Suchergebnisse

An idealized "test" object in general relativity moves along a geodesic. However, if the object has a finite mass, this will create additional curvature in the spacetime, causing it to deviate from geodesic motion. If the mass is nonetheless sufficiently small, such an effect is usually treated perturbatively and is known as the gravitational self-force due to the object. This issue is still an open problem in gravitational physics today, motivated not only by basic foundational interest, but also by the need for its direct application in gravitational wave astronomy. In particular, the observation of extreme-mass-ratio inspirals by the future space-based detector LISA will rely crucially on an accurate modeling of the self-force driving the orbital evolution and gravitational wave emission of such systems. In this paper, we present a novel derivation, based on conservation laws, of the basic equations of motion for this problem. They are formulated with the use of a quasilocal (rather than matter) stress-energy-momentum tensor—in particular, the Brown-York tensor—so as to capture gravitational effects in the momentum flux of the object, including the self-force. Our formulation and resulting equations of motion are independent of the choice of the perturbative gauge. We show that, in addition to the usual gravitational self-force term, they also lead to an additional "self-pressure" force not found in previous analyses, and also that our results correctly recover known formulas under appropriate conditions. Our approach thus offers a fresh geometrical picture from which to understand the self-force fundamentally, and potentially useful new avenues for computing it practically. ; M. O. and R. B. M. acknowledge support from the Natural Sciences and Engineering Research Council of Canada. M. O. and C. F. S. acknowledge support from Contracts No. ESP2013-47637-P, No. ESP2015-67234-P, and No. ESP2017-90084-P from the Ministry of Economy and Business of Spain (MINECO) and from Contract No. 2017-SGR-1469 from AGAUR (Catalan government). M. O. and A. D. A. M. S. acknowledge LISA CNES funding. We also acknowledge networking support by the COST Action GWverse CA16104 (Horizon 2020 Framework Programme of the European Union). ; Peer reviewed

Armano, M., et al. ; We report on the first subpicometer interferometer flown in space. It was part of ESA's Laser Interferometer Space Antenna (LISA) Pathfinder mission and performed the fundamental measurement of the positional and angular motion of two free-falling test masses. The interferometer worked immediately, stably, and reliably from switch on until the end of the mission with exceptionally low residual noise of 32.0-1.7+2.4 fm/Hz, significantly better than required. We present an upper limit for the sensor performance at millihertz frequencies and a model for the measured sensitivity above 200 mHz. ; The Albert-Einstein-Institut acknowledges the support of the German Space Agency, DLR. The work is supported by the Federal Ministry for Economic Affairs and Energy based on a resolution of the German Bundestag (FKZ 50OQ0501 and FKZ 50OQ1601). The French contribution has been supported by the CNES (Accord Specific de projet CNES 1316634/CNRS 103747), the CNRS, the Observatoire de Paris, and the University Paris-Diderot. E. P. and H. I. would also like to acknowledge the financial support of the UnivEarthS Labex program at Sorbonne Paris Cité (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02). The Italian contribution has been supported by Agenzia Spaziale Italiana and Istituto Nazionale di Fisica Nucleare. The Spanish contribution has been supported by Contracts No. AYA2010-15709 (MICINN), No. ESP2013-47637-P, No. ESP2015-67234-P, and No. ESP2017-90084-P (MINECO). Support from AGAUR (Generalitat de Catalunya) Contract No. 2017-SGR-1469 is also acknowledged. M. N. acknowledges support from Fundacion General CSIC (Programa ComFuturo). F. R. acknowledges an FPI contract from MINECO. The Swiss contribution acknowledges the support of the ETH Research Grant No. ETH-05 16-2 and the Swiss Space Office (SSO) via the PRODEX Programme of European Space Agency. L. F. is supported by the Swiss National Science Foundation. The UK groups wish to acknowledge support from the United Kingdom Space Agency (UKSA), the Scottish Universities Physics Alliance (SUPA), the University of Glasgow, the University of Birmingham, and Imperial College London. J. I. T. and J. S. acknowledge the support of the U.S. National Aeronautics and Space Administration (NASA). N. K. is thankful for the support from a CNES Fellowship.