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The Role of Neutrinos in
Astrophysics
A.B. Balantekin
University of Wisconsin
GDR Neutrino
Laboratoire Astroparticule et Cosmologie
Joint analysis of the solar
neutrino data including
final SNO salt results
along with the most recent
KamLAND data
Balantekin, et al., PLB 613, 61 (2005)
Neutrinos from core-collapse
supernovae
• Mprog ≥ 8 MSun
• E ≈ 1053 ergs ≈ 1059 MeV
• 99% of the energy is carried away by neutrinos
and antineutrinos with 10 ≤ E ≤ 30 MeV
• 1059 Neutrinos!
A recent SN remnant (Hubble Space Telescope)
X-ray remnant of the SN
observed by Chinese in 185 A.D.
X-ray remnant of Kepler’s SN (1604)
Estimated intensity in the sky of the brightest historical SN
(1066) - National Observatory of Turkey, Antalya
SN shock wave
Chandra
SN remnant
99% of the
gravitational
binding
energy of the
star
Neutron star
Recent Accomplishments with neutrinos in astrophysics
• Current theoretical prediction of solar neutrino flux and structure of
main sequence stars. Solar neutrino measurements precisely confirm the
Standard Solar Model. Temperature at the center of the Sun was
correctly calculated ab initio to better than 2%.
• Recognition of the importance of the neutrino-neutrino interactions on
neutrino propagation in dense neutrino systems. Development of the
theoretical tools to treat these effects in astrophysical sites.
• New theoretical breakthroughs in nucleosynthesis in SN and GRB’s, and
role of weak interactions in SN dynamics.
• Tritium beta decay mass limit plus knowledge of the large mixing angles
implying that all mass eigenstates are limited, meaning active neutrinos
cannot be the dark matter. This is independently confirmed by the
cosmology limits. Both results had important contributions from theory.
• New limits on diffuse SN neutrino flux. Astrophysical uncertainties are
now reduced to the point that these searches are primarily testing the
neutrino emission per supernova, which is of fundamental interest to
nuclear physics.
Recent Accomplishments with neutrinos in astrophysics
• Current theoretical prediction of solar neutrino flux and structure of
main sequence stars. Solar neutrino measurements precisely confirm the
Standard Solar Model. Temperature at the center of the Sun was
correctly calculated ab initio to better than 2%.
• Recognition of the importance of the neutrino-neutrino interactions on
neutrino propagation in dense neutrino systems. Development of the
theoretical tools to treat these effects in astrophysical sites.
• New theoretical breakthroughs in nucleosynthesis in SN and GRB’s, and
role of weak interactions in SN dynamics.
• Tritium beta decay mass limit plus knowledge of the large mixing angles
implying that all mass eigenstates are limited, meaning active neutrinos
cannot be the dark matter. This is independently confirmed by the
cosmology limits. Both results had important contributions from theory.
• New limits on diffuse SN neutrino flux. Astrophysical uncertainties are
now reduced to the point that these searches are primarily testing the
neutrino emission per supernova, which is of fundamental interest to
nuclear physics.
Neutrinos from SN1987A
50
Kamiokande II (PR D38 (1988) 448
IMB (PR D37 (1988) 3361
Baksan (PL B205 (1988) 209)
Energy (MeV)
40
30
20
10
0
0
2
4
6
8
Time of Event (sec)
10
12
14
Adopted from Raffelt
iron peak
Life stages of a core-collapse supernova
1. Collapse and bounce epoch. S/k ≈ 1
2. Shock-reheating epoch. S/k ≈ 40
3. Hot-bubble epoch. S/k ≈ 75 to 500?
Possible site of r-process
nucleosynthesis
Neutrino-driven wind in post-core bounce supernova
-sphere
injection (heating)
region
wind region
unshocked
matter
shock-wave
Mass outflow rate in
the wind region is
approximately constant
[Fe/H] ≈ -3.1
Observed
r-process
abundances
A > 100 abundance pattern fits
the solar abundances well.
Yields of r-process nucleosynthesis are determined
by neutron-to-proton ratio, n/p
Interactions of the neutrinos and antineutrinos streaming
out of the core both with nucleons and seed nuclei
determine the n/p ratio.  Hence it is crucial to
understand neutrino-nucleon cross-sections.
Before these neutrinos reach the r-process region
they undergo matter-enhanced neutrino oscillations
as well as coherently scatter over other neutrinos.
 Many-body behavior of this neutrino gas is not
understood, but may have significant impact on rprocess nucleosynthesis.
 How does neutrino mixing and neutrino-neutrino
interactions effect the yield of r-process
nucleosynthesis?
MNS mixing matrix:
Atmospheric ’s
SuperK, K2K
Reactor ’s, very
little contribution
from solar ’s
Daya Bay
Double Chooz
Solar neutrinos
SuperK, SNO,
KamLAND
Electron Fraction
Ye= (ne- - ne+) / nbaryons
p = e + eproton loss rate
n = e + e+
neutron loss rate
X alpha
fraction
Weak freeze-out radius: where neutron-to-proton
conversion rate is less than the outflow rate
dYe/dt = 0
dYe/dt = 0
If alpha particles are present
If Ye(0) < 1/2, non-zero X increases Ye.
If Ye(0) > 1/2, non-zero X decreases Ye.
If alpha particles are absent
Non-zero X
pushes Ye to 1/2
Alpha effect
Fuller, McLauglin, Meyer
Can sterile neutrino fix the problem of
alpha formation?
McLaughlin, Fetter, Balantekin, Fuller, Astropart.
Phys., 18, 433 (2003)
Neutrino transport in Dense Matter - MSW
N : Allowed values of neutrino momenta
N distinct commuting SU(2) algebras
Neutrino-Neutrino Interactions
Smirnov, Fuller and Qian,
Pantaleone, McKellar,…
For systematic corrections to these equations see Balantekin & Pehlivan,
JPG 34, 47 (2007)
Nonlinear supernova neutrino and antineutrino flavor transformation with coupled trajectories
One finds large-scale,
collective flavor oscillations
deep in the supernova
envelope, even for the
atmospheric neutrino masssquared difference and
for allowed values of 13.
Normal hierarchy
Inverted hierarchy
This is very different from
MSW; models for the rprocess, explosion, and the
neutrino signal could be
affected.
Survival probabilities
Duan, Fuller, Carlson, Qian
References:
• Balantekin & Yuksel, astro-ph/0411159,
New J. Phys. 7, 51 (2005)
• Fuller, Qian, astro-ph/0505240, PRD 73, 023004 (2006)
• Duan, Fuller, astro-ph/0511275, PRD 74, in press.
• Duan, Fuller, Carlson, Qian, PRD 74, 105014 (2006); PRL 97, 241101 (2006).
• Balantekin & Pehlivan, J. Phys. G 34, 47 (2007).
Recall that nucleosynthesis in core-collapse supernovae
occurs in conditions which are the isospin-mirror of the
conditions for Big-bang nucleosynthesis!
Big-Bang: n/p << 1
Core-collapse SN: n/p >>1
In both cases species decouple when the expansion rate
exceeds their interaction rate
Two possible hierarchies of neutrino energies:
• a) A pronounced hierarchy: E(x) > E(e) > E(e)
• b) A less-pronounced hierarchy: E(x) ~ E(e) ~ E(e)
10 MeV
15 MeV
24 MeV
13 MeV
15 MeV
16 MeV
Average
energies
Maen-field approximation for the neutrino gas:
Evolution of
neutrino fluxes
(1/r2 -dependence
removed)
e
e
x
x
L51: luminosity in
units of 1051 ergs s-1
Equilibrium electron
fraction
13~ π/10
L51 = 0.001, 0.1, 50
13~ π/20
From Balantekin and
Yuksel, New J. Phys. 7,
51 (2005).
X= 0, 0.3, 0.5 (thin,
medium, thick lines)
13 ~ π/20
with 
effect
L51
= 0.001, 0.1, 50
L51 = 0.002, 0.2, 200
13~ π/10
13~ π/20
13~ π/20
with  effect
X= 0, 0.3, 0.5
(thin, medium,
thick lines)
Conclusions
•Neutrinos dominate a good part of the physics in a corecollapse supernova.
• Understanding the neutrino-nucleon and neutrino-nucleus
cross-sections well is of crucial importance.
• Neutrinos set the value of the neutron-to-proton ratio in a
core-collapse supernova. Hence matter-enhanced neutrino
flavor transformation can impact the physics of the explosion
and the r-process nucleosynthesis.
• Neutrino-neutrino interactions could be the crucial
component. At the moment calculation of the neutrino
propagation by taking the - interactions (the two-body
term) into account is an open, unsolved, problem.