Large Scale Pressure Fluctuations and Sunyaev-Zel'dovich Effect

The Sunyaev-Zel'dovich (SZ) effect associated with pressure fluctuations of the large scale structure gas distribution will be probed with current and upcoming wide-field small angular scale cosmic microwave background experiments. We study the generation of pressure fluctuations by baryons which are present in virialized dark matter halos and by baryons present in small overdensities. For collapsed halos, assuming the gas distribution is in hydrostatic equilibrium with matter density distribution, we predict the pressure power spectrum and bispectrum associated with the large scale structure gas distribution by extending the dark matter halo approach which describes the density field in terms of correlations between and within halos. The projected pressure power spectrum allows a determination of the resulting SZ power spectrum due to virialized structures. The unshocked photoionized baryons present in smaller overdensities trace the Jeans-scale smoothed dark matter distribution. They provide a lower limit to the SZ effect due to large scale structure in the absence of massive collapsed halos. We extend our calculations to discuss higher order statistics, such as bispectrum and skewness in SZ data. The SZ-weak lensing cross-correlation is suggested as a probe of correlations between dark matter and baryon density fields, while the probability distribution functions of peak statistics of SZ halos in wide field CMB data can be used as a probe of cosmology and non-Gaussian evolution of large scale structure pressure fluctuations.Comment: 16 pages, 9 figures; Revised with expanded discussions. Phys. Rev. D. (in press

DT/T beyond linear theory

The major contribution to the anisotropy of the temperature of the Cosmic Microwave Background (CMB) radiation is believed to come from the interaction of linear density perturbations with the radiation previous to the decoupling time. Assuming a standard thermal history for the gas after recombination, only the gravitational field produced by the linear density perturbations present on a $\Omega\neq 1$ universe can generate anisotropies at low z (these anisotropies would manifest on large angular scales). However, secondary anisotropies are inevitably produced during the nonlinear evolution of matter at late times even in a universe with a standard thermal history. Two effects associated to this nonlinear phase can give rise to new anisotropies: the time-varying gravitational potential of nonlinear structures (Rees-Sciama RS effect) and the inverse Compton scattering of the microwave photons with hot electrons in clusters of galaxies (Sunyaev-Zeldovich SZ effect). These two effects can produce distinct imprints on the CMB temperature anisotropy. We discuss the amplitude of the anisotropies expected and the relevant angular scales in different cosmological scenarios. Future sensitive experiments will be able to probe the CMB anisotropies beyong the first order primary contribution.Comment: plain tex, 16 pages, 3 figures. Proceedings of the Laredo Advance School on Astrophysics "The universe at high-z, large-scale structure and the cosmic microwave background". To be publised by Springer-Verla

Simulation techniques for cosmological simulations

Modern cosmological observations allow us to study in great detail the evolution and history of the large scale structure hierarchy. The fundamental problem of accurate constraints on the cosmological parameters, within a given cosmological model, requires precise modelling of the observed structure. In this paper we briefly review the current most effective techniques of large scale structure simulations, emphasising both their advantages and shortcomings. Starting with basics of the direct N-body simulations appropriate to modelling cold dark matter evolution, we then discuss the direct-sum technique GRAPE, particle-mesh (PM) and hybrid methods, combining the PM and the tree algorithms. Simulations of baryonic matter in the Universe often use hydrodynamic codes based on both particle methods that discretise mass, and grid-based methods. We briefly describe Eulerian grid methods, and also some variants of Lagrangian smoothed particle hydrodynamics (SPH) methods.Comment: 42 pages, 16 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 12; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

Density perturbations in generalized Einstein scenarios and constraints on nonminimal couplings from the Cosmic Microwave Background

We study cosmological perturbations in generalized Einstein scenarios and show the equivalence of inflationary observables both in the Jordan frame and the Einstein frame. In particular the consistency relation relating the tensor-to-scalar ratio with the spectral index of tensor perturbations coincides with the one in Einstein gravity, which leads to the same likelihood results in terms of inflationary observables. We apply this formalism to nonminimally coupled chaotic inflationary scenarios with potential $V=c\phi^p$ and place constraints on the strength of nonminimal couplings using a compilation of latest observational data. In the case of the quadratic potential ($p=2$), the nonminimal coupling is constrained to be $\xi>-7.0 \times 10^{-3}$ for negative $\xi$ from the $1\sigma$ observational contour bound. Although the quartic potential ($p=4$) is under a strong observational pressure for $\xi=0$, this property is relaxed by taking into account negative nonminimal couplings. We find that inflationary observables are within the $1\sigma$ contour bound as long as $\xi<-1.7 \times 10^{-3}$. We also show that the $p \ge 6$ cases are disfavoured even in the presence of nonminimal couplings.Comment: 16 pages, 4 eps figure

Hysteresis and fast timescales in transport relations of toroidal plasmas

This article assesses current understanding of hysteresis in transport relations, and its impact on the field. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both core and edge plasmas. The modulation ECH experiment is explained, in which the heating power cycles on-and-off periodically, revealing hysteresis and fast changes in the gradientflux relation. The key finding is that hystereses were observed simultaneously in both the the gradientflux and gradientfluctuation relations. Hysteresis with rapid timescale exists in the channels of energy, electron and impurity densities, and plausibly in momentum. Advanced methods of data analysis are explained. Transport hysteresis can be studied by observing the higher harmonics of temperature perturbation ??Tm in heating modulation experiments. The hysteresis introduces the term ??Tm, which depends on the harmonic number m in an algebraic manner (not exponential decay). Next, the causes of hysteresis and its fast timescale are discussed. The nonlocal-in-space coupling works here, but does not suffice. One mechanism for the heating heats turbulence is that the external source S in phase space for heating has its fluctuation in turbulent plasma. This coupling can induce the direct input of heating power into fluctuations. The height of the jump in transport hysteresis is smaller for heavier hydrogen isotopes, and could be one of the origins of isotope effects on confinement. Finally, the impacts of transport hysteresis on the control system are assessed. Control systems must be designed so as to protect the system from sudden plasma loss

A MODEST review

We present an account of the state of the art in the fields explored by the research community invested in 'Modeling and Observing DEnse STellar systems'. For this purpose, we take as a basis the activities of the MODEST-17 conference, which was held at Charles University, Prague, in September 2017. Reviewed topics include recent advances in fundamental stellar dynamics, numerical methods for the solution of the gravitational N-body problem, formation and evolution of young and old star clusters and galactic nuclei, their elusive stellar populations, planetary systems, and exotic compact objects, with timely attention to black holes of different classes of mass and their role as sources of gravitational waves. Such a breadth of topics reflects the growing role played by collisional stellar dynamics in numerous areas of modern astrophysics. Indeed, in the next decade, many revolutionary instruments will enable the derivation of positions and velocities of individual stars in the Milky Way and its satellites and will detect signals from a range of astrophysical sources in different portions of the electromagnetic and gravitational spectrum, with an unprecedented sensitivity. On the one hand, this wealth of data will allow us to address a number of long-standing open questions in star cluster studies; on the other hand, many unexpected properties of these systems will come to light, stimulating further progress of our understanding of their formation and evolution.Comment: 42 pages; accepted for publication in 'Computational Astrophysics and Cosmology'. We are much grateful to the organisers of the MODEST-17 conference (Charles University, Prague, September 2017). We acknowledge the input provided by all MODEST-17 participants, and, more generally, by the members of the MODEST communit