8 research outputs found
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 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
The Void Abundance with Non-Gaussian Primordial Perturbations
We use a Press-Schechter-like calculation to study how the abundance of voids
changes in models with non-Gaussian initial conditions. While a positive
skewness increases the cluster abundance, a negative skewness does the same for
the void abundance. We determine the dependence of the void abundance on the
non-Gaussianity parameter fnl for the local-model bispectrum-which approximates
the bispectrum in some multi-field inflation models-and for the equilateral
bispectrum, which approximates the bispectrum in e.g. string-inspired DBI
models of inflation. We show that the void abundance in large-scale-structure
surveys currently being considered should probe values as small as fnl < 10 and
fnl^eq < 30, over distance scales ~10 Mpc.Comment: Submitted to JCA
Constraining Running Non-Gaussianity
The primordial non-Gaussian parameter fNL has been shown to be
scale-dependent in several models of inflation with a variable speed of sound.
Starting from a simple ansatz for a scale-dependent amplitude of the primordial
curvature bispectrum for two common phenomenological models of primordial
non-Gaussianity, we perform a Fisher matrix analysis of the bispectra of the
temperature and polarization of the Cosmic Microwave Background (CMB) radiation
and derive the expected constraints on the parameter nNG that quantifies the
running of fNL(k) for current and future CMB missions such as WMAP, Planck and
CMBPol. We find that CMB information alone, in the event of a significant
detection of the non-Gaussian component, corresponding to fNL = 50 for the
local model and fNL = 100 for the equilateral model of non-Gaussianity, is able
to determine nNG with a 1-sigma uncertainty of Delta nNG = 0.1 and Delta nNG =
0.3, respectively, for the Planck mission. In addition, we consider a Fisher
matrix analysis of the galaxy power spectrum to determine the expected
constraints on the running parameter nNG for the local model and of the galaxy
bispectrum for the equilateral model from future photometric and spectroscopic
surveys. We find that, in both cases, large-scale structure observations should
achieve results comparable to or even better than those from the CMB, while
showing some complementarity due to the different distribution of the
non-Gaussian signal over the relevant range of scales. Finally, we compare our
findings to the predictions on the amplitude and running of non-Gaussianity of
DBI inflation, showing how the constraints on a scale-dependent fNL(k)
translate into constraints on the parameter space of the theory.Comment: 37 pages, 14 figure
Relativistic Jets in Active Galactic Nuclei and Microquasars
Collimated outflows (jets) appear to be a ubiquitous phenomenon associated with the accretion of material onto a compact object. Despite this ubiquity, many fundamental physics aspects of jets are still poorly understood and constrained. These include the mechanism of launching and accelerating jets, the connection between these processes and the nature of the accretion flow, and the role of magnetic fields; the physics responsible for the collimation of jets over tens of thousands to even millions of gravitational radii of the central accreting object; the matter content of jets; the location of the region(s) accelerating particles to TeV (possibly even PeV and EeV) energies (as evidenced by (Formula presented.)-ray emission observed from many jet sources) and the physical processes responsible for this particle acceleration; the radiative processes giving rise to the observed multi-wavelength emission; and the topology of magnetic fields and their role in the jet collimation and particle acceleration processes. This chapter reviews the main knowns and unknowns in our current understanding of relativistic jets, in the context of the main model ingredients for Galactic and extragalactic jet sources. It discusses aspects specific to active Galactic nuclei (especially blazars) and microquasars, and then presents a comparative discussion of similarities and differences between them.Fil: Romero, Gustavo Esteban. Provincia de Buenos Aires. GobernaciĂłn. Comision de Investigaciones CientĂficas. Instituto Argentino de RadioastronomĂa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto Argentino de Radioastronomia; ArgentinaFil: Boettcher, Markus. North-West University; SudĂĄfricaFil: Markoff, Sera. University of Amsterdam; PaĂses BajosFil: Tavecchio, Fabrizio. Osservatorio Astronomico Di Brera; Itali