11

Pasquale Di BariPasquale Di Bari

(Max Planck, Munich)(Max Planck, Munich)

UniversitUniversità di Milanoà di Milano, February 8, 2007, February 8, 2007

Can neutrinos help to solve the puzzles

of modern cosmology ?

22

OutlineOutline

A cosmological Standard Model ? A cosmological Standard Model ?

Puzzles of Modern Cosmology Puzzles of Modern Cosmology

Right-handed neutrinos in Right-handed neutrinos in

cosmology: light vs. heavycosmology: light vs. heavy

LeptogenesisLeptogenesis

33

A cosmological A cosmological Standard Model ? Standard Model ?

WMAP

Large Scale StructureThe Universe observed: Sloan Digital Sky Survey The Universe simulated :

Open problems:• cusps (too much Dark Matter in halo centers ?)• Halo substructure issues (too many satellite galaxies ?) • Halo and galaxy merging (too much galaxy merging ?)

Toward a Cosmological SM ?

The Mass-Energy budget today

The Universe is accelerating !

( , M) = (0,1)

( , M) = (0, 0.3)

q = 0

( , M) = (0.7 , 0.3)

Hubble diagram: High-redshift type Ia supernovae probe the expansion history and reveal accelerated expansion

Cosmological Concordance

Clusters of galaxies are a laboratory for studying and measuring Dark Matter in a variety of ways: gravitational lensing effects, x-ray, radio, optical ….

Thermal history of the Universe

1111

Puzzles of Puzzles of Modern CosmologyModern Cosmology

1.1. Matter - antimatter asymmetryMatter - antimatter asymmetry

2.2. Dark matterDark matter

3.3. Accelerating UniverseAccelerating Universe

4.4. InflationInflation

Matter-antimatter asymmetry• Symmetric Universe with matter- anti matter domains ?

Excluded by CMB + cosmic rays

) = (±x>>

• Pre-existing ? It conflicts with inflation ! (Dolgov ‘97)

) dynamical generation (baryogenesis)

• A Standard Model Solution ? ¿ : too low !

New Physics is needed! New Physics is needed!

CMB

SM CMB

(Sakharov ’67)

Dark Matter• What do we need today to explain Dark Matter :

a new particle …

… or a new description of gravity ?

Modification of Newtonian Dynamics (MOND)• For accelerations a < a0' 10-8 cm s-2 usual Newton law is modified (Milgrom ’83)• Relativistic tensor-vector-scalar field theory for MOND (Bekenstein ’04)• However different observations (gravitational lensing, CMB, baryon acoustic

oscillation peak, ‘bullet’ cluster, …) tend to exclude it and we will not consider it !

It is the most conservative option with many theoretical motivations: SUSY DM (neutralinos,gravitinos,…),extra DIM’s, Wimpzilla’s, sterile neutrinos, ..Today we know that the new particles have to be slowly moving at the

matter-radiation equivalence (T ~ 3 eV ) Cold Dark Matter (M10KeV)

Particle Dark Matter

Neutrinos behave as HOT Dark Matter

Accelerating Universe

• C.C. Why small ? -SUSY breaking

- Anthropic principle (Weinberg ’87)(Weinberg ’87)

- - only the fluctuations of the vacuum energy contribute to and not its absolute value (Zel’dovich 67)(Zel’dovich 67)

• Quintessence ?A light scalar field still rolling down:

w in general

Without Dark Energy• modifying gravityAt large distances, motivated in brane world scenarios (Dvali,Gabadadze,Porrati `00)

• without modifying gravity attempt to explain acceleration

without new physics: acceleration would arise from

inhomogeneities inside the horizon

it would solve the coincidence coincidence problemproblem but……..unfortunately it is unlikely to work !

With Dark Energy

Inflation• It solves the well known problems of ‘old’ cosmology (horizon

problem, flatness problem, initial conditions, spectrum of primordial perturbations…)

• supported by CMB data• On the other hand it leads to serious problems that

require to go beyond the SM: - where inflation comes from ? what is the inflaton ?

- flatness of the potential

- trans-Planckian scales inside the horizon

- does not solve the problem of singularity

(it is only shifted at earlier times)

- cosmological constant problem (the large quantum vacuum energy of field theories does not gravitate

today and thus we do not want it….but it is necessary for inflation !)

Which model beyond the Standard Model of Which model beyond the Standard Model of Particle Physics can solve the cosmological Particle Physics can solve the cosmological

puzzles ?puzzles ?

In other words: cosmologists have cleaned their room but they

swept away all the dust in the particle physicists lounge !

Experimental long-standing issues have been solvedand the puzzles of modern cosmology are nicely expressed in a particle physics `language’ but they cannot be explained within the SM !

Some considerations

Neutrino masses: m1< m2 < m3

RH neutrinos in cosmology: light vs. heavy

Minimal RH neutrino implementation

3 limiting cases :

• pure Dirac: MR= 0

• pseudo-Dirac : MR << mD

• see-saw limit: MR >> mD

See-saw mechanism

3 light LH neutrinos: 3 light LH neutrinos:

NN2 heavy RH neutrinos: 2 heavy RH neutrinos: NN11, N, N22 , … , …

m

M

SEE-SAW

- the `see-saw’ pivot scale is then an important quantity to understand the role of RH neutrinos in cosmology

* ~ 1 GeV

> * high pivot see-saw scale `heavy’ RH neutrinos

< * low pivot see-saw scale `light’ RH neutrinos

Light RH neutrinos and….

•…..LSNDA see-saw mechanism with ~0.1eV can accommodate LSND with a ‘3+2’ data fit

(De Gouvea’05) but potential problems with BBN and CMB

• …..CMB -0.3< N < 1.6 (95% CL) (no Ly)(Hannestad,Raffelt)

0.6< N < 4.4 (95% CL) (with Ly)(Seljak,Slosar,McDonald)

~0.1eV

A future 5 th cosmological puzzle ? It would be very interesting especially for neutrinos

…Dark Matter •active-RH neutrino mixing:

N ~ mD/M << 1 ,

the RH neutrino production is enhanced by matter effects and

(Dodelson,Widrow’94;Dolgov,Hansen’01;Abazajian,Fuller,Patel’01)

• For `see-saw ‘ RH neutrinos the condition can be fullfilled if m1<10-5 eV and the Dark Matter RH neutrino is the lightest one with M1 ~ O(KeV) (Asaka,Blanchet,Shaposhnikov’05)

• Bad news: the same flavor-mixing mechanism describing the production, also lead to radiative decay: N1 + >> t0 M1 10 KeV - SDSS Ly: M1 > (10-14) KeV (Seljak et al. ’06;Lesgourgues et al)

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

108

109

1010

1011

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

102

103

104

105

106

107

108

109

1010

1011

Leptogenesis through oscillations

M2 M

3= O(10 GeV)

M1 ~ KeV

m1 10-5 eV

m2= m

sol 0.009 eV

(eV) 100 eV

m3= m

atm 0.05 eV

Dark Matter

Heavy RH neutrinos

2 solid motivations:• See-saw original philosophy is not spoiled: ~ Mew , MR~MGUT

there is no need to introduce new fundamental scales to explain neutrino masses;

• Leptogenesis from heavy RH neutrino decays: it is simple and it works easily without requiring a

particular tuning of parameters

Objections:• How to prove it ? • Can one explain Dark Matter ?

CP asymmetry

If i ≠ 0 a lepton asymmetry is generated from Ni decays and partly converted into a baryon asymmetry by sphaleron processes

if Tif Trehreh 100 GeV ! 100 GeV !

efficiency factorsefficiency factors == ## of N of Ni i decaying out-of-decaying out-of-equilibriumequilibrium

(Kuzmin,Rubakov,Shaposhnikov, ’85)

M, mD, m are complex matrices natural source of CP violation

(Fukugita,Yanagida ’86)

LeptogenesisLeptogenesis

Kinetic Equations

``decay parameters´´

CP violation in decays Wash-out term from inverse decays

• Strong wash-out when Ki 3 • Weak wash-out when Ki 3

• flavor composition of leptons is neglected

• hierarchical heavy neutrino spectrum

• asymmetry generated from the lightest RH neutrino decays (N1-dominated scenario)

The traditional pictureThe traditional picture

It does not depend on low energy phases !It does not depend on low energy phases !

Neutrino mass bounds

mm11=0=0

~ 10-6 ( M1 / 1010 GeV)

M1 (G

eV)

• N2-dominated scenario

• beyond the hierarchical limit

• flavor effects

Beyond the traditional pictureBeyond the traditional picture

• Beyond the hierarchical limit

M3 & 3 M

2

M2

M1

M

2- M

1

M1

3 Effects play simultaneously a role for 2 1 :

(Pilaftsis ’97, Hambye et al ’03, Blanchet,PDB ‘06)(Pilaftsis ’97, Hambye et al ’03, Blanchet,PDB ‘06)

• N2-dominated scenario (PDB’05)(PDB’05)

The lower bound on M1 disappears and is replaced by a lower bound on M2. The lower bound on Treh remains

(Barbieri et a l. ’01; Endo et al. ’04; Pilaftsis,Underwood ’05; Nardi,Roulet’06;Abada et al.’06;Blanchet,PDB’06)

Flavor composition:

Does it play any role ? However for lower temperatures the charged lepton Yukawa couplings,

are strong enough to break the coherent evolution of the and of the , that are then projected on a flavor basis: ‘‘flavor’ is measured and comes into flavor’ is measured and comes into play !play !

Flavor effects

It is then necessary to track the asymmetries separately in each flavor:

How flavor effects modify leptogenesis? • The kinetic equations become :

• First effect: wash-out is suppressed by the projectors:

• Second effect: additional contribution to the ‘flavored’ CP asymmetries:

Same as before!

(Nardi et al., 06)

The additional contribution depends on the low The additional contribution depends on the low energy phases !energy phases !

L

NO FLAVOR

Nj

Φ

ΦLe

LµLτ

WITH FLAVOR

Nj

Φ

ΦLeLµLτ

General scenarios (K1 >> 1)– Alignment case

– Democratic (semi-democratic) case

– One-flavor dominance

and

and

big effect!

A relevant specific case• Let us consider:

•Since the projectors and flavored asymmetries depend on U one has to plug the information from neutrino mixing experiments

m1=matm 0.05 eV

1= 0

1= -

The lowest bound does not change! (Blanchet, PDB ‘06)

Majorana phases Majorana phases play a role !! play a role !!

Leptogenesis testable at low energies ?

Let us now further impose 1= 0 setting Im(13)=0

traditional unflavored case

M1min

•More stringent lower bound but still successful leptogenesis is possible with CP violation stemming just from ‘low energy’ phases testable in: 0 decay (Majorana phases) and neutrino mixing (Dirac phase) • Considering the degenerate limit these lower bounds can be relaxed !

(Blanchet,PDB 06)

When flavor effects are important ?(Blanchet,PDB,Raffelt ‘06)

• Consider the rate of processes like

• It was believed that the condition > H is sufficient ! This is equivalent to T M1 1012

GeV In the weak wash-out regime this is true since H > ID

• However, in the strong wash-out regime the condition > ID is stronger than > H and is equivalent to

• If zfl zB WID1 M1 1012 GeV but if zfl << zB WID >> 1 much more restrictive ! This applies to the one-flavor dominated scenario through which the upper bound on neutrino masses could be circumvented .

Is the upper bound on neutrino masses be circumvented when

flavor effects are accounted for ?0.12 eV

A definitive answer requires a genuine quantum kinetic calculation ! A definitive answer requires a genuine quantum kinetic calculation !

(Blanchet,PDB,Raffelt ‘06)

Conclusions• The cosmological observations of the last ten

years have pointed to a robust phenomenological model: (the the CDM modelCDM model ) a cosmological SM ?

• 4 puzzles that can be solved only with ‘new physics’

• Discovery of neutrino masses strongly motivate solutions of the cosmological puzzles in terms of neutrino physics and RH neutrinos in the see-saw limit are the simplest way to explain neutrino masses;

• Between light and heavy RH neutrinos the second option appears more robustly

motivated;• LeptogenesisLeptogenesis is one motivation and flavor

effects open new prospects to test it in 0 decay experiments (Majorana phases) and neutrino mixing experiments (Dirac phase)