scholarly journals Gravity Tests with Radio Pulsars

Universe ◽  
2020 ◽  
Vol 6 (9) ◽  
pp. 156 ◽  
Author(s):  
Norbert Wex ◽  
Michael Kramer
Keyword(s):  
Strong Field ◽  
Slow Motion ◽  
Weak Field ◽  
Radio Pulsars ◽  
Binary Pulsars ◽  
Important Field ◽  
Tests Of Gravity ◽  
First Time ◽  
Theoretical Foundations ◽  
Experimental Gravity

The discovery of the first binary pulsar in 1974 has opened up a completely new field of experimental gravity. In numerous important ways, pulsars have taken precision gravity tests quantitatively and qualitatively beyond the weak-field slow-motion regime of the Solar System. Apart from the first verification of the existence of gravitational waves, binary pulsars for the first time gave us the possibility to study the dynamics of strongly self-gravitating bodies with high precision. To date there are several radio pulsars known which can be utilized for precision tests of gravity. Depending on their orbital properties and the nature of their companion, these pulsars probe various different predictions of general relativity and its alternatives in the mildly relativistic strong-field regime. In many aspects, pulsar tests are complementary to other present and upcoming gravity experiments, like gravitational-wave observatories or the Event Horizon Telescope. This review gives an introduction to gravity tests with radio pulsars and its theoretical foundations, highlights some of the most important results, and gives a brief outlook into the future of this important field of experimental gravity.

Binary pulsars as probes of relativistic gravity

1992 ◽  
Vol 341 (1660) ◽  
pp. 135-149 ◽  
Keyword(s):  
Binary Systems ◽  
Strong Field ◽  
Field Tests ◽  
Weak Field ◽  
Multidimensional Space ◽  
Alternative Theory ◽  
Theory Approach ◽  
Binary Pulsars ◽  
Weak Field Limit ◽  
Self Gravity

Until now, most experiments have succeeded in testing relativistic gravity only in its extreme weak-field limit. Because of the strong self-gravity of neutron stars, observations of pulsars in binary systems provide a unique opportunity for probing the strong-field régime of relativistic gravity. The two basic approaches to using binary pulsar measurements as probes of relativistic gravity are reviewed: the phenomenological (‘parametrized post-keplerian’ formalism) and the alternative-theory approach (multidimensional space of possible theories). The experimental constraints recently derived from the actual timing observations of three binary pulsars are summarized. General relativity passes these new, strong-field tests with complete success.

scholarly journals New Constraints on Preferred Frame Effects from Binary Pulsars

2012 ◽  
Vol 8 (S291) ◽  
pp. 496-498 ◽  
Author(s):  
Lijing Shao ◽  
Norbert Wex ◽  
Michael Kramer
Keyword(s):  
Strong Field ◽  
Weak Field ◽  
Optical Observations ◽  
Orbital Eccentricity ◽  
Tensor Fields ◽  
Metric Tensor ◽  
Preferred Frame ◽  
Binary Pulsars ◽  
Canonical Metric ◽  
Ppn Parameters

AbstractPreferred frame effects (PFEs) are predicted by a number of alternative gravity theories which include vector or additional tensor fields, besides the canonical metric tensor. In the framework of parametrized post-Newtonian (PPN) formalism, we investigate PFEs in the orbital dynamics of binary pulsars, characterized by the two strong-field PPN parameters, and . In the limit of a small orbital eccentricity, and contributions decouple. By utilizing recent radio timing results and optical observations of PSRs J1012+5307 and J1738+0333, we obtained the best limits of and in the strong-field regime. The constraint on also surpasses its counterpart in the weak-field regime.

scholarly journals Testing General Relativity with black hole X-ray data: a progress report

2021 ◽  
Author(s):  
Cosimo Bambi
Keyword(s):  
General Relativity ◽  
Black Hole ◽  
Strong Field ◽  
Weak Field ◽  
Progress Report ◽  
X Ray ◽  
Binary Pulsars ◽  
The Past ◽  
Modern Physics ◽  
New Generation

AbstractEinstein’s theory of General Relativity is one of the pillars of modern physics. For decades, the theory has been mainly tested in the weak field regime with experiments in the Solar System and observations of binary pulsars. Thanks to a new generation of observational facilities, the past 5 years have seen remarkable changes in this field and there are now numerous efforts for testing General Relativity in the strong field regime with black holes and neutron stars using different techniques. Here I will review the work of my group at Fudan University devoted to test General Relativity with black hole X-ray data.

scholarly journals Direct measurement of Coulomb-laser coupling

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Doron Azoury ◽  
Michael Krüger ◽  
Barry D. Bruner ◽  
Olga Smirnova ◽  
Nirit Dudovich
Keyword(s):  
Coulomb Interaction ◽  
Time Domain ◽  
Coulomb Potential ◽  
Laser Field ◽  
Large Range ◽  
Extreme Ultraviolet ◽  
Strong Field ◽  
The Time Domain ◽  
First Time ◽  
Insight Into

AbstractThe Coulomb interaction between a photoelectron and its parent ion plays an important role in a large range of light-matter interactions. In this paper we obtain a direct insight into the Coulomb interaction and resolve, for the first time, the phase accumulated by the laser-driven electron as it interacts with the Coulomb potential. Applying extreme-ultraviolet interferometry enables us to resolve this phase with attosecond precision over a large energy range. Our findings identify a strong laser-Coulomb coupling, going beyond the standard recollision picture within the strong-field framework. Transformation of the results to the time domain reveals Coulomb-induced delays of the electrons along their trajectories, which vary by tens of attoseconds with the laser field intensity.

scholarly journals The confrontation between general relativity and experiment

2009 ◽  
Vol 5 (S261) ◽  
pp. 198-199
Author(s):  
Clifford M. Will
Keyword(s):  
General Relativity ◽  
Gravitational Wave ◽  
Equivalence Principle ◽  
Gamma Ray ◽  
Strong Field ◽  
Weak Field ◽  
X Ray ◽  
Spacetime Geometry ◽  
Tests Of General Relativity ◽  
Laser Interferometric

AbstractWe review the experimental evidence for Einstein's general relativity. A variety of high precision null experiments confirm the Einstein Equivalence Principle, which underlies the concept that gravitation is synonymous with spacetime geometry, and must be described by a metric theory. Solar system experiments that test the weak-field, post-Newtonian limit of metric theories strongly favor general relativity. Binary pulsars test gravitational-wave damping and aspects of strong-field general relativity. During the coming decades, tests of general relativity in new regimes may be possible. Laser interferometric gravitational-wave observatories on Earth and in space may provide new tests via precise measurements of the properties of gravitational waves. Future efforts using X-ray, infrared, gamma-ray and gravitational-wave astronomy may one day test general relativity in the strong-field regime near black holes and neutron stars.

How can Mobile Accounting Reporting Benefit from the ‘Imagined Communities'?

2016 ◽  
Vol 7 (2) ◽  
pp. 36-52 ◽  
Author(s):  
Androniki Kavoura
Keyword(s):  
Financial Reporting ◽  
Sense Of Belonging ◽  
Community Formation ◽  
Imagined Communities ◽  
Theoretical Contribution ◽  
Multidisciplinary Study ◽  
Wide Range ◽  
Conceptual Paper ◽  
First Time ◽  
Theoretical Foundations

Are there theoretical foundations that may substantiate communication in an online environment in regard to accounting reporting and implementation of information via mobile accounting technologies that brings together communication, numbers and computing? This conceptual paper explores the creation of an imagined community that has all the characteristics to connect accountants together with the implementation of mobile devices based on Anderson's theory of imagined communities. It describes a wide range of trends in relation to current and emerging technologies used and maps processes of financial reporting into this milieu via the notion of imagined communities. It argues that a sense of coherence exists between its members who feel a sense of belonging to the same group, even if they have never met. The paper examines for the first time in this conceptual multidisciplinary study whether the characteristics of the imagined communities that construct identity are related to accounting community formation and this is the theoretical contribution of the paper.

scholarly journals Iron Complexes of a Proton-Responsive SCS Pincer Ligand with Sensitive Electronic Structure

2021 ◽  
Author(s):  
Kazimer Skubi ◽  
Reagan Hooper ◽  
Brandon Mercado ◽  
Melissa Bollmeyer ◽  
Samantha MacMillan ◽  
...  
Keyword(s):  
Strong Field ◽  
Alkali Metal Cation ◽  
Weak Field ◽  
Pincer Ligands ◽  
Zero Field ◽  
Zero Field Splitting ◽  
Pincer Ligand ◽  
Intermediate Spin ◽  
X Ray Absorption ◽  
Phosphine Complex

SCS pincer ligands have an interesting combination of strong-field and weak-field donors that is also present in the nitrogenase active site. Here, we explore the electronic structures of iron(II) and iron(III) complexes with such a pincer ligand, bearing a monodentate phosphine, thiolate S donor, amide N donor, ammonia, or CO. The ligand scaffold features a protonresponsive thioamide site, and the protonation state of the ligand greatly influences the reduction potential of iron in the phosphine complex. The N–H bond dissociation free energy can be quantitated as 56 ± 2 kcal/mol. EPR spectroscopy and SQUID magnetometry measurements show that the iron(III) complexes with S and N as the fourth donors have an intermediate spin (S = 3/2) ground state with large zero field splitting, and X-ray absorption spectra show high Fe–S covalency. The Mössbauer spectrum changes drastically with the position of a nearby alkali metal cation in the iron(III) amido complex, and DFT calculations explain this phenomenon through a change between having the doubly-occupied orbital as dz2 or dyz, as the former is more influenced by the nearby positive charge.

scholarly journals Maintaining Constant Pulse-Duration in Highly Dispersive Media Using Nonlinear Potentials

Photonics ◽  
2021 ◽  
Vol 8 (12) ◽  
pp. 570
Author(s):  
Haider Zia
Keyword(s):  
Strong Field ◽  
Propagation Distance ◽  
Weak Field ◽  
Dispersive Media ◽  
Signal Pulse ◽  
Nonlinear Phenomenon ◽  
Numerical Example ◽  
Ultrafast Optical ◽  
Nonlinear Potentials ◽  
Temporal Broadening

A method is shown for preventing temporal broadening of ultrafast optical pulses in highly dispersive and fluctuating media for arbitrary signal-pulse profiles. Pulse pairs, consisting of a strong-field control-pulse and a weak-field signal-pulse, co-propagate, whereby the specific profile of the strong-field pulse precisely compensates for the dispersive phase in the weak pulse. A numerical example is presented in an optical system consisting of both resonant and gain dispersive effects. Here, we show signal-pulses that do not temporally broaden across a vast propagation distance, even in the presence of dispersion that fluctuates several orders of magnitude and in sign (for example, within a material resonance) across the pulse’s bandwidth. Another numerical example is presented in normal dispersion telecom fiber, where the length at which an ultrafast pulse does not have significant temporal broadening is extended by at least a factor of 10. Our approach can be used in the design of dispersion-less fiber links and navigating pulses in turbulent dispersive media. Furthermore, we illustrate the potential of using cross-phase modulation to compensate for dispersive effects on a signal-pulse and fill the gap in the current understanding of this nonlinear phenomenon.

3. Extrasolar tests of gravity

2017 ◽  
pp. 35-45
Author(s):  
Timothy Clifton
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Field ◽  
Solar System ◽  
Neutron Stars ◽  
Event Horizon ◽  
Gravitational Fields ◽  
Binary Pulsars ◽  
Tests Of Gravity ◽  
Triple Star

By studying objects outside our Solar System, we can observe star systems with far greater gravitational fields. ‘Extrasolar tests of gravity’ considers stars of different sizes that have undergone gravitational collapse, including white dwarfs, neutron stars, and black holes. A black hole consists of a region of space-time enclosed by a surface called an event horizon. The gravitational field of a black hole is so strong that anything that finds its way inside the event horizon can never escape. Other star systems considered are binary pulsars and triple star systems. With the invention of even more powerful telescopes, there will be more tantalizing possibilities for testing gravity in the future.

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