167 research outputs found
KiDS-1000 Cosmology::machine learning - accelerated constraints on Interacting Dark Energy with COSMOPOWER
We derive constraints on a coupled quintessence model with pure momentum
exchange from the public 1000 deg cosmic shear measurements from the
Kilo-Degree Survey and the 2018 Cosmic Microwave Background data.
We compare this model with CDM and find similar and
log-evidence values. We accelerate parameter estimation by sourcing
cosmological power spectra from the neural network emulator COSMOPOWER. We
highlight the necessity of such emulator-based approaches to reduce the
computational runtime of future similar analyses, particularly from Stage IV
surveys. As an example, we present MCMC forecasts on the same coupled
quintessence model for a -like survey, revealing degeneracies
between the coupled quintessence parameters and the baryonic feedback and
intrinsic alignment parameters, but also highlighting the large increase in
constraining power Stage IV surveys will achieve. The contours are obtained in
a few hours with COSMOPOWER, as opposed to the few months required with a
Boltzmann code.Comment: 5 pages, 2 min. summary video available at
https://youtu.be/c2x8hzApAgE. Emulators available in the COSMOPOWER GitHub
repository, https://github.com/alessiospuriomancini/cosmopower. Matches
version published in MNRAS Letter
Prospects for cosmic magnification measurements using HI intensity mapping
We investigate the prospects of measuring the cosmic magnification effect by cross-correlating neutral hydrogen intensity mapping (H I IM) maps with background optical galaxies. We forecast the signal-to-noise ratio for H i IM data from SKA1-MID and HIRAX, combined with LSST photometric galaxy samples. We find that, thanks to their different resolutions, SKA1-MID and HIRAX are highly complementary in such an analysis. We predict that SKA1-MID can achieve a detection with a signal-to-noise ratio of ∼15 on a multipole range of ℓ ≲ 200, while HIRAX can reach a signal-to-noise ratio of ∼50 on 200 < ℓ < 2000. We conclude that measurements of the cosmic magnification signal will be possible on a wide redshift range with foreground H I intensity maps up to z ≲ 2, while optimal results are obtained when 0.6 ≲ z ≲ 1.3
Simulations for 21 cm radiation lensing at EoR redshifts
We introduce simulations aimed at assessing how well weak gravitational
lensing of 21cm radiation from the Epoch of Reionization () can be
measured by an SKA-like radio telescope. A simulation pipeline has been
implemented to study the performance of lensing reconstruction techniques. We
show how well the lensing signal can be reconstructed using the
three-dimensional quadratic lensing estimator in Fourier space assuming
different survey strategies. The numerical code introduced in this work is
capable of dealing with issues that can not be treated analytically such as the
discreteness of visibility measurements and the inclusion of a realistic model
for the antennae distribution. This paves the way for future numerical studies
implementing more realistic reionization models, foreground subtraction
schemes, and testing the performance of lensing estimators that take into
account the non-Gaussian distribution of HI after reionization. If multiple
frequency channels covering are combined, Phase 1 of SKA-Low
should be able to obtain good quality images of the lensing potential with a
total resolution of arcmin. The SKA-Low Phase 2 should be capable of
providing images with high-fidelity even using data from . We
perform tests aimed at evaluating the numerical implementation of the mapping
reconstruction. We also discuss the possibility of measuring an accurate
lensing power spectrum. Combining data from using the SKA2-Low
telescope model, we find constraints comparable to sample variance in the range
, even for survey areas as small as 25\mbox{ deg}^2.Comment: 23 pages, 18 figures. Accepted for pubblication in MNRA
Gravitational Lensing of Cosmological 21cm Emission
We investigate the feasibility of measuring weak gravitational lensing using
21cm intensity mapping with special emphasis on the performance of the planned
Square Kilometre Array (SKA). We find that the current design for SKA-Mid
should be able to measure the evolution of the lensing power spectrum at z~2-3
using this technique. This will be a probe of the expansion history of the
universe and gravity at a unique range in redshift. The signal-to-noise is
found to be highly dependent on evolution of the neutral hydrogen fraction in
the universe with a higher HI density resulting in stronger signal. With
realistic models for this, SKA Phase 1 should be capable of measuring the
lensing power spectrum and its evolution. The signal-to-noise's dependence on
the area and diameter of the telescope array is quantified. We further
demonstrate the applications of this technique by applying it to two specific
coupled dark energy models that would be difficult to observationally
distinguish without information from this range of redshift. We also
investigate measuring the lensing signal with 21cm emission from the Epoch of
Reionization (EoR) using SKA-Low and find that it is unlikely to constrain
cosmological parameters because of the small survey size, but could provide a
map of the dark matter within a small region of the sky.Comment: 18 pages, 14 figures; version accepted for publication in MNRA
Weak lensing with 21cm intensity mapping at
We study how 21 cm intensity mapping can be used to measure gravitational
lensing over a wide range of redshift. This can extend weak lensing
measurements to higher redshifts than are accessible with conventional galaxy
surveys. We construct a convergence estimator taking into account the
discreteness of galaxies and calculate the expected noise level as a function
of redshift and telescope parameters. At we find that a telescope
array with a collecting area spread over a region with
diameter would be sufficient to measure the convergence
power spectrum to high accuracy for multipoles between 10 and 1,000. We show
that these measurements can be used to constrain interacting dark energy
models.Comment: 5 pages, 3 figure
Assessing non-linear models for galaxy clustering I: unbiased growth forecasts from multipole expansion
We assess the performance of the Taruya, Nishimichi and Saito (TNS) model for
the halo redshift space power spectrum, focusing on utilising mildly non-linear
scales to constrain the growth rate of structure f. Using simulations with
volume and number density typical of forthcoming Stage IV galaxy surveys, we
determine ranges of validity for the model at redshifts z = 0.5 and z = 1. We
proceed to perform a Bayesian MCMC analysis utilising the monopole, quadrupole,
and hexadecapole spectra, followed by an exploratory Fisher matrix analysis. As
previously noted in other forecasts as well as in real data analyses, we find
that including the hexadecapole can significantly improve the constraints.
However, a restricted range of scales is required for the hexadecapole in order
for the growth parameter estimation to remain unbiased, limiting the
improvement. We consistently quantify these effects by employing the multipole
expansion formalism in both our Fisher and MCMC forecasts.Comment: 12 pages, 7 figures, 2 tables, accepted in OJ
Scaling configurations of cosmic superstring networks and their cosmological implications
We study the cosmic microwave background temperature and polarisation spectra
sourced by multi-tension cosmic superstring networks. First we obtain solutions
for the characteristic length scales and velocities associated with the
evolution of a network of F-D strings, allowing for the formation of junctions
between strings of different tensions. We find two distinct regimes describing
the resulting scaling distributions for the relative densities of the different
types of strings, depending on the magnitude of the fundamental string coupling
g_s. In one of them, corresponding to the value of the coupling being of order
unity, the network's stress-energy power spectrum is dominated by populous
light F and D strings, while the other regime, at smaller values of g_s, has
the spectrum dominated by rare heavy D strings. These regimes are seen in the
CMB anisotropies associated with the network. We focus on the dependence of the
shape of the B-mode polarisation spectrum on g_s and show that measuring the
peak position of the B-mode spectrum can point to a particular value of the
string coupling. Finally, we assess how this result, along with pulsar bounds
on the production of gravitational waves from strings, can be used to constrain
a combination of g_s and the fundamental string tension mu_F. Since CMB and
pulsar bounds constrain different combinations of the string tensions and
densities, they result in distinct shapes of bounding contours in the (mu_F,
g_s) parameter plane, thus providing complementary constraints on the
properties of cosmic superstrings.Comment: 23 pages, 8 figures, 3 tables; V2: matches published version (PRD
Testing gravity at large scales with H I intensity mapping
We investigate the possibility of testing Einstein's general theory of
relativity (GR) and the standard cosmological model via the
statistic using neutral hydrogen (HI) intensity mapping. We generalise the
Fourier space estimator for to include HI as a biased tracer of
matter and forecast statistical errors using HI clustering and lensing surveys
that can be performed in the near future, in combination with ongoing and
forthcoming optical galaxy and Cosmic Microwave Background (CMB) surveys. We
find that fractional errors in the measurement can be
achieved in a number of cases and compare the ability of various survey
combinations to differentiate between GR and specific modified gravity models.
Measuring with intensity mapping and the Square Kilometre Array can
provide exquisite tests of gravity at cosmological scales.Comment: 9 pages, 4 figures, 1 table; typo in Table 1 corrected, discussion
added; version accepted for publication in MNRA
Zipping and unzipping in string networks: dynamics of Y-junctions
We study, within the Nambu-Goto approximation, the stability of massive string junctions under the influence of the tensions of three strings joining together in a Y-type configuration. The relative angle β between the strings at the junction is in general time dependent and its evolution can lead to zipping or unzipping of the three-string configuration. We find that these configurations are stable under deformations of the tension balance condition at the junction. The angle β relaxes at its equilibrium value and the junction grows relativistically. We then discuss other potential “unzipping agents” including monopole/string forces for long strings and curvature for loops, and we investigate specific solutions exhibiting decelerated zipping and unzipping of the Y junction. These results provide motivation for incorporating the effects of realistic string interactions in network evolution models with string junctions
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