Transcript Neutrinos and the puzzles of Modern Cosmology

Università di Milano, February 8, 2007
Can neutrinos help
to solve the puzzles
of modern cosmology ?
Pasquale Di Bari
(Max Planck, Munich)
1
Outline
A
cosmological Standard Model ?
 Puzzles

of Modern Cosmology
Right-handed neutrinos in
cosmology: light vs. heavy

Leptogenesis
2
A cosmological
Standard Model ?
3
WMAP
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 ?)
Toward a Cosmological SM ?
The Mass-Energy budget today
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
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
Puzzles of
Modern Cosmology
1.
Matter - antimatter asymmetry
2.
Dark matter
3.
Accelerating Universe
4.
Inflation
11
Matter-antimatter asymmetry
• Symmetric Universe with matter- anti matter domains ?
Excluded by CMB + cosmic rays
) BCMB=
(6.3± 0.3) x 10-10 >> B
• Pre-existing ? It conflicts with inflation ! (Dolgov ‘97)
)
dynamical generation (baryogenesis)
(Sakharov ’67)
CMB
• A Standard Model Solution ? SM
¿

: too low !
B
B
New Physics is needed!
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 !
Particle Dark Matter
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 (M10KeV)
Neutrinos behave as HOT Dark Matter 
Accelerating Universe
With Dark Energy
• C.C.  ? Why small ?
-SUSY breaking
Without Dark Energy
• modifying gravity
At large distances, motivated in
brane world scenarios
(Dvali,Gabadadze,Porrati `00)
- Anthropic principle (Weinberg ’87) • without modifying gravity
- only the fluctuations of the vacuum attempt to explain acceleration
energy contribute to  and not its
absolute value (Zel’dovich 67)
• Quintessence ?
A light scalar field still rolling down:
w  -1 in general
without new physics:
acceleration would arise from
inhomogeneities inside the
horizon
it would solve the coincidence
problem but……..unfortunately it
is unlikely to work !
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 ?
- flatness of the potential
what is the inflaton ?
-
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 !)
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 ?
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
SEE-SAW
3 light LH neutrinos:
N2 heavy RH neutrinos:
mn
N1, N2 , …

M
- 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….
•…..LSND
A 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)
A future 5 th cosmological puzzle ?
It would be very interesting especially for neutrinos
~0.1eV
…Dark Matter
•active-RH neutrino mixing:
N ~ mD/M << 1 ,
10
the RH neutrino production is
enhanced by matter effects and
10
11
11
10
10
9
10
10
M2 M3= O(10 GeV)
8
10
7
7
6
<10-5 eV
condition can be fullfilled if m1
and
the Dark Matter RH neutrino is the
lightest one with
M1 ~ O(KeV)
(Asaka,Blanchet,Shaposhnikov’05)
Dark Matter
5
10
4
• For `see-saw ‘ RH neutrinos the
3
10
(eV)
2
10
 100 eV
1
0
-1
10
-2
news: the same flavor-mixing
mechanism describing the production,
also lead to radiative decay: N1   +


 >> t0  M1  10 KeV
m3= matm 0.05 eV
m2= msol 0.009 eV
- SDSS Ly: M1 > (10-14) KeV
(Seljak et al. ’06;Lesgourgues et al)
-7
10
0
10
-1
10
-2
-3
-4
-6
2
10
10
-4
10
10
3
10
10
-3
-5
10
1
10
10
5
10
10
10
• Bad
6
10
4
M1 ~ KeV
10
10
10
10
10
10
9
10
8
Leptogenesis through oscillations
10
(Dodelson,Widrow’94;Dolgov,Hansen’01;
Abazajian,Fuller,Patel’01)
10
10
-5
m1 10 eV
-5
10
-6
10
-7
10
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 ?
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
(Kuzmin,Rubakov,Shaposhnikov, ’85)
if Treh  100 GeV !
efficiency factors = # of Ni decaying out-of-equilibrium
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
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 !
Neutrino mass bounds
~ 10-6 ( M1 / 1010 GeV)
M1 (GeV)
m1=0
Beyond the traditional picture
• N2-dominated scenario
• beyond the hierarchical limit
• flavor effects
• N2-dominated scenario
(PDB’05)
The lower bound on M1 disappears and is replaced by
a lower bound on M2. The lower bound on Treh remains
• Beyond the hierarchical limit
(Pilaftsis ’97, Hambye et al ’03, Blanchet,PDB ‘06)
3 Effects play simultaneously a role for 2 
1:
M3 & 3 M2
M2
M1

 
M2- M1
M1
Flavor effects
(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 play !
It is then necessary to track the asymmetries separately in each flavor:
How flavor effects modify leptogenesis?
(Nardi et al., 06)
• The kinetic equations become :
Same as before!
• First effect: wash-out is suppressed by the projectors:
• Second effect: additional contribution to the ‘flavored’
CP asymmetries:
The additional contribution depends on the low energy phases !
NO FLAVOR
Nj
L
Le
Lµ
Lτ
Φ
Φ
WITH FLAVOR
Nj
Le
Lµ
Φ
Lτ
Φ
General scenarios (K1 >> 1)
– Alignment case
and
– Democratic (semi-democratic) case
– One-flavor dominance
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
1 = 0
The lowest bound
does not change!
(Blanchet, PDB ‘06)
1= - 
m1=matm 0.05 eV
Majorana phases
play a role !!
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)
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  WID1  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 ?
(Blanchet,PDB,Raffelt ‘06)
0.12 eV
A definitive answer requires a genuine quantum kinetic calculation !
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)