Violation Of Equivalence Principle Research Articles

Evidence for Rapid Variability at High Energies in GRBs

Abstract Intrinsic variability was searched for in arrival times of six gamma-ray bursts (GRBs) at high energies – between 30 MeV and 2 GeV – detected by the Fermi satellite’s Large Area Telescope (LAT). The GRBs were selected from the Fermi LAT catalog with preference for events with numerous photons, a strong initial pulse, and measured redshifts. Three long GRBs and three short GRBs were selected and tested. Two different variability-detection algorithms were deployed, one counting photons in pairs, and the other multiplying time gaps between photons. In both tests, a real GRB was compared to 1000 Monte-Carlo versions of itself smoothed over a wide range of different timescales. The minimum detected variability timescales for long bursts (GRB 080916C, GRB 090926A, GRB 131108A) was found to be (0.005, 10.0, 10.0) seconds for the photon pair test and (2.0, 20.0, 10.0) seconds for the time-gap multiplication test. Additionally, the minimum detected variability timescales for the short bursts (GRB 090510, GRB 140619B, GRB 160709A) was found to be (0.05, 0.01, 20.0) seconds for the photon pair test and (0.05, 0.01, 20.0) seconds for the gap multiplication test. Statistical uncertainties in these times are about a factor of 2. The durations of these variability timescales may be used to constrain the geometry, dynamics, speed, cosmological dispersion, Lorentz-invariance violations, weak equivalence principle violations, and GRB models.

Equivalence principle violation in nonminimally coupled gravity and constraints from lunar laser ranging

Equivalence principle violation in nonminimally coupled gravity and constraints from lunar laser ranging

Constraining light scalar field with torsion-balance gravity experiments

The light scalar field with a coupling to standard model particles provide a possible source of the long-range Yukawa forces or violation of the weak equivalence principle, which can be potentially explored by precision gravity experiments. We describe the searches for such light scalar fields with the three types of gravity experiments, including the G-measurement experiments, Inverse-Square Law (ISL) experiments, and equivalence principle experiments. We investigate the potential influences of the scalar field as a function of its mass, and focus on the experimental constraints from torsion-balance gravity experiments. HUST-18 G-measurement torsion-balance experiments place bounds on the photon coupling and electron coupling at up to Λγ=7×1017 GeV and Λe=1×1017 GeV in the mass ranges 10−9–10−4eV. Results from the ISL experiments by the Universities of Washington, Stanford, IUPUI, HUST, Colorado, Irvine, Yale and others allow us to set limits on the photon coupling and electron coupling at up to Λγ=5×1017 GeV and Λe=3×1016 GeV for scalar field mass ranges between 10−5 and 10−1eV. Additionally, we also discuss the limits from equivalence principle experiments, and MICROSCOPE final result updates the constrains on the coupling parameters at up to Λγ=7×1022 GeV and Λe=4×1021 GeV for mass ranges ≲10−13eV. These results contribute experimental constraints to relatively unexplored mass regions of light scalar field parameter space and improve upon previous limits in some mass ranges. This work paves the way for long-range Yukawa forces mediated by light scalar fields in future high-precision gravity experiments.

Weak equivalence principle violation for mixed scalar particles

We investigate the non-relativistic limit of the Klein–Gordon equation for mixed scalar particles and show that, in this regime, one unavoidably arrives at redefining the particle’s inertial mass. This happens because, in contrast to the case when mixing is absent, the antiparticle sector contribution cannot be neglected for particles with definite flavor. To clearly demonstrate this feature, we adopt the Feshbach–Villars formalism for Klein–Gordon particles. Furthermore, within the same framework, we also demonstrate that, in the presence of a weak gravitational field, the mass parameter that couples to gravity (gravitational mass) does not match the effective inertial mass. This, in turn, implies a violation of the weak equivalence principle. Finally, we prove that the Bargmann’s superselection rule, which prohibits oscillating particles on the basis of the Galilean transformation, is incompatible with the non-relativistic limit of the Lorentz transformation and hence does not collide with the results obtained.

Cosmologically varying kinetic mixing

The portal connecting the invisible and visible sectors is one of the most natural explanations of the dark world. However, the early-time dark matter production via the portal faces extremely stringent late-time constraints. To solve such tension, we construct the scalar-controlled kinetic mixing varying with the ultralight CP-even scalar’s cosmological evolution. To realize this and eliminate the constant mixing, we couple the ultralight scalar within 10−33eV ≲ m0 ≪ eV with the heavy doubly charged messengers and impose the ℤ2 symmetry under the dark charge conjugation. Via the varying mixing, the keV – MeV dark photon dark matter is produced through the early-time freeze-in when the scalar is misaligned from the origin and free from the late-time exclusions when the scalar does the damped oscillation and dynamically sets the kinetic mixing. We also find that the scalar-photon coupling emerges from the underlying physics, which changes the cosmological history and provides the experimental targets based on the fine-structure constant variation and the equivalence principle violation. To ensure the scalar naturalness, we discretely re-establish the broken shift symmetry by embedding the minimal model into the ℤN-protected model. When N ~ 10, the scalar’s mass quantum correction can be suppressed much below 10−33eV.

Neutrino decoherence and violation of the strong equivalence principle

We analyze the dynamics of neutrino Gaussian wave-packets, the damping of flavor oscillations and decoherence effects within the framework of extended theories of gravity. We show that, when the underlying description of the gravitational interaction admits a violation of the strong equivalence principle, the parameter quantifying such a violation modulates the wave-packet spreading, giving rise to potentially measurable effects in future neutrino experiments.

General formalism of the quantum equivalence principle

A consistent theory of quantum gravity will require a fully quantum formulation of the classical equivalence principle. Such a formulation has been recently proposed in terms of the equality of the rest, inertial and gravitational mass operators, and for non-relativistic particles in a weak gravitational field. In this work, we propose a generalization to a fully relativistic formalism of the quantum equivalence principle, valid for all background space-times, as well as for massive bosons and fermions. The principle is trivially satisfied for massless particles. We show that if the equivalence principle is broken at the quantum level, it implies the modification of the standard Lorentz transformations in flat space-time and a corresponding modification of the metric in curved space-time by the different mass ratios. In other words, the observed geometry would effectively depend on the properties of the test particle. Testable predictions of potential violations of the quantum equivalence principle are proposed.

Newtonian fractional-dimension gravity and the external field effect

We expand our analysis of Newtonian Fractional-Dimension Gravity (NFDG), an extension of the classical laws of Newtonian gravity to lower dimensional spaces, including those with fractional (i.e., non-integer) dimension. We apply our model to four rotationally supported galaxies (NGC 5033, NGC 6674, NGC 5055, NGC 1090), in addition to other three galaxies (NGC 7814, NGC 6503, NGC 3741) which were analyzed in previous studies. NFDG is able to fit the rotation curves of all these galaxies without any dark matter component. We also investigate the possible violation of the strong equivalence principle, in relation to the External Field Effect (EFE), i.e., the dependence of the internal motion of a self-gravitating system under freefall on an external gravitational field. This effect is not present in Newtonian or Einstein gravity, but is predicted by some alternative theories of gravity. On the contrary, we show that NFDG does not imply the EFE, at least for values of the fractional dimension in the range $1 \leq D \leq 3$. Using improved NFDG numerical computations, we analyze the rotation curves of the aforementioned galaxies and obtain perfect fits to the experimental data, by using a fractional-dimension function $D\left (R\right )$ which characterizes each individual galaxy. In the galactic sample studied here with NFDG methods, we do not detect any significant differences between galaxies that are supposed to show/not show the EFE according to other alternative theories. A larger sample of galaxies will be needed to fully determine the absence of any external field effect in NFDG.

The phenomenology of the external field effect in cold dark matter models

ABSTRACT In general relativity (GR), the internal dynamics of a self-gravitating system under free-fall in an external gravitational field should not depend on the external field strength. Recent work has claimed a statistical detection of an ‘external field effect’ (EFE) using galaxy rotation curve data. We show that large uncertainties in rotation curve analyses and inaccuracies in published simulation-based external field estimates compromise the significance of the claimed EFE detection. We further show analytically that a qualitatively similar statistical signal is, in fact, expected in a Λ-cold dark matter (ΛCDM) universe without any violation of the strong equivalence principle. Rather, such a signal arises simply because of the inherent correlations between galaxy clustering strength and intrinsic galaxy properties. We explicitly demonstrate the effect in a baryonified mock catalogue of a ΛCDM universe. Although the detection of an EFE-like signal is not, by itself, evidence for physics beyond GR, our work shows that the sign of the EFE-like correlation between the external field strength and the shape of the radial acceleration relation can be used to probe new physics: e.g. in MOND, the predicted sign is opposite to that in our ΛCDM mocks.

Result of the MICROSCOPE weak equivalence principle test

The space mission MICROSCOPE dedicated to the test of the equivalence principle (EP) operated from April 25, 2016 until the deactivation of the satellite on October 16, 2018. In this analysis we compare the free-fall accelerations (a A and a B) of two test masses in terms of the Eötvös parameter . No EP violation has been detected for two test masses, made from platinum and titanium alloys, in a sequence of 19 segments lasting from 13 to 198 h down to the limit of the statistical error which is smaller than 10−14 for η(Ti, Pt). Accumulating data from all segments leads to η(Ti, Pt) = [−1.5 ± 2.3 (stat) ± 1.5 (syst)] × 10−15 showing no EP violation at the level of 2.7 × 10−15 if we combine stochastic and systematic errors quadratically. This represents an improvement of almost two orders of magnitude with respect to the previous best such test performed by the Eöt-Wash group. The reliability of this limit has been verified by comparing the free falls of two test masses of the same composition (platinum) leading to a null Eötvös parameter with a statistical uncertainty of 1.1 × 10−15.

Weak equivalence principle in quantum space

Owing to the development of String Theory and Quantum Gravity, studies of quantized spaces described by deformed commutation relations for operators of coordinates and operators of momenta have received much attention. In this paper, the implementation of the weak equivalence principle is examined in the quantized spaces described by different types of deformed algebras, among them the noncommutative algebra of canonical type, Lie type, and the nonlinear deformed algebra with an arbitrary function of deformation depending on momenta. It is shown that the deformation of commutation relations leads to the mass-dependence of motion of a particle (a composite system) in a gravitational field, and, hence, to violation of the weak equivalence principle. We conclude that this principle is recovered in quantized spaces if one considers the parameters of the deformed algebras to be different for different particles (bodies) and to be determined by their masses.

Scattering times of quantum particles from the gravitational potential and equivalence principle violation

Universality of motion under gravity, the equivalence principle, is violated for quantum particles. Here, we study time it takes for a quantum particle to scatter from the gravitational potential, and show that the scattering time, formulated here using the opportune Bohmian formulation, acts as an indicator of the equivalence principle violation. The scattering times of wavepackets are distinctive enough to distinguish between the Bohmian and Copenhagen interpretations. The scattering time of mono-energetic stationary states, formulated here as a modification of the Bohmian time by probability undercurrents, turns out to be a sensitive probe of the equivalence principle violation. We derive the quantum scattering times, and analyze equivalence principle violating terms systematically. We discuss the experimental setup needed for measuring the violation, and describe implications of a possible measurement for time in quantum theory, including the tunneling time.

Equivalence principle violation from large scale structure

We explore the interplay between the equivalence principle and a generalization of the Heisenberg uncertainty relations known as extended uncertainty principle, that comprises the effects of spacetime curvature at large distances. Specifically, we observe that, when the modified uncertainty relations hold, the weak formulation of the equivalence principle is violated, since the inertial mass of quantum systems becomes position-dependent whilst the gravitational mass is left untouched. To obtain the above result, spinor and scalar fields are separately analyzed by considering the non-relativistic limit of the Dirac and the Klein-Gordon equations in the presence of the extended uncertainty principle. In both scenarios, it is found that the ratio between the inertial and the gravitational mass is the same.

Investigating the environmental dependence of ultralight scalar dark matter with atom interferometers

We study the environmental dependence of ultralight scalar dark matter (DM) with linear interactions to the standard model particles. The solution to the DM field turns out to be a sum of the cosmic harmonic oscillation term and the local exponential fluctuation term. The amplitude of the first term depends on the local DM density and the mass of the DM field. The second term is induced by the local distribution of matter, such as the Earth. And it depends not only on the mass of the Earth, but also the density of the Earth. Then, we compute the phase shift induced by the DM field in atom interferometers (AIs), through solving the trajectories of atoms. Especially, the AI signal for the violation of weak equivalence principle (WEP) caused by the DM field is calculated. Depending on the values of the DM coupling parameters, contributions to the WEP violation from the first and second terms of the DM field can be either comparable or one larger than the other. Finally, we give some constraints to DM coupling parameters using results from the terrestrial atomic WEP tests.

Violation of the equivalence principle in curvature-based extended gravity at finite temperature

We review the possible violation of the Equivalence Principle at finite temperature [Formula: see text] in the framework of curvature-based Extended Theories of Gravity. Specifically, we first show how it is possible to derive Equivalence Principle violation from Quantum Field Theory at [Formula: see text]. Subsequently, we exhibit how this result can be precisely recovered by following an alternative path that envisages the employment of generalized Einstein equations with a temperature-dependent energy-momentum tensor. Finally, we adopt the latter formalism in the context of some Extended Gravity models to quantify the amount of Equivalence Principle violation. Specifically, Brans–Dicke Theory, Standard Model Extension and Conformal Gravity are considered in detail.

A 16-parts-per-trillion measurement of the antiproton-to-proton charge-mass ratio.

The standard model of particle physics is both incredibly successful and glaringly incomplete. Among the questions left open is the striking imbalance of matter and antimatter in the observable universe1, which inspires experiments to compare the fundamental properties of matter/antimatter conjugates with high precision2-5. Our experiments deal with direct investigations of the fundamental properties of protons and antiprotons, performing spectroscopy in advanced cryogenic Penning trap systems6. For instance, we previously compared the proton/antiproton magnetic moments with 1.5 parts per billion fractional precision7,8, which improved upon previous best measurements9 by a factor of greater than 3,000. Here we report on a new comparison of the proton/antiproton charge-to-mass ratios with a fractional uncertainty of 16 parts per trillion. Our result is based on the combination of four independent long-term studies, recorded in a total time span of 1.5 years. We use different measurement methods and experimental set-ups incorporating different systematic effects. The final result, [Formula: see text], is consistent with the fundamental charge-parity-time reversal invariance, and improves the precision of our previous best measurement6 by a factor of 4.3. The measurement tests the standard model at an energy scale of 1.96 × 10-27 gigaelectronvolts (confidence level 0.68), and improves ten coefficients of the standard model extension10. Our cyclotron clock study also constrains hypothetical interactions mediating violations of the clock weak equivalence principle (WEPcc) for antimatter to less than 1.8 × 10-7, and enables the first differential test of the WEPcc using antiprotons11. From this interpretation we constrain the differential WEPcc-violating coefficient to less than 0.030.

Violation of Equivalence Principle at IceCube

We study the effects of a Violation of Equivalence Principle (VEP) on neutrino oscillations. We analyze the IceCube data on atmospheric neutrino fluxes to obtain updated constraints on the parameter space of VEP, with the benchmark choice that neutrinos with different masses couple with different strengths to the gravitational field. We find that the VEP parameters times the local gravitational potential at Earth can be constrained at the level of 10−27. The constraints from atmospheric neutrinos strongly depend on the assumption that the neutrino eigenstates interacting diagonally with the gravitational field coincide with the mass eigenstates, which is not a priori justified: as an example, if the basis of diagonal gravitational interaction coincide with the flavor basis, atmospheric neutrinos cannot constrain the model. Finally, we quantitatively study the effect of a VEP on the flavor composition of the astrophysical neutrinos, stressing again the interplay with the basis in which the VEP is diagonal: we find that some choices of such basis are already in tension with the flavor ratio of the diffuse neutrino flux measured by IceCube.

Constraining violations of the weak equivalence principle Using CHIME FRBs

ABSTRACT Einstein’s General relativity (GR) is the basis of modern astronomy and astrophysics. Testing the validity of basic assumptions of GR is important. In this work, we test a possible violation of the weak equivalence principle (WEP), i.e. there might be a time lag between photons of different frequencies caused by the effect of gravitational fields if the speeds of photons are slightly different at different frequencies. We use Fast radio bursts (FRBs), which are astronomical transients with millisecond time-scales detected in the radio frequency range. Being at cosmological distances, accumulated time delay of FRBs can be caused by the plasma in between an FRB source and an observer, and by gravitational fields in the path of the signal. We segregate the delay due to dispersion and gravitational field using the post-Newtonian formalism (PPN) parameter Δγ, which defines the space curvature due to gravity by a unit test mass. We did not detect any time delay from FRBs but obtained tight constraints on the upper limit of Δγ. For FRB20181117C with z = 1.83 ± 0.28 and νobs = $676.5\, {\rm MHz}$, the best possible constraint is obtained at log(Δγ) = $-21.58 ^{+0.10}_{-0.12}$ and log(Δγ/rE) = $-21.75 ^{+0.10}_{-0.14}$, respectively, where rE is the energy ratio of two photons of the same FRB signal. This constraint is about one order of magnitude better than the previous constraint obtained with FRBs, and five orders tighter than any constraint obtained using other cosmological sources.

The violation of equivalence principle and four neutrino oscillations for long baseline neutrinos

Violation of equivalence principle predicts that neutrinos of different flavor couple differently with gravity. Such a scenario can give rise to gravity induced flavor oscillations in addition to the usual mass flavor neutrino oscillations during the neutrino propagation. Even if the equivalence principle is indeed violated, their measure will be extremely small. We explore the possibility to probe the violation of equivalence principle (VEP) for the case of long baseline (LBL) neutrinos in a 4-flavor neutrino framework (3 active + 1 sterile) where both mass and gravity induced oscillations are considered. To this end, we have explicitly calculated the oscillation probability in 4-flavor framework that includes in addition to the mass-flavor mixing in matter, the gravity-flavor mixing also. The energy eigenvalues are then obtained by diagonalizing such a 4-flavor mixing matrix. The formalism is then employed to estimate the wrong and right sign muon yields at a far detector for neutrinos produced in a neutrino factory and travel through the Earth matter. These results are compared with the similar estimations when the usual three active neutrinos are considered.

Constraints on equivalence principle violation from gamma ray bursts

Theories of gravity that obey the Weak Equivalence Principle have the same Parametrised Post-Newtonian parameter $\gamma$ for all particles at all energies. The large Shapiro time delays of extragalactic sources allow us to put tight constraints on differences in $\gamma$ between photons of different frequencies from spectral lag data, since a non-zero $\Delta \gamma$ would result in a frequency-dependent arrival time. The majority of previous constraints have assumed that the Shapiro time delay is dominated by a few local massive objects, although this is a poor approximation for distant sources. In this work we consider the cosmological context of these sources by developing a source-by-source, Monte Carlo-based forward model for the Shapiro time delays by combining constrained realisations of the local density field using the Bayesian origin reconstruction from galaxies algorithm with unconstrained large-scale modes. Propagating uncertainties in the density field reconstruction and marginalising over an empirical model describing other contributions to the time delay, we use spectral lag data of Gamma Ray Bursts from the BATSE satellite to constrain $\Delta \gamma < 2.1 \times 10^{-15}$ at $1 \sigma$ confidence between photon energies of $25 {\rm \, keV}$ and $325 {\rm \, keV}$.