Primordial Neutrinos and
Cosmological Perturbation
in the Interacting Dark-Energy Model:
CMB and LSS
From CMB + SN1a +
structure formation
Yong-Yeon Keum
National Taiwan University
SDSS-KSG Winter Workshop
February 20-22, 2007
•Accelerated expansion of the
universe (High redshift SN)
•Structure formation scenario
compatible with observations
Matter budget of the cosmos
•Rotation of galaxies
•Speeding galaxies in
clusters
•Gravitational lensing
•Hot gas in clusters
•Light elements from early hot
universe
• Low CMB temperature
fluctuations
Fig:NASA/WMAP science team
•Starlight from Galaxies
•Stuff we are made of!!
What we know so far
From SNIa and CMB radiation observations,
 Our universe is almost flat, now accelerating.
 The dominance of a dark energy component with
negative pressure in the present era
is responsible for the universe’s accelerated
expansion.
Good old Cosmology, … New trend !
Total energy
density
Baryonic matter
density
Dark energy
density
Dawn of
Precision cosmology !!
NASA/WMAP science team
Candidates of Dark Energy
(A)
(B)
Cosmological Constant
Dynamical Cosmological constant
(Time-dependent; Quintessence )
- quintessence: potential term + canonical kinetic term
- K-essence: non-canonical kinetic term
- phantom
(C)
- quintom -Tachyon field
Modified Gravity
(Modified friedman eq.)
Classification of Dark-Energy Models
• We redefine two
parameter space of
observables:
-1.38<w<-0.82
(2s)
  P/r
  d  / d l n a  d  / Hdt
Primordial Neutrinos

The connection between cosmological observations
and neutrino physics is one of the interesting and
hot topic in astro-particle physics.

Neutrino decouple from thermal contact in the
early universe at the temperature of order 1 MeV
which coincides with the temperature where light
element synthesis occurs.

Precision observations of the cosmic microwave
background and large scale structure of galaxies
can be used to prove neutrino mass with greater
precision than current laboratory experiments.
Interacting Dark-Energy models
o
interacting between cold dark-matter and dark-energy:
(Farrar and Peebles, 2004)
o
o
interacting between photon and dark-energy:
(Feng et al., 2006; Liu et al., 2006)
interacting between neutrinos and dark-energy:
(Fardon et al. 2004, Zhang et al. 2005, yyk and Ichiki, 2006)
Neutrino Model of Dark Energy

Cosmological constant:


4
r
G

4

G
p
r

p
)
ND
E
N
D
E
p


()

1
D
E
D
E
r
3
3
2 2
3 4
S
i
n
c
e
H

(
1
.
5

0
.
1
)
x
1
0
e
V
,
r
M
H




1

e
V
)
0
D
E
Po
3
E



1

e
V
0


What physics is associated with this small energy scale ??
It is clearly a challenge to understand dynamically how the
small energy scale associated with dark-energy(DE) density
aries and how it is connected to particle physics.
Questions :

Why does the mass scale of neutrinos so small ?
cm
L
l
H
H
l

M
e
V

M
1
2
34



/1
0
1
0

about 10-3 eV ~ Eo: accidental or not ?

m
1
0
e
V

m
M

/
3
3

10
2
If not, are there any relation between Neutrinos
and Dark Energy ?
Interacting dark energy model
At low energy,
Example
nv mv)
Scalar potential
in vacuum
The condition of minimization of Vtot determines
the physical neutrino mass.
Mass Varying Neutrino Model
Fardon,Kaplan,Nelson,Weiner: PRL93, 2004

Fardon, Nelson and Weiner suggested that
r DE tracks the energy density in neutrinos r
m
 m
 (n
)

The energy density in the dark sector has twocomponents:

The neutrinos and the dark-energy are coupled because
it is assumed that dark energy density is a function of
the mass of the neutrinos:
rdark r
rDE

rDE rDE(n)

Since in the present epoch, neutrinos are non-relativistic (NR),
r

m
n
r
m
n

r
()
m






d
a
r
k

D
E
Assuming dark-energy density is stationary w.r.t. variations in the
neutrino mass,
r
r
d
D
(
m
a
r
k
E
)

n

0


m

m



Defining
r
3
H
(
r

p
)
pdark

,
rdark
rdark pdark r p rDEpDE r
mn
m
n


1   
rdark m
n
 r
D
E
Lessons-I:



Wanted neutrinos to probe DE, but actually are DE.
  -1  flat scalar potential (log good) choice,
mv < few eV.
Neutrino mass scales as mv ~ 1/nv:
- lighter in a early universe, heavier now
- lighter in clustered region, heavier in FRW region
- lighter in supernovae
 An example of the inhomogenous matter distributions:
Lessons-II
 Couplings of ordinary matter to such scalars
strongly constrained – must be weaker than
Planck: 1/Mpl
f i j H i j

[f 
+ f

]  : f or or di nar y mat t er
Mp

f ij
2
l i H  Hl j  [f
+ f
]  : f or neut r i no
M
M
Mp
R.D. Peccei; PRD71 (2005)
With exponential type potential
b
The FNW scenario is only consistent,
if there is no kinetic contributions (K=0) and
the dark-energy is a pure running cosmological constant !!
Cosmological Perturbation
in the Interacting Dark-Energy Model
CMB and Large Scale Structures
K. Ichiki and YYK
Background Equations:
Perturbation Equations:
We consider the linear perturbation in the synchronous
Gauge and the linear elements:
Varying Neutrino Mass
With full consideration of Kinetic term
V(  )=Vo exp[- l ]
M.9 eV
M.3 eV
W_eff
M.9 eV
M.3 eV
M.9 eV
M.3eV
Power-spectrum (LSS)
M.9 eV
M.3 eV
Inverse Power law potential
e
Neutrino mass vs z
W_eff(z)
CMB spectrum
Power spectrum with
Constraints from Observations
WMAP3 data on Ho vs W
Conclusions



Neutrinos are the best probe of SM into DE sector
Possible origin for accelerating universe
Motivates consideration of new matter effects to
be seen in oscillations:
- LSND interpretation (if MinibooNe has a signal)
- Matter/air analyses
- Solar MaVaN oscillation Effects
- Time delay in the gamma ray bursts.
Thanks
For
your attention!