The second EPS (European Physical Society) Conference on Gravitation will be held online from July 5th to July 7th , 2021. The conference was originally scheduled from April 7th to April 9th, 2020 at King's College London (London, UK) and postponed because of the COVID-19 pandemia. This event follows up on a previous successful conference in Rome https://agenda.infn.it/event/15395/, with the aim to discuss experimental aspects of Gravity, including General Relativity tests, measurements of the G constant, Geodesy, and Gravitational Waves. The conference is organised in days, each one focused around key topics introduced by invited speakers and asynchronous contributed talks followed by round tables. The scientific program will be finalised in the upcoming days.
There is no registration fee.
Recorded videos of the conference days are available for downloading on this web page in mp4 format , below the conference poster.
The topics for Second EPS Conference on Gravitation: measuring gravity, are:
• Experimental Challenges in Gravitational Wave Detection
• Gravity: fundamental tests and Equivalence Principle
• Geodesy and Ranging
Participation opportunities for this conference include:
• Plenary highlight talks
• Recorded talks posted in advance (asynchronous talks)
• Round tables
Participants interested in proposing contributions should submit abstracts after the registration on the Indico site of the conference.
Invited talk
Invited talk
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.
In the context of the future space mission, the Laser Interferometer Space Antenna (LISA), the stochastic background of gravitational waves (SGWB) will be very rich. LISA will simultaneously observe background signals of stochastic gravitational waves of different origins; orbitally modulated waveforms from galactic white dwarf binaries, a background produced by binaries of black holes and neutron stars, and possibly a cosmologically produced SGWB.
We present two studies to separate the different components of the SGWB, a Fisher Information study and an Adaptive Markov Chain Monte Carlo method. We simulate the galactic foreground with the Lamberts \textit{et al} distributions and generate the modulated waveform, due to the LISA orbital motion. The astrophysical background is predicted by the LIGO/Virgo observations. In this large context, we study the limit of the potential detectability of a cosmological source. We explore strategies for the study in the spectral domain with the LISA channels $ A $, $ E $ and $T $, and explore ways to best estimate the LISA noise. We also analyze LISA Pathfinder data in order estimate the effects of correlated noise on the LISA SGWB search. Finally, we are able to separate a cosmological source energy density of about $ \Omega_{GW,Cosmo} \approx 8 \times 10^{-13}$ in the LISA band.
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.
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.
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 $M _\mathrm{Total} \leq 0.4 M_\odot$.
The passage of gravitational waves (GWs) through a binary perturbs the trajectories of the two bodies, potentially causing observable changes to their orbital parameters. In the presence of a stochastic GW background (SGWB) these changes accumulate over time, causing the binary orbit to execute a random walk through parameter space. In this talk I will present a powerful new formalism for calculating the full statistical evolution of a generic binary system in the presence of a SGWB, capturing all six of the binary's orbital parameters. I will show how this formalism can be applied to laser ranging and pulsar timing observations to set novel upper limits on the SGWB spectrum in a frequency band which is inaccessible to all other GW experiments. As an example application of these searches, I examine GWs from cosmological first-order phase transitions (FOPTs), and show that binary resonance can constrain regions of the FOPT parameter space which no other experiment can access.
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.
We have analysed the time evolution of the acceleration noise in the LISA Pathfinder mission throughout the course of the entire science operations, from March 2016 to July 2017.
The noise across the LISA bandwidth turned out to be remarkably stable over the course of the mission, with a monotonic and well-understood initial decrease over time associated to the the declining residual gas pressure around the TM, while venting the experiment to space.
However, we observed a transient period of excess noise just below 100 uHz at the beginning of the mission, and a final end-of-mission two-month noisier phase, following a rapid system cooldown and the subsequent mechanical stress with long relaxation time.
We performed a Bayesian estimation of the contribution of all potential coherent noise sources for which we have some independent measurements. When adding the remaining modelled noise sources, the noise budget still does not account for the total noise observed during the core minimal-noise phase of the mission.
We present these results and discuss the most likely sources of the observed excess, based on the set of additional experiments and measurements performed during the mission. We also discuss the measures that need to be taken to maintain the LISA performance at the level demonstrated by LISA Pathfinder.
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.
We present results on the search for the coalescence of compact binary mergers using convolutional neural networks and the LIGO/Virgo data. Two-dimensional images in time and frequency are used as input, and three sets of neural networks are trained separately for low mass, high mass and asymmetric mass compact binary coalescence events. We explored neural networks trained with input information from one, two and three interferometeres, indicating that the use of information from more than one interferometers leads to an improved performance. We also explore the possibility of combining the information from the different CNNs to achieve a better discrimination. Time-shifted analysis is used to estimate the background distribution of our statistic and assign a FAR to each one of our triggers. Lastly, a scan over a large sthrech of real data is performed to understand the performance of our method and to compare it with the performance from canonical pipelines.
As part of the upgrade program, Virgo has just installed a new baffle equipped with photosensors that surrounds the end-mirror of the input mode-cleaner. This culminates more than two years of work at IFAE-Barcelona for the design and construction of a novel and innovative device to control and monitor stray light inside the experiment, a persistent source of noise in interferometers. It will serve as a demonstrator of the technology for its future implementation in the main arms of the interferometer, surrounding the test masses. The new baffle will provide valuable data for understanding the cavity and calibrating simulations that describe the propagation of light within the interferometer. The instrumented baffle is now entering a long period of commissioning and integration into Virgo's regular operations, in time to become an integral part of the new O4 observation run, currently scheduled for summer 2022. In this talk we describe the technology and we present the first results of its performance within the experiment.
The Advanced LIGO and Advanced Virgo detectors are now observing large numbers of gravitational-wave signals from compact binary coalescences, with 50 entries in the latest transient catalogue GWTC-2. With this rapidly growing event rate, our chances become better to detect rare astrophysical effects on these novel cosmic messengers. One such rare effect with a long and productive history in electromagnetic astronomy and great potential for the future of GW astrophysics is gravitational lensing. This presentation covers the first LIGO-Virgo collaboration search for signatures of gravitational lensing in data from O3a, the first half of the third advanced detector observing run. We study: 1) the expected rate of lensing at current detector sensitivity and the implications of a non-observation of strong lensing or a stochastic gravitational-wave background on the merger-rate density at high redshift; 2) how the interpretation of individual high-mass events would change if they were found to be lensed; 3) the possibility of multiple images due to strong lensing by galaxies or galaxy clusters; and 4) possible wave-optics effects due to point-mass microlenses. Several pairs of signals in the multiple-image analysis show similar parameters and, in this sense, are nominally consistent with the strong lensing hypothesis. However, taking into account population priors, selection effects, and the prior odds against lensing, these events do not provide sufficient evidence for lensing. Overall, we find no compelling evidence for lensing in the observed gravitational-wave signals from any of these analyses.
Gravitational waves excite quadrupolar vibrations of elastic bodies. Monitoring these vibrations was one of the first concepts proposed for the detection of gravitational waves by Joseph Weber. At laboratory scale, these experiments became known as resonant-bar detectors, which form an important part of the history of GW detection. Due to the dimensions of these bars, the targeted signal frequencies were in the kHz range. It was also Weber who suggested to monitor vibrations of Earth and Moon to search for gravitational waves in the mHz band. His Lunar Surface Gravimeter was deployed on the Moon in 1972 by the Apollo 17 crew. A design error made it impossible to carry out the intended search for GWs, but the idea remains intriguing. We have proposed a new concept, the Lunar Gravitational-Wave Antenna (LGWA), based on Weber’s idea. LGWA would have a rich GW and multi-messenger science case with galactic binaries and massive black-hole binaries. It would also serve as a high-precision geophysical station shedding light on the interior structure of the Moon, the mechanisms of moonquakes, and the Moon's formation history. The key component is a next-generation, high-sensitivity seismometer to be deployed on the Moon. For its most sensitive realization, LGWA would have to be deployed in a permanent shadow near the south or north pole of the Moon to benefit from the natural cryogenic environment. This would improve the sensitivity of the seismometer and also provide a lower-noise environment due to the absence of thermally induced seismic events that were observed by the Apollo seismometers. Powering of the seismic stations and data transfer pose additional challenges for such a deployment.
LISA Pathfinder (LPF) has been a successful ESA mission, operating between December 2015 and July 2017. The mission exceeded both its noise requirements and the more stringent requirements for LISA, demonstrating the feasibility of low-noise free-fall in the extended LISA frequency band between 20 microHz and 100 mHz.
Even though below the noise requirements, an excess noise with respect to the predicted one was detected at low frequencies, up to 1 mHz. We propose a method to estimate the contribution to acceleration of physical effects, related to telemetries of onboard sensors. Some contributions may be correlated with measured physical quantities, with a coupling coefficient that is not directly measured. These effects could cross-correlate with one another, and the measured time series could be affected by non-correlating noises.
The purpose of the method presented in this contribution is twofold. The main purpose is to estimate an upper limit to the contribution of physical effects to the measured noise, and the residual after subtraction. Secondly, we give an estimate of the coupling coefficients.
In this talk I will present results on constraining cosmological parameters and theories of gravity beyond General Relativity (GR) using gravitational waves (GW). Specifically, we use the GW events GW170817 and GW190521, together with their proposed electromagnetic counterparts, and consider models with a time-varying Planck mass, large extra-dimensions, and a phenomenological parametrization covering several beyond-GR theories. In all three cases, this introduces a friction term that effectively modifies the GW luminosity distance. We set constraints on Lambda-CDM and GR deviation parameters using two sets of priors on the Hubble constant and matter energy density. With priors set to the measured Planck's values, the inclusion of GW190521 improves the two GR deviation parameters constraints by a factor $\sim 10$. We report a number of space-time dimensions compatible with $4$ with an precision of $2.5\%$ (at 95\% CL) and an upper limit to the variation of Newton's constant at the epoch of GW170817 of $<20\%$. With wide priors we find that the constraints on GR deviation parameters are a factor $2-6$ worse than the ones obtained using the restricted priors.
Gravitational-wave observations of binary black holes allow new tests of general relativity to be performed on strong, dynamical gravitational fields. These tests require accurate waveform models of the gravitational-wave signal, otherwise waveform errors can erroneously suggest evidence for new physics. Existing waveforms are generally thought to be accurate enough for current observations, and each of the events observed to date appears to be individually consistent with general relativity. In the near future, with larger gravitational-wave catalogs, it will be possible to perform more stringent tests of gravity by analyzing large numbers of events together. However, there is a danger that waveform errors can accumulate among events: even if the waveform model is accurate enough for each individual event, it can still yield erroneous evidence for new physics when applied to a large catalog. We presents a simple linearised analysis, in the style of a Fisher matrix calculation, that reveals the conditions under which the apparent evidence for new physics due to waveform errors grows as the catalog size increases. We estimate that, in the worst-case scenario, evidence for a deviation from general relativity might appear in some tests using a catalog containing as few as 10-30 events above a signal-to-noise ratio of 20. This is close to the size of current catalogs and highlights the need for caution when performing these sorts of experiments.
Future ground-based gravitational-wave (GW) observatories are planned for the next decade in Europe (Einstein Telescope) and the United States (Cosmic Explorer). Additionally, possible upgrades of the existing LIGO observatories (Voyager) as well as a southern hemisphere detector (NEMO) are under discussion. In this talk, I’ll summarize a series of reports by the Gravitational Wave International Committee (GWIC) ‘3G’ Subcommittee on next generation GW facilities including a summary of the major science themes, needed detector R&D and computing challenges. I’ll also highlight some key recommendations to the GW community addressing some of the opportunities and challenges that come with building the next generation of billion euro/dollar scale GW observatories.
Fundamental Tests and Equivalence Principle
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.
Invited talk
Fundamental Tests and Equivalence Principle
The ability to control the quantum degrees of freedom of atoms using laser light opened the way to precision measurements of fundamental physical quantities. I will describe experiments for precision tests of gravitational physics using new quantum devices based on ultracold atoms, namely, atom interferometers and optical clocks. I will report on the measurement of the gravitational constant G with a Rb Raman interferometer, on experiments based on Bloch oscillations of Sr atoms confined in an optical lattice for gravity measurements at small spatial scales, and on new tests of the Einstein equivalence principle. I will also discuss prospects to use atoms as new detectors for gravitational waves and for experiments in space
The MICROSCOPE satellite was launched in April 2016 and ended its operations in October 2018. Aiming at testing the Equivalence Principle (EP) with an accuracy better than ever tested, the satellite has provided usefull scientific data during more than two years. The EP is the funding hypothesis of the General Relativity (GR) established by Einstein in 1917. It states the equivalence between gravitational and inertial mass: commonly called the universality of free-fall. The science motivation relies mainly in the observation of an eventual violation that could give the first clue of a new interaction, bridging GR to Quantum Physics.
Onera was responsible for the instrument developpement, production and test. In addition, it is also responsible for the science and the mission science center which deals with the science operations and data process. In December 2017, the first results, based on only 7$\%$ of the available data, were published in PRL and improved the best laboratory results by one order of magnitude.
The de-orbitation of MICROSCOPE has started, thanks to two deployed wings. The final data process is almost complete in conjonction to the assessment of systematic errors. A particular emphasis will be placed on the handling of glitches. The glitches are mainly produced by the satellite MLI cracking when it is more or less enlightened by the Sun or the Earth. Their temporal distribution could be in competition to an eventual violation signal.
With the preparation of the final result paper, a mission called MICROSCOPE 2 is beeing studied in order to improve by an additional factor 100 the previous mission. By taking advantage of of the MICROSCOPE experiment return, the instrument and satellite design will be improved. Three concentric test-masses are envisaged with optical sensing as the main deep change.
Antimatter as a system to test fundamental laws has the advantage of addressing both the CPT invariance of Particle Physics and the Weak Equivalence Principle of General Relativity. I will discuss gravitational tests currently planned for systems with antimatter, like antihydrogen, positronium and monism.
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.
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 mm to cm distance region. The experiment is now in the R&D phase; a prototype has been assembled for testing with a torsion pendulum facility in Napoli and is now under commissioning. 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
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.
The measurement of the Casimir Effect at a large distance, although challenging, is very interesting for the possible physical implications that stream from it. A successful measurement would allow to rule out or confirm Chameleon models as an explanation for dark energy; to put the strongest constraints on hypothetical long-range forces at the considered distances; to solve definitely the controversial problem of the thermal Casimir effect and its deep and fundamental implications on the difference between thermal and virtual photons. We propose to use a torsion pendulum to measure the force between macroscopic, centimeter size, flat metallic plates at a distance of about 10 microns. Experimental setup and discussion on how to cope with crucial aspects like absolute distance measurement and plates parallelism are discussed. We also show how modulation at a proper frequency and amplitude of the plate separation can help in disentangling the contribution of the different forces acting at such short distances.
In recent decades, a growing international group of theorists, experimentalists, and observational astronomers have been working on searches for tiny hypothetical deviations from perfect local Lorentz symmetry in nature. One key motivation for this work is that the discovery of a violation of this principle may uncover aspects of a fundamental unified theory of physics. Tests and analysis searching for Lorentz violation have been performed across many areas in both ground-based experiments, space-based tests and astrophysical observations. Many constraints already exist on many types of local Lorentz violation for different kinds of matter and fields. Despite the null results to date, many areas remain unexplored. We present an overview of the theory and phenomenology of precision tests of local Lorentz symmetry in gravity. The key aspects of a widely-used effective field theory framework for testing local Lorentz symmetry are discussed. Also, we present a summary of the recent precision tests of Lorentz symmetry in gravity including gravitational waves, pulsar tests, lunar laser ranging, ground-based gravimetry, and short-range gravity tests.
Observations of metal absorption systems in the spectra of distant quasars allow stringent tests of the Einstein Equivalence Principle, through constraints on possible variations of the fine-structure constant. A new generation of high-resolution ultra-stable spectrographs, of which ESPRESSO is the first example, enables major advances in this field. Here we summarize the status quo and outline the goals of the ESPRESSO fundamental physics GTO program, leading to Einstein Equivalence Principle constraints that are competitive with the local ones.
Gravity measurements are a crucial tool to peek through the surface of planetary bodies and reveal their interior structure. As a consequence of the equivalence principle, every gravity measurement in space must be a differential one, therefore requiring two test masses. Microwave links provide the observable quantities needed to follow the free fall of a probe mass (the spacecraft) in the gravity field of a planet or a satellite from a vantage point (the Earth). This talk will present the state of the art in deep space tracking systems (such as those used by the Juno and BepiColombo spacecraft) and provide examples of recent advancements in planetary science attained by means of precision spacecraft tracking.
Invited talk
Optical atomic clocks have demonstrated unprecedented stability and estimated systematic uncertainty, far surpassing the current generation of caesium primary frequency standards. Large-scale efforts are underway to verify their uncertainty budgets by means of international comparisons using optical fibre networks or satellite-based frequency comparison techniques. Such comparisons, together with the incorporation of optical clocks into International Atomic Time (TAI), are an essential prerequisite for an anticipated future redefinition of the SI second in terms of an optical transition frequency.
General relativity predicts that time, and hence clocks, are affected by gravity. When the frequencies of clocks are compared, or when they contribute data to international time scales, it is therefore necessary to account for the gravitational redshift of their frequencies. But state-of-the-art laboratory optical clocks have now reached the point where their estimated systematic uncertainties are below the uncertainty with which we are able to correct for gravitational effects at the Earth’s surface. This offers the exciting prospect of using optical clocks as sensors for measuring gravity potential differences, an approach termed chronometric levelling or relativistic geodesy.
In this talk I will describe a proof-of-principle demonstration of chronometric levelling using a transportable optical clock and discuss the future prospects of this new approach.
There are laser retroreflector arrays (LRAs) on the Moon since 50+ years ago (deployed by Apollo and Luna missions). There were no laser retroreflectors on Mars until microreflectors (of ~25 gr mass) were recently deployed on Mars (deployed by the InSight and Perseverance missions). These instruments are positioned using specialized ephemeris software (Planetary Ephemeris Program, from the Harvard-Smithsonian Center for Astrophysics) and data acquired with the Satellite or Lunar Laser Ranging (SLR/LLR) technique by the International Laser Ranging Service (ILRS, ilrs.gsfc.nasa.gov, part of the IAG) or by orbiting spacecrafts, like NASA's Lunar Reconnaissance Orbiter (LRO, equipped with a laser altimeter). Examples of LLR station are the French station in Grasse, the US station, APOLLO (Apache Point Lunar Laser-ranging Operation) and MLRO, the Matera Laser Ranging Observatory of the Italian Space Agency. SLR, LLR and their interplanetary equivalents at the Mars system (and, in the future, beyond) enable accurate tests of relativistic gravity, establishing reliable planetary geodetic reference frames, interesting studies of planetary interiors and support planetary exploration.
For 50+ years LLR to Apollo/Lunokhod LRAs supplied accurate tests of General Relativity (GR) and new gravitational physics: possible changes of the gravitational constant Gdot/G, weak and strong equivalence principle, gravitational self-energy (post Newtonian parameter beta), geodetic precession, inverse-square force-law (Williams 2006, Dell’Agnello 2009, Currie 2013, Dell’Agnello 2018), spacetime torsion (March 2011-1, 2) and nonminimally coupled gravity (March 2017, March 2013). LLR has also provided significant information on the composition of the deep interior of the Moon, complementary to that of NASA's mission GRAIL (Gravity Recovery And Lunar Interior Laboratory). In fact, already in the later 1990s LLR first provided evidence of the existence of a fluid component of the deep lunar interior (Williams 2006), confirmed later by a re-analysis of Apollo lunar seismometry data in 2011 (Weber 2011). Therefore, lunar LRAs form the first realization of a passive Lunar Geophysical Network (LGN) for lunar science, exploration and precisions tests of GR (LGN-LPSC 2019).
In 1969 LRAs contributed a negligible fraction of the LLR error budget. Since laser station range accuracy improved by more than a factor 100, now, because of lunar librations, the lunar LRAs dominate the error due to their multi-reflector geometry and large physical size. For direct LLR by ILRS, a next-generation, single, large reflector, MoonLIGHT (Moon Laser Instrumentation for General relativity and Geodesy high-accuracy test, of kg-level mass) was developed, whose LLR accuracy is unaffected by librations (Ciocci 2017). This class of next-gen reflectors supports an improvement from a factor 10 up to a factor 100 of the space segment of the LLR accuracy (Dell’Agnello 2009) and will be deployed on the Moon with two lunar landing mission opportunities by ESA and NASA in late 2023 or early 2024.
The extension of the LLR gravitational science program to ongoing or approved missions to Mars (InSight 2018, Perseverance 2020, ExoMars 2022, Mars Sample Return 2026-2028) and to Phobos (MMX 2024) will also be described.
The GRACE-FO twin satellites were launched in mid 2018 to continue the enormously useful Earth gravity field measurements from GRACE (2002-2017). The novel feature is the Laser Ranging Interferometer (LRI), which improves the noise of the inter-satellite separation measurement from 2 μm to 200 pm at high frequencies. The LRI was designed as an experimental demonstrator, but continues to work exceptionally well until today. Due to its success it will be the basis for future missions. In this presentation I will present the design and results of the LRI and give a brief outlook for the next generation of such missions.
A strong candidate for the Next Generation Gravity Mission (NGGM) is a mission like GRACE Follow-On, with laser interferometry measurements between the two satellites, but with a much lower non-gravitational acceleration noise level requirement for the satellites. That level could be reduced to below 1x10-12 m/(s2)/(Hz0.5) from 0.3 mHz to 1 Hz by making use of a much simplified version of the Gravitational Reference Sensors (GRSs) flown very successfully on the LISA Pathfinder mission. A satellite altitude of 362 km is assumed, which corresponds to 172 orbital revolutions in 11 days. For this case, simplified estimates give quite low levels for the geopotential height variations over 1 revolution arcs of data. For orbital frequencies of 20, 40, 60, 80, 100, and 120 cycles per revolution, the resulting geopotential height variation uncertainties are as follows: [ 4.0, 2.1, 1.6, 1.4, 1.2, 1.1 ] x 10-9 m/(cycles/rev)0.5.
In the future, with this level of measurement asccuracy, it is expected that the along-track resolution for one revolution arcs of data would be improved to about 200 km. However, there still would be serious limitations in interpreting the results because of temporal aliasing and from the difficulty of separating the effects of mass variations due to the atmosphere from those due to hydrology or the oceans. But the high measurement accuracy would permit strong tests to be made of potential improved methods for understanding the observed mass distribution changes based on other types of geophysical data. Also, including a second pair of satellites with about 70 degree inclination would strongly increase the scientific benefits of the NGGM.
The advancement of quantum technology brings new opportunities in precision measurements, which yields novel sensors for accelerometry, gradiometry, chronometry and so on. For chronometry, high-performance clock networks, i.e., optical clocks connected by dedicated frequency transfer techniques, are capable to observe the gravitational redshift effect. This can be applied to infer the point-wise gravity potential (or physical height) difference between long-distance sites. This concept is termed as relativistic geodesy with clocks, or chronometric geodesy. It opens a new door to obtain geodetic measurements.
In this study, we address the potential of high-performance clock networks for a few typical geodetic applications. Since clock networks with a fractional frequency uncertainty of 1.0 x 10-18 can determine the physical height differences between distant points with the target accuracy level of 1.0 cm, we study their potential for the realization of a homogeneous and accurate global physical height reference frame. We will show simulation results to demonstrate that clocks are powerful to unify the practically-used local height systems. Clocks are also considered to be operated at locations of interest, e.g., in Greenland and Amazon, where they can continuously track changes w.r.t. reference clock stations. The resulting time-series of gravity potential values can probably reveal the time-variable gravity signals at these locations. Moreover, clocks are assumed on-board a pair of co-orbiting satellites to collect relative gravity potential values with a global coverage. In this scenario, we will run closed-loop simulations to evaluate the potential of clocks for detecting time-variable gravity signals from space.
We gratefully acknowledge the financial support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy EXC-2123 “QuantumFrontiers” (Project-ID: 390837967). The study is also funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under the research program SFB 1464 “TerraQ - Relativistic and Quantum-based Geodesy” (Project-ID 434617780).
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
From 1969 on, Lunar Laser Ranging data are collected by various observatories and analyzed by different analysis groups. In the past years observations with larger telescopes (APOLLO) and at infrared frequencies (OCA, Wettzell) 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, from the early 80ies on, 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 and, with special modifications, tests of Einstein’s theory of relativity. Including the new data, we show recent results for relativity parameters related to the equivalence principle, temporal variation of the gravitational constant and for a selection of PPN (Parametrized Post-Newtonian) parameters.
We acknowledge with thanks that more than 50 years of processed LLR data have been obtained under the efforts of the personnel at the Observatoire de la Côte dAzur in France, the LURE Observatory in Maui, Hawaii, the McDonald Observatory in Texas, the Apache Point Observatory in New Mexico, the Matera Laser Ranging station in Italy and the Wettzell Laser Ranging System in Germany. This research was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy – EXC-2123 QuantumFrontiers – 390837967. Further financial supports were from the Strategic Priority Research Program of the Chinese Academy of Sciences, the National Natural Science Foundation of China and the Deutsches Zentrum für Luft- und Raumfahrt (DLR).
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.
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.
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)
Owing to new highly sensitive devices 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 clocks on 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 non-stationarity 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.