Neutrino Mysteries Unveiled: Current Cosmological Constraints
Jan Hamann
Rencontres de 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 mass-squared differences…
… but what is their absolute mass scale?
oscillations
β-decay
experiments
solar neutrinos
atmospheric neutrinos
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
3
Are there additional
(light)
sterile
neutrinos?
Anomalies
observed by
•
Accelerator experiments
•
Reactor experiments
•
Gallium experiments
Hints for additional state
with
Δm
2
≈ eV
2
?
What do we
not
know about neutrinos?
[Aguilar-Arevalo+ 2013
]
[Mention+ 2010] [An+ 2016
]
[Giunti&Laveder 2011
]
[Giunti+ 2014
]
neutrinos
decouple
e
+
e
-
-
annihilation
The Cosmic Neutrino Background (CνB)
•
Neutrino decoupling around
T
= 1 MeV, shortly before
goes out of equilibrium
•
Annihilation heats CMB relative to CνB
•
Neutrino mixing equilibrates momentum distributions
•
If
T
reheating
> 10 MeV, all three flavours populated
Impact of cosmological neutrinos
Structure formation
Neutrinos
Big Bang Nucleosynthesis
Neutrino parameters
How 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)
Neutrino parameters
How 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)
Impact of cosmological neutrinos
Structure formation
Evolution of
perturbations
Background
e
volution
Neutrinos
Big Bang Nucleosynthesis
Background
e
volution
Nuclear
reactions
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
neutrino
Structure formation with
massive neutrinos
Σ
m
ν
= 0 eV
Σ
m
ν
= 7 eV
[simulation and movie by T. Haugbølle]
Matter power spectrum with
massive neutrinos
[Figure from
Abazajian+
2013
]
wavenumber
Neutrino masses and the
CMB angular power spectrum
•
Changing neutrino mass affects
z
eq
and
d
A
(
z
rec
)
•
Can shift CMB peaks back in place by tweaking ω
c
and
H
0
(
geometric degeneracy of the CMB
)
•
Remaining effects (early ISW, late ISW, lensing) rather subtle for
sub-eV masses
•
For better sensitivity, combine with external data (or CMB lensing)
[
Planck
collaboration 2015
]
Planck
constraints on the sum of
neutrino masses
[
Planck
collaboration 2015
]
No sign of non-zero neutrino masses…
Effective number of neutrinos and the
CMB angular power spectrum
•
Also subject to geometric degeneracy
•
In 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
]
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
)
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 measurements
Planck
constraints on
eV-mass sterile neutrinos
[
Planck
collaboration 2015
]
Planck
data not compatible with a
fully thermalised eV-mass neutrino
Want to save the scenario?
Need to suppress production of
steriles (e.g., lepton asymmetry,
new interactions, etc.
)
Matter power spectrum with
massive neutrinos
wavenumber
[Figure from
Abazajian+
2013
]
Matter power spectrum with
massive neutrinos
wavenumber
Linear regime
Non-linear regime
[Figure from
Abazajian+
2013
]
Nonlinear structure formation
with 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…
Probes of the matter power spectrum
Cluster counts
Galaxy clustering
Cosmic shear
CMB lensing
Lyman-α forest
21 cm
Future sensitivity:
CMB Stage-IV + CMB lensing (+BAO)
[
Abazajian+
2013
]
Future Large Scale Structure surveys
Cluster counts
Galaxy clustering
Type Ia supernovae
BAO scale
Cosmic shear
Geometric observables
Perturbation-based observables
•
Sensitivity up to
10 meV
for sum of neutrino masses, and up to
0.02
for effective number of neutrino species when observables are
combined
•
Can cleanly distinguish between effects of dark energy and
neutrinos
[
Basse
+
2013
]
Future sensitivity:
Planck
+ EUCLID shear PS/galaxy PS/clusters
[
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 observables
Direct sensitivity to mass hierarchy?
Assume minimal
mass in inverted
hierarchy
Probably not…
[
Hamann+
2012
]
Conclusions
•
The Universe continues to be boring: no evidence for
anything unexpected in the cosmological neutrino
sector
•
With 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
Delve into the enigmatic world of neutrinos with a focus on their elusive properties like mass hierarchy, additional light neutrinos, and impact on cosmic background. Explore the unresolved questions surrounding neutrino physics from cosmological perspectives.
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Presentation Transcript
Current and future constraints on neutrino physics from cosmology Jan Hamann Rencontres de Moriond (Cosmology) 21stMarch 2016
What do we not know about neutrinos? We only know their mass-squared differences solar neutrinos atmospheric neutrinos but what is their absolute mass scale? -decay experiments oscillations
What do we not know about neutrinos? What is their mass hierarchy? normal m3 mass m2 m1 inverted m1 m2 mass m3
What do we not know about neutrinos? Are there additional(light) sterileneutrinos? Anomalies observed by Accelerator experiments Reactor experiments Gallium experiments Hints for additional state with m2 eV2? [Aguilar-Arevalo+ 2013] [Mention+ 2010] [An+ 2016] [Giunti&Laveder 2011] [Giunti+ 2014]
neutrinos decouple e+e-- annihilation
The Cosmic Neutrino Background (CB) Neutrino decoupling around T = 1 MeV, shortly before goes out of equilibrium Annihilation heats CMB relative to C B Neutrino mixing equilibrates momentum distributions If Treheating > 10 MeV, all three flavours populated
Impact of cosmological neutrinos Structure formation Neutrinos Big Bang Nucleosynthesis
Neutrino parameters How much energy density do neutrinos contribute at early times? Fermi-Dirac vs. Bose-Einstein lower neutrino temperature photon energy density radiation energy density Effective number of neutrino species CDM: Neff = 3.046 (small deviation from Fermi-Dirac)
Neutrino parameters How much energy density do neutrinos contribute at late times? at early times? Fermi-Dirac vs. Bose-Einstein lower neutrino temperature photon energy density neutrino energy density Sum of radiation energy density Effective number of neutrino species neutrino masses CDM: Neff = 3.046 (small deviation from Fermi-Dirac) CDM: m = 0.06 eV (assumes lightest mass state is massless)
Impact of cosmological neutrinos Structure formation Background evolution Evolution of perturbations Neutrinos Background evolution Nuclear reactions Big Bang Nucleosynthesis
Free streaming Velocity dispersion large wrt size of potential well gravitational potential initial time x Cold dark matter Neutrinos escape from potential well, density perturbations get washed out neutrino gravitational potential later time x
Structure formation with massive neutrinos m = 0 eV m = 7 eV [simulation and movie by T. Haugb lle]
Matter power spectrum with massive neutrinos wavenumber [Figure from Abazajian+ 2013]
Neutrino masses and the CMB angular power spectrum [Planck collaboration 2015] Changing neutrino mass affects zeq and dA(zrec) Can shift CMB peaks back in place by tweaking c and H0 (geometric degeneracy of the CMB) Remaining effects (early ISW, late ISW, lensing) rather subtle for sub-eV masses For better sensitivity, combine with external data (or CMB lensing)
Planck constraints on the sum of neutrino masses No sign of non-zero neutrino masses [Planck collaboration 2015]
Effective number of neutrinos and the CMB angular power spectrum [Planck collaboration 2015] Also subject to geometric degeneracy In addition, changes damping scale, anisotropic stress (partially degenerate with spectral index/amplitude of primordial spectrum) Planck measurement of damping tail greatly improved sensitivity
Planck constraints on the effective number of relativistic species Data confirm standard model expectation (C B only, no more hints of additional light particles) [Planck collaboration 2015]
Planck results vs. BBN Deuterium abundance from damped Ly- system 4He abundance from H II-regions Excellent match with BBN expectation + astrophysical element abundance measurements [Planck collaboration 2015]
Planck constraints on eV-mass sterile neutrinos Planck data not compatible with a fully thermalised eV-mass neutrino Want to save the scenario? Need to suppress production of steriles (e.g., lepton asymmetry, new interactions, etc.) [Planck collaboration 2015]
Matter power spectrum with massive neutrinos wavenumber [Figure from Abazajian+ 2013]
Matter power spectrum with massive neutrinos Non-linear regime Linear regime wavenumber [Figure from Abazajian+ 2013]
Nonlinear structure formation with massive neutrinos 0.15 eV 0.3 eV linear theory 0.45 eV 0.6 eV Theoretical prediction of matter power spectrum with massive neutrinos in the non-linear regime is a big challenge Simulations with CDM and neutrino particles Analytical methods [see previous talks] N-body simulations with neutrino particles, grid-based, hybrid approach [Brandbyge+ 2008,2009,2010; Viel+ 2010, Ali-Haimoud+ 2012]
Probes of the matter power spectrum CMB lensing 21 cm Lyman- forest Galaxy clustering Cluster counts Cosmic shear
Future sensitivity: CMB Stage-IV + CMB lensing (+BAO) [Abazajian+ 2013]
Future Large Scale Structure surveys BAO scale Cosmic shear Cluster counts Galaxy clustering Type Ia supernovae Geometric observables Perturbation-based observables
Future sensitivity: Planck + EUCLID shear PS/galaxy PS/clusters Sensitivity up to 10 meV for sum of neutrino masses, and up to 0.02 for effective number of neutrino species when observables are combined Can cleanly distinguish between effects of dark energy and neutrinos [Basse+ 2013]
Future sensitivity: Combining LSS observables Shear Galaxies (pessimistic) Galaxies (optimistic) CMB Beautiful complementarity between different observables: combination breaks parameter degeneracies of individual probes [Hamann+ 2012]
Direct sensitivity to mass hierarchy? Assume minimal mass in inverted hierarchy Probably not [Hamann+ 2012]
Conclusions The Universe continues to be boring: no evidence for anything unexpected in the cosmological neutrino sector With 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
