Moriond Cosmology 21 st March 2016 Current and future constraints on n eutrino physics from c osmology What do we not know about neutrinos We only know their masssquared differences ID: 631623
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Slide1
Jan HamannRencontres de Moriond (Cosmology)21st March 2016
Current and future constraints
on
n
eutrino
physics
from
c
osmologySlide2
What do we not know about neutrinos?We only know their mass-squared differences…
… but what is their absolute mass scale?
oscillations
β
-decay
experiments
solar neutrinos
atmospheric neutrinosSlide3
What do we not know about neutrinos?
What is their mass hierarchy?
mass
normal
m
3
m
2
m
1
mass
inverted
m
1
m
2
m
3Slide4
Are there additional (light) sterile neutrinos?Anomalies observed byAccelerator experiments
Reactor experimentsGallium experiments
Hints
for additional
state with
Δm2 ≈ eV2?What do we not know about neutrinos?
[Aguilar-
Arevalo+ 2013]
[Mention+ 2010] [An+ 2016]
[
Giunti&Laveder 2011
]
[
Giunti
+ 2014
]Slide5
neutrinos decouple
e
+
e
-
-annihilationSlide6
The Cosmic Neutrino Background (CνB)Neutrino decoupling around T = 1 MeV, shortly before goes out of equilibriumAnnihilation heats CMB relative to CνB
Neutrino mixing equilibrates momentum distributions If T
reheating > 10 MeV, all three
flavours
populatedSlide7
Impact of cosmological neutrinosStructure formation
Neutrinos
Gravity
Big Bang
Nucleosynthesis
Gravity
Weak
interactionSlide8
Neutrino parametersHow much energy density do neutrinos contribute…
… a
t
early times?
Fermi-Dirac vs.
Bose-Einstein
photon
e
nergy density
lower
n
eutrino
temperature
radiation
e
ner
gy
density
Effective number of
neutrino species
ΛCDM:
N
eff
= 3.046
(small deviation from
Fermi-Dirac)Slide9
Neutrino parametersHow much energy density do neutrinos contribute…
… a
t
early times?
… a
t
late
times?
Fermi-Dirac vs.
Bose-Einstein
photon
e
nergy
density
lower
n
eutrino
temperature
radiation
e
ner
gy
density
Effective number of
neutrino species
neutrino
e
nergy
density
Sum of
neutrino masses
ΛCDM:
N
eff
= 3.046
ΛCDM:
Σ
m
ν
= 0.06
eV
(assumes lightest mass
state is
massless
)
(small deviation from
Fermi-Dirac)Slide10
Impact of cosmological neutrinosStructure formation
Evolution of
perturbations
Background
e
volution
Neutrinos
Gravity
Big Bang
Nucleosynthesis
Gravity
Weak
interaction
Background
e
volution
Nuclear
reactionsSlide11
Free streaming
g
ravitational
potential
x
initial time
g
ravitational
potential
x
later time
Velocity dispersion
large
wrt
size of potential well
Neutrinos escape from potential well,
d
ensity
perturbations get washed out
Cold dark matter
neutrinoSlide12
Structure formation with massive neutrinos
Σ
m
ν
= 0
eV
Σ
m
ν = 7 eV
[simulation and movie by T.
Haugbølle]Slide13
Matter power spectrum withmassive neutrinos
[Figure from
Abazajian
+
2013
]
Suppression of the matter power spectrum
wrt
massless neutrino casewavenumberSlide14
Neutrino masses and theCMB angular power spectrumChanging neutrino mass affects zeq and dA
(zrec)
Can shift CMB peaks back in place by tweaking ωc and
H
0
(geometric degeneracy of the CMB)Remaining effects (early ISW, late ISW, lensing) rather subtle for sub-eV massesFor better sensitivity, combine with external data (or CMB lensing)
[
Planck
collaboration 2015]Slide15
Planck constraints on the sum of neutrino masses
[
Planck
collaboration 2015
]
No sign of non-zero neutrino masses…Slide16
Effective number of neutrinos and theCMB angular power spectrumAlso subject to geometric degeneracyIn addition, changes damping scale, anisotropic stress (partially degenerate with spectral index/amplitude of primordial spectrum)Planck measurement of damping tail greatly improved sensitivity
[
Planck
collaboration 2015
]Slide17
Planck constraints on the effective number of relativistic species
[
Planck
collaboration 2015
]
Data confirm standard model expectation
(CνB only, no
more hints o
f additional light particles)Slide18
Planck results vs. BBN
Deuterium
abundance from
d
amped Ly-
α system
4
He abundance from H II-regions
[
Planck collaboration 2015
]
Excellent
match with BBN expectation + astrophysical element abundance measurementsSlide19
Planck constraints oneV-mass sterile neutrinos
[
Planck
collaboration 2015
]
Planck
data not compatible with a fully
thermalised
eV-mass neutrinoWant to save the scenario?
Need to suppress production of
steriles (e.g., lepton asymmetry, new interactions, etc.)Slide20
Matter power spectrum withmassive neutrinos
Suppression of the matter power spectrum
wrt
massless
neutrino case
wavenumber
[Figure from
Abazajian
+ 2013
]Slide21
Matter power spectrum withmassive neutrinos
Suppression of the matter power spectrum
wrt
massless
neutrino case
wavenumber
Linear regime
Non-linear regime
[Figure from
Abazajian
+
2013
]Slide22
Nonlinear structure formationwith massive neutrinos
linear
theory
[
Brandbyge
+
2008,2009,2010;
Viel
+ 2010, Ali-
Haimoud
+ 2012]
Simulations with
CDM and neutrino
particles
0.15
eV
0.3
eV
0.45
eV
0.6
eV
Theoretical
prediction of matter power spectrum with massive neutrinos in the non-linear
regime is a
big
challenge
Analytical methods
[see previous talks]
N
-body simulations with neutrino particles, grid-based, hybrid approach…Slide23
Probes of the matter power spectrum
Cluster counts
Galaxy clustering
Cosmic shear
CMB
lensing
Lyman-
α
forest
21 cmSlide24
Future sensitivity: CMB Stage-IV + CMB lensing (+BAO)
[
Abazajian
+
2013
]Slide25
Future Large Scale Structure surveys
Cluster counts
Galaxy clustering
Type
Ia
supernovae
BAO scale
Cosmic shear
Geometric observables
Perturbation-based observablesSlide26
Sensitivity up to 10 meV for sum of neutrino masses, and up to 0.02 for effective number of neutrino species when observables are combinedCan cleanly distinguish between effects of dark energy and neutrinos
[
Basse
+
2013
]
Future sensitivity:
Planck + EUCLID shear PS/galaxy PS/clustersSlide27
[
Hamann+
2012
]
CMB
Shear
Galaxies
(pessimistic)
Galaxies
(
opt
imistic)
Beautiful
complementarity
between different observables:
c
ombination breaks
parameter
degeneracies
of individual probes
Future sensitivity:
Combining LSS observablesSlide28
Direct sensitivity to mass hierarchy?
Assume minimal mass in inverted hierarchy
Probably not…
[
Hamann
+
2012
]Slide29
ConclusionsThe Universe continues to be boring: no evidence for anything unexpected in the cosmological neutrino sectorWith the next generation of large-volume galaxy surveys and CMB lensing measurements, a detection of the sum of neutrino masses is extremely likely, provided non-linear growth can be understood sufficiently well