# Second European Physical Society Conference on Gravitation: measuring gravity

Europe/London
Great Hall, Strand Campus (King's College)

### Great Hall, Strand Campus

#### King's College

Strand, London WC2R 2LS, United Kingdom
Description

Given the current situation with the increasing spread of the coronavirus COVID19  in Europe, we regret to announce that the organizing committee decided to postpone the meeting.

We apologize for any inconvience, and hope you are and will do well. We would also expecially thanks all speakers and contributors who had been preparing to this meeting, and to all the people who worked hard to make it possible.

The secretary of Physics department of King's college will send an email to all participants who had paid, they will be reimbursed directly from the University

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The second EPS (European Physical Society) Conference on Gravitation is held at King's College  (London, UK) from April 7th to April 9th, 2020. The aim of the conference is to discuss experimental aspects of Gravity, including General Relativity tests, measurements of the G constant, Geodesy, and Gravitational Waves. Details about registration will be communicated in the next announcement. The conference is organised in days focused around key topics introduced by invited speakers and followed by contributed talks and posters. The scientific program will be finalised in the upcoming days. The Local and Scientific Organising Committees are looking forward to welcome you in London.

Please note that the conference desk will be open on Monday 6th, from 17:00 to 19:00 at the  the Department of Physics of King's College. Then, it will open again the morning of 7th at 8:30.

Early registration ends 1st March, 2020 and abstract submission ends 17th February, 2020

Participants
• Aaron Held
• Alexander Jenkins
• André Großardt
• BOILEAU Guillaume
• Claus Laemmerzahl
• Daniele Vetrugno
• David Wands
• Davide Dal Bosco
• Dorothee Tell
• Eleonora Castelli
• Fabrizio De Marchi
• Fienga Agnes
• Fulvio Ricci
• Gerhard Heinzel
• Guglielmo M. Tino
• Helen Margolis
• Jürgen Müller
• Katarina Martinovic
• Luciano Iess
• Luigi Cacciapuoti
• Léo Bernus
• Manuel Rodrigues
• Maria Haney
• Martin Pernot-Borràs
• Matteo Barsuglia
• Michael Ebersold
• Nelson CHRISTENSEN
• Paola Puppo
• Patrice PEREZ
• Patrick Gill
• Peter Bender
• Philippe Bouyer
• Philippe Jetzer
• Pierre Grandemange
• Pieter Visser
• Quentin Baghi
• Rita Dolesi
• Simone Dell'Agnello
• Stefano VITALE
• Sweta Shah
• Vivek Venkatraman Krishnan
• Zachary Picker
Support
• Tuesday, 7 April
• 09:00 09:30
Welcome
• 09:30 10:30
Experimental Challenges in Gravitational Wave Detection
• 09:30
Instrumental challenges in ground-based gravitational wave detectors 30m

Invited talk

Speaker: Matteo Barsuglia (APC-CNRS)
• 10:00
Instrumental challenges in space-based gravitational wave detectors 30m

Invited talk

Speaker: Rita Dolesi (TIFP)
• 10:30 11:00
Coffee Break
• 11:00 12:40
Geodesy and Ranging: Geodesy
• 11:00
Future costallations for observing Earth's time variable gravity field 30m

Invited talk

Speaker: Pieter Vissier (Delft University of Technology)
• 11:30
Lunar and interplanetary laser ranging 30m

Invited talk

Speaker: Simone Dell'Agnello (LNF)
• 12:00
SHORT PERIOD MASS VARIATION PROCESSES 20m

A number of options for the design of a Next Generation Gravity Mission (NGGM) are being considered in various countries. A widely discussed option is a mission like GRACE Follow-On (GRACE-FO), but with three major changes. One is to leave out the K-band ranging system, and rely on the much more accurate Laser Ranging System (LRS) tested on the GRACE-FO mission to measure changes in the satellite separation. The second is to fly the mission in a nearly drag-free mode. And the third is to replace the accelorometers on each satellite by simplified versions of the Gravitational Reference Sensors (GRSs) that were tested very successfully on the LISA Pathfinder mission. It appears that the noise level of each simplified GRS would be below 10^-12 m/(s^2)/(Hz^0.5) at frequencies down to 0.1 mHz, with the mass and volume of each one being less than 10 kg and 10^4 cm^3 (Conklin, J. W., private communication). It will be assumed here that the satellite altitude would be near 500 km, like for GRACE and GRACE-FO.

For such a mission, the main issue is how much improvement in our knowledge of short period mass variations on the Earth, and of their causes, could be obtained. For roughly 30 day global averages, it has been shown in other studies that the improvement in the geopotential compared with the GRACE-FO mission would be small because of temporal aliasing. However, alternate analysis approaches are now being used in which the geopotential variations along the orbital arcs are solved for instead of global averages (Jekeli, 1999; Han et al., 2006; Ghobadi-Far et al., 2018). About 70% of the geopotential variation amplitude at medium to short wavelengths can be represented by the AOerr data set (Dobslaw et al., 2016), and we have used this data set for comparison with the measurement noise levels for the satellite separations and accelerations if these levels are the same as those for the laser interferometer data and the accelerometer data from GRACE-FO. This comparison makes it clear that the accelerometer noise level would strongly dominate the total measurement noise over most of the interesting wavelength range, but be somewhat below the present geopotential variation level at the medium and short wavelengths. But substantial improvements in auxillary geophysical data and in procedures for using it to estimate the geopotential variations are likely by the time that a NGGM takes most of its data, so that a reduced acceleration noise level would be needed to validate the improvements at the shorter wavelengths. This alone appears to be a good justification for switching to the use of GRSs instead of accelerometers for the NGGM.

In addition, it also is worth considering that a much lower acceleration noise level would make it possible to compare different procedures for estimating the geopotential variations at medium wavelengths, even if the remaining uncertainty levels in the procedures are above the measurement noise level. As an example, an important part of the information concerning hydrology that we get from the satellite measurements is a better understanding of the overall process of how times of rainfall, evapo-transpiration rates, runoff, etc., combine to produce short period changes in the geopotential. If we compare different sets of proceedures for estimating the geopotential variations from the geophysical variations or different sets of geophysical variation data with what is found from the satellite observations at particular times and locations, this helps directly to improve our understanding of the whole process. This ability to test different procedures, etc., adds considerably to the scientific benefits of flying GRSs instead of accelerometers on the NGGM, and on other future Earth gravity variation missions.

          References


Conklin, J. W., (2020), private communication.
Dobslaw, H., et al., (2016), Journal of Geodesy 90(5), 423-436.
Ghobadi-Far , K., et al., (2018), Jour. Geophys. Res.: Solid Earth 123(10), 9186-9201.
Han, S-C, et al., (2006), Jour. Geophys. Res., 111, B04411.
Jekeli, C., (1999), Celestial Mechanics and Dynamical Astronomy 75(2), 85-101.

Speaker: Dr Peter Bender (JILA and Dept. of Physics, Univ. of Colorado)
• 12:20
Geodesy and non-newtonian gravity 20m

In the past decades, Earth’s geoid has been successfully measured by the GOCE and GRACE missions. The usual data analysis consists in making a spherical harmonic expansion of the measured gravity field, which nonetheless restricts to the case of Newtonian gravity in published works.
In this talk, I will present the impact of considering a finite coupling scale Yukawa deviation to a Newtonian potential.
In particular, I will show that for this model, we can still derive harmonic coefficients, which now depend on the distance to the source of gravity. This implies a new degeneracy between Yukawa parameters and the extracted geoid models that depends on the altitude at which geodesy experiments are performed. I will then discuss how one could, in principle, detect a Yukawa deviation by comparing the extracted geoid models at different altitudes.

arXiv:1808.00340
DOI: 10.1088/1361-6382/aae9a1

Speaker: Martin Pernot-Borràs (ONERA / IAP)
• 12:40 14:00
Lunch 1h 20m
• 14:00 15:40
Experimental Challenges in Gravitational Wave Detection
• 14:20
Studies of the correlated noise with LISA Pathfinder data. 20m

We are conducing studies of the LISA Pathfinder data, acceleration and auxiliary channels, to develop an understanding for potential noise sources for the future Laser Interferometry Space Antenna (LISA) Mission. The understanding of correlated noise is a goal to establish limits for the attempts to measure a stochastic gravitational wave background using LISA data. The differential acceleration of the test-masses, as well as the temperature, magnetic fields, µ-thruster signals and photodiode currents are examined. We also develop a Wiener filter for the LISA Pathfinder differential acceleration data to decrease the level of the correlated noise in the LISA observational frequency band.

Speaker: Guillaume BOILEAU (Artemis OCA UMR 7250)
• 14:40
Low frequency noise disturbances in LISA: results from LISA Pathfinder 20m

LISA Pathfinder (LPF) was a European Space Agency mission with the aim to demonstrate free-fall motion of test bodies with unprecedented level of precision. It was operated between December 3rd, 2015 and July 18th, 2017, delivering outstanding results that exceeded its original requirements and are fundamental in view of space-based gravitational wave detectors like LISA.

The experimental results obtained in the course of the mission, analyzed using partially original statistical techniques, are illustrated together with their consequences for LISA. In particular, a series of observations is discussed for which a definitive physical model is still lacking. These are the excess low frequency noise with respect to the modeled noise sources so far, and the occurrence of spurious force signals on the test bodies.

Possible explanations to these phenomena are discussed with the aim to reduce the number of available interpretations, and in order to lay the basis for a feasible on-ground experimental campaign in view of LISA.

Speaker: Eleonora Castelli (Università degli Studi di Trento - INFN)
• 15:00
LISA Instrumentation - interferometry and noise challenges 20m

The space based GW detector `Laser Interferometer Space Antenna' (LISA) will probe the low-frequency GW sources such as mergers between massive black holes and compact binaries among others. It will complement the existing ground based GW detectors probing the high frequency sources. LISA is an ESA mission with NASA partnership and a planned launch date in 2034. To achieve it's science goals the laser interferometry that will measure the distance variations between freely falling test-masses is required to achieve sensitivity of picometers in the given frequency range. The presentation covers an overview of the noises challenges in the interferometry chain and solutions to overcome them.

Speaker: Dr Sweta Shah (Max Planck Institute for Gravitational Physics, Albert Einstein Institute, Hannover, Germany)
• 15:20
Space-based Gravitational-wave Data Analysis Beyond Time Delay Interferometry 20m

The future space-based gravitational wave detector LISA will form a network of laser interferometers across a triangular constellation with 2.5 million-kilometer arms. Among other challenges, the success of the mission strongly depends on our ability to cancel laser frequency noise, whose power lies eight orders of magnitude above the gravitational signal. The standard technique to remove this noise is time-delay interferometry (TDI), a set of linear combinations of delayed phasemeter measurements tailored to cancel noise terms. Previous works have demonstrated the relationship between TDI and principal component analysis. We build on this idea to develop an alternative approach to TDI based on a model likelihood that directly depends on single-link measurements and accounts for their correlations. We obtain a comprehensive and compact framework that we call PCI for "principal component interferometry," and show that it provides a powerful description of the LISA data analysis problem.

Speaker: Dr Quentin Baghi (USRA/NASA GSFC)
• 15:40 16:00
Poster presentations
• 15:40
Determining the Earth’s gravity field using space-borne clocks 3m

The precise determination of the Earth’s gravity field is a central topic of geodesy, which is also essential for various geoscience applications, such as the understanding of mass redistribution, the monitoring of sea level rise, the realization of a global height system and so on. The successful application of satellite gravity missions like GRACE(-FO) and GOCE has advanced our knowledge of the Earth’s gravity field in terms of accuracy and spatial-temporal resolution. However, efforts are still required to further improve the performance of future satellite missions in order to meet the increasing demands of geoscience applications.
One effort is to develop and apply emerging quantum optics sensors, like optical clocks. In the past three decades, optical clocks and relevant frequency link techniques have experienced rapid development, which make them now promising to realize “relativistic geodesy” in practice, i.e., measuring the gravitational redshift between two distant clocks. This opens a new door to directly obtain gravity potential values by the ultra-precise comparison of clocks’ frequencies. In this context, we propose to apply an optical clock on-board of a satellite to measure the gravity potential (difference) values along the orbit through its frequency comparison with ground clocks or with a co-orbital clock. We synthesize the relevant clock observations and recover the gravity field models from them. This closed-loop simulation can rigorously map the clocks’ sensitivity to gravity field coefficients. With that, the potential benefit of clock measurements for determining the static and time-variable gravity field will be quantified, and the required clock performance to meet the geodetic needs will be elaborated.

Speaker: Prof. Jürgen Müller (Leibniz University Hannover)
• 15:43
Benefit of infrared LLR data for constraining a possible violation of the equivalence principle 3m

From 1969 on, Lunar Laser Ranging (LLR) data are collected by various observatories and analysed by different analysis groups. In the past years observations with bigger telescopes (APOLLO) and at infrared frequencies (OCA) are carried out, which resulted in a better spread of precise LLR data over the lunar orbit and the observed reflectors on the Moon. In Germany the software package LUNAR has been developed to study the Earth-Moon system and to determine several related model parameters. Research covered physical libration and orbit of the Moon, coordinates of observatories and retro-reflectors, Earth orientation parameters, lunar interior and, with special modifications, tests of Einstein’s theory of relativity. Including the new infrared data in the analysis, we show recent results and the high benefit for relativity parameters like a possible temporal variation of the gravitational constant and a selection of PPN (Parametrized Post-Newtonian) parameters. Special effort has been put in the investigation of the equivalence principle as one cornerstone of Einstein’s theory of General Relativity. Here, LLR measurements with high accuracy also give us the opportunity to precisely test the equivalence principle for dark matter assumed in the center of our galaxy. We estimated the amplitude of the sidereal range oscillation from LLR post-fit residuals. To get the best results based on the residuals, we analysed the characteristics of the residuals for the OCA, APOLLO and MLRS stations which delivered an overwhelming proportion of all LLR observations. In addition, a spectral analysis of the non-uniform LLR residuals has been performed. All LLR results confirm impressingly the validity of Einstein’s relativity theory.

Speakers: Liliane Biskupek (Institute of Geodesy, Leibniz University Hannover), Jürgen Müller (Institute of Geodesy, Leibniz University Hannover )
• 15:46
On-ground technology testing for space-based GW detectors: updates from a torsion pendulum equipped with an exact copy of the LISA Pathfinder sensor. 3m

Every space mission requires extensive testing campaigns to validate the crucial
technological aspects and ensure that the key science objectives are achieved.

In our laboratory, torsion pendulums have been successfully employed to design and test the
technology for the LISA Pathfinder mission, in particular regarding the performance
of the Gravitational Reference Sensor (GRS).

Building from this heritage, we are now undertaking the task of verifying experimentally some aspects of
the LISA technology package.

Torsion pendulums are indeed invaluable tools to measure small forces and can
reproduce on ground free-falling conditions which allow testing specific disturbances on a level which is
significant also for LISA.

We will present the noise performance of our torsion pendulum, which hosts the flight-model replica of the
LISA Pathfinder GRS and a fully representative capacitive sensor readout. We will aim at explaining the noise sources that
limit our sensitivity and propose some possible upgrades.

Moreover, we will give updates on the experimental campaign aimed at testing the UV-LED Charge Management prototype
currently foreseen for LISA.

Speaker: Mr Davide Dal Bosco (University of Trento and TIFPA)
• 15:49
The MIGA large scale Atom Interferometer 3m

We are building a large-scale gravity antenna, MIGA [1], demonstrator for low frequency Gravitational Waves (GW) detection based on atom interferometry. This new infrastructure will be embedded into the LSBB underground laboratory, ideally located away from major anthropogenic disturbances and benefitting from very low background noise. MIGA will provide precise measurements of the local gravity sensed by a network of three free-falling atom test masses distant up to 150 m. Each atom test mass of the network will be manipulated by cavity enhanced Bragg pulses to create an atom interferometer.
Fluctuation of the earth gravity field is expected to be a major source of noise for future infrasound GW detectors. In these experiments, mass density variations caused by local seismic or atmospheric perturbations determine spurious displacements of the free-falling test masses called Gravity Gradient Noise (GGN), that mimics GW effects. This noise source is expected to become dominant in the infrasound domain and must be tackled for the future realization of observatories exploring GWs at low frequency. Using a network of test masses, it becomes possible to exploit the GGN spatial correlation properties and provide a GW measurement with a strong GGN filtering [2].
The MIGA project is carried out by a consortium that gathers 17 expert French laboratories and companies in atomic physics, metrology, optics, geosciences and gravitational physics. This poster will present the main objectives of the project, the status of the construction of the instrument and the motivation for the applications of MIGA in GW physics.

References
[1] Benjamin Canuel et al., Exploring gravity with the MIGA large scale atom interferometer, Sci. Rep. 8 14064 (2018).
[2] Walid Chaibi et al., Low frequency gravitational wave detection with ground-based atom interferometer arrays, Phys. Rev. D 93, 021101 (2016).

Speakers: Dr Benjamin Canuel (LP2N-CNRS/IOGS/Université de Bordeaux), MIGA consortium
• 15:52
High frequency gravitational waves generation in laser plasma and vacuum interaction 3m

Gravitational waves have recently been detected on the LIGO-VIRGO interferometers [1]. The gravitational waves predicted by Einstein 100 years ago [2], have become a reality and a new astronomy is emerging. We will discuss the possibility of producing gravitational waves using high power laser beams, during laser-matter interaction, and with the laser light only.
The search for gravitational waves (GW) radiated by extraterrestrial sources is carried out by large gravitational interferometer detectors LIGO and VIRGO. However, these detectors address the low frequency spectral band between 10 Hz and 10 kHz. Recently, astrophysical sources of high frequency gravitational waves (HFGW: ν > 100 kHz) radiation were considered and this renew an interest for a GW Hertz experiment [3], which consists in generation and receiving the GW signal on Earth. One of the first considerations of the gravitational Hertz experiment in laboratory was done by Weber [4] in a low frequency domain. In the high frequency domain the possibilities of GW generation in laboratory were considered by Rudenko [5] and by Chapline [6].
In this work, we present analytical estimations and numerical simulations of generation of the HFGW in interaction of high power laser pulse, with a medium in three different situations. First, during the time of laser plasma interaction, a strong shock driven by the ablation pressure is generated in the bulk material. In this configuration a material is accelerated in the shock front and in the ablation zone. Because of a short laser pulse duration HFGW are generated in the GHz domain. Another configuration is a thin foil accelerated by a high ablation pressure produced by the laser heating and ablation. Finally, a HFGW could be produced with high power laser facilities dedicated to the inertial confinement fusion like the National Ignition Facility (NIF in USA), the Laser Mégajoule (LMJ in France), or the European project for the inertial fusion energy HiPER [7]. The laser driven implosion fusion can radiate HFGWs if the implosion of cryogenic deuterium-tritium (DT) micro-sphere would be asymmetric and produce a quadrupolar momentum. Then the fusion reactions produce in central DT core high velocity jets which radiate HFGW in 100 GHz domain during the plasma expansion. Calculations are performed to estimate the luminosity spectrum and energy of GWs emitted by sources that are technologically available now or may be available in near future [8,9].
Another possibility that has not yet been completely explored with high intensity lasers is the generation of gravitational waves with only electromagnetic fields. Indeed, for example, during the passage of an electromagnetic wave in a constant magnetic field a gravitational wave can be generated. This is the Gertseinshtein effect [10,11]. A generalization of this effect, during the laser pulses propagation must allow the generation of gravitational wave more efficiently.
References
[1] Abbott et al. Phys. Rev. Lett. 116, 061102 (2016).
[2] Einstein A., Preuss. Akad. Wiss. Berlin, Sitzber. p.154, (1916); Einstein A., Preuss. Akad. Wiss. Berlin, Sitzber. p.688, (1918)
[3] Bisnovatyi-Kogan G. S. and Rudenko V. N., Class. Quantum Grav., 21 3347 (2004)
[4] Weber J., Phys. Rev. 117 306, (1960)
[5] Rudenko V. B., Preprint gr-qc/0307105 (2003)
[6] Chapline J. F. et al., Phys. Rev. D 10 1064, (1974)
[7] Ribeyre X. et al. Plasmas Phys. and Control. Fusion, 51 015013 (2009)
[8] Ribeyre X. and Tikhonchuk V. T. in Proceedings of 12th, Marcel Grossmann Meeting on General Relativity, Paris, 2009, edited by T. Damour, R.T. Jantzen, R. Ruffini, (World Scientific, 2012), pp. 1640–1642
[9] Gelfer E. G. et al., Physics of Plasmas, 23, 093107 (2016); Kadlekova H., Eur. Phys. J. D 71, 89 (2017)
[10] Gertseinshtein M. E. JETP, 14 1 (1962)
[11] Kolosnitsyn N.I, Rudenko V.N. Phys. Scr. 90 (2015).

Speaker: Dr Xavier Ribeyre (Univ. Bordeaux-CNRS-CEA, CELIA UMR 5107)
• 15:55
Antigravity, a Force yet to be Recognized by Physics 3m

The general belief is that the gravitational force is always attractive and no repulsive force could result. This is contrary to properties of electric and magnetic forces, which can cause in both attraction and repulsion. The investigation presented here on the movement of liquid water droplets in still air, prompts us to believe a hidden force, a force against the gravitational pull, hitherto unknown to the world of science. Anti-gravity is proportionate to the temperature, which is an indication of the thermal energy of the matter. It is widely accepted that gravity is proportionate to the mass of the matter. Any gravitational interaction could be considered the resultant effect of the gravitational and antigravitational forces inherent in the two bodies under consideration. The gravitational force is considered a weak force in classical physics. Being what we can observe in nature is the resultant of these two forces, the gravitational force manifests itself as a weak force. It is felt, as shown by the reasoning adduced herein, that the upward movement of the water droplets cannot be explained by the conventional principles of physics known to us. Hence the need of the antigravity hypothesis.

• 16:00 16:30
Coffee Break
• 16:30 17:40
Geodesy and Ranging
• 16:40
General Relativistic geodesy - a new shape of the earth 20m

Owing to new higly sensitive divices like clocks, freely falling particles, spinning tops, and laser and atom interferometers on ground and in space the relativistic gravitational field of the Earth can now be measured with unprecedented accuracy. This requires a relativistic formulation of geodesy. Here a fully general relativistic scheme for geodesy is presented. Starting from stationarity two geoids can be defined for the Earth, one related to the norm of the underlying Killing vector, the other related to its twist. The first one can be measured with clockson ground and in space, falling bodies, or atom interferometry, the other can be measured with spinning tops or by measuring a Sagnac effect with laser or atom interferometry. For using clocks in space a special approach is needed taking into account the nonstationarity of the moving clocks. Finally, based on analyses by Hansen, Simon, and Beig a scheme is presented for measuring the full gravitational field of the Earth using laser interferometry employed by GRACE Follow On.

Speaker: Prof. Claus Laemmerzahl (University of Bremen)
• 17:00
Measuring Gravity with Very Long Baseline Atom Interferometry 20m

Matter-wave interferometers with ultracold atoms are highly sensitive to inertial quantities. In the Hannover Very Long Baseline Atom Interferometry (VLBAI) facility, we aim to exploit the linear scaling of this sensitivity with the free fall time of the atoms in a 10 m baseline[1]. This will enable precision measurements of gravitational acceleration, as well as tests of the weak equivalence principle and gravitational redshift [2,3].

In this contribution, I will show details on the construction of the VLBAI facility in the newly founded Hannover Institute of Technology (HITec). The combination of high-flux sources of Bose-Einstein condensates, a high-performance magnetic shield around the 10 m baseline and an in-vacuum vibration isolation platform are anticipated to provide shot-noise limited short-term instabilities below $10^{-9} \text{m/s}^2$ in 1 s, competing with state-of-the-art superconducting gravimeters, and tests of the universality of free fall at the $10^{-13}$ level [4].

This work is funded by the DFG as a major research equipment (VLBAI facility), via the CRCs 1128 “geo Q” and 1227 “DQ-mat”, under Germany’s Excellence Strategy (EXC 2123) “QuantumFrontiers”, and by the Federal Ministry of Education and Research (BMBF) through the funding program Photonics Research Germany (contract number 13N14875).

[1] J. Hartwig et al., New J. Phys. 17 (2015)
[2] D. Schlippert et al., arXiv:1909.08524 (2019)
[3] S. Loriani et al., Sci. Adv. 5 (2019)
[4] É. Wodey et al., arXiv:1911.12320 (2019)

Speaker: Mrs Dorothee Tell (Leibniz University Hannover, Institute of Quantum Optics, Germany)
• 17:20
Testing alternative theories of gravity with INPOP planetary ephemerides 20m

We will present an overview including recent results obtained with the INPOP planetary ephemerides. Classic PPN tests as well as graviton constraints obtained with planetary orbits will be presented as well as tests of the equivalence tests deduced from the construction of lunar ephemeris.

Speaker: Agnes Fienga (Geoazur, Observatoire de la Côte d'Azur)
• Wednesday, 8 April
• 09:00 10:30
Gravity: Fundamental Tests
• 09:00
Testing fundamentally semiclassical gravity 30m

Invited talk

Speaker: Andre Grossardt (University of Trieste)
• 09:30
Clock developments for fundamental physics tests and space 30m
Speaker: Patrick Gill (National Physical Laboratory UK)
• 10:00
Space clocks and fundamental tests: The ACES experiment 30m

Atomic Clock Ensemble in Space (ACES) is developing high performance clocks and links to test Einstein’s theory of general relativity. From the International Space Station, the ACES payload will distribute a clock signal with fractional frequency instability and inaccuracy of 1E-16 establishing a global network to compare clocks in space and on the ground. ACES will provide an accurate measurement of the Einstein’s gravitational redshift, it will search for time variations of fundamental constant and perform Standard Model Extension tests.
The two on-board clocks, PHARAO and SHM, have been tested and integrated on the ACES payload. The microwave (MWL) and optical (ELT) link are currently under test. Once installed on ACES, performance and environmental tests on the complete system will follow to release the final acceptance for flight of the payload.
Recent test results will be presented together with the major milestones that will lead us to the ACES launch.

Speaker: Dr Cacciapuoti Luigi (European Space Agency)
• 10:30 11:00
Coffee Break
• 11:00 12:30
Equivalence Principle
• 11:30
Testing Gravity with Atoms 30m

Invited talk

Speaker: Guglielmo Tino (University of Florence)
• 12:00
Gravity & Antimatter 30m

Invited talk

Speaker: Patrice Perez (CEA - France)
• 12:30 14:30
Lunch 2h
• 14:30 15:10
Equivalence Principle
• 14:30
Measuring gravitation with antihydrogen: the ALPHA-g experiment 20m

ALPHA (Antihydrogen Laser PHysics Apparatus) is a leading antihydrogen experiment located at CERN, the European Organization for Nuclear Research in Geneva, Switzerland. The ALPHA-g project is a new initiative by the ALPHA collaboration to measure the gravitational interaction of antimatter. ALPHA-g apparatus features a 3 meter tall cryogenic, superconducting magnetic trap. Antihydrogen atoms will be created, captured, cooled and then dropped, in order to study if antimatter behaves the same way as matter does in the field of the Earth gravity.

Speaker: Pierre Grandemange (CERN)
• 14:50
Testing general relativity in the solar system: present and future perspectives 20m

The increasing precision of spacecraft radiometric tracking data experienced in the last decade, combined with the huge amount of data collected from space missions and the long time span of the available datasets, has enabled a refined analysis of the Solar System dynamics. High precision tests of General Relativity can be performed through the measurement of the post-Newtonian parameters, including the Nordtvedt parameter $\eta$, and the Compton wavelength of the graviton. In this work we investigate the relative contributions to these tests provided by the most relevant past, present and future interplanetary missions, with the goal of assessing the accuracies that can be realistically reached in the next 10–15 years.

A semi-analytical model, validated by means of a comparison with well-established numerical models, has been developed to compute the signatures generated by the parameters of interest in the measurements and to assess the precision of their retrieval. We also revisit some of the hypotheses and constrained analysis schemes that have been proposed until now to overcome geometric weaknesses and model degeneracies, proving that many of the previously adopted strategies introduce model inconsistencies.

We apply our semi-analytical model to perform a covariance analysis on three groups of interplanetary missions:
(1) those for which data are available now (e.g. Cassini, MESSENGER, MRO, Juno),
(2) those expected in the next years (BepiColombo) and
(3) those still to be launched or proposed, such as JUICE and VERITAS (the latter, chosen as a representative of a state-of-the-art Venus orbiter).

Finally, we describe the preliminary results of a more rigorous and general procedure: a global, multi-mission data analysis.

Speaker: Dr Fabrizio De Marchi (University of Rome "La Sapienza")
• 15:10 15:50
Gravity: Fundamental Tests
• 15:10
Probing Quadratic Gravity with Binary Inspirals 20m

We study gravitational waves generated by binary systems within an extension of General Relativity which is described by the addition of quadratic in curvature tensor terms to the Einstein-Hilbert action. Treating quadratic gravity as an effective theory valid in the low energy/curvature regime, we argue that reliable calculations can be performed in the early inspiral phase, and furthermore, no flux of additional massive waves can be detected. We then compute the -1PN and -2PN leading corrections to the post-Newtonian (PN) expansion of the standard waveform. By confronting these theoretical calculations with available experimental data, we constrain both unknown parameters of quadratic gravity.

Speaker: Zachary Picker (University of Sydney)
• 15:30
Constraint on the Yukawa suppression from the planetary ephemeris INPOP19a 20m

We use the latest solution of the ephemeris INPOP (19a) in order to improve our previous constraint on the existence of a Yukawa suppression to the Newtonian potential [1], generically associated to the graviton's mass. Unlike the solution INPOP17a, several residuals are found to degrade significantly at roughly the same amplitudes of the Compton wavelength associated to the mass of the Yukawa field. As a consequence, we introduce a novel statistical method in order to derive the constraint with INPOP19a. After checking that it leads to a constaint consistent with our previous result when applied on INPOP17b, we apply the method to the new solution INPOP19a. We show that the residuals of Mars orbiters, Cassini, Messenger, and Juno, degrade significantly when $\lambda_g >2.61 \times 10^{13}$ km with a 99,7% confidence level---corresponding to a graviton mass bigger than $4.75 \times 10^{-23}$ eV$/c^2$. The solar system constraint on the Compton wavelength becomes better than the one obtained so far by the LIGO-Virgo collaboration in the radiative regime [2].

References :

[1] L. Bernus, O. Minazzoli, A. Fienga, M. Gastineau,
J. Laskar, and P. Deram, “Constraining the mass of the
graviton with the planetary ephemeris inpop,” Phys. Rev.
Lett. 123, 161103 (2019).

[2] The LIGO Scientific Collaboration and the Virgo Col-
laboration, “Tests of General Relativity with the Bi-
nary Black Hole Signals from the LIGO-Virgo Cata-
log GWTC-1,” Phys. Rev. D. 100, 104036 (2019)

Speaker: Léo Bernus (IMCCE)
• 15:50 16:20
Coffee Break
• 16:20 18:00
Gravity: Fundamental Tests
• 16:20
The Archimedes Experiment 20m

Saverio Avino, Enrico Calloni, Sergio Caprara, Martina De Laurentis,
Rosario De Rosa, Tristano Di Girolamo, Luciano Errico, Gianluca Gagliardi,
Marco Grilli, Valentina Mangano, Maria Antonietta Marsella, Luca Naticchioni,
Giovanni Piero Pepe, Maurizio Perciballi, Gabriel Pillant, Paola Puppo, Piero Rapagnani,
Fulvio Ricci, Luigi Rosa, Carlo Rovelli, Paolo Ruggi, Naurang L. Saini, Daniela
Stornaiuolo, Francesco Tafuri and Arturo Tagliacozzo

The Archimedes project aims to measure the interaction between the electromagnetic vacuum fluctuations and the gravitational field. The experiment can shed light on some question marks still open in cosmology like the dark energy nature.
A very sensitive balance has been constructed to weight the vacuum e.m. field energy induced in a multi-Casimir cavity system by temperature modulation techniques. The system is a high TC superconductor like the YBCo material having multilayered structure useful for this purpose.
This experiment is being installed in the SARGRAV laboratory placed Sardinia a very low seismic noise site, suitable for null force experiments.
In this talk the status of the experiment will be reported.

Speaker: Paola Puppo (ROMA1)
• 16:40
Present status of the LAG experiment 20m

LAG (Liquid Actuated Gravity) is an experiment funded by the INFN (National Institute of Nuclear Physics) for the development and testing of a new actuation technique for gravity experiments based on a liquid field mass. The basic idea of the experiment is to modulate the gravitational force acting on a test mass by controlling the level of a liquid in a suitable container, thereby producing a periodically varying gravitational force without moving parts (apart from the liquid level) close to the test mass. The scientific goal is to improve upon present limits that test the gravitational inverse-square law in the cm to mm distance region. The experiment is now in the R&D phase, and a prototype is being assembled for testing with a torsion pendulum facility in Napoli. First data with the prototype apparatus are expected this year. We will report on present status, next steps and scientific perspectives for the LAG experiment.

Speaker: Martina De Laurentis (Dipartimento di Fisica "Ettore Pancini", Università di Napoli “Federico II” and INFN, Sezione di Napoli, Napoli, Italy)
• 17:00
Coherent Gravitational Waveforms and Memory from Cosmic String Loops 20m

We construct, for the first time, the time-domain gravitational wave strain waveform from the collapse of a strongly gravitating Abelian Higgs cosmic string loop in full general relativity. We show that the strain exhibits a large memory effect during merger, ending with a burst and the characteristic ringdown as a black hole is formed. Furthermore, we investigate the waveform and energy emitted as a function of string width, loop radius and string tension $G\mu$. We find that the mass normalized gravitational wave energy displays a strong dependence on the inverse of the string tension $E_{\mathrm{GW}}/M_0\propto 1/G\mu$, with $E_{\mathrm{GW}}/M_0 \sim {\cal O}(1)\%$ at the percent level, for the regime where $G\mu\geq 10^{-3}$. Conversely, we show that the efficiency is only weakly dependent on the initial string width and initial loop radii. Using these results, we argue that gravitational wave production is dominated by kinematical instead of geometrical considerations.

Speaker: Thomas Helfer (Johns Hopkins University )
• 17:20
Search for nonlinear memory from subsolar mass compact binary mergers 20m

We present the first search for the nonlinear memory from subsolar mass binary black hole (BBH) mergers during the second observing run of the LIGO and Virgo detectors. The oscillatory chirp signal from the inspiral and merger of low mass BBHs ($M _\mathrm{Total} \leq 0.4 M_\odot$) are at very high frequencies and fall outside the sensitivity band of the current ground-based detectors. However, the non-oscillatory memory signal during the merger saturates towards the lower frequencies and can be detected for those hypothetical BBHs. We show that the morphology of the memory signal depends minimally upon the binary parameters, only the overall amplitude of the signal is changed, hence the result can be interpolated for extremely low mass BBH mergers. We did not find any signal which can be interpreted as a memory signal and thus for the first time we put upper limits on the rate of BBH mergers with $M _\mathrm{Total} \leq 0.4 M_\odot$.

Speaker: Michael Ebersold (Institute of Physics - University of Zurich)
• Thursday, 9 April
• 09:00 10:30
Geodesy and Ranging
• 09:00
Gravity in the solar system 30m

Invited talk

Speaker: Luciano Iess (Universita' La Sapienza)
• 09:30
Relativistic Geodesy Using Optical Clocks 30m

Invited Talk

Speaker: Helen Margolis (National Physical Laboratory Teddington UK)
• 10:00
The first interspacecraft laser ranging interfrometer on GRACE Follow-On and conclusions for future gravity missions 30m
Speaker: Gerhard Heinzel (AEI Max-Planck Institut)
• 10:30 11:00
Coffee Break
• 11:00 16:55
Experimental Challenges in Gravitational Wave Detection
• 11:00
Pulsar and Relativistic Gravity 30m
Speaker: Venkatraman Krishnan (Max Plank Institute Bonn, Germany)
• 11:30
Large-scale atom interferometers toward observation of Gravitational Waves and more 30m
Speaker: Philippe Bouyer (Institut d'Optique d'Aquitaine - France)
• 12:00
Parametric Instability Observation in Advanced Virgo 15m

We present the first observation of a parametric instability event in Advanced Virgo. The event occurred on January the 2020 during the locking acquisition procedure and involves for the first time, for a long-arm interferometer, a very high frequency mechanical mode. We will describe this event and the mean adopted for its dampening.

Speaker: Paola Puppo (ROMA1)
• 12:15
Targeted search for the kinematic dipole of the gravitational-wave background 15m

One of the most important and exciting observational challenges in gravitational-wave (GW) astronomy is the detection of the stochastic GW background (SGWB): the persistent, pseudo-random GW strain associated with the superposition of many astrophysical and cosmological sources throughout cosmic history. The LIGO/Virgo Collaboration (LVC) has performed both isotropic and directional searches for the SGWB, and has already succeeded in placing the most stringent upper limits to date on the SGWB intensity, and its distribution on the sky.

Here we describe a novel SGWB search method, which targets the kinematic dipole (KD) of the SGWB. This dipole is generated by the Earth's motion with respect to the cosmic rest frame, due to GW sources being blueshifted in the direction the Earth is moving toward, and vice versa. The direction of the KD is already known with excellent precision thanks to Planck and other CMB missions; we leverage this knowledge to optimise the sensitivity of the search. We also comment on the physics encoded in the KD magnitude, and how, once detected, this could be a powerful new tool to characterise the source(s) of the SGWB.

Speaker: Alexander Jenkins (King's College London)
• 12:30
Lunch 1h 30m
• 14:00
In orbit calibration of LISA Pathfinder dynamics: results and implications for LISA 15m

In 2015 LISA Pathfinder (LPF), the LISA technological demonstrator, was launched from Kourou, French Guyana. The main goal of the demonstrator was to measure the differential acceleration noise between two freely falling test-masses, $\Delta g(t)$, such that $S^{1/2}_{\Delta g} < 30 ~\textrm{fm}/\textrm{s}^2/\sqrt{\textrm{Hz}}$ at 1 $\textrm{mHz}$. The in-orbit results showed an unprecedented level of differential acceleration noise, much better than the mission requirement, giving a new impulse to the LISA mission, the gravitational wave observer in the mHz band from space. A key step toward reaching this result was the correct calibration of the dynamics of LPF. In this talk, I will present the calibration procedures adopted, the physical parameters of the dynamical model, and the analysis of the performed experiments. The results demonstrate that the dynamics of the system was accurately modeled on-ground and the dynamical parameters were stationary throughout the mission, with impacts on the LISA mission that is now been developing. The possibility to calibrate the system dynamics for future space-based gravitational wave observatories is also briefly discussed.

Speaker: Dr Daniele Vetrugno (University of Trento)
• 14:15
Limitations on LISA sensitivity to gravitational waves from local spacecraft gravitational field 15m

The Laser Interferometer Space Antenna mission LISA measures the strain in 2.5 million km distant free falling test masses couples, for detecting gravitational waves from galactic and extra galactic sources in the low frequency regime between 20 micro-Hz to 1 Hz. The instrument sensitivity is such that LISA would be able also to detect the effect of the gravitational field on its test masses originating from the mass distribution of their housing spacecrafts. We discuss the different levels of coupling, the foreseen design requirements, and the resultant contribution to the current LISA performance budget.

Speaker: Dr Valerio Ferroni (University of Trento, TIFPA)
• 14:30
Removing Schumann noise from stochastic gravitational wave data 15m

Unlike for transient signals, the stochastic searches at LIGO-Virgo have the trouble of the signal not being greater than the intrinsic noise of the detector, and one should be particularly careful when trying to extract the gravitational wave signal from the data. Correlated noise coming from the Earth's electromagnetic field, in the form of Schumann resonances, could be comparable to the sensitivity of the LIGO-Virgo gravitational wave detectors in the near future. If this is the case, the detection of a stochastic background will not be possible and it will be completely limited by the magnetic noise. In our most recent work, we model the presence of the Schumann noise and remove it from the detector data.

Speaker: Katarina Martinovic (King's College London)
• 14:45
Testing the speed of gravity and deviations from GR with LISA 15m

We explore prospects for measuring the speed of gravity using future gravitational-wave surveys in the multi-messenger approach, and probe implications for cosmological models.

Speaker: Dr Maria Haney (University of Zurich)
• 15:00
Generation of gravitational waves using high-power lasers 15m

Gravitationnal waves have been predicted from Einstein’s equations since he wrote his theory on General Relativity [1]. A century later, the LIGO [2] and VIRGO interferometers were at last able to pick up a gravitationnal wave from the merging of extremely massive astrophysical objects. The existence of gravitationnal waves now being proved, there is a need to study these waves to better understand how gravitation works, and fondamentally how does the geometry of space-time exactly affects physical phenomenons.
However, observations still rely on the occurrence of a rare and intense astrophysical phenomenon, as if, as a comparison, the only reliable source of observation for high energy photons were gamma-ray bursts. An interesting possibility would be to generate and detect gravitationnal waves in laboratory, which would allow for a more controlled environment for the observation of gravitationnal waves. Unfortunately, deplacements of matter generated in laboratory do not seem to have a big enough yield to allow any detection [3].
Continuing on the path led in 1962 by Gertsenshtein [4] and more recently in a study by Kolosnitsyn and Rudenko [5], we will here evaluate if the generation of gravitationnal waves by light only is a good alternative to the deplacement of mass. We will then discuss on the possibilities of an experiment making use of the peculiar aspects of light only gravitational waves generation and bring more details on what could be a new interesting way to look for gravitationnal waves in the laboratory, but also in the universe. High-power lasers present themselves as an interesting answer for the needs of a source for gravitational wave generation, as they can provide coherent ultra high intensity light beams.
[1] A. Einstein. Sitz. Preuss. Akad. Wiss. Berlin, (1918) [4] M. E. Gertsenshtein. Soviet Phys. JETP, (1962) [2] B.P. Abbott et al. Phys. Rev. X 6, (2016) [5] N. I. Kolosnitsyn, V. N. Rudenko. Phys. Scr., 90, (2015) [3] X. Ribeyre, V. T. Tikhonchuk. WSPC, (2010); E. G. Gelfer et al., Physics of Plasmas, 23, (2016)

Speaker: Lageyre (CNRS-CEA)