Exploring degeneracies in modified gravity with weak lensing

By considering linear-order departures from general relativity, we compute a novel expression for the weak lensing convergence power spectrum under alternative theories of gravity. This comprises an integral over a 'kernel' of general relativistic quantities multiplied by a theory-dependent 'source' term. The clear separation between theory-independent and -dependent terms allows for an explicit understanding of each physical effect introduced by altering the theory of gravity. We take advantage of this to explore the degeneracies between gravitational parameters in weak lensing observations.Comment: 17 pages, 7 figures. v2: Minor changes to match version accepted by PR

A general theory of linear cosmological perturbations: stability conditions, the quasistatic limit and dynamics

We analyse cosmological perturbations around a homogeneous and isotropic background for scalar-tensor, vector-tensor and bimetric theories of gravity. Building on previous results, we propose a unified view of the effective parameters of all these theories. Based on this structure, we explore the viable space of parameters for each family of models by imposing the absence of ghosts and gradient instabilities. We then focus on the quasistatic regime and confirm that all these theories can be approximated by the phenomenological two-parameter model described by an effective Newton's constant and the gravitational slip. Within the quasistatic regime we pinpoint signatures which can distinguish between the broad classes of models (scalar-tensor, vector-tensor or bimetric). Finally, we present the equations of motion for our unified approach in such a way that they can be implemented in Einstein-Boltzmann solvers

Fast production of cosmological emulators in modified gravity: the matter power spectrum

We test the convergence of fast simulations based on the COmoving Lagrangian Acceleration (COLA) method for predictions of the matter power spectrum, specialising our analysis in the redshift range $1 \le z \le 1.65$, relevant to high-redshift spectroscopic galaxy surveys. We then focus on the enhancement of the matter power spectrum in modified gravity (MG), the boost factor, using the Dvali-Gabadadze-Porrati (DGP) theory as a test case but developing a general approach that can be applied to other MG theories. After identifying the minimal simulation requirements for accurate DGP boost factors, we design and produce a COLA simulation suite that we use to train a neural network emulator for the DGP boost factor. Using MG-AREPO simulations as a reference, we estimate the emulator accuracy to be of $\sim 3\%$ up to $k=5 \, h {\rm Mpc}^{-1}$ at $0 \leq z \leq 2$. We make the emulator publicly available at: https://github.com/BartolomeoF/nDGPemu.Comment: 24 pages, 17 figures, Comments are welcome - Accepted for publication in JCA

Testing the nature of gravitational wave propagation using dark sirens and galaxy catalogues

The dark sirens method enables us to use gravitational wave events without electromagnetic counterparts as tools for cosmology and tests of gravity. Furthermore, the dark sirens analysis code gwcosmo can now robustly account for information coming from both galaxy catalogues and the compact object mass distribution. We present here an extension of the gwcosmo code and methodology to constrain parameterized deviations from General Relativity that affect the propagation of gravitational waves. We show results of our analysis using data from the GWTC-3 gravitational wave catalogues, in preparation for application to the O4 observing run. After testing our pipelines using the First Two Years mock data set, we reanalyse 46 events from GWTC-3, and combine the posterior for BBH and NSBH sampling results for the first time. We obtain joint constraints on H0 and parameterized deviations from General Relativity in the Power Law + Peak BBH population model. With increased galaxy catalogue support in the future, our work sets the stage for dark sirens to become a powerful tool for testing gravity

Magnification and evolution bias of transient sources: GWs and SNIa

Third-generation gravitational wave (GW) observatories such as the Einstein Telescope and Cosmic Explorer, together with the LSST survey at the Vera Rubin Observatory, will yield an abundance of extra-galactic transient objects. This opens the exciting possibility of using GW sources and Supernovae Type Ia (SNIa) as luminosity distance tracers of large-scale structure for the first time. The large volumes accessible to these surveys imply that we may need to include relativistic corrections, such as lensing and Doppler magnification. However, the amplitude of these effects depends on the magnification and evolution biases of the transient sources, which are not yet understood. In this paper we develop comprehensive frameworks to address and model these biases for both populations of transient objects; in particular, we define how to compute these biases for GW sources. We then analyse the impact of magnification and evolution biases on the relativistic corrections and on the angular power spectrum of these sources. We show that correct modelling and implementation of these biases is crucial for measuring the cross-correlations of transient sources at higher redshifts.Comment: 28 pages, 14 figures, 4 tables, comments welcom

Modified Gravity and Dark Energy models Beyond w(z)w(z)CDM Testable by LSST

One of the main science goals of the Large Synoptic Survey Telescope (LSST) is to uncover the nature of cosmic acceleration. In the base analysis, possible deviations from the Lambda-Cold-Dark-Matter ($\Lambda$CDM) background evolution will be probed by fitting a $w(z)$CDM model, which allows for a redshift-dependent dark energy equation of state with $w(z)$, within general relativity (GR). A rich array of other phenomena can arise due to deviations from the standard $\Lambda$CDM+GR model though, including modifications to the growth rate of structure and lensing, and novel screening effects on non-linear scales. Concrete physical models are needed to provide consistent predictions for these (potentially small) effects, to give us the best chance of detecting them and separating them from astrophysical systematics. A complex plethora of possible models has been constructed over the past few decades, with none emerging as a particular favorite. This document prioritizes a subset of these models along with rationales for further study and inclusion into the LSST Dark Energy Science Collaboration (DESC) data analysis pipelines, based on their observational viability, theoretical plausibility, and level of theoretical development. We provide references and theoretical expressions to aid the integration of these models into DESC software and simulations, and give justifications for why other models were not prioritized. While DESC efforts are free to pursue other models, we provide here guidelines on which theories appear to have higher priority for collaboration efforts due to their perceived promise and greater instructional value.Comment: 61 pages. Some acknowledgments and references added. This is version-1.1 of an internal collaboration document of LSST-DESC that is being made public and is not planned for submission to a journa

Testing the nature of gravitational wave propagation using dark sirens and galaxy catalogues

The dark sirens method enables us to use gravitational wave events without electromagnetic counterparts as tools for cosmology and tests of gravity. Furthermore, the dark sirens analysis code gwcosmo can now robustly account for information coming from both galaxy catalogues and the compact object mass distribution. We present here an extension of the gwcosmo code and methodology to constrain parameterized deviations from General Relativity that affect the propagation of gravitational waves under the ΛCDM expansion history of the universe. We show results of our analysis using data from the GWTC-3 gravitational wave catalogues, in preparation for application to the O4 observing run. After testing our pipelines using the First Two Years mock data set, we reanalyse 46 events from GWTC-3, and combine the posterior for BBH and NSBH sampling results for the first time. We obtain joint constraints on H0 and parameterized deviations from General Relativity in the Power Law + Peak BBH population model. With increased galaxy catalogue support in the future, our work sets the stage for dark sirens to become a powerful tool for testing gravity

Testing gravitational wave propagation with multiband detections

Effective field theories (EFT) of dark energy (DE) -- built to parameterise the properties of DE in an agnostic manner -- are severely constrained by measurements of the propagation speed of gravitational waves (GW). However, GW frequencies probed by ground-based interferometers lie around the typical strong coupling scale of the EFT, and it is likely that the effective description breaks down before even reaching that scale. We discuss how this leaves the possibility that an appropriate ultraviolet completion of DE scenarios, valid at scales beyond an EFT description, can avoid present constraints on the GW speed. Instead, additional constraints in the lower frequency LISA band would be harder to escape, since the energies involved are orders of magnitude lower. By implementing a method based on GW multiband detections, we show indeed that a single joint observation of a GW150914-like event by LISA and a terrestrial interferometer would allow one to constrain the speed of light and gravitons to match to within $10^{-15}$. Multiband GW observations can therefore firmly constrain scenarios based on the EFT of DE, in a robust and unambiguous way.Comment: 11 pages, 4 figures. Updated to match the version published in JCA

Differences in Nonmedical Use of Prescription Stimulants Among Fraternity- and Sorority-Afiliated Students

The current study reviewed data from the 2022 College Prescription Drug Study of 4,967 undergraduate students to examine differences in lifetime and past-year misuse of prescription stimulants, academic motivations and consequences of misuse, and misperceptions of prescription stimulants. Results indicate that fraternity- and sorority-affiliated students are more likely to report misusing a prescription stimulant in their lifetime and within the past year than nonaffiliated students. Fraternity and sorority members are more influenced by academic reasons and social norms than nonaffiliated students, with gender identity further predicting level of risk. Implications for prevention programming for fraternity and sorority members are discussed