Neutrinos and the Universe

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Neutrinos, flavour and the origin of the Universe
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Standard Model of particle physics has many
remaining puzzles, in particular   1. The origin
of mass the origin of the weak scale, its
stability under radiative corrections, and the
solution to the hierarchy problem.   2. The
problem of flavour the problem of the
undetermined fermion masses and mixing angles
(including neutrino masses and mixing angles)
together with the CP violating phases, in
conjunction with the observed smallness of
flavour changing neutral currents and very small
strong CP violation.   3. The question of
unification the question of whether the three
known forces of the standard model may be related
into a grand unified theory, and whether such a
theory could also include a unification with
gravity.
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• The Standard Model of Cosmology also has its own
  remaining puzzles, in particular
•  
• The origin of dark matter and dark energy the
  embarrassing fact that 96 of the mass-energy of
  the Universe is in a form that is presently
  unknown, including 23 dark matter and 73 dark
  energy.
•  
• 2. The problem of matter-antimatter asymmetry
  the problem of why there is a tiny excess of
  matter over antimatter in the Universe, at a
  level of one part in a billion, without which
  there would be no stars, planets or life.
•  
• 3. The question of the size, age, flatness and
  smoothness of the Universe the question of why
  the Universe is much larger and older than the
  Planck size and time, and why it has a globally
  flat geometry with a very smooth cosmic microwave
  background radiation containing just enough
  fluctuations to seed the observed galaxy
  structures.

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The Flavour Problem

• Why are neutrino masses so small and mixings so
  large?
• What is the origin of quark and lepton
  masses/mixings?
• Do GUT/Family symmetries play a role?

t
Charge 2/3 quarks
u
Charge 1/3 quarks
d
c
Charged leptons
e
s
b
A neutrino hierarchy
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GUTs

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Family Symmetry

Nothing
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Why are neutrinos so light?
A natural mechanism
Light neutrinos
Heavy particles
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The see-saw mechanism
Type II see-saw mechanism (SUSY)
Type I see-saw mechanism
Lazarides, Magg, Mohapatra, Senjanovic, Shafi,
Wetterich (1981)
P. Minkowski (1977), Gell-Mann, Glashow,
Mohapatra, Ramond, Senjanovic, Slanski, Yanagida
(1979/1980),Valle
Type II
Type I
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Type I see-saw for hierarchical neutrinos
Need to understand
Technically need a small 23 sub-determinant

• Why is the sub-determinant small?
• Why is the solar angle large?

Right-handed neutrino dominance
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Single Right-Handed Neutrino Dominance
If one right-handed neutrino of mass Y dominates
then sub-determinant is naturally small
Natural explanation of and
large atmospheric angle if ef
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Sequential dominance
Same features as SRHND plus natural explanation
of large solar angle if ab-c
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Tri-bimaximal mixing from Constrained Sequential
dominance
Constrained sequential dominance (plus previous)
conditions
Harrison, Perkins and Scott Pauls talk
Tri-bimaximal neutrino mixing
but what about charged lepton contributions to
mixing?
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Effect of small charged lepton mixing angles
Antusch, SFK 05
Typically 35.26 or 45
If 13 angles are small have sum rule
q12q13cos(d -p)¼ qn12
q13 and d then come from the charged lepton sector
This means that d is irrelevant for leptogenesis
(the bad news)
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but d is predicted (the good news)
e.g. tri-bimaximal neutrino mixing plus
quark-lepton unification leads to
? gives prediction for q12 as function of d
Current 3s experimental range
Tri-bimaximal value predicts maximal CP
violation! (NOT zero CP violation!)
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Muon Flavour Violation
Borzumati, Masiero Hisano, Moroi, Tobe,
Yamaguchi SFK, Oliveira Casas, Ibarra
Lavignac, Masina, Savoy
If SUSY is present then neutrino masses
inevitably lead to lepton flavour violation due
to radiatively generated off-diagonal slepton
masses
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Unanswered cosmological questions

• Are neutrinos (partly) responsible for dark
  matter?
• Are right-handed neutrinos responsible for
  leptogenesis? (Silvia Pascoli)
• Are right-handed sneutrinos responsible for
  cosmological inflation?
• Are right-handed neutrinos responsible for dark
  energy?

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WMAP
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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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Member of Physics WG
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Kinney astro-ph/0406670
?
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Motivation for Inflation

• Horizon problem
• Flatness problem
• Relic removal
• Structure formation
• Present universe is inflating

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Sneutrino inflation

• slow roll of right-handed sneutrino in a false
  vacuum generates accelerated expansion in the
  very early universe

Right-handed sneutrino
Slow roll parameters
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Allowed regions of and
Sneutrino chaotic
(Yanagida et al 93)
astro-ph/0407372
(Antusch et al 04)
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Dark Energy and Right-handed neutrinos
Barbieri, Hall, Oliver,Strumia hep-ph/0505124 Antu
sch, Eyton-Williams, SFK (in progress)
The accelerated expansion of the Universe could
be due to a tiny but non-zero dark energy of
order the neutrino mass scale
A possible microscopic origin of dark energy is a
quintessence field associated with a
pseudo-Goldstone boson arising from the mass
generating mechanism of right-handed neutrinos
The model predicts Dirac neutrinos plus extra
light sterile neutrinos with interesting
phenomenological and cosmological consequences
(MiniBoone, BBN,)
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TOE (M-theory)
Summary
GUTFlavour theory
See-saw model
Leptogenesis
No direct link (need to go via see-saw model)
RGE
Neutrino masses and mixings
Muon flavour violation
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Discussion
1. The origin of flavour and the quest for
unification In terms of the unanswered questions
of the Standard Model, whereas the LHC teaches us
about mainly about the origin of mass, the
Neutrino Factory will teach us about the problem
of flavour and the question of unification. Neutri
no masses are very small, and this probably means
new physics beyond the Standard Model the
alternative is to have extremely small
unexplained Yukawa couplings. The smallness of
neutrino masses is commonly explained by the
see-saw mechanism, which implies heavy
right-handed neutrino Majorana masses. The
explanation of the large lepton mixing angles can
be readily accounted for in the see-saw
mechanism, by the sequential dominance of
right-handed neutrinos for example, leading to
relations between elements of the neutrino Yukawa
matrices. This adds information about the
neutrino Yukawa matrices to the information
already known in the quark and charged lepton
sectors. When this information is taken all
together it becomes possible to consider the
problem of flavour in the framework of the
question of unification. Theories of unification
relate quarks to leptons, and motivate the
measurement of lepton mixing angles to the same
precision as the quark mixing angles. (Antusch,
Pascoli, SFK)
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2. The origin of matter in the Universe In terms
of the unanswered questions of Cosmology, whereas
the LHC may teach us about the origin of dark
matter, a Neutrino Factory may help to provide
the solution to the problem of matter-antimatter
asymmetry. The basic scenario assumes the see-saw
mechanism and heavy right-handed Majorana
neutrinos, which are produced in the early
Universe and subsequently decay resulting in
lepton-antilepton asymmetry in the early
Universe, which subsequently becomes converted
into baryon-antibaryon asymmetry. The asymmetry
requires CP violating phases in the couplings of
right-handed neutrinos. The relation between
these phases and the oscillation phase is
model-dependent. In a particular (GUT ) theory of
flavour there may or may not be a relation (if
q13 is small there is no relation) (Pascoli,
Antusch) 3. The origin of the Universe The
question of the size, age, flatness and
smoothness of the Universe is commonly answered
by Inflation. The relation of Inflation to
neutrino physics (if any) is unclear, but it has
been suggested that the right-handed sneutrino
(the superpartner to the right-handed neutrino)
could be a suitable candidate for the inflaton
field. (Antusch, SFK) 4. The origin of dark
matter in the Universe There are strong
cosmological limits on the neutrino mass scale
from galaxy structure formation ways out?
(Hannestad) 5. The origin of dark energy in the
Universe There may even be a connection between
neutrinos and dark energy. The motivation is that
the energy scale of dark energy is about , which
is similar to the possible mass of some neutrino
state e.g. the solar neutrino mass in
hierarchical models. Models have been constructed
which have experimental implications.(Antusch,
SFK)
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These are not disconnected subjects the plan is
to write a coherent document which makes a strong
theory case for a neutrino factory The case must
be both scientifically sound, and be appealing to
a wide readership The main goal main is not to
write refereed scientific papers, but this
possibility should not be excluded if interesting
new results emerge, especially if this benefits
the non-tenured authors in any case such
studies frequently stimulate new
research Interactions between members of a
particular subgroup, and between different
sub-groups is essential since the science is
interconnected.