159 research outputs found
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 , 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 up to at . 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 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 (CDM) background evolution
will be probed by fitting a CDM model, which allows for a
redshift-dependent dark energy equation of state with , within general
relativity (GR). A rich array of other phenomena can arise due to deviations
from the standard 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 . 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
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