1. NEUTRINOS IN THE INTERGALACTIC MEDIUM Matteo Viel, Martin Haehnelt. Volker Springel: arXiv today Rencontres de Moriond – La Thuile 15/03/2010

2. Neutrinos exist Neutrinos are massive Neutrinos must impact on the matter power spectrum Intergalactic diffuse gas (Lyman-  1s  2p resonant transition) unique cosmological probe and cosmic laboratory for fundamental physics (systematics not fully under control at the present moment) FACTS ! Thomas: tight constraints using large scale structure Bird: exploiting the Lyman-  power spectrum

3. LYMAN-  INTRO: theory & observations From 3D matter to 1D flux

4. LYMAN-  INTRO – II: present constraints on matter power

5. Lesgourgues & Pastor Phys.Rept. 2006, 429, 307 Lyman-   forest  m = 0.138 eV  m  = 1.38 eV Neutrinos – I: linear theory Thermal (and fast) motion

6. Seljak, Slosar, McDonald, 2006, JCAP, 0610, 014  m (eV) < 0.17 (95 %C.L.), < 0.19 eV (Fogli et al. 08) r < 0.22 (95 % C.L.) running = -0.015 ± 0.012 Neff = 5.2 (3.2 without Ly  ) CMB + SN + SDSS gal+ SDSS Ly-  normal inverted 1 2 3 1,2 3 Goobar et al. 06, Mantz et al. 2009 for forecasting see Gratton, Lewis, Efstathiou 2007 Tight constraints because data are marginally compatible 2  limit DISFAVOURED BY LYMAN-  Neutrinos – II: present cosmological constraints

7. SIMULATING NEUTRINOS in the IGM - I Particle representation: suffers from Poisson noise at small scales, memory requirement could be demanding Grid representation: neutrino gravitational potential is calculated on the long range forces Particle-Mesh (PM part), faster but fully linear Systematics: Velocities in the initial conditions (ICs), Redshift of the initial conditions, Poisson noise, Momentum conserving scheme in ICs, Interfacing with CAMB code See also Brandbyge et al. 2008, Brandbyge & Hannestad 2009, Brandbyge & Hannestad 2010 PARTICLE GRID

8. DM GAS DM GAS FULL HYDRO: 4 comoving kpc/h resolution

9. SIMULATING NEUTRINOS in the IGM – II: methods Matter power @ z = 3 1) Significant non linear evolution at the smallest scales 2) Percent level discrepancies between particle and grid methods 3) Poissonian contribution affects small scales Methods differ at the 2% level

10. NEUTRINOS in the IGM – III: impact on matter power spectrum Increasing neutrino mass – Decreasing  8 1)Scale dependent non-linear suppression which is redshift dependent 2)Suppression larger than linear theory extrapolation  P(k)/P(k) ~ -10 f   matter Massive / Massless

11. NEUTRINOS in the IGM – IV: impact on neutrino power spectrum Increasing neutrino mass

12. NEUTRINOS in the IGM – V: impact on matter power (same  8 ) Increasing neutrino mass Effect is of course smaller if P(k) is normalized at the forest scale 88

13. NEUTRINOS in the IGM – VI: impact on flux statistics FLUX PDF FLUX POWER Increasing neutrino mass

14. NEUTRINOS in the IGM – VII: constraints from flux power  m < 0.9 eV at the 2  confidence level – SDSS alone Impact on flux power is at the 5% level for ~ 1 eV z=2.2  4.2 – 132 data points McDonald et al. 05,06

15. SUMMARY Simulating cosmological neutrinos fundamental task for theoreticians due to the ongoing and future large scale structure surveys (e.g. BOSS, LSST) and KATRIN experiment (0.2 eV) Linear theory is not accurate at small scales and reaching the 1% level of accuracy is still computationally demanding: neutrinos are fast and light particles that could be followed only with approximate method (grid or particle based) Results seem exciting: the non-linear signature is scale and redshift dependent  Its future observation will be highly non-degenerate with other probes and/or systematic effects Impact on flux statistics smaller than the one on matter but already measurable from SDSS quasar spectra alone (1 eV 2  upper limit)

16. MV et al., Phys.Rev.Lett. 100 (2008) 041304 Boyarsky et al., 2008, 2009 Tightest constraints on mass of WDM particles to date: m WDM > 4 keV (early decoupled thermal relics) m sterile > 28 keV (standard Dodelson- Widrow mechanism) SDSS + HIRES data (SDSS still very constraining!) SDSS range Completely new small scale regime Lyman-  and sterile neutrinos - I

17. Lyman-  and sterile neutrinos - II SDSS+WMAP5 SDSS + VHS Boyarsky, Lesgourgues, Ruchayskiy, Viel, 2009, JCAP, 05, 012

18. LYMAN-  INTRO – III: present constraints on matter power

20. 80 % of the baryons at z=3 are in the Lyman-  forest baryons as tracer of the dark matter density field  IGM ~  DM at scales larger than the Jeans length ~ 1 com Mpc flux = exp(-  ~ exp(-(  IGM ) 1.6 T -0.7 ) LYMAN-  INTRO – I: modelling GAS in a LCDM universe Bi & Davidsen (1997), Rauch (1998)