New Nuclear and Weak Physics in Big Bang Nucleosynthesis

New Nuclear and Weak New Nuclear and Weak Physics in Big Bang Physics in Big Bang

NucleosynthesisNucleosynthesis

Christel SmithChristel Smith

Arizona State UniversityArizona State University

Erice, ItalyErice, Italy

September 17, 2010September 17, 2010

OutlineOutline

Review of BBNReview of BBN Current status of BBN predictions & Current status of BBN predictions &

observationsobservations New nuclear and weak physicsNew nuclear and weak physics BBN in light of WMAP-7BBN in light of WMAP-7 Constraining the heavy sterile neutrino Constraining the heavy sterile neutrino

parameter spaceparameter space

BBN is one of our oldest BBN is one of our oldest windows into the early universewindows into the early universe

Weak Decoupling T ~ 3 MeV Weak Decoupling T ~ 3 MeV

Neutrinos decouple from the universe.

Rates for neutrino/antineutrino scattering on electrons and positrons become slow

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neutrino scattering rate λ ν ~ GF2 T 2

( ) T 3( ) = GF

2 T 5

where the Fermi constant is GF ≈1.166 ×10−11 MeV -2

Adiabatically expand

Retain their thermal Fermi-Dirac Shape (unless another process occurs)

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Tν = Tdecoupling /a

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Tν = (4 /11)(1/ 3)Tγ

Continue to interact with the baryons

Weak reactions (interconvert neutrons and protons)

After the neutrinos decouple…After the neutrinos decouple…

-At T ~ few MeV, rate of these reactions are fast enough -At T ~ few MeV, rate of these reactions are fast enough that they are in chemical equilibrium so that:that they are in chemical equilibrium so that:

-Eventually the universe gets cool enough that the weak -Eventually the universe gets cool enough that the weak rates become slow compared to the expansion rate of rates become slow compared to the expansion rate of the universethe universe

-This is “Weak Freeze Out”-This is “Weak Freeze Out”

weak reactions /H ~ (T/0.8 MeV)3

Weak Freeze OutWeak Freeze Out


Key issues:Expansion rate vs. weak ratesLepton asymmetry Crucial role of neutrinos

Nucleosynthesis Nucleosynthesis t t ~ 1s, T~1 MeV~ 1s, T~1 MeV

Entropy--setting temp. scale for nucleosynthesis --effect on deuterium

Current Status of BBN ComparisonsCurrent Status of BBN Comparisons

Element abundance Element abundance yield prediction as a yield prediction as a function of baryon-function of baryon-to-photon ratio:to-photon ratio:

Boxes are the Boxes are the observational observational measurements of measurements of the primordial the primordial element element abundances.abundances.

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η =nb − n

b

nγ

Hints of Unknown Physics Hints of Unknown Physics 77Li?Li?

Factor of 2-3 over-predicted.Factor of 2-3 over-predicted.(measured by absorption (measured by absorption spectra in the surface of old spectra in the surface of old metal poor stars) metal poor stars)

Many theories invoked (such as Many theories invoked (such as cosmic ray spallation, cosmic ray spallation, rotational effects to dilute rotational effects to dilute lithium in the surface, lithium in the surface, nuclear physics nuclear physics uncertainties)uncertainties)

66Li?Li?

New observational evidence New observational evidence (Asplund et al 2006) suggest (Asplund et al 2006) suggest ~4 orders of magnitude more ~4 orders of magnitude more than predictionthan prediction

Addressing Addressing 77Li and Li and 66Li Issues with Li Issues with Nuclear PhysicsNuclear Physics

Extend the BBN nuclear reaction network to contain more reactions Extend the BBN nuclear reaction network to contain more reactions involving beryllium and lithium isotopesinvolving beryllium and lithium isotopes

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Arxiv:1008.0848

Lepton Capture ReactionsLepton Capture Reactions Green - Beta DecayGreen - Beta Decay Magenta - electron neutrino Magenta - electron neutrino

and positron captureand positron capture

Blue - electron anti neutrino Blue - electron anti neutrino and electron captureand electron capture







n

G. Fuller & C. Smith Arxiv:1009.0277

Lepton Capture ReactionsLepton Capture Reactions






Lepton Capture ReactionsLepton Capture Reactions






•Inclusion of these weak rates do little in standard BBN

•May be important to include for non-standard BBN

Hints of Unknown Physics Hints of Unknown Physics

4He

Two new interesting new observations:

WMAP -7-higher measurement of relativistic energy density

Izotov & Thuan 2010



Yp= 0.2565 ± 0.0010(stat.) ± 0.0050(syst.)



L. Krauss, C. Lunardini, C. Smith (in preparation)

Helium considerationsHelium considerations

Constraining ~10-100 MeV Sterile Constraining ~10-100 MeV Sterile Neutrino Parameter SpaceNeutrino Parameter Space

G. Fuller, C. Kishimoto, C. Smith (in preparation)

It’s not obvious what this will doIt’s not obvious what this will do A fully populated state would A fully populated state would

decouple from the universe decouple from the universe around T ~ 1 GeVaround T ~ 1 GeV

Start out relativistic, go non-Start out relativistic, go non-relativistic by BBN timesrelativistic by BBN times

Significant non-relativistic Significant non-relativistic contribution to energy density (H ~ contribution to energy density (H ~ TT3 3 instead of H ~ T instead of H ~ T44))

High energy decay products High energy decay products (photons energize the plasma and (photons energize the plasma and add entropy, neutrinos could add entropy, neutrinos could distort neutrino distribution distort neutrino distribution functions)functions)



The end.The end.

New Nuclear and Weak Physics in Big Bang Nucleosynthesis

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