“Dark Matter in Modern Cosmology” Sergio Colafrancesco

Summary Introduction 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 MatterScientific 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 (б v ) Mean density ~ 400 times greater Huge amount of “Dunkle Kalte Materie” (Cold Dark Matter)

Smith (1936)Mass of Virgo cluster Unexpected high massExcess 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~510 5 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 NeutrinosHigh velocitiesHOT 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 Neutralinos Sterile 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 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 ) 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 < (Mχ/TeV) -2 cm 3 /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 emission Coma 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?