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Interacting relic neutrinos and free streaming

Interacting relic neutrinos and free streaming. Gianpiero Mangano INFN, Sezione di Napoli Italy. P. rimo exponitur usitatam neutrinorum naturam. Considerandum est utrum neutrinos habeant insolitum vel novum novorum entium commercium . Et circa hoc quaeruntur tres:.

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Interacting relic neutrinos and free streaming

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

  2. 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 commercioobscurae etiam levis materiae dispositionem mutetur NOW 2006

  4. Primo exponitur usitatam neutrinorum naturam Standard picture Pseudo-thermal distribution: T = 1.95 K Number density ( v + v ): 112 cm-3 /flavor Mean kinetic energy: 10-7(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) 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 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 NOW 2006

  7. Articulus I 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 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 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. NOW 2006

  10. 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)) NOW 2006

  11. 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 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) NOW 2006

  13. Beacom, Bell and Dodelson 2004 NOW 2006

  14. 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 NOW 2006

  15. Massive decaying Massless interacting NOW 2006

  16. Massive decaying NOW 2006

  17. Articulus III Tertio utrum novorum entium commercioobscurae 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 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) NOW 2006

  19. Constraints 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 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? 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…) NOW 2006

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

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

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

  27. NOW 2006

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

  29. 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) NOW 2006

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

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