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Lorentz invariance violation in quantum gravity (QG) models or a nonzero photon mass, mγ, 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 marginalizing over empirical noise models describing other contributions to the time delay, we derive constraints on mγ and the QG length scale, ℓQG, using spectral lag data from the BATSE satellite. We find mγ<4.0×10-5 h  eV/c² and ℓQG<5.3×10-18 h  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 mγ, although weaker than from using radio data, provides an independent constraint which is less sensitive to the effects of dispersion by electrons. [ABSTRACT FROM AUTHOR]

Theories of gravity that obey the weak equivalence principle have the same parametrized post-Newtonian parameter γ for all particles at all energies. The large Shapiro time delays of extragalactic sources allow us to put tight constraints on differences in γ between photons of different frequencies from spectral lag data, since a nonzero Δγ 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 realizations 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 marginalizing 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 Δγ < 2.1 × 10-15 at 1σ confidence between photon energies of 25 keV and 325 keV. [ABSTRACT FROM AUTHOR]

Galactic-scale tests have proven to be powerful tools in constraining fundamental physics in previously underexplored regions of parameter space. The astrophysical regime which they probe is inherently complicated, and the inference methods used to make these constraints should be robust to baryonic effects. Previous analyses have assumed simple empirical models for astrophysical noise without detailed calibration or justification. We outline a framework for assessing the reliability of such methods by constructing and testing more advanced baryonic models using cosmological hydrodynamical simulations. As a case study, we use the Horizon-AGN simulation to investigate warping of stellar disks and offsets between gas and stars within galaxies, which are powerful probes of screened fifth forces. We show that the degree of U-shaped warping of galaxies is well modeled by Gaussian random noise but that the magnitude of the gas-star offset is correlated with the virial radius of the host halo. By incorporating this correlation we confirm recent results ruling out astrophysically relevant Hu-Sawicki f(R) gravity and identify an ~30% systematic uncertainty due to baryonic physics. Such an analysis must be performed case by case for future galactic tests of fundamental physics. [ABSTRACT FROM AUTHOR]

Galileons are scalar field theories which obey the Galileon symmetry f f + b + c µ x µ and are capable of self-acceleration if they have an inverted sign for the kinetic term. These theories violate the strong equivalence principle, such that black holes (BHs) do not couple to the Galileon field, whereas nonrelativistic objects experience a fifth force with strength G / G N relative to gravity. For galaxies falling down a gradient in the Galileon field, this results in an offset between the center of the galaxy and its host supermassive BH. We reconstruct the local gravitational and Galileon fields through a suite of constrained N-body simulations (which we dub CSiBORG) and develop a Monte Carlo-based forward model for these offsets on a galaxy-by-galaxy basis. Using the measured offset between the optical center and active galactic nucleus of 1916 galaxies from the literature, propagating uncertainties in the input quantities and marginalizing over an empirical noise model describing astrophysical and observational noise, we constrain the Galileon coupling to be G / G N < 0.16 at 1 s confidence for Galileons with crossover scale r C H - 1 0. [ABSTRACT FROM AUTHOR]