Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGeneral Relativistic Effects in Weak Lensing Angular Power Spectra
108
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Advances in upcoming weak lensing surveys pose new challenges for an accurate modeling of the lensing observables. With their large sky coverage, common approximations based on a flat-sky geometry cannot be used anymore to evaluate all measurable angular scales. Moreover, additional relativistic effects manifest themselves on large scales and thus need to be accounted for. In particular, the lensing magnification cannot be correctly described by the standard lensing convergence only. We present the analytical solutions for the fully-relativistic weak lensing angular power spectra, including the contribution from primordial gravitational waves. We compare the results obtained by using the Limber approximation with the precise all-sky calculations using spherical harmonics. Our numerical evaluations show that general relativistic corrections are one order-of-magnitude below cosmic variance at small scales ($lgeq 10$). At large scales ($l<10$), however, neglecting them leads to more significant errors, especially when combined with the Limber approximation. Hence, a precise, fully-relativistic modeling is necessary at these largest scales.
rate research
Read More
Angular two-point statistics of large-scale structure observables are important cosmological probes. To reach the high accuracy required by the statistical precision of future surveys, some of these statistics may need to be computed without the commonly employed Limber approximation; the exact computation however requires integration over Bessel functions, and a brute-force evaluation is slow to converge. We present a new method based on our generalized FFTLog algorithm for the efficient computation of angular power spectra beyond the Limber approximation. The new method significantly simplifies the calculation and improves the numerical speed and stability. It is easily extended to handle integrals involving derivatives of Bessel functions, making it equally applicable to numerically more challenging cases such as contributions from redshift-space distortions and Doppler effects. We implement our method for galaxy clustering and galaxy-galaxy lensing power spectra. We find that using the Limber approximation for galaxy clustering in future analyses like LSST Year 1 and DES Year 6 may cause significant biases in cosmological parameters, indicating that going beyond the Limber approximation is necessary for these analyses.
Future galaxy clustering surveys will probe small scales where non-linearities become important. Since the number of modes accessible on intermediate to small scales is very high, having a precise model at these scales is important especially in the context of discriminating alternative cosmological models from the standard one. In the mildly non-linear regime, such models typically differ from each other, and galaxy clustering data will become very precise on these scales in the near future. As the observable quantity is the angular power spectrum in redshift space, it is important to study the effects of non-linear density and redshift space distortion (RSD) in the angular power spectrum. We compute non-linear contributions to the angular power spectrum using a flat-sky approximation that we introduce in this work, and compare the results of different perturbative approaches with $N$-body simulations. We find that the TNS perturbative approach is significantly closer to the $N$-body result than Eulerian or Lagrangian 1-loop approximations, effective field theory of large scale structure or a halofit-inspired model. However, none of these prescriptions is accurate enough to model the angular power spectrum well into the non-linear regime. In addition, for narrow redshift bins, $Delta z lesssim 0.01$, the angular power spectrum acquires non-linear contributions on all scales, right down to $ell=2$, and is hence not a reliable tool at this time. To overcome this problem, we need to model non-linear RSD terms, for example as TNS does, but for a matter power spectrum that remains reasonably accurate well into the deeply non-linear regime, such as halofit.
The study of relativistic, higher order and nonlinear effects has become necessary in recent years in the pursuit of precision cosmology. We develop and apply here a framework to study gravitational lensing in exact models in general relativity that are not restricted to homogeneity and isotropy, and where full nonlinearity and relativistic effects are included. We apply the framework to a specific, anisotropic galaxy cluster model which is based on a modified NFW halo density profile and described by the Szekeres metric. We examine the effects of increasing levels of anisotropy in the galaxy cluster on lensing observables like the convergence and shear for various lensing geometries, finding a strong nonlinear response in both the convergence and shear for rays passing through anisotropic regions of the cluster. Deviation from the expected values in a spherically symmetric structure are asymmetric with respect to path direction and thus will persist as a statistical effect when averaged over some ensemble of such clusters. The resulting relative difference in various geometries can be as large as approximately 2%, 8%, and 24% in the measure of convergence for levels of anisotropy of 5%, 10%, and 15%, respectively, as a fraction of total cluster mass. For the total magnitude of shear, the relative difference can grow near the center of the structure to be as large as 15%, 32%, and 44% for the same levels of anisotropy, averaged over the two extreme geometries. The convergence is impacted most strongly for rays which pass in directions along the axis of maximum dipole anisotropy in the structure, while the shear is most strongly impacted for rays which pass in directions orthogonal to this axis, as expected. These effects due to anisotropic structures will affect lensing measurements and must be fully examined in an era of precision cosmology.
We present initial results from the Jubilee ISW project, which models the expected LambdaCDM Integrated Sachs-Wolfe (ISW) effect in the Jubilee simulation. The simulation volume is (6 Gpc/h)^3, allowing power on very large-scales to be incorporated into the calculation. Haloes are resolved down to a mass of 1.5x10^12 M_sun/h, which allows us to derive a catalogue of mock Luminous Red Galaxies (LRGs) for cross-correlation analysis with the ISW signal. We find the ISW effect observed on a projected sky to grow stronger at late times with the evolution of the ISW power spectrum matching expectations from linear theory. Maps of the gravitational lensing effect, including the convergence and deflection fields, are calculated using the same potential as for the ISW. We calculate the redshift dependence of the ISW-LRG cross-correlation signal for a full sky survey with no noise considerations. For l < 30, the signal is strongest for lower redshift bins (z ~ 0.2 to 0.5), whereas for l > 30 the signal is best observed with surveys covering z ~ 0.6-1.0.
We examine general physical parameterisations for viable gravitational models in the $f(R)$ framework. This is related to the mass of an additional scalar field, called the scalaron, that is introduced by the theories. Using a simple parameterisation for the scalaron mass $M(a)$ we show there is an exact correspondence between the model and popular parameterisations of the modified Poisson equation $mu(a,k)$ and the ratio of the Newtonian potentials $eta(a,k)$. However, by comparing the aforementioned model against other viable scalaron theories we highlight that the common form of $mu(a,k)$ and $eta(a,k)$ in the literature does not accurately represent $f(R)$ behaviour. We subsequently construct an improved description for the scalaron mass (and therefore $mu(a,k)$ and $eta(a,k)$) which captures their essential features and has benefits derived from a more physical origin. We study the scalarons observational signatures and show the modification to the background Friedmann equation and CMB power spectrum to be small. We also investigate its effects in the linear and non linear matter power spectrum--where the signatures are evident--thus giving particular importance to weak lensing as a probe of these models. Using this new form, we demonstrate how the next generation Euclid survey will constrain these theories and its complementarity to current solar system tests. In the most optimistic case Euclid, together with a Planck prior, can constrain a fiducial scalaron mass $M_{0} = 9.4 times 10^{-30}{rm eV}$ at the $sim 20 %$ level. However, the decay rate of the scalaron mass, with fiducial value $ u = 1.5$, can be constrained to $sim 3%$ uncertainty.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
