1 pasquale di bari (max planck, munich) università di milano, february 8, 2007 can neutrinos help...
TRANSCRIPT
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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 ?
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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
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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
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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
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10-2
10-1
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1010
1011
10-7
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10-5
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10-1
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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)