“Dark Matter in Modern Cosmology”
Sergio Colafrancesco
SummaryIntroduction
Dark Matter probes
Future of Dark Matter
Hystorical background and gained evidence
Motivations Dark Matter candidates
Types of probes Analysis of neutralino annihilations
Problems in DM probes
Multi-approch of DM problem The alternative approch:modified gravity
Introduction
Dark Matter Scientific revolution
DM
Local Global
Close to the plane of the Galaxy
Baryonic
Low amount
Dominating mass component
Large structures
Hystorical background and gained evidence
The problem
Radial velocities of galaxies in Coma cluster
Zwicky (1933)
Unexpected large velocity dispersion (бv)
Mean density ~ 400 times greater
Huge amount of “Dunkle Kalte Materie” (Cold Dark Matter)
Smith (1936) Mass of Virgo cluster
Unexpected high mass Excess of mass
“Great mass of internebular material within the cluster”
Babcock(1939) Spectra of M31
Unexpected high rotational velocity in the outer regions
High mass to light ratio in the periphery
Strong dust absorption
Oort(1940) Rotation and surface brightness of one edge-on SO galaxy (NGC3115)
“Distribution of mass in this system appears to bear almost no relation to that of light”
Kahn & Woltjer(1959) Motion of the galaxy M31 and of the Milky Way
M31 and the Galaxy started to move apart ~ 15Gyr ago
The mass of the Local Group had to be greater than the sum of galaxies masses
Missing mass in the form of hot gas (T~5•105 k)
Rotation curve of M31
Roberts & Whitehurst (1975)
No Kleperian drop-off High mass to light ratio in the outermost regions(› 200)
Missing mass exist in cosmologically significant amounts
Confirmation of the presence of unknown matter by indipendent sources (beginning of the 1980’s)
Dynamics of galaxies and of stars within galaxies
Mass determinations of galaxy clusters based on gravitational lensing
X-ray studies of clusters of galaxies
N-body simulations of large scale structure formation
The CMB contribution
Theory of fluctuations to explain the formation of structures
Expected amplitude of the baryonic density fluctuations at the epoch of recombination
First detection of the CMB (1965): relic emission coming from the epoch of recombination
COBE(1992): the amplitude of the fluctuations appears to be lower than expected
Solution: Non-baryonic dominating DM component
Dark Matter candidates
Neutrinos High velocities HOT DARK MATTER
No galaxy can be formed
Hypothetical non baryonic particles
Low velocities
COLD DARK MATTER
Astro-particle connection
Search of the nature of Cold Dark Matter
Properties of CDM candidates
Fluid on galactic scales and above
Must behave sufficiently classically to be confined on galactic scales
Dissipationless
Collisionless
Cold
Upper and lower bounds on the mass of the particle
Most important candidates
NeutralinosSterile neutrinos
Light DM
Lightest particle of the minimal supersymmetric extension of the Standard Model (MSSM)
Lightest right-handed neutrino
Motivations
Galaxy rotation curves
Dwarf galaxy mass estimators
Lensing reconstruction of the gravitational potential of galaxy clusters and large scale structures
Combination of global geometrical probes of the Universe(CMB) and distance measurements (Sne)
Galaxy cluster mass estimators
Large scale structure simulations
Dark matter probes
Types of probes
Inference probesPresence, the total amount and the spatial distribution of DM in the large scale structures
Dynamics of galaxies
Hydrodynamics of hot intra-cluster gas
Gravitational lensing distortion of background galaxies
Physical probes Nature and physical properties of DM particles
Astrophysical signals of annihilation or decay
Wide range of frequencies
Analysis of neutralino annihilations
Focus
Particle: neutralino (Mχ range: few GeV to a several hundreds of GeV )
Astrophysical laboratories:Galaxy cluster
Dwarf spheroidal galaxies
Neutralino annihilation
у-ray emission
Synchrotron radiation
Bremsstrahlung radiation
Inverse Compton Scattering (ICS)
Neutrinos
SED
mass
cross section
composition
A general view
General informations
Annihilation rate: R = n (r) <>
n (r) = n g(r)
Annihilation cross section: <>
Wide range of values (theoretical upper limit <> < 10-22 (Mχ/TeV)-2
cm3/s)
Particles produced
Annihilation χ-χ
Quarks, leptons vector bosons and Higgs bosons
Depending on physical composition
Decay
Secondary electrons and positrons
Energy losses
Spatial diffusion(relevant on galactic and sub-galactic scales)
SED
Gamma rays emission:
Decay: Continuum spectrum
Bremsstrahlung and ICS of secondary e±
Coma cluster:
Draco dwarf galaxy:
Radio emission:Synchrotron emission of secondary e±
Diffuse radio emissionComa cluster:
ICS of CMB: from microwaves to gamma-ray
Secondary e± up-scatter CMB photons that will redistribuite over a wide frequency range up to gamma-ray frequencies
ICS of CMB: SZ effect from DM annihilation
Secondary e± up-scatter CMB photons to higher frequecies producing a peculiar SZ effect
Heating: Secondary e± produced heat the intra-cluster gas by Coulomb collisions
The radius of the region in which DM produce an excess heating increases with neutralino mass
Cosmic rays: Neutralino annihilation in nearby DM clumps produce cosmic rays that diffuse away
Future of Dark Matter
Problems in DM probes
Direct and indirect probes for DM have not yet given a definite answer
Some of the anomalies are not easy to explain within canonical DM models
DM that has no standard model gauge interactions
The DM induced signals are expected to be confused or overcome by other astrophysical signals
Ideal systems Multi approach
Multi approach of DM problem
Multi - frequency
Multi - messenger
Multi - experiment
The alternative approach:modified gravity
Mismatch between the predicted gravitational field and the observed one
When effective gravitational acceleration is around or below: a~10-7 cms-2 (weak gravitational field)
Newtonian theory of gravity break down?