Cosmological/phenomenological implications of neutrino oscillations

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Cosmological/phenomenological implications of
neutrino oscillations

• Steve King

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Atmospheric Neutrino Oscillations
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Solar Neutrino Oscillations
LMA
LOW
Choubey talk
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I. Cosmological Implications
See e.g. Kainulainen and Olive, hep-ph/0206163

• Cosmological relic density and dark matter
• Galaxy structure limits on neutrino mass
• Neutrinos and nucleosynthesis
• Neutrinos and supernova
• Neutrinos and cosmic rays

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Cosmological relic density and dark matter
In the early universe neutrinos were in thermal
equilibrium with photons, electrons and
positrons. When the universe cooled to
temperatures of order 1 MeV the neutrinos
decoupled, leading to a present day number
density similar to photons. If neutrinos have
mass they will contribute to mass density of
universe, leading to the constraint
corresponding to
.

From the lab limit on the electron-like neutrino
mass . together with the
atmospheric and solar mass splittings we have a
stronger constraint
corresponding to the range
which
implies that neutrinos cannot be the dominant
component of dark matter.
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Galaxy structure limits neutrino mass
Tegmark (opposite), Wang, Zaldarriaga
CMB power spectrum
2dF Galaxy Redshift survey astro-ph/0204152
Galaxy power spectrum
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Neutrinos and nucleosynthesis
The number of light neutrino species (or any
light species) affects the freeze-out temperature
of weak processes which determine n/p, and
successful nucleosynthesis gives a constraint
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What about sterile neutrinos? The limit on
applies to them also, but they need to be
produced during the time when nucleosynthesis was
taking place, and the only way to produce them is
via neutrino oscillations. This leads to strong
limits on the sterile-active neutrino mixing
angles which disfavour LSND assuming the
primordial lepton asymmetry is not anomalously
large (Y.Y.Y.Wong et al)
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Neutrinos and Supernovae
99 of a supernova energy is emitted in neutrinos.
From SN1987A in Small Magellanic Cloud neutrinos
were observed. Studying the spread in arrival
times over 10 s leads to
LMA affects SN1987A (Valle talk)
However SN have their own problems such as how
they explode at all, and how the neutron star
remnant is kick-started.
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Neutrinos and Cosmic Rays
GZK cut-off may be exceeded if UHE neutrinos
scatter off relic background nus to produce Zs
within 50 Mpc need nu mass
But recent data from Flys Eye, HiRes and Yakutsk
strongly suggest (7 sigma) that GZK cut-off is
present after all (Bahcall and Waxman
hep-ph/0206217)
Z-burst model
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II. Phenomenological Implications

• Neutrino mass patterns
• Neutrino mass matrices
• Neutrinoless double beta decay
• SUSY and LFV
• Highlights of theory talks yesterday in WG1/4

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Possible three neutrino mass patterns
Normal
Inverted
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Successful leading order light Majorana
matricesBarbieri,Hall,Smith,Strumia,WeinerAltare
lli,FeruglioSFK hep-ph/0204360Ross talk
Type A (zero in 11)
Type B (non-zero 11)
Green natural
Hierarchy
Large neutrinoless double beta decay
Inverted hierarchy
Pseudo-Dirac
Degenerate
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Neutrinoless double beta decay
If the electron neutrino is Majorana, then
neutrinoless double beta decay
Klapdor-Kleingrothaus et al (2001) have claimed a
signal based on re-analysis of Heidelberg-Moscow
data
(Criticised by Aalseth et al, Feruglio et al.)
GENIUS would resolve this problem with
sensitivity down to 0.01 eV
Degenerate B
From Pascoli and Petcov (assume LMA)
Inverted hierarchy B
Hierarchy and Inverted A
c.f. KATRIN tritium decay sensitivity
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SUSY and LFV
If SUSY is present then neutrino masses
inevitably lead to lepton flavour violation due
to radiatively generated off-diagonal slepton
masses
e.g.
Blazek, SFK
This will lead to large 23 lepton flavour
violation and
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Blazek,SFK
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WG1/4 talks yesterday
Y. Shimizu MSSM with neutrino masses leads to
sizeable LFV. Plots below are for minimal
supergravity in realistic string models even
larger rates would be expected due to
non-universal A-terms (Ross)
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N. Shimoyama In a simplified model where the
right-handed neutrino masses are universal the
MSSM with neutrino masses leads to too-large
rates for with a
hierarchical neutrino mass spectrum

In such a scheme BR(deg)ltBR(inv)BR(hier)
M. Koike He studied
. He concluded that Z30-60 is best
for experimental searches, and it is possible to
distinguish models of new physics by measurement
of several kinds of nuclei.
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J. Sato He discussed the possibility that the
signal of wrong sign muons in a long baseline
experiment may either be due to neutrino
oscillations or to some new flavour changing
interaction involving neutrinos. Such
interactions may be generated in SUSY models,
with the mu-tau channel being the most effective
leading to an enhanced oscillation effect at
CNGS.
K. Babu
Proposed an explanation of LSND involving three
active neutrinos, but with lepton number
violating decay
. Predicts that MiniBoone sees no
oscillation signal since it uses neutrinos from
pion decay. Michel parameter rho0.7485 (not ¾).
Fermi constant from muon decay differs by 0.2.
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Final Remarks

• Neutrino mass and mixing angles as inferred from
  oscillations plays a crucial role in cosmology in
  particular dark matter, galaxy structure,
  nucleosynthesis, supernovae and cosmic rays.
• Superbeams in medium term, and neutrino factory
  in longer term are required to determine the 13
  mixing angle, the CP phase and the pattern of
  neutrino masses to really pin down our universe.
• We also need to know the absolute scale of
  neutrino mass from neutrinoless double beta decay
  or tritium beta decay present best limit is
  from galaxy structure. GRBs could also provide
  strong limits in future (Choubey,SFK).
• If SUSY is present neutrino masses (via the
  see-saw mechanism) lead to lepton flavour
  violation which according to talks at this
  workshop could be observed soon.
• In summary neutrino oscillations not only are the
  most important discovery in particle physics for
  20 years but also have profound cosmological and
  phenomenological implications.