244 research outputs found
NON-RIEMANNIAN THEORIES OF GRAVITY AND LUNAR AND SATELLITE LASER RANGING
No full textTheories of gravity with a non-Riemannian manifold have been studied since the advent of Einstein's general relativity. In this paper, after an introduction on theories of gravity with a non-Riemannian spacetime and in particular on the nonsymmetric Moffat theory, we briefly describe the techniques of lunar and satellite laser ranging. Among the various applications of lunar and satellite laser ranging are several important measurements and tests of Einstein's general relativity as well as constraints on some alternative gravity theories. In particular, lunar and satellite laser ranging put strong validity limits on the 1983 nonsymmetric Moffat theory
Introduction to General Relativity and John Archibald Wheeler
No full textJohn Archibald Wheeler was born on July 9, 1911, in Jacksonville, Florida, and passed away on April 13, 2008, in Hightstown, New Jersey; his influence on gravitational physics and science in general will remain forever. Among his many and important contributions to physics, he was one of the fathers of the renaissance of General Relativity. After a golden starting age of General Relativity, a few years after the Einstein’s papers of 1915–1916, Einstein’s gravitational theory was for many years, to quote the preface of a 1960 book of General Relativity [1], confined to “an ivory tower...and no doubt many a relativist looks forward to the day when the governments will seek his opinion on important questions”
The LARES Space Experiment: LARES Orbit, Error Analysis and Satellite Structure
No full textThe LARES space experiment, by the Italian Space Agency (ASI), is based on the launch of a new laser ranged satellite, called LARES (LAser RElativity Satellite), using the new launch vehicle VEGA (Veicolo Europeo di Generazione. Avanzata, provided by ESA). LARES will have an altitude of about 1,450 km, orbital inclination of about 71. 5∘ and nearly zero eccentricity. The LARES satellite together with the satellites LAGEOS (LAser GEOdynamics Satellite launched by NASA) and LAGEOS 2 (built by ASI and launched by NASA and ASI) and with improved GRACE (Gravity Recovery and Climate Experiment, a NASA/DLR, German Space Agency, mission) Earth’s gravity field models will allow a measurement of the Earth’s gravitomagnetic field and of Lense–Thirring effect with an uncertainty of a few percent. After a description of the LARES experiment and of the orbit of LARES, we present an analysis of the main error sources affecting the measurement of gravitomagnetism; these are due to the uncertainties in the Earth’s gravitational field, and in particular to the Earth’s even zonal harmonics, to the time dependent Earth’s gravitational field, and in particular to dot{J}6 and to the K 1 tide. We also discuss the effect of particle drag and the error due to the uncertainties in the measurement of the orbital inclination. We finally describe some technical and engineering aspects of the LARES mission, and in particular: the laser ranging technique, the cube corner reflectors and the satellite body. We conclude with a brief discussion of LARES separation system and the selected launcher
Testing gravitational physics with satellite laser ranging
No full textLaser ranging, both Lunar (LLR) and Satellite Laser Ranging (SLR), is one of the most accurate techniques to test gravitational physics and Einstein's theory of General Relativity. Lunar Laser Ranging has provided very accurate tests of both the strong equivalence principle, at the foundations of General Relativity, and of the weak equivalence principle, at the basis of any metric theory of gravity; it has provided strong limits to the values of the so-called PPN (Parametrized Post-Newtonian) parameters, that are used to test the post-Newtonian limit of General Relativity, strong limits to conceivable deviations to the inverse square law for very weak gravity and accurate measurements of the geodetic precession, an effect predicted by General Relativity. Satellite laser ranging has provided strong limits to deviations to the inverse square gravity law, at a different range with respect to LLR, and in particular has given the first direct test of the gravitomagnetic field by measuring the gravitomagnetic shift of the node of a satellite, a frame-dragging effect also called Lense-Thirring effect. Here, after an introduction to gravitomagnetism and frame-dragging, we describe the latest results in measuring the Lense-Thirring effect using the LAGEOS satellites and the latest gravity field models obtained by the space mission GRACE. Finally, we describe an update of the LARES (LAser RElativity Satellite) mission. LARES is planned for launch in 2011 to further improve the accuracy in the measurement of frame-dragging
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Improving searches for gravitational waves and searching for exotic objects
No full textThis dissertation explores advancements made in gravitational wave searches, with a focus on techniques and methods that improve detection sensitivity as well as the search for novel sources of gravitational waves in the form of exotic objects, such as primordial black holes and boson stars. It is divided into 7 chapters, where chapter 1 introduces foundational concepts, including the derivation of gravitational waves and their detection through interferometric observatories, such as LIGO, VIRGO, and KAGRA (LVK). The subsequent subsections in chapter 1 provides brief introductions to specialized topics such as the gravitational wave detection pipeline GstLAL, the statistical inference framework iDQ, and the search for exotic objects. These introductions each lead into discussions of my contributions to two related papers that are found in accompanying chapters. Chapters 2 and 3 are GstLAL based projects which discuss improvements to GstLAL's search sensitivity through an improved ranking statistic and the implementation of a neural network that can lead to faster parameter estimation. Chapter 4 and 5 are iDQ papers which discuss the overall improvements to the framework made between the third and fourth observing runs of LVK and a study that demonstrates how the inclusion of data quality in the GstLAL pipeline can lead to increased search sensitivity. Finally, Chapters 6 and 7 are exotic object search papers which discuss the implementation of a waveform that can be used to search for exotic objects and a novel method that allows for the rapid generation of gravitational wave template banks.Physic
The Bekenstein Quantum Particle Horizon Approach to Avoid the Cosmological Singularity
No full textThe author has granted permission for their work to be available to the general public.The cosmological singularity of infinite density, temperature, and spacetime curvature is the classical limit of Friedmann's general relativity models extrapolated to the origin of the standard model of cosmology. Jacob Bekenstein questions whether the singularity is thermodynamically possible in a 1989 paper in which he outlines four approaches to eliminate the singularity from cosmology. He concludes that none of these is satisfactory, and then reexamines the particle horizon in the early radiation-dominated universe suggesting it holds the key as a feasible alternative to the classical inevitability of the singularity. This minimum-radius particle horizon determined from Bekenstein's entropy bound, and necessarily quantum in nature precludes the singularity just as quantum mechanics provided the solution for singularities in atomic transitions as r → 0. An initial cosmological radius of zero may never be attained quantum mechanically, avoiding the spacetime singularity, and supporting Bekenstein's argument that Friedmann models cannot be extrapolated to the very beginning of the universe but only to a boundary which is 'something like a particle horizon'. The universe may have begun in the bright flash and quantum flux of radiation and particles at a minimum, irreducible quantum particle horizon rather than at the classical mathematical limit and unrealizable state of an infinite singularity.Physics and Astronom
A new laser-ranged satellite for General Relativity and space geodesy: II. Monte Carlo simulations and covariance analyses of the LARES 2 experiment
No full textIn the previous paper we have introduced the LARES 2 space experiment. The LARES 2 laser-ranged satellite is planned for a launch in 2019 with the new VEGA C launch vehicle of the Italian Space Agency (ASI), ESA and ELV. The main objectives of the LARES 2 experiment are accurate measurements of General Relativity, gravitational and fundamental physics and accurate determinations in space geodesy and geodynamics. In particular LARES 2 is aimed to achieve a very accurate test of frame-dragging, an intriguing phenomenon predicted by General Relativity. Here we report the results of Monte Carlo simulations and covariance analyses fully confirming an error budget of a few parts in one thousand in the measurement of frame-dragging with LARES 2 as calculated in our previous paper
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Signal Processing Compact Binary Coalescence Gravitational Wave Data from the Advanced LIGO Detectors
No full textAbstract or description:
This thesis explores the complex signal processing tools and techniques used to perform gravitational
wave astronomy. The first ever direct observation of spatial strain caused by a gravitational wave was
achieved by the Laser Interferometer Gravitational-Wave Observatory (LIGO) on September 14th, 2015,
nearly 100 years after Albert Einstein predicted their existence. Because the amplitude of the strain is so
small (on the order of 10-21), it must be measured by a 4 kilometer long interferometer equipped with
extremely advanced thermal and seismic vibration isolation systems. Furthermore, the data must
undergo significant processing in the form of whitening, matched filtering, and bandpass filtering. We
present a detailed study of the steps undergone to identify and validate potential gravitational wavesignals using the LIGO-designed PyCBC software framework for the observation of compact binary
coalescence.Physic
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