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NEUTRINOS
AND
BIG BANG NUCLEOSYNTHESIS
GARY STEIGMAN
THE OHIO STATE UNIVERSITY
Nobel Symposium: Neutrino Physics
Haga Slott, Sweden, August 2004
• The Universe is expanding
• The Universe is filled with radiation
• The Early Universe was Hot & Dense
⇒ The Early Universe was a Cosmic Nuclear Reactor
Neutrinos Play A Key Role
~ 100 s after the Big Bang :Primordial Nucleosynthesis
Abundances of D, 3He, 7Li
Are RATE Limited
⇒ D, 3He, 7Li Are
Possible Baryometers
η ≡ nN / nγ
η10 ≡ 1010 η ≡ 274 ΩB h2
BBN – Predicted Primordial Abundances
DEUTERIUM --- The Baryometer Of Choice
• As the Universe evolves, D is only DESTROYED ⇒
* Anywhere, Anytime : (D/H) t ≤ (D/H) P
* For t << t 0 (Z << Z ; z >> 0) : (D/H) t → (D/H) P
• BUT* H Ι and D Ι spectra are identical ⇒ H Ι Interlopers?
* Unresolved velocity structure ⇒ Errors in N(H Ι) ?
• (D/H) P is sensitive to the baryon density ( ∝ η10−1.6 )
“Measure” ( D / H ) P
Use BBN ( D / H ) P vs. η10
Infer η (ΩB) At 20 Min.
( Nν = 3 )
D - Abundance Data
X = O, Si, …
(D/H)P = 2.6 ± 0.4 x 10−5
(D/H)P = 2.6 ± 0.4 x 10−5 + SBBN ⇒ η10 ≈ 6.1 ± 0.6
BBN
~ 400 kyr after the Big Bang :Relic Photons (CBR) are free
ΩB h2 = 0.018, 0.023, 0.028
← θ
CBR (WMAP) constrains ΩB h2 (η)
CBR Temperature Anisotropy Spectrum (∆T vs. θ)
WMAP ⇒ η10 = 6.3 ± 0.3
CBR
WMAP
WMAP – Predicted vs. Observed D/H
BBN (20 min) & CBR (380 kyr) AGREE !
BBN CBR
4He (mass fraction Y)
IS NOT Rate Limited Nν = 2, 3, 4
4He IS n/p Limited
⇒ νe’s play a key role
Y Is Sensitive To The
EXPANSION Rate (H)
⇒ ALL ν’s play a role
S ≡ H'/H ≡ (1 + 7∆Nν / 43)1/2
Nν ≡ 3 + ∆Nν
∆Y ≈ 0.013 ∆Nν
SBBN/WMAP (Predicted)
LPRST
PSTE
OSS
IT IT
A History of YP Determinations
PSTE
SBBN/WMAP
OSS
IT IT
OSW
Adopt OSW : YP = 0.238 ± 0.005
Nν = 2, 3, 4
Nν < 3 ?
yD≡ 105(D/H)P = 2.6± 0.4D and 4He Isoabundance curves in the Expansion Rate – Baryon Density plane
ΩBh2 = 0.021 ± 0.002
S = 0.94 ± 0.03
(∆Nν = − 0.70 ± 0.35)
&
YP = 0.238 ± 0.005&
⇒
(D & 4He)
Nν < 3 ?
Low Reheat Temp.
(TR ∼ MeV)
Nνeff < 3
Kawasaki, Kohri & Sugiyama
Late Decay of
Massive Particle
⇒
⇒
BBN Best Fit Point (x)
η10 = 5.7 (ΩB h2 = 0.021) ; ∆Nν = − 0.70
Joint fit of D/H & YP
SBBN Consistent at ~ 2 σ
BBN (D & 4He) + CBR (WMAP)
BBN
CBR
Joint BBN + WMAP Fit
1 < Nν < 4
e – Neutrino Degeneracy
For ξe = µe/kT > 0
⇒ More νe
⇒ n/p ↓ ⇒ YP ↓
⇒ ξe = 0.044 ± 0.022
⇒ ΩBh2 = 0.022 ± 0.002
(D & 4He)
Alternate New Physics
JOINT BBN & CBR CONTOURS
WITH η10 , ξe & ∆Nν ALL FREE
1 < Nν < 8
yLi ≡ 1010 (Li/H)P
Halo Stars :
yLi = 1.2
Glob. Cl. Stars :
yLi = 2.2(D & 4He)
yLi ≡ 1010 (Li/H)P
Halo Stars :
yLi = 1.2
Glob. Cl. Stars :
yLi = 2.2
yLi ≡ 1010 (Li/H)P
(D & 4He)
SUMMARY AND CONCLUSIONS
BBN (D & 4He) and the CBR are consistent ⇒
The Universe at 20 min. and 380 kyr AGREE !
Provided that ( @ 95% ) : 1.80 ≤ Nν ≤ 2.94
Or : ξe ≈ ξµ ≈ ξτ ≈ 0.044 ± 0.022
But … 7Li ?
Observational Uncertainties Or New Physics?