Transcript Neutrino mass and dark matter

Erice2013
21 Sept., 2013
Neutrino mass and
DM direct detection
Daijiro Suematsu (Kanazawa Univ.)
Based on the collaboration with S.Kashiwase
PRD86 (2012) 053001, EPJC73 (2013) 2484
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Outline
• Motivation and ｂasic idea
• Model and its features
Neutrino mass and mixing
Dark matter
Leptogenesis
• Dark matter direct search
• Summary
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Motivation

The SM is a successful model to explain various
experimental results. However, several recent
experimental results require to extend the SM.
existence of neutrino masses
existence of dark matter
baryon number asymmetry in the Universe
 We consider the extension of the SM on the basis
of these experimental results.
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Basic idea
Neutrino oscillation data suggest neutrino masses are
(
@Planck)
very small :
• Dirac mass terms exist at tree level
⇒ right-handed neutrinos should be heavy enough.
ordinary seesaw mechanism
• Dirac mass terms are forbidden at tree level by some symmetry
⇒ small neutrino masses may be induced radiatively even for
rather light right-handed neutrinos.
radiative seesaw mechanism
The same symmetry may guarantee the stability of some
neutral particle (a dark matter candidate).
origin of neutrino mass
origin of dark matter 4
A radiative neutrino mass model
Ma
is imposed to forbid Dirac neutrino masses at tree level.
 Field contents
 Z２ invariant interaction and potential
• Lightest one with odd
parity is stable ⇒ DM
• No Dirac mass term
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Neutrino mass
Correction to the ordinary
Seesaw formula
even if masses of
are
small neutrino masses are realized
New physics is expected in lepton sector at TeV regions.
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Dark matter
Two dark matter candidates :
Neutrino mass
constraint
(real part of
neutral components)
Neutrino Yukawa couplings
New particle masses
Dark matter abundance
Lepton flavor violating processes
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Two scenarios for dark matter
• If
is DM, the neutrino Yukawa coupling should be
to explain its relic abundance.
⇒ LFV imposes severe constraints.
Ma, Kubo, D.S.
D.S., Toma, Yoshida
• If
is DM, the neutrino Yukawa coupling could be
irrelevant to the relic abundance of DM.
Barbieri, et al.
Hambye, et al.
…….
the neutrino Yukawa couplings could be small consistently
with DM relic abundance.
⇒ LFV constraint might be easily evaded.
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Dark matter abundance
DM abundance follows the usual thermal relic scenario.
It is determined by the number density at the freeze-out
temperature TF.
In the
DM scenario, there is
coannihilation among
Freeze-out
Dominant parts of annihilation cross
section could be determined by the scalar
quartic couplings
.
Hambye, et al.,
Longitudinal components of gauge bosons give large contribution.
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
Relic abundance
Relic abundance
Relic abundance of
or
required relic abundance is realized
 Neutrino Yukawa couplings are irrelevant to
the relic abundance.
⇒ Neutrino Yukawa couplings could be small.
LFV constraints are easily satisfied.
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Constraints on
Neutrino mass satisfies
Constraint on
is crucial.
DM direct search gives such a constraint.
Inelastic scattering can contribute
to the direct search experiments.
Since the direct search finds no confirmed evidence,
Cui, et al.
the mass difference should be δ＞150 keV .
Arina, et al.
Neutrino mass has to be considered under this constraints.
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Determination of model parameters
To explain the neutrino oscillation data, we just assume
flavor structure of the neutrino Yukawa couplings :
can be diagonalized by tri-bimaximal mixing matrix
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Normal hierarchy
For out-of equilibrium
decay of
in leptogenesis
One mass eigenvalue is extremely small
solutions
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An example of favored parameters
Diagonalization of
Fixed parameters
q3
Contours of neutrino oscillation
parameters in (q2,q3) plane
Region consistent with
all neutrino oscillation data
q2
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Inverted hierarchy
For out-of equilibrium
decay of
One mass eigenvalue is extremely small
solutions
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An example of favored parameters
Fixed parameters
q2
Contours of neutrino oscillation
parameters in (q1,q2) plane
Region consistent with
all neutrino oscillation data
q1
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Leptogenesis
Lepton number asymmetry is expected to be generated
through the out-of equilibrium decay of
at TeV-scale.
CP asymmetry
Generated lepton asymmetry
⇒ smaller than the required value
Washout effects are large
Lepton asymmetry
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Resonant leptogenesis
To suppress the washout effects, we can make neutrino
Yukawa couplings smaller.
However, there appear other effects.
 neutrino masses become smaller.
This can be recovered by taking a larger
 CP asymmetry becomes smaller.
This can be recovered by assuming the nearly
⇒ TeV scale resonant leptogenesis
degenerate
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Required degeneracy
Generated Baryon number asymmetry
Inverted hierarchy
Baryon number asymmetry
Normal hierarchy
The required baryon asymmetry can be generated
for
This degeneracy is rather mild compared with the
ordinary case
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Dark matter direct search
Two possible scattering processes
Inelastic scattering
Inelastic scattering occurs only if
the DM velocity satisfies
Escape velocity from our galaxy
required for the present Xenon100
bound has already exceeded
It might be difficult to detect this DM
through this process by Xenon1T.
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 Elastic scattering due to Higgs exchange
DM-nucleon scattering cross section
Promising parameter region in
for Xenon1T
Xenon1T
cannot reach
Xenon1T
cannot reach
Xenon1T
cannot reach
Excluded by
Xenon100
Xenon1T could find this DM for the parameters which are consistent
with other phenomenological constraints.
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Summary
Neutrino masses and dark matter could be closely related
each other. The radiative neutrino mass model by Ma
gives a simple example for such an idea. There are
noticeable phenomenological features.
 The model could explain neutrino oscillation data, dark matter
abundance, baryon number asymmetry, simultaneously.
 The observed baryon asymmetry can be explained through
resonant leptogenesis. However, the required mass degeneracy
can be rather mild compared with the ordinary TeV scale
resonant leptogenesis.
 Inert doublet DM could be found through the direct search
experiment at Xenon1T for the parameters which could explain
other experimental results consistently.
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