COSMOLOGY AND GRAVITATIONAL WAVES. Chiara Caprini (APC)

COSMOLOGY AND GRAVITATIONAL WAVES Chiara Caprini (APC)

the direct detection of GW by the LIGO interferometers has opened a new era in Astronomy - we now have a new messenger bringing complementary informations with respect to those accessible up to now with electromagnetic radiation (example: we can now probe the intrinsic nature of black holes) - we discover the existence of new astrophysical objects (example: black holes of a few tents of M ) - GW interact very weekly: they bring direct information from early epochs, high redshift (example: LISA can detect black hole binaries up to redshift 10-15) THIS AMAZING DISCOVERY POTENTIAL CAN BE DIRECTLY APPLIED TO THE EARLY UNIVERSE AND COSMOLOGY

following the Big Bang theory, the univers is expanding

A journey in the past age = temperature = energy today : age: 13.8 billion years temperature: - 271 energy: 2 10-13 GeV

A journey in the past age = temperature = energy GW150914 one billion years ago today : age: 13.8 billion years temperature: - 271 energy: 2 10-13 GeV

A journey in the past age = temperature = energy we observe stars, galaxies, clusters the recent universe is transparent to em radiation today : age: 13.8 billion years temperature: - 271 energy: 2 10-13 GeV

A journey in the past age = temperature = energy age: 380000 ans temperature: 3200 energy: 3 10-10 GeV photon decoupling COSMIC MICROWAVE BACKGROUND

recombination and photon decoupling plasma: free electrons and protons hydrogen atoms and free photons before : the universe is ionised, photons are emitted and absorbed. Opaque! after : the universe is neutral, the photons are free to travel up to us. Transparent! free photons: COSMIC MICROWAVE BACKGROUND

free photons: COSMIC MICROWAVE BACKGROUND a huge amount of information came from its detection: the birth of modern cosmology

A journey in the past age = temperature = energy we would also like to know what happened before

A journey in the past age = temperature = energy we would also like to know what happened before BUT WE CAN T USE ELECTROMAGNETIC WAVES ALL IS LOST?

A journey in the past age = temperature = energy MAYBE NOT! the universe is transparent to gravitational waves since its beginning age: 10-44 sec temperature: 10 32 Celsius energy: 10 19 GeV

A journey in the past age = temperature = energy LIGO and Virgo LISA gravitational waves can be seen as MESSENGERS FROM THE EARLY UNIVERSE

GW from the early universe because of the weakness of the gravitational interaction the universe is transparent to GW rate of interaction rate of expansion (T ) H(T ) G2 T 5 T 2 /M Pl T M Pl 3 < 1 can this fact be used? which kind of detectors are available? which kind of sources do we expect?

CMB anisotropies GW GW light elements Inflation Cosmological dark age (reheating, baryogenesis, phase transitions...) BBN h ij E Planck? 10 10 GeV EW QCD MeV ev CMB LIGO elisa Pulsars CMB

Current situation for GW detection terrestrial interferometers : advanced LIGO/Virgo (direct, operating) frequency range of detection: 1 Hz <f<1 khz

Current situation for GW detection pulsar timing arrays (indirect, operating) frequency range of detection: 10 9 Hz <f<10 7 Hz

Current situation for GW detection cosmic microwave background (indirect, operating) frequency range of detection: 10 18 Hz <f<10 16 Hz

LISA : a future interferometer in space (direct, future) www.elisascience.org

LISA : a future interferometer in space

Current situation for GW detection terrestrial interferometers : advanced LIGO/Virgo (direct, operating) frequency range of detection: 1 Hz <f<1 khz 4 km length of the arm determines the frequency range of detection (the same as sound waves)

LISA : a future interferometer in space 2.5 million km the frequency range of detection is much lower 10 4 Hz <f<1 Hz

Characteristic frequency for a cosmological GW source f = H(T ) apple 1 parameter depending on the dynamics of the source Hubble rate is related to temperature in the universe : assuming standard thermal history f c = f a a 0 = 2 10 5 T 1 TeV Hz characteristic frequency today temperature (energy density) of the universe at the source time

Temperature (age, energy) in the early universe 0.001 T HGeVL T / (GeV) 1 10 2 10 4 10 6 10 8 10 10 h 2 WGW 10-5 10-7 10-9 LIGO 10-11 10-13 elisa PTA ET 10-9 10-7 10-5 0.001 0.1 10 1000 f HHzL

Temperature (age, energy) in the early universe 0.001 T HGeVL T / (GeV) 1 10 2 10 4 10 6 10 8 10 10 h 2 WGW 10-5 10-7 10-9 LIGO physics beyond the standard model 10-11 10-13 elisa PTA ET 10-9 10-7 10-5 0.001 0.1 10 1000 f HHzL

h 2 W GW 0.001 10-5 10-7 10-9 10-11 10-13 Observational bounds/sensitivities for GWSB T * êe * HGeVL 10-8 10-5 10-2 1 10 2 10 4 10 6 10 8 10 10 COBE BBN CMB LIGOêVirgo CMB anisotropies PTA Adv LIGO elisa FUTURE POSSIBLE BOUNDS 10-15 10-18 10-14 10-10 10-6 0.01 100 f HHzL

One remarkable example of GW source from the early universe

from the early universe: LISA LISA can probe a very important epoch age: 10-10 sec temperature: 10 15 Celsius energy: 100 GeV

The universe changes its state through a phase transition

First order electroweak phase transition potential barrier separates true and false vacua Higgs field

quantum tunneling across the barrier: nucleation of bubbles of true vacuum GW production from collisions of bubble walls sound waves and turbulence in the fluid primordial magnetic fields (MHD turbulence)

Example of GW signal 10-8 10-10 h 2 W GW HfL 10-12 total wall collision 10-14 sound waves MHD turbulence 10-16 10-5 -4 10 0.001 0.01 0.1 f@hzd

GW background from first order phase transitions we know the theoretical physics model to describe the universe up to about 100 GeV: the standard model of particle physics, tested at the LHC (CERN) but cosmology shows us that this model is not complete: neutrino masses, baryon asymmetry, dark matter, inflation models beyond the standard model can predict a first order PT and can therefore be tested by their GW emission LISA as a new probe of beyond standard model physics complementary to future colliders

Possible GW sources in the early universe non-standard inflation particle production during inflation fluid stiffer than radiation after inflation preheating after inflation phase transitions at the end or during inflation... first order phase transitions in the radiation dominated era cosmic strings other topological defects e.g. domain walls primordial black holes scalar field self-ordering...

Using compact binaries to probe cosmology : LISA and standard sirens

Using compact binaries to probe cosmology : LISA and standard sirens GW emission by black hole binaries can be used as SNIa (standard candles) to test the content of the universe

standard sirens GW emission by BH binaries: luminosity distance of the object

standard sirens GW emission by BH binaries: luminosity distance of the object + redshift by an EM counterpart

standard sirens luminosity distance from GW observation theoretical curve depending on cosmological parameters simulated data redshift

standard sirens with LISA LISA can constrain the Dark Energy content with about 6% error LISA can constrain the Hubble expansion with about 0.5% error

Conclusions we have assisted to a historical event, the aligo/virgo detection, which (so far) confirms GR this has opened the era of GW astronomy and cosmology : we have a new, independent messenger to be added to electromagnetic emission GW could be a powerful mean to probe the early universe (and consequently high energy physics) and the cosmological expansion: detection is difficult but great payoff

Advanced LIGO interferometers arm length L = 4 km laser power 20 W beam radius about 6 cm test masses 40 kg laser wavelength 0.1μm h ' L L ' 10 21 displacement of the mirrors : (collective - averaged over beam size) L 2 10 18 m dephasing : ' '! LhF (Fabry-Perot) ' 10 8 rad noise sources: seismic, thermal, radiation pressure, shot noise