1. Interacting relic neutrinos and free streaming
Gianpiero Mangano
INFN, Sezione di Napoli
Italy
G. Mangano
NOW 2006

2. G. Mangano
NOW 2006

3. P
rimo exponitur usitatam neutrinorum naturam. Considerandum est utrum neutrinos habeant insolitum vel novum novorum entium commercium . Et circa hoc quaeruntur tres:
Primo utrum entes in neutrinis defluant postquam neutrini segregati sunt ab electronibus
Secundo utrum mundum sine neutrinis sint
Tertio utrum novorum entium commercio obscurae etiam levis materiae dispositionem mutetur
G. Mangano
NOW 2006

4. Standard picture Primo exponitur usitatam neutrinorum naturam
Pseudo-thermal distribution: T = 1.95 K
Number density ( v + v ): cm-3 /flavor
Mean kinetic energy: (eV/m) eV
Direct searches:
 GF2me Ev 10-50 (Ev/eV) cm2 hopeless ?
Indirect searches: cosmological observables
neutrino influence weak + gravity (T> 1 MeV)
gravity (T< 1 MeV)
G. Mangano
NOW 2006

5. Neutrinos and CMB Neff affects the radiation-matter equality point
ISW: Integrated Sachs-Wolfe Effect on acoustic peaks
The large number of cosmological parameters does not allow for a stringent limit
G. Mangano
NOW 2006

6. Neutrinos and Large Scale Structures
neutrinos suppress inhomogeneities which grow for gravitational instability until they become nonrelativistic
Key parameters:
mv=1.2 eV
mv=2.3 eV
mv=4.6 eV
mv=6.9 eV
G. Mangano
NOW 2006

7. Articulus I How strong are present (and future) bounds
Primo utrum entes in neutrinis defluant postquam neutrini segregati sunt ab electronibus
How strong are present (and future) bounds
on exotic features in v distribution?
General parametrization
an in one to one correspondence
with moments of distribution Qn
Pn orthogonal polynomials with
respect to Fermi-Dirac distribution
G. Mangano
NOW 2006

8. Non thermal features in neutrino distributions
Effects seen in CMB and LSS
A model
Cuoco, Lesgourgues, G.M. and Pastor 2005
Extra neutrinos from out of equilibrium decay of scalars after neutrino decoupling
In the instantaneous decay limit at TD
G. Mangano
NOW 2006

9. Bounds from BBN
 particles (decoupled) should not contribute too much to the expansion rate H
A < 0.1 at 95% C.L.
G. Mangano
NOW 2006

10. Model: standard CDM + nonthermal v’s
Present constraints from CMB (WMAP+ACBAR+VSA+CBI) and LSS (2dFGRS+SDSS) + SNIa data (Riess et al.)
Model: standard CDM + nonthermal v’s
Cl and P(k) computed using CAMB code (Lewis and Challinor 2002)
Likelihoods (using COSMOMC Lewis and Bridle 2002))
G. Mangano
NOW 2006

11. “conservative”: Planck+ SDSS
Forecast:
“conservative”: Planck+ SDSS
“ambitious”: CMBPOL+ 40 h-3 Gpc survey with kmax=0.1 h Mpc-1
=vh2(93.2eV/m0)
m0 and vh2 (q) large degeneracy
G. Mangano
NOW 2006

12. Articulus II Secundo utrum mundum sine neutrinis sint
A neutrinoless Universe?
Models where v’s interact with light (pseudo)scalar particles
Beacom, Bell and Dodelson 2004
couplings < 10-5 from several data (meson decay, 0, SN)
For the tightly coupled regime
v density strongly reduced, v’s play no role in LSS
Delay in matter domination epoch, different content in relativistic species after v decays (Neff=6.6 after decays)
G. Mangano
NOW 2006

13. Beacom, Bell and Dodelson 2004
G. Mangano
NOW 2006

14. Including CMB in the analysis:
Bell, Pierpaoli and Sigurdson 2005
Hannestad 2005
Including CMB in the analysis:
No free streaming (no anisotropic stress) leads to
smaller effects on LSS (for massive v’s)
change of sub-horizon perturbations at CMB epoch
Change of sound speed and equation of state of the the titghly coupled v -  fluid
v decays
larger Neff i.e. larger ISW effect for CMB
smaller effects on LSS (no v left at LSS formation epoch
G. Mangano
NOW 2006

15. Massive decaying
Massless interacting
G. Mangano
NOW 2006

16. Massive decaying
G. Mangano
NOW 2006

17. Articulus III
Tertio utrum novorum entium commercio obscurae etiam levis materiae dispositionem mutetur
Usual picture of Dark Matter: cold collisionless massive particles which decoupled around the weak scale for freeze-out of annihilation processes
Ex: neutralino in MSSM with mass of O(100 GeV)
Difficulties:
Excess of small scale structures
Far more satellite galaxies in the Milky Way than observed (from numerical simulation)
DM in the MeV range: SPI spectrometer on the INTEGRAL satellite observed a bright 511 KeV gamma line from the galactic bulge
Boehm, Fayet and Silk 2003
G. Mangano
NOW 2006

18. Framework: light (MeV) DM interacting with neutrinos
Several options for lagrangian density
G.M., Melchiorri, Serra, Cooray and Kamionkowski 2006
Effects on cosmological scales: if DM - v’s scatterings at work during LSS formation we expect an oscillating behavior in the power spectrum (analogous to baryon – photon fluid during CMB epoch)
G. Mangano
NOW 2006

19. Constraints mDM > 10 MeV
from BBN: if DM annihilate with a picobarn cross section (correct relic density) then its mass cannot be too large or it would distrub light nuclide formation
from SNII: if DM also inteacts more than weakly with nucleons neutrinos woulb be kept in equilibrium inside a SN down to a lower temperature neutrinosphere
Serpico and Raffelt 2004
Fayet, Hooper and Sigl 2006
mDM > 10 MeV
G. Mangano
NOW 2006

20. Effects on LSS DM is not collisionless v’s are not free streaming
Scattering cross section depends upon the model
Ex. Scalar DM
mF  mDM
mF = mDM
Scatterings leave an imprint only if efficient at very late times. Is this compatible with a picobarn DM annihilation cross section into neutrinos?
G. Mangano
NOW 2006

21. NOT AT ALL ! mF  mDM mF = mDM
If annihilations freeze-out around mDM (order MeV), also scatterings do so!
DM relic abundance produced rather than e.g. an asymmetry in particle/antiparticle (as baryons, electrons…)
G. Mangano
NOW 2006

22. Equation for velocity perturbations
Effect depends upon the parameter Q
mF  mDM
mF = mDM
G. Mangano
NOW 2006

23. Bounds on differential opacity Q from SDSS data
mDM  mF scenario almost
ruled out. Requires coupling
of order one
mDM = mF still viable
G. Mangano
NOW 2006

24. Very small effect on CMB sub-horizon scales
G. Mangano
NOW 2006

25. Astrophysical bounds
Neutrinos from SN 1987A from LMC were not disturbed by scatterings with DM, since their spectrum at earth is in agreement with SN model
Scattering length for high energy neutrinos emitted by astrophysical sources:
G. Mangano
NOW 2006

26. Conclusions Keeping in mind Occam razor……
Worth studying exotic properties of v’s as a tool to explore physics beyond standard model
Keeping in mind Occam razor……
G. Mangano
NOW 2006

27. G. Mangano
NOW 2006

28. Neff >4 not forbidden by BBN !
Degeneracies:
DM, Neff and m0
Neff >4 not forbidden
by BBN !
Future perspectives:
can we remove the
degeneracy?
G. Mangano
NOW 2006

29. Way to solve the degeneracy:
If we add extra relativistic particles the situation gets even more involved
For each non thermal model there is a “twin” model with extra thermal relativistic particles, sharing the same value of Neff, vh2 but a different value of the neutrino mass scale.
Way to solve the degeneracy:
independent information on the absolute neutrino mass scale (beta decay experiments)
G. Mangano
NOW 2006

30. If neutrino interacts during LSS formation the picture can be quite different even for massless v’s!
G. Mangano
NOW 2006