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Register a new userConstraints on Quantum Gravity and the Photon Mass from Gamma Ray Bursts
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Lorentz Invariance Violation in Quantum Gravity (QG) models or a non-zero photon mass, $m_gamma$, would lead to an energy-dependent propagation speed for photons, such that photons of different energies from a distant source would arrive at different times, even if they were emitted simultaneously. By developing source-by-source, Monte Carlo-based forward models for such time delays from Gamma Ray Bursts, and marginalising over empirical noise models describing other contributions to the time delay, we derive constraints on $m_gamma$ and the QG length scale, $ell_{rm QG}$, using spectral lag data from the BATSE satellite. We find $m_gamma < 4.0 times 10^{-5} , h , {rm eV}/c^2$ and $ell_{rm QG} < 5.3 times 10^{-18} , h , {rm , GeV^{-1}}$ at 95% confidence, and demonstrate that these constraints are robust to the choice of noise model. The QG constraint is among the tightest from studies which consider multiple Gamma Ray Bursts and the constraint on $m_gamma$, although weaker than from using radio data, provides an independent constraint which is less sensitive to the effects of dispersion by electrons.
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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 BORG 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 $Delta gamma < 3.4 times 10^{-15}$ at $1 sigma$ confidence between photon energies of $25 {rm , keV}$ and $325 {rm , keV}$.
The effect of Quantum Gravity (QG) may bring a tiny light speed variation as $v(E)=c(1-E/E_{rm LV})$, where $E$ is the photon energy and $E_{rm LV}$ is a Lorentz violation scale. A remarkable regularity was suggested in previous studies to look for the light speed variation from high energy photon events of Gamma Ray Bursts (GRBs). We provide a general analysis on the data of 25 bright GRBs observed by the Fermi Gamma-ray Space Telescope (FGST). Such method allows a completed scan over all possibilities in a more clean and impartial way without any bias compared to previous intuitive analysis. The results show that with the increase in the intrinsic energies of photons, such regularity truly emerges and gradually becomes significant. For photons with intrinsic energies higher than 40~GeV, the regularity exists at a significance of 3-5~$sigma$ with $E_{rm LV}=3.6times 10^{17}~rm GeV$ determined by the GRB data.
The delay in the arrival times between high and low energy photons from cosmic sources can be used to test the violation of the Lorentz invariance (LIV), predicted by some quantum gravity theories, and to constrain its characteristic energy scale ${rm E_{QG}}$ that is of the order of the Planck energy. Gamma-ray bursts (GRBs) and blazars are ideal for this purpose thanks to their broad spectral energy distribution and cosmological distances: at first order approximation, the constraints on ${rm E_{QG}}$ are proportional to the photon energy separation and the distance of the source. However, the LIV tiny contribution to the total time delay can be dominated by intrinsic delays related to the physics of the sources: long GRBs typically show a delay between high and low energy photons related to their spectral evolution (spectral lag). Short GRBs have null intrinsic spectral lags and are therefore an ideal tool to measure any LIV effect. We considered a sample of $15$ short GRBs with known redshift observed by Swift and we estimate a limit on ${rm E_{QG}}gtrsim 1.5times 10^{16}$ GeV. Our estimate represents an improvement with respect to the limit obtained with a larger (double) sample of long GRBs and is more robust than the estimates on single events because it accounts for the intrinsic delay in a statistical sense.
We give precise details to support that observations of gravitational lensing at scales of individual, groups and clusters of galaxies can be understood in terms of non-Newtonian gravitational interactions with a relativistic structure compatible with the Einstein Equivalence Principle. This result is derived on very general grounds without knowing the underlying structure of the gravitational field equations. As such, any developed gravitational theory built to deal with these astrophysical scales needs to reproduce the obtained results of this article.
The MOND paradigm to the missing mass problem requires introducing a functional that is to be identified through observations and experiments. We consider AQUAL theory as a realization of the MOND. We show that the accurate value of the Earth GM measured by the Lunar Laser Ranging and that by various artificial Earth satellites, including the accurate tracking of the LAGEOS satellites, constrain this functional such that some of the chosen/proposed functional are refuted.
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