Gravitational waves from the early Universe

Transcription

1 Gravitational waves from the early Universe Part 1 Sachiko Kuroyanagi (Nagoya University) 26 Aug 2017 Summer Institute 2017

2 What is a Gravitational Wave?

3 What is a Gravitational Wave?

4 11 Feb 2016 We have detected gravitational waves. We did it! Hanford Washington Livingston, Louisiana

5 Detection on 14 Sep 2015

6 It was from a binary black hole GWs from Black hole binary 1.3billion light years away = 62 solar mass black hole

7 Detection with a interferometer

8 If a gravitational wave pass through

9

10 Note: what is strain? h D h D max/min = D 0 [1 ± 1 2 h] LIGO: strain Fabry-Perot D0 h = (4km 200) ~ m ~ size of atomic nucleus

11 Observation run 2: 30 Nov Aug 2017 More detections GW Msun + 29Msun All from black hole binaries GW Msun + 7.5Msun Observation run 1: 12 Sep Jan 2016 GW Msun + 19Msun

12 Hints for black hole formation history Test of strong gravity ~400Mpc ~900Mpc Event rate

13 More GW sources are expected Astrophysical Neutron star binaries Supernovae Pulsars

14 More GW sources are expected Astrophysical Cosmological Inflation Neutron star binaries Reheating Supernovae Phase transitions Pulsars Cosmic strings My talk

15 Observing the early Universe

16 The most distant galaxy (March 2016): GN-z11 light was emitted 13.4 billion years ago 31.9 billion light-year away now 0.4 billion years after the birth old galaxies new galaxies The further the galaxy, the older the signal

17 The oldest signal: Cosmic Microwave background (CMB) lights from 13.8 billion years ago 0.38 million years after the birth

18 Can we see further? No (currently) The temperature of the Universe was high in the past high 3000K low 3K electron photon photons are scattered by electrons

19 Can we see further? Gravitational waves can! Gravitational waves do not interact with electrons

20 Advantages of gravitational wave observation Only gravitational waves can directly bring us the information of the early Universe! log(time) 380,000 years 13.8 billion years Cosmic Microwave Background now Inflation light gravitational waves observer reheating cosmic phase transitions Full of information on high energy physics!

21 Multi wavelength observation of GWs

22 Sensitivities of gravitational wave experiments GWs from inflation

23 Ground-based interferometers LIGO-India (2024) Advanced-LIGO (2015) KAGRA (2018) full design sensitivity in 2019 Advanced-VIRGO (2017) 3km Started observation on 1st August 2017 full design sensitivity in 2021 Test run with room temperature has done in March 2016 Cryogenic test run is planned in March 2018 full design sensitivity in 2022

24 Interferometers in space LISA ESA + NASA launch in 2034 pathfinder (test for technology) in 2015 better sensitivity than expected B-DECIGO proposed in Japan 2020 s DECIGO 2030 s 40 s? Triangle formation 4 better angular resolution correlation analysis for GW background

25 How to detect a stochastic background GWs from the early Universe random phase no directional dependence strain very similar to noise Cross Correlation time [s] detector1 s 1 (t) =h(t)+n 1 (t) detector2 s 2 (t) =h(t)+n 2 (t) s: observed signal h: gravitational waves n: noise no correlations 0 GW signal We need multiple detectors

26 Indirect detection of GWs Pulsar timing array SKA (Square Kilometer Array) International project for radio telescope Pulsar (= rotating neutron star) precise period GWs change the arrival time of the pulses B-mode polarization in CMB Many ground-based and space project LiteBIRD GWs induece polarizations in the Cosmic Microwave background

27 large detector size small GWs from inflation

28 Generation of GWs in the early Universe

29 Equation for GWs in the expanding Universe Einstein equation G µ =8 GT µ Curvature of the space-time = Gravity Matter

30 Equation for GWs in the expanding Universe Einstein equation G µ =8 GT µ Geometry Flat Universe tensor perturbations (=GWs) a(t) : scale factor 1 ḧ ij +3Hḣij a 2 2 h ij = 16 G ij H ȧ a H affects GW evolution anisotropic stress : transverse-traceless part of T µ

31 Hubble expansion rate Friedmann equation: H 2 = 8 G 3 K a 2 H ȧ a : Hubble parameter = r + m + density H 2 radiation a -4 matter a -3 sum of energy densities radiation matter r a 4 m a 3 dark energy? constant scale factor : a

32 Meaning of H H ȧ a speed of expansion d H ch 1 : Hubble horizon region of causality x v = Hx v<c we have information of the object v>c no information To be precise L H = Z t 0 cdt a(t) d H for radiation- and matter-dominated Universe

33 What happened in the early Universe? From Cosmological observations radiation- matterdark energy? dominated dominated (relativistic particles) (non-relativistic particles) observer log(time) 380,000 years 13.8 billion years

34 What happened in the early Universe? accelerated expansion inflation reheating mechanism to heat the Universe cold dense and hot observer log(time) 380,000 years 13.8 billion years

35 What happened in the early Universe? The grand unification theory predicts separation of forces inflation reheating cosmic phase transitions observer log(time) 380,000 years 13.8 billion years

36 What happened in the early Universe? cosmic superstrings GUT scale string: kg/cm ~1000 Mt.Fuji inflation reheating cosmic phase transitions cosmic strings observer log(time) 380,000 years 13.8 billion years

37 Equation for GWs GW generation 1 ḧ ij +3Hḣij a 2 2 h ij = 16 G ij 1. Non-negligible initial condition Inflation quantum fluctuations 2. Sourced by matter component of the Universe Preheating rapid particle productions Phase transition bubble collisions Cosmic strings heavy string objects generated in phase transition

38 Equation for GWs GW generation 1 ḧ ij +3Hḣij a 2 2 h ij = 16 G ij wavelength of GWs at generation < Hubble horizon size f/a < H Hubble horizon = region of causality 1 H / 2 / T 2 rad a / T f / T 2. Sourced by matter component of the Universe Preheating rapid particle productions Phase transition bubble collisions Cosmic strings heavy string objects generated in phase transition

39 Sensitivities of gravitational wave experiments GWs from inflation

40 Sensitivities of gravitational wave experiments GWs from inflation Reheating T~10 7 GeV ~10 10 GeV Reheating change the expansion rate

41 Sensitivities of gravitational wave experiments T~10 4 GeV ~10 7 GeV GWs from inflation Reheating exotic model of the expansion can enhance the amplitude

42 frequency at the generation ~ (Hubble horizon) -1 present f / T past GWs from rapid particle productions Preheating T~10 9 GeV ~10 15 GeV

43 frequency at the generation ~ (Hubble horizon) -1 present f / T past Electroweak phase transition T~100GeV GWs from bubble collisions

44 frequency at the generation ~ (Hubble horizon) -1 present f / T past tension Gμ~10-10 Gμ~10-12 cosmic string heavy string objects originating from phase transition or superstring theory

45 Summary GWs can become a powerful probe of the very early Universe! log(time) Inflation 380,000 years Current observation 13.8 billion years now Observations observer reheating cosmic phase transitions more details on inflation and cosmic strings in part 2