Institut für Kern- und Teilchenphysik Neutrinos & Cosmology

Transcription

1 Neutrinos & Cosmology 1

2 Cosmology: WHY??? From laboratory experiment limits can be set ONLY in neutrino mass difference No information if neutrino masses are degenerated From kinematic experiment limits on neutrino masses are set -> very hard o have limits better than 0.2 ev (weakness of neutrinos interaction) BUT = neutrino plays a key role in the early stage of the Universe Relic neutrino background is the most abundant relics of primordial Universe Several cosmological objects are infuenced by neutrinos -> bounds on the properties 2

3 3

4 Cosmology: General 1 study of the Universe in its totality and its evolution Assumptions: - Universe is isotropic - Local physical laws are valid - Universe is homogeneous Cosmological principle: Viewed on a suffciently large scale, the properties of the Universe are the same for all observers -> cosmic time = at any time objects evolve in the same way Robertson e Walker (RW) metric a(t) = scale factor of the Universe. The dependence on time takes into account the motion of the Universe 4

5 Cosmology: Hubble law Hubble law: with where H0=100 h km s-1 Mpc-1 (0.5 < h < 1) Hubble space telescope 5

6 Cosmology: Redshift e Density Observer Emitter Friedman equation Critical density 6

7 Cosmology: Redshift e Density Density parameter 7

8 Cosmology: Redshift e Density Matter - stars Baryons Halos SZ effect 8

9 CMB Cosmic Microwave Background (CMB) radiation is thermal radiation flling the universe almost uniformly; discovered in 1964 by American radio astronomers Arno Penzias and Robert Wilson; radiation left over from an early stage in the development of the universe; its discovery is considered a landmark test of the Big Bang model of the universe; As the universe expanded, both the plasma and the radiation flling it grew cooler. When the universe cooled enough, stable atoms could form. These atoms could no longer absorb the thermal radiation, and the universe became transparent The photons that existed at that time have been propagating ever since, though growing fainter -> relic radiation; The CMB has a thermal black body spectrum at a temperature of K; Anisotropies: acoustic oscillations (competition between photons and baryons) 9

10 CMB 10

11 CMB 11

12 CMB -Angular scale of the frst peak determines the curvature of the universe - The next peak ratio of the odd peaks to the even peaks determines the reduced baryon density. -The third peak can be used to pull information about the dark matter density. -Locations of the peaks information on nature of the primordial density perturbations. 12

13 CMB and neutrinos 13

14 Large Scale Structure 14

15 Large Scale Structure 15

16 Large Scale Structure 2dF Galaxy Redshift Survey 16

17 Large Scale Structure - Sky surveys and mappings of the various wavelength bands of electromagnetic radiation (in particular 21-cm emission) have yielded much information on the content and character of the universe's structure. - Hierarchical model with organization up to the scale of superclusters and flaments. 1. Stellar level, 2. galaxies, 3. clusters and superclusters that are separated by immense voids. - Prior to 1989, it was commonly assumed that virialized galaxy clusters were the largest structures in existence, and that they were distributed more or less uniformly throughout the universe in every direction. - New redshift survey data, in 1989 Margaret Geller and John Huchra discovered the "Great Wall", a sheet of galaxies more than 500 million light-years long and 200 million wide, but only 15 million light-years thick. - In April 2003, another large-scale structure was discovered, the Sloan Great Wall. - In more recent studies the universe appears as a collection of giant bubble-like voids separated by sheets and flaments of galaxies, with the superclusters appearing as occasional relatively dense nodes. 17

18 Large Scale Structure - The power spectrum of the cosmic structure is different from the CMBR power spectrum since there is insuffcient repulsive force to counteract the gravitational attraction. - The power spectrum reveals some information about the cosmic structure: 1. The fuctuations become weaker with larger scales. Weak fuctuations mean that the galaxy distribution is very close to homogeneity. 2.Deviation from straight line confrms that the dynamics of the universe have changed with time. From other astronomical observations, it is concluded that the universe is dominated by matter and dark energy. 3. The exact scale of this deviation provides a measure of the total density of matter in the universe, and the result in agreement with the value from other measurements. 18

19 Large Scale Structure - Neutrinos contribute to Ωm m h = N 94.57eV 2 - The total matter contribution is Ωm = 0.3 -> Ωneutrino < 0.12 m 11eV N - Neutrinos tend to stream freely across gravitation potential weels -> erase density perturbation - This is true in the Jeans scale (distance that neutrinos can travel in a Hubble time) - If neutrinos are non relativistic then the Jeans scale change - If m<0.3 ev -> Relativistic - If 1 mev < m < 0.3 ev -> transition to non relativistic occur during structure formation -> matter power spectrum will be affected in a mass-dependent way - smaller wavelength are suppressed by free streaming, larger are not affected - suppression of all wavelength smaller than the Jeans scale 19

20 Large Scale Structure 20

21 Relic Neutrino Background - 21

22 Relic Neutrino Background - 22

23 Relic Neutrino Background - 23

24 Relic Neutrino Background - Evidence for relic neutrino background: - Big bang nucleosynthesis - Precision cosmology Cosmic microwave background anisotropies Large scale structure distribution 24

25 Big Bang Nucleosynthesis (BBN) - BBN probes the evolution of the Universe during its frst few minutes (about 3 min) - the density of particles is defned as: Where μ is the chemical potential and g id the number of spins of particles ( g=1 if m=0,s=0; g=2 se m=0, s 0; g=2s+1 se m 0; gγ=2, ge=2, but gν=1 since we have only left handed neutrinos) - The total density of the radiation dominated Universe is: - The total entropy (conserved) is: 25

26 Big Bang Nucleosynthesis (BBN) - During the earlier evolution of the Universe an universal matter antimatter asymmetry was established by particle physics processes yet to be uniquely determinated. - The ratio of the number of baryons to CMB photons in a comoving volume post electron/positron annihilation is a dimensionless time-invariant parameter in the contest of standard model physics 10 B n B /n 10 10=273.9 B h

27 Big Bang Nucleosynthesis (BBN) - Any modifcation of the Universe expansion rate can be due to the presence of non standard energy density relativistic particles or new physics which modifes the SBBN model. - A non-standard particle content is parameterized by the equivalent number of additional neutrinos defned, prior electron/positron annihilation, by: N N 3 - if this term is not equal to zero -> change the early Universe expansion rate - SM predicts that neutrinos where not fully decoupled at electron/positron annihilation temperature -> they are sensitive to the energy released N N Prediction of light element abundance vs observation can shed light on the effective number of neutrinos 27

28 Big Bang Nucleosynthesis (BBN) 28

29 Deuterium - Nucleosynthesis starts with deuterium formation. Even if KT > B (binding energy) the reaction is not effective due to the high energy photons which dissociate the produced deuterium (bottleneck) - Deuterium is an ideal baryometer since its abundance can only decrease during the evolution of the Universe - Observation: - QAS (Quasar Absorption System at low metallicity and high redshift) Lyman-alpha absorption (D/H) p=(3.4±0.3) meteor (D/H) p=(2.6±0.7) Observation of interstellar medium BBN Theory Obs. QAS 29

30 Helium 3 - From the value of D after primordial nucleosynthesis the abundance of 3He is 5 3 y 3P 10 He/ H P =1.1 ± post BB evolution is model dependent and more complicated since Deuterium can be burned by stars to give 3He - in the outer layer 3He and deuterium are preserved - in the stellar interior 3He is burned and then returns to interstellar medium - is not possible to use it as a bariometer - observation are based on low metallcity stars and rich H region (less burning of 3He) 5 3 y 3P,obs 10 He/ H P 1.1 ± Excellent agreement with SBBN BBN Theory 30

31 Helium 4 - SBBN -> simple to obtain a prediction determined by the rate of interaction that convert neutrons in protons as neutrons and protons decoupled the formations of light elements begin at the freeze out temperature the ratio n/p is about 1/6 slight decrease due to residual beta decay Y P 2n / n / p - very weakly dependent on barion number - strongly dependent on the decoupling time - SBBN ± extrapolation to primordial value ± Unfortunately thelarge error is due to the uncertainties on the neutron half life needs more accurate measurement to set bounds on the neutrino number. BBN Theory 31

32 Lithium 7 - SBBN -> prediction from the deuterium abundance 0.06 [ Li] P 12 log Li / H P = Li -> increase abundance after BBN: - burned in stars - 40% produced by cosmic rays interaction - destroyed in stellar convection - Observation from the surface abundance of old stars (metal poor) - No presence of plateau (?) - Diffcult to extrapolate a value - First data show a disagreement of a factor 3 between prediction and observation - New physics??????????? Observation BBN Theory 32

33 Summary - From SBBN the only adjustable parameter is the baryon density parameter - Deuterium is the baryometer of choice B SBBN = 10 SBBN = ; B h SBBN = Data can be compared with CMB prediction: B CMB = 10 CMB = ; B h CMB = Relax the standard model expansion rate -> variation in 4He prediction -> N(neutrino) =2.5 - if the expansion rate is fxed that the effective neutrino number is larger than 3. 33

34 Summary 34

35 Summary 2.5!!!!! 35

36 Dark Matter - Neutrinos are a source of dark matter in thr present Universe simply because they contribute to the Ωm. - If neutrinos are the main source of dark matter -> must make up most part of the galactic dark matter - Using Milky Way -> neutrino mass should be larger than 25 ev - Dwarf galaxies -> ev - They are only a SMALL contribution to dark matter - Are they COLD or HOT DARK MATTER? - Hot dark matter is composed of particles that have zero or near-zero mass. Very low mass particles must move at very high velocities and thus form (by the kinetic theory of gases) very hot gases. - Cold dark matter is composed of objects suffciently massive that they move at sub-relativistic velocities. They thus form much colder gases. The difference between cold dark matter and hot dark matter is signifcant in the Lozzaof hot dark matter cause it to wipe 36 formation of structure, because the highvalentina velocities out structure on small scales.

37 HOT Dark Matter - From cosmology observation we have the general mass limit: m 46eV N - It is possible to set better constraints regarding neutrinos as Hot dark matter candidates - With respect to the other HDM candidates they behave in a unique way -> they became non-relativistic very late -First formation of LLS and then small structures (TOP-DOWN) - BUT recent observation -> Galaxies formed too late -> Failure of HDM 37

38 Mixed Dark Matter - Neutrinos were not relativistic at the epoch of matter-dominated -> Cold dark matter candidate - but still some problems: observations support neutrinos as HDM subdominant candidate 38

39 Mixed Dark Matter 39

40 Mixed Dark Matter 40

41 Summary - The effect of massive neutrinos are: - on background -> shift in time of matter radiation equality - on perturbation (CMB) -> suppress of growth - on matter power spectrum -> distort the spectrum - There is NOT a unique cosmological bound on neutrino masses - The limits are dependent on cosmological models or in some cases the uncertainties are too large - The combination of BBN,CMB and LSS data are often used 41

42 Summary SDSS Coll, PRD 69 (2004)

43 Summary 43

44 Future sensitivities to Σmν: new ideas galaxy weak lensing and no bias uncertainty small scalecs in linear regime CMB lensing makes CMB sensitive to much smaller masses 44

45 Future sensitivities to Σmν: new ideas galaxy weak lensing and sensitivity of future weak lensing survey (4000º)2 to mν CMB lensing sensitivity of CMB (primary + lensing) to mν σ(mν) = 0.15 ev (Planck) σ(mν) ~ 0.1 ev σ(mν) = 0.04 ev (CMBpol) Abazajian & Dodelson Kaplinghat, Knox & Song PRL 91 (2003) PRL 91 (2003)

46 Absolute neutrino mass measurements 46