To actively encourage Belgian research on Gravitational Wave Physics and other astrophysical observations that can make contact with fundamental physics, we hold:

GW MEETINGS: a regular set of half-day meetings (~6/year). A GW meeting typically starts in the afternoon with a seminar by an international expert, followed by a talk by a  local researcher (local = working in Belgium-affiliated group). As the main aim is to stimulate the local community, there will be ample time for breaks and discussions over coffee and drinks.

 GW SEMINARS: organized by one of our associated institutions. Those will also be announced on this website.

TUE 26/03@ULB

Location

ULB, Campus Plaine, Solvay Room

Speakers

2.00pm-3.00pm: Maarten van  de Meent (MPI Potsdam)
3.00pm-3.30pm: coffee
3.30pm-4.30pm: Peter Tinyakov (ULB)

Maarten van de Meent

Title: The motion of small objects around spinning black holes

Abstract: The motion of objects around a spinning (Kerr) black hole is much more complicated than in the case of a non-spinning (Schwarzschild) black hole. In the first part of this talk, I will discuss some of the fascinating phenomonolgy of the motion of test particles around Kerr black holes.
I then move on to including corrections to this motion by computing the so-called the gravitational self-force; the apparant force that is exerted on a small body due to its own gravitational field.
I will conclude by discussing some interesting results from self-force calculations for nearly extremal Kerr black holes.

Peter Tinyakov

Title: Solar mass black holes and dark matter

Abstract: Black holes (BH) with masses around or below one Solar mass are not produced as a result of conventional stellar evolution. This range of BH masses is, therefore, of a particular interest: if such a black hole is detected, it would almost certainly mean that some beyond-Standard-Model production mechanism is at work. One possibility presently debated in the literature is that solar mass BH might be of a primordial origin. We will discuss an alternative possibility that light black holes may result from collapse of (otherwise stable) neutron stars induced by accumulated dark matter.
 

Tue 30 April@Brussels

No separate GW seminar, coincidence with Brout-Englert-Lemaitre-meeting

FRI 10 May@Leuven

1pm-4.45pm: GW Seminar & Belgian-Dutch Theoretical Cosmology Meeting

Speakers & Location tba

Past gw seminars

2018-2019

TUE 27/11@ULB

Location

ULB, Campus Plaine, Solvay Room

Schedule

Early start!!

Two talks followed by the Solvay colloquium.

13.30 Chris Kavanagh (IHES, Paris on the move to AEI, Berlin)
14.30 Christophe Ringeval (UCL) New insights on the cosmic strings stochastic gravitational wave background  
15.30 coffee break
16.00 Jo van den Brand (Nikhef) - Solvay Colloquium

Chris Kavanagh

Title: Analytical self-force and Effective-One-Body approaches to extreme mass-ratio black hole binaries. 

Abstract:  The space based gravitational wave observatory LISA aims to study a diverse range of low frequency gravitational wave sources. One main system of such interest are extreme mass-ratio binaries, where one has a galactic centre type massive black hole with a smaller compact body in a highly relativistic inspiralling orbit. The gravitational self-force approach models these binaries as a point particle sourcing a perturbation to a black hole spacetime. The perturbation influences the point particle's trajectory accelerating it off a geodesic, this effect is called the self-force. In this talk I will briefly overview some of the main techniques and challenges in this perturbative approach to the two body problem. I will then present recent work using asymptotic expansions within the self-force approach, and how this can be used with the effective-one-body model.

Christophe Ringeval

Title: New insights on the cosmic strings stochastic gravitational wave background  

Abstract: In less than two years, GW detections have confirmed the omnipresence of black holes in the Universe and have shed lights on the origin of short gamma ray bursts and kilonovae. What's next?  Cosmic strings are one the expected outcome of phase transitions in the Early Universe. They have unique signatures in terms of GWs that strongly depend on various properties associated with the loops they produce, but not only. In this talk, after having reviewed the cosmological properties of a cosmic string network, I'll discuss a new estimate of the stochastic gravitational wave spectrum generated by a string network, including various effects neglected so far. In particular, for some string tensions, the signal ends up be boosted in the LIGO and VIRGO frequency range and these are already constrained. The stochastic GW background is a new window to search for cosmic strings, which encompasses the complete range of possible GUT phase transitions. Such a situation has never occurred before.

Jo van den Brand

See http://www.solvayinstitutes.be/html/colloquia.html http://www.solvayinstitutes.be/pdf/Colloquia/2018/jo_van_den_brand.pdf

Title: Gravitational waves science from LIGO and  Virgo to Einstein Telescope

Abstract: The  LIGO  Virgo  Consortium  achieved  the  first  detection  of  gravitation - al  waves.    A  century  after  the  fundamental  predictions  of  Einstein,  we  re - port  the  first  direct  observations  of  binary  black  hole  systems  merging  to  form  single  black  holes.  The  detected  waveforms  match  the  predictions  of  general  relativity  for  the  inspiral  and  merger  of  a  pair  of  black  holes  and  the  ringdown  of  the  resulting  single  black  hole.  Our  observations  provide  unique  access  to  the  properties  of  space-time  at  extreme  curvatures:  the  strong-field and high velocity regime. It allows unprecedented tests of gen - eral  relativity  for  the  nonlinear  dynamics  of  highly  disturbed  black  holes.  Last  year  the  gravitational  waves  from  the  merger  of  a  binary  neutron  star  were  observed.  This  discovery  marks  the  start  of  multi-messenger  astron - omy  and  the  aftermath  of  this  merger  was  studied  by  using  70  observato - ries on seven continents and in space, across the electromagnetic spectrum.

The  scientific  impact  of  the  recent  detections  will  be  explained.  In  addition  key technological aspects will be addressed, such as the interferometric de - tection principle, optics,  and sensors and  actuators. Attention is  paid  to  the  largest challenges in the field, including plans for Einstein Telescope, an in - strument  that  will  allow  us  to  observe  black  hole  coalescence  in  the  entire  visible  Universe.  Einstein  Telescope  will  be  an  underground  observatory  housing multiple (cryogenic) interferometers for gravitational waves science. 

Tue 23/10@KU Leuven

Location

Auditorium "Oude Molen"
Kasteelpark Arenberg 50
3001 HEVERLEE

(opposite Celestijnenlaan 200 campus - meet us in Celestijnenlaan 200D by 1.30pm for directions)

Schedule

14:00: Sera Markoff (API/GRAPPA, University of Amsterdam): Imaging (and imagining) Black Holes   
15:00: coffee
15:30: Tom Lemmens (KU Leuven): Shadows of 5D black objects

Sera Markoff

Title: Imaging (and imagining) Black Holes

Abstract: Black holes are one of the most exotic consequences of Einstein’s general relativity, objects so compact that they warp spacetime around them, preventing light (and everything else) from escaping their pull.   Yet they are also very common players in the Universe, on scales ranging from the stellar up to beasts over a billion times more massive than our sun.   Contrary to their reputation as cosmic vacuum cleaners, they actually serve as engines for extremely energetic processes, playing a major role in regulating the growth of galaxies.  Some black holes also launch enormous jets of relativistic plasma that accelerate particles to energies millions of times higher than the Large Hadron Collider at CERN.   Astronomers, astrophysicists and physicists all have reasons for wanting to understand black holes, yet we have been limited by the resolution of our telescopes from actually seeing one directly.   This situation has changed dramatically with the coming of the Event Horizon Telescope, an Earth-sized array operating in the millimeter wavelength regime, that can actually make pictures (think Interstellar) of a couple of nearby supermassive black holes such as the one in our Galactic center, Sgr A*, and the active galactic nucleus M87.  I will briefly introduce black holes and show some examples of the havoc they inflict on their environments.  Then I will discuss some of the key problems we are still facing in terms of building a complete model for the (astro)physics around them, and give some examples of the current cutting edge in modeling and interpretation.  Finally I will explain what the Event Horizon Telescope is, and how we anticipate the groundbreaking data from the first full run in April 2017 (note: I will not be able to show the results yet!) will revolutionise our field.

Tom Lemmens

Title: Shadows of 5D black objects

Abstract: String theory provides us with a way to solve the information paradox but to do this it requires the existence of higher dimensional objects. Higher dimensions allow us greater freedom in the objects we can construct and we can ask if there is any observable difference between them. In this talk we will look at signals coming from a variety of higher dimensional black objects.  In particular we are interested in the shadow and lensing effects of black holes and black rings. To find out what those objects look like we will shoot null geodesics originating at a distant observer in the various geometries.

TUE 25/09@UCL

Schedule

Abstracts below the map. Local website: https://curl.group/news/2018/09/12/BGW.html

2pm: Stefan Antusch (Basel U.): "Oscillons and gravitational waves from preheating after inflation" 

3pm: coffee break

3.30pm: Giulia Cusin (Oxford U.): "Astrophysical background of gravitational waves: from cosmology to a new era of precision astrophysics"

Location

Room E349. Bâtiment de Hemptinne, tower E, 3rd floor, 2 chemin du cyclotron, Louvain-la-Neuve.

Stefan Antusch

Title: "Oscillons and gravitational waves from preheating after inflation" 

Abstract: We discuss the preheating phase after inflation in particle physics motivated models of the early universe. We show that the non-linear dynamics after hilltop-type inflation models, where inflation can be linked to a particle physics phase transition, can lead to the formation of oscillons, comparatively long-lived and strong local fluctuations of the inflaton field. Similar types of scalar field potentials also appear in the KKLT scenario in string phenomenology, and oscillons can form for the modulus field. We argue that when the oscillons are asymmetric for a sufficiently long period, they can generate a peak in the otherwise rather broad gravitational wave spectrum produced during the earlier phases of preheating.   

Giulia Cusin

Title: "Astrophysical background of gravitational waves: from cosmology to a new era of precision astrophysics"
 

Abstract: The astrophysical background of gravitational waves (AGWB) is made up by the incoherent superposition of gravitational wave signals emitted by a large number of resolved and unresolved astrophysical sources from the onset of stellar activity until today, and that we collect at our detectors. I present a theoretical framework  to fully characterize the AGWB in terms of energy density anisotropies and polarization and I show the first numerical predictions for the angular power spectra of anisotropies in different frequency bands and for cross-correlations with electromagnetic observables such as weak leaning and galaxy number counts. l then illustrate and discuss the astrophysical implications of this study.  By properly modelling the properties of the  AGWB, it will be possible to extract for the first time precise data on galactic and stellar physics and on astrophysical processes of GW emission. In the same way as the discovery and study of the cosmic microwave background has represented a turning point for cosmology,  the study of the AGWB will represent a true revolution for astrophysics eventually leading to a new era of precision astrophysics. 

2017-2018

tuesday 27 March 2018: GW meeting

Location

KU Leuven, Celestijnenlaan 200D, room 200D 05.11

Schedule

14:00: Germano Nardini (Bern & LISA)
15:00: coffee
15:30: Aidan Chatwin-Davies (Caltech)

Germano Nardini

Title: Probing the electroweak scale via gravitational wave experiments

Abstract:  A first-order phase transition produces gravitational waves and such a transition only occurs if there is physics Beyond the Standard Model (BSM). Because of this, gravitational wave observatories are sensitive to new physics. In this talk we review the status of gravitational wave detectors and their capabilities for probing first-order phase transitions. We demonstrate that gravitational wave detectors are able to discover new physics arising at the electroweak scale or even much above. For some BSM scenarios the complementarity between the LHC and the space-based interferometer LISA is manifest.

Aidan Chatwin-Davies

Title: "Decoherence and the Black Hole Information Puzzle"

In a fully quantum gravitational treatment, the wave function that characterizes the process of black hole formation and evaporation must describe an ensemble of possible black hole geometries and matter configurations. I will discuss a proposal to understand the emergence of such an ensemble as a decoherence process, in which decohered branches of the wavefunction correspond to semiclassical geometries together with effective field theoretic states. Quantum mechanics dictates that evolution at the level of the global wave function should be unitary. On the other hand, questions about the position and smoothness of horizons only make sense at the level of individual branches. I will discuss the implications of this proposal for the AMPS construction and argue that it permits firewall-free branches while maintaining unitarity at the level of the global wavefunction.

MONDAY (!) 26 february 2018: GW meeting

Location

Room change! ULB, Campus Plaine, building NO room NO.9.06
(same building as Solvay Room, just 4 floors up)

Schedule

14:00: Adam Pound (Southampton)
15:00: coffee
15:30: Sébastien Clesse (UCL and UNamur)

Adam Pound

Title: Extreme-mass-ratio inspirals and the second-order gravitational self-force

Abstract: The recent observations of gravitational waves represent a remarkable success of relativistic binary modelling. However, accurate models have so far been restricted to binaries in which the two members have comparable masses. For binaries with more disparate masses, modelling is far less mature. This is especially relevant for extreme-mass-ratio inspirals (EMRIs), in which a stellar-mass object orbits a supermassive black hole. EMRIs will be key targets for the space-based detector LISA, and in principle they are well modelled by gravitational self-force theory, in which the smaller object generates a small gravitational perturbation that reacts back on it to produce a "self-force". But until recently, self-force models have been restricted to linear perturbation theory, which is insufficiently accurate for LISA science. In this talk, I discuss ongoing work to develop second-order, nonlinear self-force theory -- and present results from its first successful numerical implementation.

Sébastien Clesse

Title:  Gravitational Waves and Cosmology:  seven hints for primordial black hole dark matter

Abstract:  After a brief review on the interest of gravitational-wave astronomy for cosmology, I will focus on a particular model that has recently received a lot of attention:  primordial black holes as a dark matter candidate.  I will present the current status of this scenario, as well as seven observations, including the gravitational waves from massive black hole mergers detected by LIGO/VIRGO, pointing towards the possible existence of primordial black holes, with abundances comparable to the one of dark matter.  Finding an evidence of even a single primordial black hole could have groundbreaking consequences for our understanding of the early Universe and of High Energy physics. 

tuesday 6 february 2018: seminar

Laura Cadonati  (Georgia Tech and Deputy Spokesperson of Ligo Scientific Collaboration)

Location and schedule: ULB, Campus Plaine, Solvay Room,  11am

Tuesday 28 November 2017

Location and schedule

Note: different rooms for the talks!

KU Leuven, Celestijnenlaan, Heverlee:

14:00-15:00: 200D 06.32 - "Gravitational wave astrophysics with LIGO/Virgo sources", Gijs Nelemans (RU Nijmegen & KU Leuven)
15:00-15:30: coffee
15:30-16:30: 200C 01.09 - "Echoes of Kerr-like wormholes", Frederik Goelen (KU Leuven)

Gijs Nelemans

Title: Gravitational wave astrophysics with LIGO/Virgo sources 

Abstract: With the detection of gravitational waves and the detection of an electromagnetic counterpart to the double neutron star merger GW170817, multi-messenger gravitational wave astrophysics really has started. I will give an overview of the discoveries so far and the potential for astrophysical research with the current and future instruments.

Frederik Goelen

Title: Echoes of Kerr-like wormholes

Abstract: Structure at the horizon scale of black holes would give rise to echoes of the gravitational wave signal associated with the post-merger ringdown phase in binary coalescences. We study the waveform of echoes in static and stationary, traversable wormholes in which perturbations are governed by a symmetric effective potential. We argue that echoes are dominated by the wormhole quasinormal frequency nearest to the fundamental black hole frequency that controls the primary signal. We put forward an accurate method to construct the echoes waveform(s) from the primary signal and the quasinormal frequencies of the wormhole, which we characterize. We illustrate this in the static Damour-Solodukhin wormhole and in a new, rotating generalization that approximates a Kerr black hole outside the throat. Rotation gives rise to a potential with an intermediate plateau region that breaks the degeneracy of the quasinormal frequencies. Rotation also leads to late-time instabilities which, however, fade away for small angular momentum.

thursday 23 november 2017

Location - changed!

Schedule

Gustavo E. Romero

Tuesday 24 October 2017

Location

ULB, Campus Plaine, Solvay Room

Schedule

14:00: Carlos Herdeiro (Aveiro)
15:00: coffee
This will take place during the two-day PhD school of Luc Blanchet.

Carlos Herdeiro

Title: Kerr black holes with bosonic hair: theory and phenomenology

Abstract: Over the last three years it has been found that new classes of asymptotically flat black hole solutions, regular on and outside the event horizon, bifurcating from the vacuum Kerr solution, exist in General Relativity, with simple matter contents that obey all energy conditions, namely Kerr black holes with scalar hair and Proca hair. In this talk, after briefly reviewing the observational evidence for black holes and their standard theoretical description, I will describe the general mechanism that allows the new solutions to exist, intimately connected to superradiance, how these solutions circumvent well known no-hair theorems and some of their phenomenology (shadows and x-ray spectra) which can be considerably distinct from that of Kerr.

References:

- Carlos A. R. Herdeiro, Eugen Radu
Kerr black holes with scalar hair
Phys.Rev.Lett. 112 (2014) 221101

- Carlos Herdeiro, Eugen Radu, Helgi Runarsson
Kerr black holes with Proca hair
Class.Quant.Grav. 33 (2016) no.15, 154001

- Pedro V. P. Cunha, Carlos A. R. Herdeiro, Eugen Radu, Helgi F. Runarsson
Shadows of Kerr black holes with scalar hair
Phys.Rev.Lett. 115 (2015) 21, 211102

- F.H. Vincent, E. Gourgoulhon, C. Herdeiro, E. Radu
Astrophysical imaging of Kerr black holes with scalar hair
Phys.Rev. D94 (2016) no.8, 084045

- Yueying Ni, Menglei Zhou, Alejandro Cardenas-Avendano, Cosimo Bambi, Carlos A. R. Herdeiro, Eugen Radu
Iron Kα-line of Kerr black holes with scalar hair
JCAP 1607 (2016) no.07, 049

- C. A. R. Herdeiro and E. Radu,
  Kerr black holes with synchronised hair: an analytic model and dynamical formation,
  arXiv:1706.06597 [gr-qc].

Tuesday 19 September 2017

Location

KU Leuven, Celestijnenlaand 200D, room 06.32 (coffee break and drinks @coffee room next door)

Schedule

14.00-15:00:  Chris Moore (Cambridge and LIGO) "An astrometric search method for individually resolvable gravitational wave sources with Gaia"

15:00-15:30: Coffee

15:30-16:15: Jiang Long: "Extreme mass ratio inspirals into near extremal Kerr black holes: orbits and gravitational waves"

16:15-17:30: Discussion + drinks: "fundamental physics prospects from LIGO"

Chris Moore (Cambridge)

Jiang Long (ULB)

Title: Extreme mass ratio inspirals into near extremal Kerr black holes: orbits and gravitational waves

Abstract: Gravitational waves encode useful information of spacetime and allow us to test general relativity. One important question is the gravitational wave production by extreme-mass-ratio-inspirals(EMRI) into near-extremal Kerr BHs which could be detected by eLISA. In this talk, I will classify general equatorial timelike orbits of EMRIs around near-extremal Kerr BHs. All orbits can be related to circular orbits in NHEK or near-NHEK region due to the enhancement of conformal symmetry. Gravitational wave signals are computed analytically for these orbits.

2016-2017

Tuesday 6 june 2017

Location

ULB, Solvay room

Schedule

11:30 Frans Pretorius (Princeton), "Observation of Dynamical, Strong-field Gravity"

14:30 Christophe Collette (ULB and LIGO), "Challenges in seismic isolation for the next generation of gravitational wave observatories  "

15:45 Coffee

16:00 Solvay Colloquium by Frans Pretorius: "Black Holes in the Era of Gravitational Wave Astronomy"

Frans Pretorius (Princeton)

Title:  Observation of Dynamical, Strong-field Gravity

Abstract: As well-tested as general relativity is in the weak field  through laboratory experiments, solar system measurements and binary pulsar observations, until the recent detection of gravitational waves by LIGO all evidence for the general relativistic description of dynamical strong-field gravity has been circumstantial at best. Given the mystery of dark energy, and the many theoretical puzzles associated with black holes, both of which are strong-field phenomena, testing gravity in this regime is crucial to either give more confidence in the general relativistic description, or gain evidence for new physics here. I will discuss some ongoing efforts to do this using gravitational wave observation of  binary black hole merger events; in particular using parameterized post-Einstein (ppE) models to test the inspiral regime, and searching for sub-dominant ring-down modes from the post-merger remnant. However, one significant theoretical challenge here is the dearth of concrete predictions of the non-linear phase of merger events in modified theories of gravity. I will discuss what some of these challenges are, and how they might be overcome.

Christophe Collette (ULB & LIGO)

Title: Challenges in seismic isolation for the next generation of gravitational wave observatories    

Abstract:  One century after their prediction by the general theory of relativity, gravitational waves have been directly measured by LIGO instruments. More than a validation of Einstein’s theory, it is a new window that has been open on universe, and the beginning of gravitational wave astronomy. In the next decades, the exploration of the Universe through this new window using Earth-based instruments will continue, both with upgrading existing instruments, and with the construction of new detectors, allowing to increase the number and diversity of detections. However, due to the extremely small amplitude of the signals, the exploration ultimately relies on our capability to isolate the instruments from two main sources of low-frequency disturbances on Earth: seismic activity and fluctuations of gravity field (Newtonian noise).  This presentation will describe the methods used to decouple the instruments from Earth and their performance, and will give directions for improving instruments sensitivity in the low-frequency range.

thursday 27 april 2017

Location

Celestijnenlaan 200E, room 01.209, directions to campus

Schedule

2pm: "Testing GR with GWs" - Vitor Cardoso (Lisbon)

3pm: coffee

3.30pm: "Self-similar accretion in thin disks around near-extremal black holes" - Roberto Oliveri (ULB)

Vitor Cardoso

Title: Testing GR with GWs

Abstract: Two pivotal breakthroughs in physics recently turned respectable centennials: the discovery of the Schwarzschild solution, describing a non-rotating black hole, and Einstein's prediction of gravitational waves.

Gravitational waves offer a unique glimpse into the unseen universe in different ways, and allow us to test the basic tenets of General Relativity, some of which have been taken for granted without observations: are gravitons massless? Are black holes the simplest possible macroscopic objects? do event horizons and black holes really exist, or is their formation halted by some as-yet unknown mechanism? Do singularities arise in our universe as the outcome of violent collisions? Can gravitational waves carry information about the nature of the elusive dark matter?

In this talk, I will describe the science encoded in a gravitational wave signal and what the upcoming years might have in store regarding fundamental physics and gravitational waves.

Roberto Oliveri

Title: Self-similar accretion in thin disks around near-extremal black holes

Abstract:
Near-extremal black holes display conformal symmetry in their near-horizon region, where critical phenoma might take place.
We first show how conformal symmetry constraints physical observables in the near-horizon region of near-extremal black holes.
Then we introduce the Novikov-Thorne model of accretion thin disk and discuss its main features.
Finally, we investigate the physics of accretion thin disks in the extremely high spin regime, where (a) a novel phase transition occurs and (b) the critical (self-similar) behavior of accretion is manifest.

The talk is mainly based on arXiv:1703.00022 [astro-ph.HE] with G. Compère.