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 (v)
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~5105 k) Roberts & Whitehurst (1975) Rotation curve of M31 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 1980s) 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 (M range: few GeV to a several hundreds of GeV ) Galaxy cluster Astrophysical laboratories:
Dwarf spheroidal galaxies -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 = n (r) <> n (r) = n g(r) Annihilation cross section: <> Wide range of values
(theoretical upper limit <> < 10-22 (M/TeV)TeV)-2 cm3/TeV)s) Particles produced Annihilation - 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: Gamma rays emission:
Continuum spectrum Bremsstrahlung and ICS of secondary e Coma cluster: Draco dwarf galaxy: Radio emission: Coma cluster:
Synchrotron emission of secondary e 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?
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