Studying Fundamental Physics Using Current and Future Gravitational-Wave Detectors

Martin Hendry

Institute for Gravitational Research

SUPA School of Physics & Astronomy

University of Glasgow, UK

Gravitational waves are ripples in spacetime propagating atthe speed of light (according to GR)

Created by acceleration of massive compact objects

Gravitational Waves: the Story So Far

In General Relativity gravity is described by the curvature of space-time

◼Matter tells spacetime how to curve.

◼Spacetime tells matter how to move

Gravitational wave detectors measure changes inthe separation between free test masses in thisspacetime

L+L

L-L

◼

Interferometers monitor the position of suspended test masses separated by a few km

A passing gravitational wave will lengthen one arm and shrink the other arm; transducer of GW strain-intensity (10-18 m over 4 km)

Interferometric Detectors

41016m

10-5m

GEO600TAMA, CLIO

LIGO Livingston

LIGO Hanford

4 km2 km

600 m300 m100 m

4 km

VIRGO 3 kmLIGO Livingston

Ground-based network of detectors: 2002-2010

From Initial to Advanced LIGO

Developed

in Glasgow,

UK supplied:

fused silica

suspensions,

fibre-pulling,

bonding and

welding

10kg test masses on simplependulums become 40kgmonolithic suspensions inquadruple pendulums, withbetter quality optics

GW150914 – a burst of gravitational waves…

… matching a BBH inspiral and merger waveform from General Relativity

Abbott, et al., LIGO Scientific Collaboration and Virgo Collaboration,

“Properties of the binary black hole merger GW150914”,

https://arxiv.org/abs/1602.03840

Does General Relativity really fit?

Compton Wavelength of the GravitonPost-Newtonian Approximation to GR

• GW150914 was the first observation of a binary black hole merger

• Our best test of GR in the strong field, dynamical, nonlinear regime

• Constraints better than the binary pulsar system PSR J0737-3039

Abbott, et al., LIGO Scientific Collaboration and Virgo Collaboration, “Tests of general relativity with GW150914”,

https://arxiv.org/abs/1602.03841

Further tests of General Relativity: GW170104 Abbott, et al., “GW170104: Observation of a 50-solar binary black hole coalescence at redshift 0.2”https://arxiv.org/abs/1706.01812

Parameterised test of PN expansion

Modified dispersion relation

Lower limit on QG energy scale

With three or more interferometers we can triangulate the sky position of a

gravitational wave source much more precisely.

Source

location

From Aasi et al., https://arxiv.org/abs/1304.0670

Advanced Virgo joined O2 on Aug 1st 2017

Much better sky localisation

Abbott, et al., LIGO Scientific Collaboration and Virgo Collaboration, “GW170814: A Three-Detector Observation of Gravitational Waves from a Binary Black Hole Coalescence”, https://arxiv.org/abs/1709.09660

Antenna patterns Likelihood function

p(Tensor)

p(Vector)

p(Tensor)

p(Scalar)> 200 > 1000

See also Isi et al. arxiv:1703.05730 and Abbott et al. arxiv:1709.09203:

First search for non-tensorial continuous GWs from known pulsars

Polarisation tests: GW170814

Abbott et al., “GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Binary Mergers Observed by LIGO and Virgo During the First and Second Observing Runs”, http://arxiv.org/abs/1811.12907

Improved Tests of GR With the GWTC-1 BBHsAbbott, et al., “Tests of General Relativity with the Binary Black Hole Signals from the LIGO-Virgo Catalog GWTC-1”arxiv.org/1903.04467

Abbott et al., “Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A”, https://arxiv.org/abs/1710.05834

Constraining the speed of gravity: GW170817

Tests of GR, nuclear EoS with GW170817

Abbott et al., “Tests of General Relativity with GW170817”,https://arxiv.org/abs/1811.00364

Abbott et al., “GW170817: Measurements of Neutron Star Radii and Equation of State”, https://arxiv.org/abs/1805.11581

Schutz, “Determining the Hubble Constant from gravitational wave observation”Nature, 323, 310 (1986)

Cosmology with Standard Sirens

Independent route to the Hubble Constant

Freedman, “Cosmology at a Crossroads: Tension with the Hubble Constant”, https://arxiv.org/abs/1706.02739

Tension between:

• Measurement of H0 from

cosmic distance ladder

(e.g. SH0ES)

• Inference of H0 from CMBR /

LSS and cosmological

model (e.g. Planck)

Tension increases in e.g.

Riess et al. 1903.07603:

Abbott et al. “A Gravitational Wave Standard Siren Measurement of the Hubble Constant“ Nature, 551, 85 (2017)https://dcc.ligo.org/public/0145/P1700296/005/LIGO-P1700296.pdf

Maximum posterior value

minimal68% C.I.

Can compare EM and GW luminosity distance –these scale differently in many higher-D models.

Adopt simple phenomenological model:

Number of spacetime dimensions: GW170817 Abbott et al., “Tests of General Relativity with GW170817”,https://arxiv.org/abs/1811.00364

Proximity of GW170817 limits effectiveness of constraints so far, but watch this space(-time)!…

Computed Bayesian posterior on D, fixing EM luminosity distance to Planck or SHoESHubble constant

Computed Bayesian posterior on D, for different fixed values of the screening scale

Pardo et al., “Limits on the number of spacetime dimensions from GW170817”, https://arxiv.org/abs/1811.00364

We can also use “dark sirens” – no explicit EM counterpart

We ‘marginalise’ over the redshifts of possible host galaxies

Soares-Santos et al., “First measurement of the Hubble constant from a dark standard siren using the Dark Energy Survey galaxies and the LIGO/Virgo binary black hole merger GW170814”, http://arxiv.org/abs/1901.01540

Useful ‘proof of concept’

GEO600 (HF)

Advanced LIGO

Hanford

Advanced LIGO

Livingston

Advanced

Virgo

LIGO-India

KAGRA

Network of advanced detectors

Coming attractions…

Nissanke et al., “Determining the Hubble constant from gravitational-waveobservations of merging compact binaries”, https://arxiv.org/abs/1307.2638

Coming attractions…

Chen et al., “Precision Standard Siren Cosmology”,https://arxiv.org/abs/1712.06531

Cowperthwaite et al., “Joint Gravitational Wave and Electromagnetic Astronomy with LIGO and LSST in the 2020s”, https://arxiv.org/abs/1712.06531

Third Generation GW Network

Aimed at having excellent sensitivity from ~1 Hz to ~104 Hz.

US-led project: “Cosmic Explorer” http://www.cosmicexplorer.org/

FP7 European design study: the

Einstein Telescope (ET).

Goal: 100 times better sensitivity

than first generation instruments.

See http://www.et-gw.eu/

See also Dwyer et al. arxiv: 1410.0612

https://gwic.ligo.org/3Gsubcomm/

~106 NS-NS mergers observed by 3G networks

Different models for spatial distribution,

source evolution

Cosmological constraints from 3G detectors

z

zwwzw a

++=

1)( 0

GW constraints similar to those from BAO, SNIe.

BUT assumes z known for ~1000 sources, z < 2

Significant ‘multi-messenger’ challenge

BNS: ET-D + CE

Zhao & Wen: http://arxiv.org/abs/1710.05325

See also Zhao et al. http://arxiv.org/abs/1009.0206

Assume we can measure flexion from

galaxy surveys, giving better estimate of

matter density on small angular scales.

EELT

Shapiro et al (2010): Shear varies spatially

Gradient of shear → arcing, or flexion

Correcting for Weak Lensing?...

Euclid

GW sources will be (de-)magnified by weak lensing due to LSS No correction

Shear map only, ELT

Shear + flexion, ELTShear + flexion,

ELT + Space

→ 1.8% at

→ 1.4% at EELT

LD 2=z

LD 1=z

Shapiro et al. arxiv:0907.3635

Space detectors

The Gravitational Wave Spectrum

Adapted from M. Evans (LIGO G1300662-v4)

10-9 Hz 10-4 Hz 100 Hz 103 Hz

Relic radiation

Cosmic Strings

Supermassive BH Binaries

BH and NS Binaries

Binaries coalescences

Extreme Mass Ratio

Inspirals

Supernovae

Spinning NS

10-16 HzInflation Probe Pulsar timing Ground based

Long tail due to

parameter degeneracies

Holz and Hughes 2005Colpi et al. 2019

LISA will ‘see’ very high-SNR massive black hole

binary mergers to z > 20

• Exquisite tests of GR from waveforms

• Standard siren Hubble diagram to high redshift

Extreme Mass Ratio Inspirals

• Among the most interesting and important low-frequency sources, probing fundamental physics, astrophysics and cosmology:

➢ Study immediate environment of MW-like MBHs at low redshift

➢ Perform precision tests of GR

➢ Explore multipolar structure of MBH gravitational fields

➢ Test GW propagation properties

➢ Measure cosmic expansion rate with GW observations alone (“dark sirens”)

➢ Probe dynamics of dense nuclear star clusters

Long, complex waveforms; major data analysis challenge!

Constraining extra-D models with LISA

Corman and Hendry (in prep.)

Realistic LISA data constrain well and .

But for better with steep transition.

Bayes factors strongly depend on errors,

weakly depend on MBH formation model

Heavy ‘seeds’, no delay

Strong Lensing of GWs?...

…Not yet, but clear future potential

For example: diagnostic of wave dark matter

Schive et al. “Cosmic structure as the quantum interference of a coherent dark wave”, arxiv:1406.6586

arxiv:1901.02674

A. Herrera Martin (2018)

“Wave dark matter as a gravitational lensfor electromagnetic and gravitational waves”

http://theses.gla.ac.uk/9027/

See also e.g. these arxiv papers on constraints from lensed GW+EM systems : 1901.10638; 1809.07079; 1703.04151; 1612.04095; 1508.05000

GWs and Primordial Black Holes?

Carr et al., https://arxiv.org/abs/1607.06077

arxiv:1603.00464

Abbott et al., http://arxiv.org/abs/1811.12907

Possible mass window in LIGO BH mass range?...

Useful discriminator could be isotropy of BH spins:• Random alignment for PBH origin models• Aligned distribution for other scenarios

Summary: Lots of coming attractions....

• Improved tests of GR:

➢ P-N orders; Compton wavelength➢ polarisation constraints (from ➢ speed of gravity – EM arrival, dispersion➢ EMRI mapping spacetime around SMBHs➢ joint GW-EM observations of lensed sources

• Constraining non-standard cosmologies:

➢ Hubble diagram of sirens; event rates➢ Primordial BHs – strong constraints from spin distribution➢ Strong lensing by DM haloes: probe of wave DM?➢ ????