Pasquale Di Bari

1
Università di Milano, February 8, 2007
Can neutrinos help to solve the puzzles of
modern cosmology ?

• Pasquale Di Bari
• (Max Planck, Munich)

2
Outline

• A cosmological Standard Model ?
• Puzzles of Modern Cosmology
• Right-handed neutrinos in cosmology light
  vs. heavy
• Leptogenesis

3
A cosmological Standard Model ?
4
WMAP
5
Large Scale Structure
The 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 ?)

6
Toward a Cosmological SM ?
7
The Mass-Energy budget today
8
The Universe is accelerating !
(?? , ?M) (0.7 , 0.3)
q 0
(?? , ?M) (0, 0.3)
(?? , ?M) (0,1)
Hubble diagram High-redshift type Ia supernovae
probe the expansion history and reveal
accelerated expansion
9
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 .
10
Thermal history of the Universe
11
Puzzles of Modern Cosmology

• Matter - antimatter asymmetry
• Dark matter
• Accelerating Universe
• Inflation

12
Matter-antimatter asymmetry

• Symmetric Universe with matter- anti matter
  domains ? Excluded by CMB cosmic rays
• ) ?B (6.3 0.3) x 10-10 gtgt ?B
  
• Pre-existing ? It conflicts with inflation !
  (Dolgov 97)
• ) dynamical generation (baryogenesis)
• A Standard Model Solution ? ?B ?B too
  low !

CMB
(Sakharov 67)
CMB
SM
New Physics is needed!
13
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 lt 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 !

Particle Dark Matter
It is the most conservative option with many
theoretical motivations SUSY DM
(neutralinos,gravitinos,),extra DIMs,
Wimpzillas, 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 (M?10KeV)
Neutrinos behave as HOT Dark Matter ?
14
Accelerating Universe

• Without Dark Energy
• modifying gravity
• At 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 problem
  but..unfortunately it is unlikely to work !

With Dark Energy

• C.C. ? ? Why small ?
• SUSY breaking
• - Anthropic principle (Weinberg 87)
• - only the fluctuations of the vacuum energy
  contribute to ? and not its absolute value
  (Zeldovich 67)
• Quintessence ?
• A light scalar field still rolling down
• w ? -1 in general

15
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 !)

16
Some considerations
Experimental long-standing issues have been
solved and the puzzles of modern cosmology are
nicely expressed in a particle physics
language but they cannot be explained within
the SM !
In other words cosmologists have cleaned their
room but they swept away all the dust in the
particle physicists lounge !
Which model beyond the Standard Model of Particle
Physics can solve the cosmological puzzles ?
17
Neutrino masses m1lt m2 lt m3
18
RH neutrinos in cosmology light vs.
heavy
19
Minimal RH neutrino implementation

• 3 limiting cases
• pure Dirac MR 0
• pseudo-Dirac MR ltlt mD
• see-saw limit MR gtgt mD

20
See-saw mechanism

• 3 light LH neutrinos
• N?2 heavy RH neutrinos N1,
  N2 ,

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

21
? 1 GeV

• gt ? ? high pivot see-saw scale ? heavy RH
  neutrinos

• lt ? ? low pivot see-saw scale ? light RH
  neutrinos

22
Light RH neutrinos and.

• ..LSND
• A see-saw mechanism with ?0.1eV can accommodate
  LSND with a 32 data fit
• (De Gouvea05)
• but potential problems with BBN and CMB

?0.1eV

• ..CMB
• -0.3lt ?N? lt 1.6 (95 CL) (no Ly?)
• (Hannestad,Raffelt)
• 0.6lt ?N? lt 4.4 (95 CL) (with Ly?)
• (Seljak,Slosar,McDonald)

A future 5 th cosmological puzzle ? It would be
very interesting especially for neutrinos
23
Dark Matter

• active-RH neutrino mixing
• ??N mD/M ltlt 1 ,
• the RH neutrino production is enhanced by
  matter effects and
• (Dodelson,Widrow94Dolgov,Hansen01
• Abazajian,Fuller,Patel01)
• For see-saw RH neutrinos the condition can be
  fullfilled if m1lt10-5 eV and the Dark Matter RH
  neutrino is the lightest one with
• M1 O(KeV)
• (Asaka,Blanchet,Shaposhnikov05)
• Bad news the same flavor-mixing mechanism
  describing the production, also lead to
  radiative decay N1 ? ?? ?
• ? gtgt t0 ? M1 ? 10 KeV
• - SDSS Ly? M1 gt (10-14) KeV
• (Seljak et al. 06Lesgourgues et al)

24
Heavy RH neutrinos

• 2 solid motivations
• See-saw original philosophy is not spoiled
• ? Mew , MRMGUT
• 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 ?

25
Leptogenesis
(Fukugita,Yanagida 86)
M, mD, m? are complex matrices ? natural
source of CP violation
CP asymmetry
If ?i ? 0 a lepton asymmetry is generated from
Ni decays and partly converted into a baryon
asymmetry by sphaleron processes if Treh ? 100
GeV !
(Kuzmin,Rubakov,Shaposhnikov, 85)
efficiency factors of Ni decaying
out-of-equilibrium
26
Kinetic Equations
CP violation in decays
Wash-out term from inverse decays
decay parameters

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

27
The traditional picture

• flavor composition of leptons is neglected
• hierarchical heavy neutrino spectrum
• asymmetry generated from the lightest RH
• neutrino decays (N1-dominated scenario)
  

It does not depend on low energy phases !
28
(No Transcript)
29
(No Transcript)
30
Dependence on the initial conditions
m1? msol
M1?1014 GeV
Neutrino mixing data favor the strong wash-out
regime !
31
z M1/ T
K1 tU(TM1)/?1
WEAK WASH-OUT
STRONG WASH-OUT
zd
32
Neutrino mass bounds
10-6 ( M1 / 1010 GeV)
m10
M1 (GeV)
33
(No Transcript)
34
Beyond the traditional picture

• N2-dominated scenario
• beyond the hierarchical limit
• flavor effects

35
N2-dominated scenario
(PDB05)
See-saw orthogonal matrix
?
For
The lower bound on M1 disappears and is
replaced by a lower bound on M2. The lower bound
on Treh remains
36
Beyond the hierarchical limit
(Pilalftsis 97, Hambye et al 03, Blanchet,PDB
06)
Assume

• partial hierarchy M3 gtgt M2 , M1

• heavy N3 M3 gtgt 1014 GeV

3 Effects play simultaneously a role for ?2 ? 1

37
Flavor effects
(Barbieri et a l. 01 Endo et al. 04
Pilaftsis,Underwood 05 Nardi,Roulet06Abada et
al.06Blanchet,PDB06)
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 play !
It is then necessary to track the asymmetries
separately in each flavor
38
How flavor effects modify leptogenesis?
(Nardi et al., 06)

• 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!
The additional contribution depends on the low
energy phases !
39
NO FLAVOR
Nj
F
L
Le
Lµ
Ni
Lt
F
40
WITH FLAVOR
Nj
F
Le
Lµ
Lt
Ni
F
41
General scenarios (K1 gtgt 1)

• Alignment case
• Democratic (semi-democratic) case
• One-flavor dominance

and
big effect!
and
42
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

?1 0
The lowest bound does not change! (Blanchet,
PDB 06)
?1 - ?
m1matm? 0.05 eV
Majorana phases play a role !!
43
Leptogenesis testable at low energies ?
Let us now further impose ?1 0 setting
Im(?13)0
M1min
traditional unflavored case

• 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)
44
When flavor effects are important ?
(Blanchet,PDB,Raffelt 06)

• Consider the rate ?? of processes like
• It was believed that the condition ?? gt H is
  sufficient !
• This implies T ? M1 ? 1012 GeV
• In the weak wash-out regime this is true
  since H gt ?ID
• However, in the strong wash-out regime the
  condition ?? gt ?ID is stronger than ?? gt H and
  is equivalent to
• If zfl ? zB ? WID?1 ? M1 ? 1012 GeV
• but if zfl ltlt zB ? WID gtgt 1 ? much more
  restrictive !
• This applies to the one-flavor dominated
  scenario through which the upper bound on
  neutrino masses could be circumvented .

45
Is the upper bound on neutrino masses be
circumvented when flavor effects are accounted
for ?
0.12 eV
(Blanchet,PDB,Raffelt 06)
A definitive answer requires a genuine quantum
kinetic calculation !
46
Conclusions

• The cosmological observations of the last ten
  years have pointed to a robust
  phenomenological model (the ?CDM 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
• Leptogenesis is one motivation and flavor
  effects open new prospects to test it in
• ??0? decay experiments (Majorana phases)
  and
• neutrino mixing experiments (Dirac phase)
  

47
(No Transcript)