Transcript Dark Matter in Modern Cosmology”

“Dark Matter in Modern
Cosmology”
Sergio Colafrancesco
Summary
Introduction
Hystorical background and gained evidence
Dark Matter candidates
Motivations
Dark Matter probes
Types of probes
Analysis of neutralino annihilations
Future of Dark Matter
Problems in DM probes
Multi-approch of DM problem
The alternative approch:modified gravity
Introduction
Dark Matter
Scientific revolution
DM
Local
Close to the plane of
the Galaxy
Baryonic
Low amount
Global
Dominating mass component
Large structures
Hystorical background and gained evidence
The problem
Zwicky (1933)
Radial velocities of
galaxies in Coma cluster
Unexpected large velocity
dispersion (бv)
Mean density ~ 400 times
greater
Huge amount of “Dunkle Kalte Materie”
(Cold Dark Matter)
Smith (1936)
Unexpected high mass
Mass of Virgo cluster
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)
Roberts & Whitehurst (1975)
No Kleperian drop-off
Rotation curve
of M31
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
Search of the nature of Cold Dark Matter
Astro-particle connection
Properties of CDM candidates
Dissipationless
Collisionless
Upper and lower bounds on
the mass of the particle
Cold
Fluid on galactic scales and above
Must behave sufficiently classically to
be confined on galactic scales
Most important candidates
Light DM
Neutralinos
Lightest particle of
the minimal
supersymmetric
extension of the
Standard Model (MSSM)
Sterile neutrinos
Lightest right-handed
neutrino
Motivations
Galaxy rotation curves
Dwarf galaxy mass estimators
Galaxy cluster 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)
Large scale structure simulations
Dark matter probes
Types of probes
Inference probes
Presence, 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 )
Galaxy cluster
Astrophysical laboratories:
Dwarf spheroidal galaxies
у-ray emission
Neutralino
annihilation
mass
Synchrotron radiation
Bremsstrahlung radiation
SED
Inverse Compton Scattering
composition
(ICS)
Neutrinos
cross section
A general view
General informations
Annihilation rate: R = nC (r) <s >
nC (r) = nC,0 g(r)
Annihilation cross section: <s >
Wide range of values
(theoretical upper limit
<s > < 10-22 (Mχ/TeV)-2
cm3/s)
Particles produced
Annihilation χ-χ
Depending on
physical composition
Quarks, leptons vector bosons
and Higgs bosons
Decay
Secondary electrons and
positrons
Spatial diffusion
(relevant on galactic and
sub-galactic scales)
Energy
losses
SED
Decay:p0 g+g
Gamma rays emission:
Continuum
spectrum
Bremsstrahlung and ICS of
secondary e±
Coma cluster:
Draco dwarf galaxy:
Synchrotron emission of
Radio emission: secondary e±
Coma cluster:
Diffuse radio
emission
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
Multi approach of DM problem
The DM induced signals are expected to be
confused or overcome by other
astrophysical signals
Ideal systems
Multi approach
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?