (Navarro etal. 1996, 1997), it has been realized that, at any given redshift, there is a strongcorrelation between cvir and Mvir, with larger concentrations found in lighter

halos. This trend may be intuitively explained by the fact that mean overdensities in halosshould be correlated with the mean background densities at the time of collapse,and in the hierarchical structure formation model small objects form first, when theUniverse was indeed denser. The correlation between cvir and Mvir is relevant at two levels: • when discussing the mean density profile• when including substructures

[Bullock et al]

[ENS]

64

DM Halo structureFor a given shape of the DM halo profile we fit of the parameters Mvir and cvir against the available dynamical constraints for the Coma cluster. We consider bounds on the cluster total mass at large radii and on density profile in its inner region. • Redshift-space caustics (Geller 1999)• HE condition (Hughes 1989)• Velocity moments of a tracer population (Binney & Mamon 1982)

[Colafrancesco et al. 2006 A&A 455, 21–43]

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DM Halo structure

ρ2DMρDM

Sub-structures

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DM Halo structureTo discuss substructures in a cluster, To discuss substructures in a cluster, analogously to the general picture introduced analogously to the general picture introduced above for DM halos, we label a subhalo through above for DM halos, we label a subhalo through

• virial mass virial mass MMs s • concentration parameter concentration parameter ccs.s.

• The subhalo profile shape is considered hereThe subhalo profile shape is considered here to be spherical and of the same form as for theto be spherical and of the same form as for the parent halo.parent halo.

• The distribution of subhalos in a DM halo isThe distribution of subhalos in a DM halo is taken to be spherically symmetrictaken to be spherically symmetric.

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DM Halo structureThe subhalo number density probability distribution can then be fully specifiedthrough Ms, cs and the radial coordinate for the subhalo position r.

The sub-halo mas function is [Diemand 2005]

A(Mvir) is derived imposing

The quantity Ps(cs) is a log-normal distribution in concentration parameters around a mean value set by the substructure mass.The 1σ deviation Δ(log10 cs) around the mean in Ps(cs), is assumed to be independent of Ms and of cosmology, and to be, numerically, Δ(log10 cs) = 0.14

ps(r) is the spatial distribution of substructures within the cluster.

(with a’>a) and normalized as:

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DM annihilation distributionFor any stable particle species i, generated promptly in the annihilation orproduced in the decay and fragmentation processes of the annihilationyields, the source function Qi(r, E) gives the number of particles per unit time, energy and volume element produced locally in space:

Npairs(r) is obtained by summing the contribution from the smooth DM component and the contributions from each subhalo

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DM annihilation distributionΔ2

Ms gives the average enhancement in the source due to a subhalo of mass Ms,Δ2 is the sum over all contributions weighted over the subhalo MF times Ms

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Viable DM candidates: signalsNeutralinos

Radiative decay: line

νs → να + γ

Sterile ν’s

[ ]

×

⟩⟨∝

νχ

σρχ

ddEEf

VM

rD

F

ann

DM

L

);(

)(12

2

2

[ ]

×

⟩Γ⟨∝

ν

ρ

γ ddEME

Mr

DF

v

radv

DM

L

)(

)(12

DM annihilation flux DM decay flux

Astro physics

Particle physics

Annihilation

71

OutlineMulti-epoch

The Dark Matter TimelineThe present

Multi-Scale + M3

Galactic centerGalactic structuresGalaxy Clusters

The FutureThe DM search challenge

72

THANKS

for your attention !