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?