Violation Of Strong Equivalence Principle Research Articles

An improved test of the strong equivalence principle with the pulsar in a triple star system

Context.The gravitational strong equivalence principle (SEP) is a cornerstone of the general theory of relativity (GR). Hence, testing the validity of SEP is of great importance when confronting GR, or its alternatives, with experimental data. Pulsars that are orbited by white dwarf companions provide an excellent laboratory, where the extreme difference in binding energy between neutron stars and white dwarfs allows for precision tests of the SEP via the technique of radio pulsar timing.Aims.To date, the best limit on the validity of SEP under strong-field conditions was obtained with a unique pulsar in a triple stellar system, PSR J0337+1715. We report here on an improvement of this test using an independent data set acquired over a period of 6 years with the Nançay radio telescope. The improvements arise from a uniformly sampled data set, a theoretical analysis, and a treatment that fixes some short-comings in the previously published results, leading to better precision and reliability of the test.Methods.In contrast to the previously published test, we use a different long-term timing data set, developed a new timing model and an independent numerical integration of the motion of the system, and determined the masses and orbital parameters with a different methodology that treats the parameter Δ, describing a possible strong-field SEP violation, identically to all other parameters.Results.We obtain a violation parameter Δ = ( + 0.5 ± 1.8) × 10−6at 95% confidence level, which is compatible with and improves upon the previous study by 30%. This result is statistics-limited and avoids limitation by systematics as previously encountered. We find evidence for red noise in the pulsar spin frequency, which is responsible for up to 10% of the reported uncertainty. We use the improved limit on SEP violation to place constraints on a class of well-studied scalar-tensor theories, in particular we findωBD > 140 000 for the Brans-Dicke parameter. The conservative limits presented here fully take into account current uncertainties in the equation for state of neutron-star matter.

Conquering systematics in the timing of the pulsar triple system J0337+1715: Towards a unique and robust test of the strong equivalence principle

PSR J0337+1715 is a millisecond radio pulsar in a hierarchical stellar triple system containing two white dwarfs. The pulsar orbits the inner white dwarf every 1.6 days. In turn, this inner binary system orbits the outer white dwarf every 327 days. The gravitational influence of the outer white dwarf strongly accelerates the inner binary, making this system an excellent laboratory in which to test the strong equivalence principle (SEP) of general relativity – especially because the neutron star has significant gravitational self-binding energy. This system has been intensively monitored using three radio telescopes: Arecibo, Green Bank and Westerbork. Using the more than 25000 pulse times of arrival (TOAs) collected to date, we have modeled the system using direct 3-body numerical integration. Here we present our efforts to quantify the effects of systematics in the TOAs and timing residuals, which can limit the precision to which we can test the SEP in this system. In this work we describe Fourier-based techniques that we apply to the residuals in order to isolate the effects of systematics that could masquerade as an SEP violation. We also demonstrate that tidal effects are insignificant in the modeling.

Conquering systematics in the timing of the pulsar triple system J0337+1715: Towards a unique and robust test of the strong equivalence principle

AbstractPSR J0337+1715 is a millisecond radio pulsar in a hierarchical stellar triple system with two white dwarfs. This system is a unique and excellent laboratory in which to test the strong equivalence principle (SEP) of general relativity. An initial SEP-violation test was performed using direct 3-body numerical integration of the orbit in order to model the more than 25000 pulse times of arrival (TOAs) from three radio telescopes: Arecibo, Green Bank and Westerbork. In this work I present our efforts to quantify the effects of systematics in the TOAs and timing residuals, which limit the precision of an SEP test. In particular, we apply Fourier-based techniques to the timing residuals in order to isolate the effects of systematics that can masquerade as an SEP violation.

TESTING THEORIES OF GRAVITATION USING 21-YEAR TIMING OF PULSAR BINARY J1713+0747

We report 21-yr timing of one of the most precise pulsars: PSR J1713+0747. Its pulse times of arrival are well modeled by a comprehensive pulsar binary model including its three-dimensional orbit and a noise model that incorporates correlated noise such as jitter and red noise. Its timing residuals have weighted root mean square $\sim 92$ ns. The new dataset allows us to update and improve previous measurements of the system properties, including the masses of the neutron star ($1.31\pm0.11$ $M_{\odot}$) and the companion white dwarf ($0.286\pm0.012$ $M_{\odot}$) and the parallax distance $1.15\pm0.03$ kpc. We measured the intrinsic change in orbital period, $\dot{P}^{\rm Int}_{\rm b}$, is $-0.20\pm0.17$ ps s$^{-1}$, which is not distinguishable from zero. This result, combined with the measured $\dot{P}^{\rm Int}_{\rm b}$ of other pulsars, can place a generic limit on potential changes in the gravitational constant $G$. We found that $\dot{G}/G$ is consistent with zero [$(-0.6\pm1.1)\times10^{-12}$ yr$^{-1}$, 95\% confidence] and changes at least a factor of $31$ (99.7\% confidence) more slowly than the average expansion rate of the Universe. This is the best $\dot{G}/G$ limit from pulsar binary systems. The $\dot{P}^{\rm Int}_{\rm b}$ of pulsar binaries can also place limits on the putative coupling constant for dipole gravitational radiation $\kappa_D=(-0.9\pm3.3)\times10^{-4}$ (95\% confidence). Finally, the nearly circular orbit of this pulsar binary allows us to constrain statistically the strong-field post-Newtonian parameters $\Delta$, which describes the violation of strong equivalence principle, and $\hat{\alpha}_3$, which describes a breaking of both Lorentz invariance in gravitation and conservation of momentum. We found, at 95\% confidence, $\Delta<0.01$ and $\hat{\alpha}_3<2\times10^{-20}$ based on PSR J1713+0747.

Tests of the universality of free fall for strongly self-gravitating bodies with radio pulsars

In this paper, we review tests of the strong equivalence principle (SEP) derived from pulsar–white dwarf binary data. The extreme difference in the binding energy between both components and the precise measurement of the orbital motion provided by pulsar timing allow the only current precision SEP tests for strongly self-gravitating bodies. We start by highlighting why such tests are conceptually important. We then review previous work where limits on SEP violation are obtained with an ensemble of wide binary systems with small eccentricity orbits. Then, we propose a new SEP violation test based on the measurement of the variation of the orbital eccentricity (ė). This new method has the following advantages: (a) unlike previous methods it is not based on probabilistic considerations, (b) it can make a direct detection of SEP violation and (c) the measurement of ė is not contaminated by any known external effects, which implies that this SEP test is only restricted by the measurement precision of ė. In the final part of the review, we conceptually compare the SEP test with the test for dipolar radiation damping, a phenomenon closely related to SEP violation, and speculate on future prospects by new types of tests in globular clusters and future triple systems.

LUNAR LASER RANGING TESTS OF THE EQUIVALENCE PRINCIPLE WITH THE EARTH AND MOON

A primary objective of the lunar laser ranging (LLR) experiment is to provide precise observations of the lunar orbit that contribute to a wide range of science investigations. In particular, time series of the highly accurate measurements of the distance between the Earth and the Moon provide unique information used to determine whether, in accordance with the equivalence principle (EP), these two celestial bodies are falling toward the Sun at the same rate, despite their different masses, compositions, and gravitational self-energies. Thirty-five years since their initiation, analyses of precision laser ranges to the Moon continue to provide increasingly stringent limits on any violation of the EP. Current LLR solutions give (-1.0 ± 1.4) × 10-13for any possible inequality in the ratios of the gravitational and inertial masses for the Earth and Moon, Δ(MG/MI). This result, in combination with laboratory experiments on the weak equivalence principle, yields a strong equivalence principle (SEP) test of Δ(MG/MI)SEP= (-2.0 ± 2.0) × 10-13. Such an accurate result allows other tests of gravitational theories. The result of the SEP test translates into a value for the corresponding SEP violation parameter η of (4.4 ± 4.5) × 10-4, where η = 4β - γ - 3 and both γ and β are parametrized post-Newtonian (PPN) parameters. Using the recent result for the parameter γ derived from the radiometric tracking data from the Cassini mission, the PPN parameter β (quantifying the nonlinearity of gravitational superposition) is determined to be β - 1 = (1.2 ± 1.1) × 10-4. We also present the history of the LLR effort and describe the technique that is being used. Focusing on the tests of the EP, we discuss the existing data, and characterize the modeling and data analysis techniques. The robustness of the LLR solutions is demonstrated with several different approaches that are presented in the text. We emphasize that near-term improvements in the LLR accuracy will further advance the research on relativistic gravity in the solar system and, most notably, will continue to provide highly accurate tests of the EP.

Progress in Lunar Laser Ranging Tests of Relativistic Gravity

Analyses of laser ranges to the Moon provide increasingly stringent limits on any violation of the equivalence principle (EP); they also enable several very accurate tests of relativistic gravity. These analyses give an EP test of Delta(MG/MI)EP=(-1.0+/-1.4) x 10(-13). This result yields a strong equivalence principle (SEP) test of Delta(MG/MI)SEP=(-2.0+/-2.0) x 10(-13). Also, the corresponding SEP violation parameter eta is (4.4+/-4.5) x 10(-4), where eta=4beta-gamma-3 and both beta and gamma are post-Newtonian parameters. Using the Cassini gamma, the eta result yields beta-1=(1.2+/-1.1) x 10(-4). The geodetic precession test, expressed as a relative deviation from general relativity, is Kgp=-0.0019+/-0.0064. The search for a time variation in the gravitational constant results in G /G=(4+/-9) x 10(-13) yr(-1); consequently there is no evidence for local (approximately 1 AU) scale expansion of the solar system.

Cosmic microwave background constraints on the strong equivalence principle

We study the effect of a violation of the strong equivalence principle (SEP) on the cosmic microwave background (CMB). Such a violation would modify the weight of baryons in the primordial gravitational potentials and hence their impact in the establishment of the photon-baryon plasma acoustic oscillations before recombination. This cosmological Nordtvedt effect alters the odd peaks height of the CMB temperature anisotropy power spectrum. A gravitational baryonic mass density of the universe may already be inferred at the first peak scale from the analysis of WMAP data. Experimental constraints on a primordial SEP violation are derived from a comparison with the universe's inertial baryonic mass density measured either in a full analysis of the CMB, or in the framework of the standard big bang nucleosynthesis (BBN).

PSR 0655 + 64 - an astrophysical laboratory for testing relativistic gravity theories

The binary radio pulsar PSR 0655+64 is shown to be an effective astrophysical laboratory for testing gravity theories that violate the strong equivalence principle (SEP). Its observed spin-down rate has been used by us recently to test one aspect of SEP violation: the variability of the gravitational constant with cosmic time. Here it is suggested that PSR 0655+64 has the characteristics required for testing another aspect of SEP violation: the emission of dipole gravitational radiation. The companion of PSR 0655+64 is a white dwarf with a specific binding energy much smaller than that of the neutron star

Limits on a possible violation of the strong equivalence principle from primordial nucleosynthesis

view Abstract Citations (8) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Limits on a Possible Violation of the Strong Equivalence Principle from Primordial Nucleosynthesis Serna, A. ; Dominguez-Tenreiro, R. Abstract We present a detailed calculation of light element production in scale-covariant FRW cosmological models, where the modifications in the equations of nuclear kinetics due to scale-covariant kinetic theory effects are taken into account. The comparison of the results of our calculation with current observational data implies that the gauge function β(t) at primordial nucleosynthesis cannot deviate from its present value by more than a 1.5%. If we assume, as usual, that β is a power of time, these bounds leave little room for a possible strong equivalence principle violation. Publication: The Astrophysical Journal Pub Date: April 1992 DOI: 10.1086/171184 Bibcode: 1992ApJ...389....1S Keywords: Astronomical Models; Cosmology; Light Elements; Nuclear Astrophysics; Nuclear Fusion; Abundance; Deuterium; Helium; Kinetic Theory; Lithium; Astrophysics; COSMOLOGY: THEORY; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES full text sources ADS |

Violation of the Strong Equivalence Principle due to the self-force in a Kerr spacetime

As is known, a charge in a gravitational field experiences a (gravitationally-induced) self-interaction force (“self-force”) only in curved space-times (in any reference frame), but not in the accelerated frames in flat spacetimes. Therefore, the presence of any self-force indicates, from a formal point of view, a violation of the Strong Equivalence Principle (SEP); as a result, “observability of the self-force in the validity domain of classical electrodynamics” (CE) means “observability of the related violation of SEP”. In this paper we investigate the observability of the self-force on a charge at rest on the symmetry axis in a Kerr spacetime, as recently calculated in a paper by the same authors, in the validity domain of CE. Analysis shows that, in the validity domain of CE, no effect of the self-force is observable outside the Schwarzschild radius. In contrast, some effect is observable for very large values of the angular momentum, in a small neighbourhood of the “turning point” (where a reversal of the tidal forces direction takes place), between the outer horizon and the Schwarzschild radius. This is the only case we have found where SEP fails because of the self-force.

Astrophysical consequences of a violation of the strong equivalence principle

A previous analysis of the consequences of a violation of the strong equivalence principle (SEP) for massive particles has now been extended to the case of photons and leads to the prediction that the photon number is conserved. Comparison of the predictions of our theory with observations, especially those on big-bang nucleosynthesis, shows that a violation of the SEP is not ruled out by the data available, and that further direct measurements are required.

Atomic and gravitational clock

Atomic and gravitational clocks are governed by the laws of electrodynamics and gravity, respectively. While the strong equivalence principle (SEP) assumes that the two clocks have been synchronous at all times, recent planetary data seem to suggest a possible violation of the SEP. Our past analysis of the implications of an SEP violation on different physical phenomena revealed no disagreement. However, these studies assumed that the two different clocks can be consistently constructed within the framework. The concept of scale invariance, and the physical meaning of different systems of units, are now reviewed and the construction of two clocks that do not remain synchronous—whose rates are related by a nonconstant functionβ a—is demonstrated. The cosmological character ofβ a is also discussed.

Testing the strong equivalence principle by radio ranging

Planetary range data offer the most promising means to test the validity of the Strong Equivalence Principle (SEP). Analytical expressions for the perturbation in the 'range' expected from an SEP violation predicted by the 'variation-of-G' method and by the 'two-times' approach are derived and compared. The dominant term in both expressions is quadratic in time. Analysis of existing range data should allow a determination of the coefficient of this term with a one-standard-deviation uncertainty of about 1 part in 100 billion/yr.

Atomic and gravitational clocks

Atomic and gravitational clocks are governed by the laws of electrodynamics and gravity respectively. While the strong equivalence principle (SEP) assumes that the two clocks have been synchronous at all times, recent planetary data seem to suggest a possible violation of the SEP. Our past analysis of the implications of an SEP violation on different physical phenomena revealed no disagreement. However, these studies assumed that the two different clocks can be consistently constructed within the framework. The concept of scale invariance, and the physical meaning of different systems of units, are now reviewed and the construction of two clocks that do not remain synchronous—whose rates are related by a non-constant function βa—is demonstrated. The cosmological character of βa is also discussed.