Nuclear Reactions in Primordial Nucleosynthesis

1
Nuclear Reactions in Primordial Nucleosynthesis

• Pasquale Dario Serpico
• MPI für Physik
• München

V Meeting Italiano di Astrofisica Nucleare 20-22
Aprile 2005 -Teramo
based on work in collab. with S. Esposito, F.
Iocco, G. Miele, G. Mangano and O. Pisanti -
Federico II University and INFN Naples
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Overview of the Talk
(2H) (4He) (7Li)

• BBN in the Precision Cosmology Epoch
• n-decoupling n?p rates The Weak reaction
  stage
• The Road to the Nuclides The Nuclear reaction
  stage

As BBN is ruled by Non-linear Differential
equations

• present status theory versus observations

• Outlook perspectives

P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
3
BBN Flowchart
Primordial Elements Observations
Cosmology
Yi
Systematics!
Nuclear Astrophysics
BBN
Data Regression!
Astrophysics
s(E)
wb , dwb/wb ltlt1!!!
CMB

• PDG
• stuff
• ?n , GN, a,
• Physics...

New Physics?
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Weak rates
Freeze out of weak rates fixes n/p ratio (crucial
for 4He)

• Big improvements in the last decade
• QED radiative corrections
• Finite nucleon mass corrections
• Plasma effects
• Neutrino spectral distortion

Rates are accurate at the O(0.1 ), i.e. as (d?n/
?n)exp
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
5
4He status
Once WMAP value for wb fixed, theoretical
predictions are quite robust, unless some
unknown systematics affect the STANDARD PHYSICS
data (e.g., ?nexp, G. Matthews et. al. 04)
Yp th0.2481 0.0005 For wb0.023 0.001
General agreement among several groups. Error
dominated by (d?n/ ?n)exp New evaluation of GN
negligible contribution to the uncertainty (PDG
2004)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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The observational side is still confused BCG
(metal poor, extragal. obj., HII regions) give an
unreasonable spread of values, changing with the
sample, the regression method to Z0, the
analyzers group
Not shown, Ypb0.2421(44)0.0021 (Iz Th
04) Other Determinat. 0.244 (I) 0.2480.009
(II), 0.004 (II)
Yp0.239 0.002
Yp0.2345 0.0026
Yp0.244(5) 0.001
Olive Skillman 04
Yp0.249 0.009
0.232Yp 0.258
Conservative Range
The estimate is systematics dominated (e.g.,
degeneracies among astrophysical parameters).
Further (high quality) data, and possible
complementary techniques needed to improve the
determination.
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
7
Bounds to Non-standard Physics the case of
neutrino sector
At this stage it is impossible to severely bound
Neff from BBN.
However always much better than CMB alone
according to the assumed value for Yp -but
quite conservatively- DNefflt1-1.5. Analogously,
the BBN bound on lepton degeneracy x is by far
the most stringent
Cuoco et al. 03 See also Barger et al. 03
DCMB
Extended to all flavors! Dolgov, Hansen, Pastor,
Petcov, Raffelt, Semikoz 2002
D 4He CMB
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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Road 1
4He Observations
Cosmology
Yp
Systematics!
Only loose check of Standard Cosmological Model
BBN
CMB
New Physics?
Till now, many bounds (DNeff,xe. ) Could be
improved!!!
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Nuclear rates
Apart for Helium, all the other nuclides are
sensitive to the Nuclear reaction Network.
To refine the predictions, it is then mandatory
to properly evaluate the thermal averaged
nuclear rates and their uncertainties
Well, where is the problem?
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
10
Nuclear rates- II
No First Principle Theory exists, as for the n?p
rates. Only partial information (Detailed
Balance linking direct and Reverse Rates, Nuclear
Model calculations suggesting fitting formulae,
etc.) ? Huge amount of experimental data needed!

• Main Experimental problems extract the cross
  section from data in the low energy range of
  interest for BBN (0.01 ? 1 MeV)
• Crucial role of Coulomb repulsion
• Strong energy dependence
• Low cross sections (pb)
• Spurious effects (e.g. atomic/molecular
  screening)
• Extrapolation (e.g., S-factor) to low E
• Difficulties with handling n and radioactive
  beams (e.g. 7Be, 3H)
• No BBN-dedicated experiments, always stellar
  purposes.

P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
11
Nuclear rates- III

1. Data from different experiments with different
   systematics
2. For several crucial reactions present data show
   evidence for ununderstood systematics
3. Experimental results typically overlap only
   partially in energy
4. Cross section for some (at the moment)
   sub-leading process is still poorly known

Recent (2004) BBN-oriented Compilations Cyburt De
scouvemont et al. Serpico et al.
However, with respect to the historical data
analysis ( from Fowler and Hoyle 1964...to
Smith, Kawano and Malaney 1993) Important recent
steps in the field NACRE Coll. Database
pntpm.ulb.ac.be/nacre.htm Other data (e.g.
2H(p,?)3He by LUNA Collaboration 2002)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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Fit method and error estimates
Sik S factor at Ei of k-th experiment ?ik
statistical uncertainty ?k normalization
uncertainty Sth fit (often polynomial) of the S
factor depending on coefficients an to be
determined by the fit
Regression approach minimization of
?k offset of the k-th experiment (free parameter
determined by the fit)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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NOTE The choice of the regression technique and
error estimate is a non-trivial task!!! Other
compilations are based on biased methods (as in
Cyburt 04 see D Agostini 94) or on some
arbitrary criterion (as in Descouvemont 04)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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Rate estimate
best fit values
Boltzmann-Gamow kernel
Error estimate
for reduced ?n2 larger than 1 the error is
inflated by a factor
(PDG minimal prescripition)
The minimum measured scale error is added in
quadrature (conservative, but not
OVER-conservative as in Cyburt 04)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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From nuclear rates to nuclide abundances
BBN evolution equations numerically solved via a
new code
Theoretical uncertainties on Xi due to the rates
?k generalization of the linear propagation
(Fiorentini, Lisi, Sarkar and Villante 1998)
Allows T-dependent and/or asymmetric errors!
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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2H - 2H reactions leading source of uncertainty
for Deuterium
Small statistical errors but quite large
systematics due to scale normalization or
unknown poor ?2
2H(d,p)3H
2H(d,n)3He
Systematics-dominated, higly desiderable a new
single measurement covering most of the E-range,
and filling the gap of data at E0.2-1 MeV
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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A good example
2H(p,?)3He
LUNA 02 data a low energy discrepancy solved,
error on 2H reduced
A still debated case
4He(3He,?)7Be
dominant channel for 7Be production, crucial for
7Li error budget. New measurement ongoing
Important also for solar n fluxes (B Be)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
18
2H status
Deuterium is the most sensitive nuclide to wb
Best BBN baryometer
wb(D)0.021 0.002
105(2H /H) th 2.440.20 0.17
For wb0.023 0.001
Rate ??2/ ?2 ()
2H(p,?)3He 49
2H(d,n)3He 37
2H(d,p)3H 14
only 0.04!!! due to nuclear uncertainties
Essential agreement between two completely
independent determinations of wb !!! Wonderful
check of Standard Cosmological Model
Deuterium in QSOAS Kirkman et al. 2003
One More Observation! Crighton et al. 2004
105 lt2H /Hgt obs (2.780.44 0.38)
105 lt2H /Hgt obs 2.42 0.27(0.57)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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Deuterium in QSOAS Ly-a abs
Road 2
Low Statistics (5-7 data) Systematics? (?n2 4)
Cosmology
Theoretical Central Value and Error sligthly
dependent on regression analysis
for 2H(d,p)3H-2H(d,n)3He-2H(p,g)3He
BBN
Perfect Agreement! 2H /H strongly depends on wb
CMB
Important Check of Standard Cosmological Model!
But
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7Li status

1. Given the WMAP result, the road to 7Li is
   clarified

Propaganda we did not limit to reanalyze the
O(10) reactions believed to be dominant. We
revised and update the whole network (O(100)),
improved the analysis or looking for new
important reactions, and checked again the
relative weights of the different channels.
Almost two years of work... A (partial!!!)
list 2H(d,?)4He, 3He(t,d)4He, 3He(t,np)4He,
3H(t,nn)4He, 4He(d,?)6Li, 6Li(p,3He)4He, 3H(p,
?)4He, 7Li(p, ?)4He4He, 7Be(n,?)4He,
7Li(d,n)4He4He, 7Be(d,p)4He4He, 6Li(d, p/n)7Li/
7Be, 7X(3X,p/n)9Be ,three body, partition
functions...
First 7Li bump T70 keV, via 4He(t,g) 7Li
Equilibrium determined by wb, and the relative
weight of the two paths
Then plateau reached because of competion of
7Li(p,a) 4He
Indirect 7Li production via 4He(3He,g) 7Be and
late EC decays to 7Li
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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We get
rate ??Li2/ ?Li2()
7Be(n,4He)4He 40.9
4He(3He, ?)7Be 25.1
7Be(d,p)4He4He 16.2
3He(d,p)4He 8.6
2H(p,?)3He 4
others 5.2
1010(7Li /H) th 4.8 0.4 0.4
Due to nuclear uncertainties
Due to dwb0.001
Experimentally, in ancient metal poor stars (halo
or extragal.) one finds a plateau (Spite pl.) for
low Z ? Hint of Primordial Origin. Several
determinations, suggesting the (conservative)
range
1lt1010(7Li /H)explt2 d (7Li /H)exp lt0.5
Very difficult measurements, tiny fraction of
neutral Li, crucial importance of T
Low dispersion, compatible with 0, hard to
explain by depletion/diffusion models!
Still an open problem the most puzzling for
Standard BBN New clues on Astrophysics? A window
on non-standard Physics in the Early Universe?
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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Nuclear Physics Solution disfavored, tough not
yet completely ruled out
Wrong normalization in 4He(3He,g) 7Be to
reconcile Spite Plateau BBN excluded at (at
least) 2 s from the measured solar Boron n-flux
in SNO Cyburt et al., PRD 69 (2004)
Possible underestimate of 7Be(d,p)2 4He by 2-3
orders of magnitude Coc et al. ApJ 600 (2004)
seems excluded by new measurements (C. Angulo _at_
NIC VIII)
x30
x100
x300
x1000
We expect this issue to be soon (and finally)
clarified by forthcoming measurements.
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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Exotica
K Jedamzik, PRD 70 (2004)
In Non-standard BBN, other interesting
possibilities. For example, decay or annihilation
of CDM relics (neutralinos?) ? Prediction of a
6Li plateau
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
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Exotica an intriguing hint
Recent hint for a 6Li plateau (see review in
Lambert, astro-ph/0410418)
A possible window on non-standard physics!
In this context, other interesting possibilities
for Nuclear Astrophysics Experimentalists in
improved measurements of (e.g.) 6Lip?3He4He,
6Lin?3H4He, other possibly neglected
reactions Indirectly (CR nucleosynthesis), the
spallation aa reactions at middle-high energies
also quite important!
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
25
Road 3
Spite Plateau
Systematics in Astrophysical models?
New Measurements
4He(3He, ?)7Be
7Be(n,4He)4He
7Be(d,p)4He4He
....
BBN
Astrophysics
CMB
New Physics?
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Outlook
I focused on the difference between 4He
prediction (depending on weak rates and n
effects, theoretically well understood) and the
other nuclides, sensitive to the Nuclear Network
details.

• We performed a deep and wide review and analysis
  of the network
• We compiled an updated BBN-oriented nuclear
  database
• We used a new, self-consistent and unbiased
  protocol for data
• regression.

The error budget was put on a more statistical
ground, and typically a reduction of the errors
with respect to previous compilations was
found. I compared the predictions for the three
most relevant nuclides with observations
(2H) (4He) (7Li)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
27
A Summary Plot of present Standard BBN Situation
1 s nuclear error bars included, observational
conservative ranges or upper limits shown.
hb x1010
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
28
Perspectives
We expect from
Nuclear physicists new measurements in the
energy range of interest for BBN (0.01 ? 1 MeV)
4He(3He, ?)7Be, 2H-2H, 7Be(n,4He)4He, 4He(2H,
?)6Li,...
Astrophysicists better understanding of possible
systematics affecting 4He measurement and 7Li,
but also more data for 2H
Astroparticle physicists If both the previous
communities will confirm actual results...
Should try to find some smart idea to solve the
puzzle, as usual!!!
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
29
QED radiative effects Check the neutron lifetime
inner corrections
outer corrections
Perturbative QCD
Leading log resummation
Coulomb correction rescattering of electron in
the proton field, Weak magnetism
?nexp 885.7 0.8 s ?nth 886.5 s
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
30

• Plasma effects
• Interactions with photons/electrons of the plasma
• Change in the e.m. equation of state due to
  photon/electron thermal masses
• PP(?)
• New Process (? only allowed at finite T. Checked
  negligible)

Very small corrections O(0.1 )
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
31
Neutrino decoupling

• neutrinos are in chemical equilibrium with the
  e.m. plasma till weak reactions freeze out at T?
  few MeV
• First approximation instantaneous decoupling.
  Neutrino decoupling has no overlap in time with
  e-e- annihilation

• Asymptotic value reached for T? /T

• All n species keep FD distribution

• Standard Contribution to Hubble Expansion
  Law

P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
32
More accurate calculations by solving the kinetic
equations show a partial entropy transfer during
e-e- annihilation phase
Spectral Distortions, ffn(p,T?)1df(p)
different for ne (both CC NC) and nx(NC only)

• How distortions in neutrino distributions can
  affect BBN ?
• change in total n energy density 1
• change in n-p weak rates fne enters the thermal
  averaged rate

Tiny effects, 10-4 on 4He mass fraction!!
For details and references Dolgov, Phys. Rep.
370 (2002)
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo
33
?nexp Problem?
If confirmed, quite embarassing for most of the
previous determinations!!!
In G. Matthews et. al. 04, used
?nexp 878.5 0.7 s 0.3 s from Serebrov et al,
unpublished, 04 instead of ?nPDB 885.7 0.8 s
Yp th0.248?0.246
Gravitational trap, cold n Estrapolation to
?stor-1 ?0, Best storage time determination
claimed
P. D. Serpico, MPI für Physik - Munich
Nuclear Reactions in Primordial Nucleosynthesis
20-22/04 Teramo