Gravitational waves from the early...
Transcript of Gravitational waves from the early...
Gravitational waves from the early Universe
Sachiko Kuroyanagi (Nagoya University)
26 Aug 2017
Summer Institute 2017
Part 1
gravity = distortion of the spacetime
General relativity(1916)
What is a Gravitational Wave?
without object with object
space(3) + time(1) = 4
The spacetime distortion propagates as waves
What is a Gravitational Wave?
2 years later
= Gravitational wave
We have detected gravitational waves. We did it!
11 Feb 2016
Hanford Washington
Livingston, Louisiana
It was from a binary black hole
GWs from Black hole binary 1.3billion light years away
36 + 29 = 62 solar mass black hole
mirror1
mirror2 beam splitter
leser
same phase
photodetector
strong signal
Detection with a interferometer
4km
4km
different phase
mirror1
mirror2 beam splitter
leser
photodetector
weak signal
If a gravitational wave pass through …
Fabry-Perot interferometer
multiple reflections → effectively increase the length
mirror1
mirror2 beam splitter
leser
different phase
weak signal
photodetector
Note: what is strain?
strain
D0×h = (4km×200)×10-21 ~ 10-15m~ size of atomic nucleus
LIGO:
Fabry-Perot↓
h1 12
h
D0
Dmax/min = D0[1±12h]
GW150914
GW151226
GW170104
More detections
36Msun + 29Msun
All from black hole binaries
14Msun + 7.5Msun
31Msun + 19Msun
Observation run 2: 30 Nov 2016 - 25 Aug 2017
Observation run 1: 12 Sep 2015 - 19 Jan 2016
More GW sources are expected
New window of observation has just opened !
Astrophysical
・Neutron star binaries
・Supernovae
・Pulsars
Astrophysical Cosmological
・Neutron star binaries
・Supernovae
・Pulsars
・Inflation
・Reheating
・Phase transitions
・Cosmic strings
↑ My talk
New window of observation has just opened !
More GW sources are expected
light was emitted 13.4 billion years ago31.9 billion light-year away now
new galaxies
old galaxies
The most distant galaxy (March 2016): GN-z11
The further the galaxy, the older the signal
→0.4 billion years after the birth
lights from 13.8 billion years agoCosmic Microwave background (CMB) The oldest signal:
→0.38 million years after the birth
?
photons are scattered by electrons
high
low3K
3000KThe temperature of the Universe was high in the past
Can we see further? → No (currently)
electronphoton
Inflation nowCosmic Microwave Background
light
gravitational waves
380,000 years 13.8 billion years
cosmic phase transitions
reheating
observer
Only gravitational waves can directly bring us the information of the early Universe!
log(time)
Advantages of gravitational wave observation
→ Full of information on high energy physics!
LIGO-India (2024)
KAGRA (2018)Advanced-LIGO (2015)
Advanced-VIRGO (2017)
Ground-based interferometers
Test run with room temperature has done in March 2016Cryogenic test run is planned in March 2018full design sensitivity in 2022
3km
Started observation on 1st August 2017full design sensitivity in 2021
full design sensitivity in 2019
Interferometers in space
LISA
B-DECIGO
ESA + NASAlaunch in 2034pathfinder (test for technology) in 2015→ better sensitivity than expected
proposed in Japan2020’s
DECIGO
1millon km
2030’s 40’s?Triangle formation × 4
→ better angular resolution correlation analysis for GW background
How to detect a stochastic background
GWs from the early Universe
stra
in
time [s]
→ random phase no directional dependence→ very similar to noise
Cross Correlationdetector1 detector2
s: observed signalh: gravitational wavesn: noise
no correlations → 0
GW signal
s2(t) = h(t) + n2(t)s1(t) = h(t) + n1(t)
We need multiple detectors
Pulsar timing array
B-mode polarization in CMB
Pulsar (= rotating neutron star) → precise period GWs change the arrival time of the pulses
SKA (Square Kilometer Array) 2020-International project for radio telescope
Many ground-based and space project
LiteBIRD 2022- GWs induece polarizations in the Cosmic Microwave background
Indirect detection of GWs
= GravityMatterCurvature of the space-time
Equation for GWs in the expanding Universe
Gµ� = 8�GTµ�
Einstein equation
Flat Universe + tensor perturbations (=GWs)
Gµ� = 8�GTµ�
hij + 3Hhij �1a2�2hij = 16�G�ij
Tµ�transverse-traceless part of anisotropic stress :
Equation for GWs in the expanding UniverseEinstein equation
a(t) : scale factor
Geometry
H affects GW evolutionH � a
a
Friedmann equation:
→ sum of energy densities
radiation
matter
�r � a�4
�m � a�3
H � a
a: Hubble parameter
⇢ = ⇢r + ⇢m + · · ·
H2 =8⇡G
3⇢� K
a2
density
scale factor : a
∝a-4
∝a-3
radiation
matter
dark energy?
� � H2
constant∝
Hubble expansion rate
H � a
a: Hubble horizon
~ region of causality
Meaning of H
dH ⌘ cH�1
speed of expansion
x
v = Hx
v > cv < cwe have information of the object no information
To be precise… LH =
Z t
0
cdt
a(t)∝ dH
for radiation- and matter-dominated Universe
observer
radiation- dominated
matter- dominated dark energy?
380,000 years 13.8 billion yearslog(time)
(relativistic particles) (non-relativistic particles)
What happened in the early Universe?From Cosmological observations…
What happened in the early Universe?
observer
inflation reheating
accelerated expansion
380,000 years 13.8 billion yearslog(time)
mechanism to heat the Universe
dense and hotcold
What happened in the early Universe?
observer
inflation cosmic phase
transitions
reheating
380,000 years 13.8 billion yearslog(time)
The grand unification theory predicts separation of forces
What happened in the early Universe?
observer
inflation
cosmic phase transitions
380,000 years 13.8 billion yearslog(time)
cosmic strings
cosmic superstrings
GUT scale string: 1018kg/cm
~1000 × Mt.Fuji
reheating
GW generation
hij + 3Hhij �1a2�2hij = 16�G�ij
Equation for GWs
2. Sourced by matter component of the Universe
• Preheating
• Phase transition
• Cosmic strings
1. Non-negligible initial condition • Inflation→ quantum fluctuations
→ rapid particle productions
→ bubble collisions
→ heavy string objects generated in phase transition
GW generation
hij + 3Hhij �1a2�2hij = 16�G�ij
Equation for GWs
2. Sourced by matter component of the Universe
• Preheating
• Phase transition
• Cosmic strings
→ rapid particle productions
→ bubble collisions
→ heavy string objects generated in phase transition
Hubble horizon= region of causality
wavelength of GWs at generation< Hubble horizon size
f/a < H→
H / ⇢12rad / T 2
a / T
f / T→
Reheating T~107GeV ~1010GeV
Reheating change the expansion rate
GWs from inflation
Sensitivities of gravitational wave experiments
Reheating
T~104GeV ~107GeV
exotic model of the expansion can enhance the amplitude
GWs from inflation
Sensitivities of gravitational wave experiments
pastpresent
~1015GeVPreheating T~109GeV
frequency at the generation ~ (Hubble horizon)-1
GWs from rapid particle productions
f / T→
pastpresent
Electroweak phase transition
T~100GeV
GWs from bubble collisions
frequency at the generation ~ (Hubble horizon)-1 f / T→
pastpresent
cosmic string
Gμ~10-12
tensionGμ~10-10
heavy string objects originating from phase transition or superstring theory
frequency at the generation ~ (Hubble horizon)-1 f / T→