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The article discusses the self-force on a static scalar and electrostatic field within the five-dimensional (5D) spacetime of a Schwarzschild-Tangherlini black hole, including several mathematical equations depiction this subject. An overview of the electric charges in the static scalar and electrostatic fields in the 5D black hole spacetime is provided.

The article discusses the problem of test particles and test scalar fields which propagate on the background of a class of wormhole space-times. Topics include causal geodesics and geodesic trajectories, computations for the geodesic to traverse the wormhole, and solutions of the scalar wave equation. The violations of energy conditions in quantum field theories is discussed.

In this paper, we consider the problem of computing the self-force and self-energy for a static scalar charge in a wormhole space-time with throat profile r(p) = √p² + a² for arbitrary coupling of the field to the curvature. This calculation has previously been considered numerically by Bexerra and Khusnutdinov [Phys. Rev. D 79, 064012 (2009)], while analytic results have been obtained in the special cases of minimal (ζ = 0) coupling [N. R. Khusnutdinov and 1. V. Bakhmatov, Phys. Rev. D 76, 124015 (2007)] and conformal coupling [yB. Bezerra and N.R. Khusnutdinov Phys. Rev. D 79, 064012 (2009)] (ζ = 1/8 in three dimensions). We present here a closed form expression for the static Green's function for arbitrary coupling and hence we obtain an analytic expression for the self-force. The self-force depends crucially on the coupling of the field to the curvature of the space-time and hence it is useful to determine the dependence explicitly. The numerical computation can identify some qualitative aspects of this dependence such as the change in the sign of the force as it passes through the conformally coupled value, as well as the fact that the self-force diverges for ζ = 1/2. From the closed form expression, it is straightforward to see that there is an infinite set of values of the coupling constant for which the self-force diverges, but we also see that there is an infinite set of values for which the self-force vanishes. [ABSTRACT FROM AUTHOR]

We consider the problem of quantum field theory on the Bertotti-Robinson space-time, which arises naturally as the near-horizon geometry of an extremal Reissner-Nordström black hole, but can also arise in certain near-horizon limits of nonextremal Reissner-Nordström space-time. The various vacuum states have been considered in the context of AdS2 black holes [M. Spradlin and A. Strominger, J. High Energy Phys. 11 (1999) 021] where it was shown that the Poincaré vacuum, the global vacuum and the Hartle-Hawking vacuum are all equivalent, while the Boulware vacuum and the Schwarzschild vacuum are equivalent. We verify this by explicitly computing the Green's functions in closed form for a massless scalar field corresponding to each of these vacua. Obtaining a closed form for the Green's function corresponding to the Boulware vacuum is nontrivial, and the novel computational technique employed may well be useful in deriving closed form Green's functions in other space-times. Having obtained the propagator for the Boulware vacuum, which is a zero-temperature Green's function, we can then consider the case of a scalar field at an arbitrary temperature by an infinite image imaginary-time sum, which yields the Hartle-Hawking propagator upon setting the temperature to the Hawking temperature. Finally, we compute the renormalized stress-energy tensor for a massless scalar field in the various quantum vacua. [ABSTRACT FROM AUTHOR]

We derive a closed-form solution for the Green's function for the wave equation of a static (with respect to an undragged, static observer at infinity) scalar charge in the Kerr space-time. We employ our solution to obtain an analytic expression for the self-force on such a charge, comparing our results to those of L. M. Burko and Y. T. Liu, Phys. Rev. D 64, 024006 (2001). [ABSTRACT FROM AUTHOR]

Using Subaru Hyper Suprime-Cam (HSC) year 1 data, we perform the first k-cut cosmic shear analysis constraining both Λ CDM and f(R) Hu-Sawicki modified gravity. To generate the f(R) cosmic shear theory vector, we use the matter power spectrum emulator trained on COLA (COmoving Lagrangian Acceleration) simulations [Phys. Rev. D 103, 123525 (2021). The k-cut method is used to significantly down-weight sensitivity to small scale(k > 1 h Mpc-1) modes in the matter power spectrum where the emulator is less accurate, while simultaneously ensuring our results are robust to baryonic feedback model uncertainty. We have also developed a test to ensure that the effects of poorly modeled small scales are nulled as intended. For Λ CDM we find S8 = σ8(Ωm/0.3)0.5 = 0.789-0.022+0.039, while the constraints on the f(R) modified gravity parameters are prior dominated. In the future, the k-cut method could be used to constrain a large number of theories of gravity where computational limitations make it infeasible to model the matter power spectrum down to extremely small scales. [ABSTRACT FROM AUTHOR]

We present a new method, called x-cut cosmic shear, which optimally removes sensitivity to poorly modeled scales from the two-point cosmic shear signal. We show that the x-cut cosmic shear covariance matrix can be computed from the correlation function covariance matrix in a few minutes, enabling a likelihood analysis at virtually no additional computational cost. Further we show how to generalize x-cut cosmic shear to galaxy-galaxy lensing. Performing an x-cut cosmic shear analysis of the Dark Energy Survey Year 1 (DESY1) shear data, we reduce the error on S8=s8(Om/0.3)0.5 by 32% relative to a correlation function analysis with the same priors and angular scale cut criterion, while showing our constraints are robust to different baryonic feedback models. Largely driven by information at small angular scales, our result, S8=0.734±0.026, yields a 2.6s tension with the Planck Legacy analysis of the cosmic microwave background. As well as alleviating baryonic modeling uncertainties, our method can be used to optimally constrain a large number of theories of modified gravity where computational limitations make it infeasible to model the power spectrum down to extremely small scales. [ABSTRACT FROM AUTHOR]

We consider a quantum scalar field on the classical background of an asymptotically anti-de Sitter black hole and the backreaction the field's stress-energy tensor induces on the black hole geometry. The backreaction is computed by solving the reduced-order semiclassical Einstein field equations sourced by simple analytical approximations for the renormalized expectation value of the scalar field stress-energy tensor. When the field is massless and conformally coupled, we adopt Page's approximation to the renormalized stress-energy tensor, while for massive fields we adopt a modified version of the DeWitt-Schwinger approximation. The latter approximation must be modified so that it possesses the correct renormalization freedom required to ensure the semiclassical equations are consistent. Equipped with these approximations, the reduced-order field equations are easily integrated and the first-order (in ?) corrections to the metric are obtained. We also compute the corrections to the black hole event horizon, surface gravity, and minimum temperature as well as corrections to the photon sphere and quadratic curvature invariants. We pay particular attention to the temperature profiles of the semiclassical black holes compared with their classical counterparts, pointing out some interesting qualitative features produced by the backreaction. These results ought to provide reasonable approximations to the first-order (one-loop) quantum backreaction on the geometry of asymptotically anti-de Sitter black holes when the exact numerical stress-energy tensor sources the semiclassical equations. [ABSTRACT FROM AUTHOR]

The precision of Stage IV cosmic shear surveys will enable us to probe smaller physical scales than ever before, however, model uncertainties from baryonic physics and non-linear structure formation will become a significant concern. The k-cut method--applying a redshift-dependent ℓ-cut after making the Bernardeau-Nishimichi-Taruya transform--can reduce sensitivity to baryonic physics; allowing Stage IV surveys to include information from increasingly higher ℓ-modes. Here we address the question of whether it can also mitigate the impact of making the reduced shear approximation; which is also important in the high-κ, small-scale regime. The standard procedure for relaxing this approximation requires the repeated evaluation of the convergence bispectrum, and consequently can be prohibitively computationally expensive when included in Monte Carlo analyses. We find that the k-cut cosmic shear procedure suppresses the w0wa CDM cosmological parameter biases expected from the reduced shear approximation for Stage IV experiments, when ℓ-modes up to 5000 are probed. The maximum cut required for biases from the reduced shear approximation to be below the threshold of significance is at k=5.37 h Mpc-1. With this cut, the predicted 1s constraints increase, relative to the case where the correction is directly computed, by less than 10% for all parameters. This represents a significant improvement in constraints compared to the more conservative case where only ℓ-modes up to 1500 are probed [A. Blanchard et al., (Euclid Collaboration), arXiv:1910.09273], and no k-cut is used. We also repeat this analysis for a hypothetical, comparable kinematic weak lensing survey. The key parts of code used for this analysis are made publicly available. [ABSTRACT FROM AUTHOR]

Density-estimation likelihood-free inference (DELFI) has recently been proposed as an efficient method for simulation-based cosmological parameter inference. Compared to the standard likelihood-based Markov chain Monte Carlo (MCMC) approach, DELFI has several advantages: it is highly parallelizable, there is no need to assume a possibly incorrect functional form for the likelihood, and complicated effects (e.g., the mask and detector systematics) are easier to handle with forward models. In light of this, we present two DELFI pipelines to perform weak lensing parameter inference with log-normal realizations of the tomographic shear field--using the Cℓ summary statistic. The first pipeline accounts for the non-Gaussianities of the shear field, intrinsic alignments, and photometric-redshift error. We validate that it is accurate enough for Stage III experiments and estimate that O(1000) simulations are needed to perform inference on Stage IV data. By comparing the second DELFI pipeline, which makes no assumption about the functional form of the likelihood, with the standard MCMC approach, which assumes a Gaussian likelihood, we test the impact of the Gaussian likelihood approximation in the MCMC analysis. We find it has a negligible impact on Stage IV parameter constraints. Our pipeline is a step towards seamlessly propagating all data-processing, instrumental, theoretical, and astrophysical systematics through to the final parameter constraints. [ABSTRACT FROM AUTHOR]

In this paper, we address the problem of finding optimal cosmic shear tomographic bins. We generalize the definition of a cosmic shear tomographic bin to be a set of commonly labeled voxels in photometric color space; rather than bins defined directly in redshift. We explore this approach by using a self-organizing map to define the multidimensional color space, and a we define a "label space" of connected regions on the self-organizing map using overlapping elliptical disks. This allows us to then find optimal labeling schemes by searching the label space. We use a metric that is the signal-to-noise ratio of a dark energy equation of state measurement, and in this case we find that for up to five tomographic bins the optimal color-space labeling is an approximation of an equally spaced binning in redshift; that is in all cases the best configuration. We also show that such a redefinition is more robust to photometric redshift outliers than a standard tomographic bin selection. [ABSTRACT FROM AUTHOR]

We present a method to measure the growth of structure and the background geometry of the Universe--with no a priori assumption about the underlying cosmological model. Using Canada-France-Hawaii Lensing Survey (CFHTLenS) shear data, we simultaneously reconstruct the lensing amplitude, the linear intrinsic alignment amplitude, the redshift evolving matter power spectrum, P(k,z), and the comoving distance, r(z). We find that lensing predominately constrains a single global power spectrum amplitude and several comoving distance bins. Our approach can localize the precise scales (k-modes in the matter power spectrum) and redshifts where lambda-cold dark matter (LCDM) fails--if any. We find that below z=0.4, the measured comoving distance r(z) is higher than that expected from the Planck LCDM cosmology by ∼1.5σ, while at higher redshifts, our reconstruction is fully consistent. To validate our reconstruction, we compare LCDM parameter constraints from the standard cosmic shear likelihood analysis to those found by fitting to the nonparametric information and we find good agreement. [ABSTRACT FROM AUTHOR]

Equipped with new powerful and efficient methods for computing quantum expectation values in static-spherically symmetric spacetimes in arbitrary dimensions, we perform an in-depth investigation of how the quantum vacuum polarization varies with the parameters in the theory. In particular, we compute and compare the vacuum polarization for a quantum scalar field in the Schwarzschild-anti-de Sitter black hole spacetime for a range of values of the field mass and field coupling constant as well as the black hole mass and number of spacetime dimensions. In addition, a new approximation for the vacuum polarization in asymptotically anti-de Sitter black hole spacetimes is presented. [ABSTRACT FROM AUTHOR]

If left unchecked modeling uncertainties at small scales, due to poorly understood baryonic physics and nonlinear structure formation, will significantly bias Stage IV cosmic shear two-point statistic parameter constraints. While it is perhaps possible to run N-body or hydrodynamical simulations to determine the impact of these effects this approach is computationally expensive; especially to test a large number of theories of gravity. Instead we propose directly removing sensitivity to small-scale structure from the lensing spectrum, creating a statistic that is robust to these uncertainties. We do this by taking a redshift-dependent ℓ-cut after applying the Bernardeau-Nishimichi-Taruya (BNT) nulling scheme. This reorganizes the information in the lensing spectrum to make the relationship between the angular scale, ℓ, and the structure scale, k, much clearer compared to standard cosmic shear power spectra--for which no direct relationship exists. We quantify the effectiveness of this method at removing sensitivity to small scales and compute the predicted Fisher error on the dark energy equation of state, w0, for different k-cuts in the matter power spectrum. [ABSTRACT FROM AUTHOR]

Upcoming photometric lensing surveys will considerably tighten constraints on the neutrino mass and the dark energy equation of state. Nevertheless it remains an open question of how to optimally extract the information and how well the matter power spectrum must be known to obtain unbiased cosmological parameter estimates. By performing a principal component analysis (PCA), we quantify the sensitivity of 3D cosmic shear and tomography with different binning strategies to different regions of the lensing kernel and matter power spectrum, and hence the background geometry and growth of structure in the Universe. We find that a large number of equally spaced tomographic bins in redshift can extract nearly all the cosmological information without the additional computational expense of 3D cosmic shear. Meanwhile a large fraction of the information comes from small poorly understood scales in the matter power spectrum, that can lead to biases on measurements of cosmological parameters. In light of this, we define and compute a cosmology-independent measure of the bias due to imperfect knowledge of the power spectrum. For a Euclid-like survey, we find that the power spectrum must be known to an accuracy of less than 1% on scales with k≤7h Mpc-1. This requirement is not absolute since the bias depends on the magnitude of modeling errors, where they occur in k-z space, and the correlation between them, all of which are specific to any particular model. We therefore compute the bias in several of the most likely modeling scenarios and introduce a general formalism and public code, RequiSim, to compute the expected bias from any nonlinear model. [ABSTRACT FROM AUTHOR]

We introduce the Generalised Lensing and Shear Spectra (GLaSS) code which is available for download from https://github.com/astro-informatics/GLaSS It is a fast and flexible public code, written in Python, that computes generalized spherical cosmic shear spectra. The commonly used tomographic and spherical Bessel lensing spectra come as built-in run-mode options. GLaSS is integrated into the Cosmosis modular cosmological pipeline package. We outline several computational choices that accelerate the computation of cosmic shear power spectra. Using GLaSS, we test whether the assumption that using the lensing and projection kernels for a spatially-flat universe--in a universe with a small amount of spatial curvature--negligibly impacts the lensing spectrum. We refer to this assumption as the spatially-flat universe approximation, that has been implicitly assumed in all cosmic shear studies to date. We confirm that the spatially-flat universe approximation has a negligible impact on Stage IV cosmic shear experiments. [ABSTRACT FROM AUTHOR]

The self-force problem--which asks how self-interaction affects a body's motion--has been poorly studied for spacetime dimensions d≠4. We remedy this for all d≥3 by nonperturbatively constructing momenta such that forces and torques acting on extended, self-interacting electromagnetic charges have the same functional forms as their test body counterparts. The electromagnetic field which appears in the resulting laws of motion is not however the physical one, but a certain effective surrogate which we derive. For even d≥4, explicit momenta are identified such that this surrogate field satisfies the source-free Maxwell equations; laws of motion in these cases can be obtained similarly to those in the well-known four-dimensional Detweiler-Whiting prescription. For odd d, no analog of the Detweiler-Whiting prescription exists. Nevertheless, we derive its replacement. These general results are used to obtain explicit point-particle self-forces and self-torques in Minkowski spacetimes with various dimensions. Among various characteristics of the resulting equations, perhaps the most arresting is that an initially stationary charge which is briefly kicked in 2+1 dimensions asymptotically returns to rest. [ABSTRACT FROM AUTHOR]

We present a mode-sum regularization prescription for computing the vacuum polarization of a scalar field in static spherically symmetric black hole spacetimes in even dimensions. This is the first general and systematic approach to regularized vacuum polarization in higher even dimensions, building upon a previous scheme we developed for odd dimensions. Things are more complicated here since the even-dimensional propagator possesses logarithmic singularities which must be regularized. However, in spite of this complication, the regularization parameters can be computed in closed form in arbitrary even dimensions and for arbitrary metric function f(r). As an explicit example of our method, we show plots for vacuum polarization of a massless scalar field in the Schwarzschild-Tangherlini spacetime for even d=4,...,10. However, the method presented applies straightforwardly to massive fields or to nonvacuum spacetimes. [ABSTRACT FROM AUTHOR]

We present a new mode-sum regularization prescription for computing the vacuum polarization of a scalar field in static spherically symmetric black hole spacetimes in odd dimensions. This is the first general and systematic approach to regularized vacuum polarization in higher dimensions. Remarkably, the regularization parameters can be computed in closed form in arbitrary dimensions and for arbitrary metric function f(r). In fact, we show that in spite of the increasing severity and number of the divergences to be regularized, the method presented is mostly agnostic to the number of dimensions. Finally, as an explicit example of our method, we show plots for vacuum polarization in the Schwarzschild-Tangherlini spacetime for odd d=5,11. [ABSTRACT FROM AUTHOR]

We compute the renormalized vacuum polarization for a massless, conformally coupled scalar field on asymptotically anti-de Sitter black hole backgrounds. Mixed (Robin) boundary conditions are applied on the spacetime boundary. We consider black holes with nonspherical event horizon topology as well as spherical event horizons. The quantum scalar field is in the Hartle-Hawking state, and we employ Euclidean methods to calculate the renormalized expectation values. Far from the black hole, we find that the vacuum polarization approaches a finite limit, which is the same for all boundary conditions except Dirichlet boundary conditions. [ABSTRACT FROM AUTHOR]