1. University of Rome “La Sapienza”
Neutrinos and Reionization
Maria Archidiacono
University of Rome “La Sapienza”

2. Introduction
The connection between cosmological observations and neutrino physics is one of the most interesting and hot topics in astroparticle physics.
Precision observations of the cosmic microwave background and large scale structure of galaxies can be used to probe neutrino mass with greater precision than current laboratory experiments. But the cosmological results are model dependent. So it’s important to investigate the changes on neutrino mass bounds if we use different theoretichal assumptions.
In this case we look at the influence of the reionization model on neutrino mass bounds. Until now these cosmological data have been analyzed in the framework of a standard reionization scenario. But how could these constraints change if we analyze these cosmological data using a different parametrization for the reionization process?

3. Neutrinos

4. Oscillation experiments
Subdury Neutrino Observatory: solar neutrinos: ne → nm
SuperKamiokande: atmospheric neutrinos: nm → nt
Only mass squared differences
m ≠0

5. Beta decay
Essentially a search for a distortion in the shape of the b-spectrum in the endpoint energy region
Normal hierarchy

6. Neutrinos in cosmology
p + e‾ ↔ n + ne
neutrinos decoupling kT=1MeV
free streaming
lFS~vth /H where vth ≈ 150 (1+z) (1eV/Mn) Km/s
Matter power spectrum suppression
DPm(k)/Pm(k) ~ -8 Ωn/Ωm= -8 fn, where Ωn h²=NnMn/92.5eV
non-relativistic transition knr ≈ (√ Ωm) (Mn/1eV)^½ hMpc ^-1

7. Neutrinos effects on CMB
At the state of art of the nuclear physics experiments, we know that at the energy of plasma when neutrinos decoupled they were higly relativistic and so they were a radiation component and the equivalence was delayed
Conservative limit
Early
ISW
arXiv: v2
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Power Spectra and WMAP-Derived Parameters
D. Larson, J. Dunkley, G. Hinshaw, E. Komatsu, M. R. Nolta et al.
But is this result stable if we change the reionization process?...

8. Reionization

9. Ionization history Ionized Universe Neutral Universe Dark Age Quasar
Reionized Universe
Quasar
Reionization
20>z>6
Gunn-Peterson
effect

10. The Gunn-Peterson effect
The Gunn-Peterson trough is a feature of the spectra of the quasars
due to the presence of neutral hydrogen in the intergalactic medium. The trough is characterized by suppression of electromagnetic emission from the quasar at wavelengths less than that of Lyman alpha line at the redshift of the emitted light.
Gunn-Peterson trough
The effect has been observed only in the spectra of the quasars at z>6
"Evidence For Reionization at z ~ 6: Detection of a Gunn-Peterson Trough In A z=6.28 Quasar“Becker, R. H.; et al. (2001).

11. CMB and Reionization
Durig reionization the rescattering of photons suppresses the anisotropies on angular scales below the horizon at the rescattering epoch by a damping factor exp(-treion) where
treion = c sT ∫ dt ne (1+z)³
The uniform reduction of power at small scales has the same effect as a change in the overall normalization.
Moreover at l<30 the observations are limited by “cosmic variance”. So you cannot see reionization effects in temperature spectrum.

12. CMB and Reionization
Instead you can clearly recognize reionization effects in the polarization spectrum at l<30.
Infacts, CMB photons cannot spread themselves on such large scales before the recombination has ended. The polarization signal is expected to be zero at low l. So the peak at low l is due to the rescattering of CMB photons during reionization.
arXiv:astro-ph/ v1
A CMB Polarization Primer
Wayne Hu and Martin White

13. Mortonson & Hu (2008) ApJ, 672, 737, arXiv:0705.1132
Reionization Models
Sudden reionization
Double peak reionization
The sudden reionization model produces only one single peak at l < 10. Instead the models with a partial reionization at higher redshift produce a less high peak, but also a bump at < l < 30.
t=0.090
WMAP-3
t=0.105
Mortonson & Hu (2008) ApJ, 672, 737, arXiv:
NB: there is no direct correspondence between z and l
Moreover we don’t know the behaviour of xe between z=20 and z=6

14. Principal Components zmin = 6 (QSO)
Dz = 0.25 (Dz→0 results indipendent of the bin)
zMAX = 30
Nz = 95
Nz + 1 = (zMAX – zmin)/Dz
PCs: Fisher matrix eigenfunctions
lMAX = 100 (beyond the effects are negligible), xe,fid = 0.15 (not important)
PC variance

15. Principal Components
The higher the modes, the higher the oscillation frequency in redshift

16. Principal Components
The PCs satisfy the orthogonality and completeness relations
Any reionization process can be decomposed in PCs
The mode amplitudes are
Any reionization process between zMAX and zmin is fully described by a set of mode amplitudes.

17. Utility
The first 3-5 modes provide all the informations about reionization that are relevant in the E mode polarization spectrum at larger scales. The higher mode oscillations in redshift at higher frequency can be mediate to zero.
NB: This is not true for the whole reionization process.
The default case is with 10 PCs

18. Caveat: the physical consistence
The constraints on the fraction of ionized hydrogen 0≤xe≤1 are not built in to the method.
A necessary but not sufficient condition is:
where
It’s important to notice that the higher modes have a great effect on xe(z), while they are irrelevant for the polarization spectrum.

19. CMB neutrino mass bounds and reionization
/PhysRevD
How do the constraints on the cosmological parameters (in particular on the neutrinos mass) change, if, instead of using a sudden reionization model, we analyze the process of reionization through the Principal Components, making it indipendent from the model?

20. (Sudden reionization) (model indipendent reionization)
Results
CosmoMC modifiyed to account for a model independent reionization with the first 5 PCs.
Parameters
WMAP7
(Sudden reionization)
(model indipendent reionization)
Wbh^2
0.0221±0.0012
0.0226±0.0015
Wch^2
0.117±0.013
0.115±0.017 WL
0.674±0.134
0.675±0.148 n
0.955±0.033
0.975±0.045 H0
65.7±8.2
66.0±10.2
Smn
<1.15eV(95%)
<1.66eV(95%)

21. Results Positive correlation: Massive neutrinos Sudden reionization
Model indipendent reionization
Sudden reionization
Model indipendent reionization
Positive correlation:
Massive neutrinos

22. Results
Sudden reionization
Model indipendent reionization
The model indipendent reionization agrees with the Harrison Zel’dovich primordial spectrum within 1s
Sudden reionization
Model indipendent reionization
Negative correlation:
Free streaming

23. Conclusions
We investigated the influence of the theoretical assumptions about reionization on the cosmological neutrino mass bounds. We saw that the cosmological constraints on the neutrino masses are weakened if we parametrize the reionization process trough the Principal Components, making it independent from the model.

24. THANKS

25. Number of effective neutrino species and Reionization
The current best measurement of the number of neutrino types comes from observing the decay of the Z boson.
Early
ISW

26. (Sudden reionization) (model indipendent reionization)
Results
CosmoMC modifiyed to account for a model independent reionization with the first 5 PCs.
Parameters
WMAP7
(Sudden reionization)
(model indipendent reionization)
Wbh^2 ±
±0.0007
Wch^2
0.147±0.037
0.151±0.035 WL
0.738±0.029
0.727±0.032 n
0.986±0.022
0.987±0.023
Neff
>0.45(95%)
>1.13(95%)

27. Results Work in progress … Sudden reionization
Model indipendent reionization
Work in progress …