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Title:

Hydrodynamical instabilities and the trace of dark energy within the CMB

Publisher:

Ludwig-Maximilians-Universität München

Year of Publication:

2010-12-20

Document Type:

Dissertation ; NonPeerReviewed

Subjects:

Fakultät für Physik

Fakultät für Physik Minimize

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http://edoc.ub.uni-muenchen.de/13334/

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Title:

Cosmic Microwave Background Bispectrum from the Lensing--Rees-Sciama Correlation Reexamined: Effects of Non-linear Matter Clustering

Description:

The bispectrum of the cosmic microwave background (CMB) generated by a correlation between a time-dependent gravitational potential and the weak gravitational lensing effect provides a direct measurement of the influence of dark energy on CMB. This bispectrum is also known to yield the most important contamination of the so-called "local-form" p...

The bispectrum of the cosmic microwave background (CMB) generated by a correlation between a time-dependent gravitational potential and the weak gravitational lensing effect provides a direct measurement of the influence of dark energy on CMB. This bispectrum is also known to yield the most important contamination of the so-called "local-form" primordial bispectrum, which can be used to rule out all single-field inflation models. In this paper, we reexamine the effect of non-linear matter clustering on this bispectrum. We compare three different approaches: the 3rd-order perturbation theory (3PT), and two empirical fitting formulae available in the literature, finding that detailed modeling of non-linearity appears to be not very important, as most of the signal-to-noise comes from the squeezed triangle, for which the correlation in the linear regime dominates. The expected signal-to-noise ratio for an experiment dominated by the cosmic variance up to $l_{\rm max}=1500$ is about 5, which is much smaller than the previous estimates including non-linearity, but agrees with the estimates based on the linear calculation. We find that the difference between the linear and non-linear predictions is undetectable, and does not alter the contamination of the local-form primordial non-Gaussianity. ; Comment: 9 pages, 7 figures; Submitted to PRD. The unlensed Cl in the lensing-ISW bispectrum has been replaced by the lensed Cl following arXiv:1101.2234 Minimize

Year of Publication:

2012-04-17

Document Type:

text

Subjects:

Astrophysics - Cosmology and Extragalactic Astrophysics

Astrophysics - Cosmology and Extragalactic Astrophysics Minimize

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Title:

Modelling shear flows with smoothed particle hydrodynamics and grid-based methods

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Description:

Given the importance of shear flows for astrophysical gas dynamics, we study the evolution of the Kelvin–Helmholtz instability (KHI) analytically and numerically. We derive the dispersion relation for the two-dimensional KHI including viscous dissipation. The resulting expression for the growth rate is then used to estimate the intrinsic viscosi...

Given the importance of shear flows for astrophysical gas dynamics, we study the evolution of the Kelvin–Helmholtz instability (KHI) analytically and numerically. We derive the dispersion relation for the two-dimensional KHI including viscous dissipation. The resulting expression for the growth rate is then used to estimate the intrinsic viscosity of four numerical schemes depending on code-specific as well as on physical parameters. Our set of numerical schemes includes the Tree-SPH code <scp>vine</scp>, an alternative smoothed particle hydrodynamics (SPH) formulation developed by Price and the finite-volume grid codes <scp>flash</scp> and <scp>pluto</scp>. In the first part, we explicitly demonstrate the effect of dissipation-inhibiting mechanisms such as the Balsara viscosity on the evolution of the KHI. With <scp>vine</scp>, increasing density contrasts lead to a continuously increasing suppression of the KHI (with complete suppression from a contrast of 6:1 or higher). The alternative SPH formulation including an artificial thermal conductivity reproduces the analytically expected growth rates up to a density contrast of 10:1. The second part addresses the shear flow evolution with <scp>flash</scp> and <scp>pluto</scp>. Both codes result in a consistent non-viscous evolution (in the equal as well as in the different density case) in agreement with the analytical prediction. The viscous evolution studied with <scp>flash</scp> shows minor deviations from the analytical prediction. Minimize

Publisher:

Oxford University Press

Year of Publication:

2010-09-21 00:00:00.0

Document Type:

TEXT

Language:

en

Subjects:

Papers

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DDC:

532 Fluid mechanics; liquid mechanics *(computed)*

Rights:

Copyright (C) 2010, Oxford University Press

Copyright (C) 2010, Oxford University Press Minimize

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Title:

Modelling Shear Flows with SPH and Grid Based Methods

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Given the importance of shear flows for astrophysical gas dynamics, we study the evolution of the Kelvin-Helmholtz instability (KHI) analytically and numerically. We derive the dispersion relation for the two-dimensional KHI including viscous dissipation. The resulting expression for the growth rate is then used to estimate the intrinsic viscosi...

Given the importance of shear flows for astrophysical gas dynamics, we study the evolution of the Kelvin-Helmholtz instability (KHI) analytically and numerically. We derive the dispersion relation for the two-dimensional KHI including viscous dissipation. The resulting expression for the growth rate is then used to estimate the intrinsic viscosity of four numerical schemes depending on code-specific as well as on physical parameters. Our set of numerical schemes includes the Tree-SPH code VINE, an alternative SPH formulation developed by Price (2008), and the finite-volume grid codes FLASH and PLUTO. In the first part, we explicitly demonstrate the effect of dissipation-inhibiting mechanisms such as the Balsara viscosity on the evolution of the KHI. With VINE, increasing density contrasts lead to a continuously increasing suppression of the KHI (with complete suppression from a contrast of 6:1 or higher). The alternative SPH formulation including an artificial thermal conductivity reproduces the analytically expected growth rates up to a density contrast of 10:1. The second part addresses the shear flow evolution with FLASH and PLUTO. Both codes result in a consistent non-viscous evolution (in the equal as well as in the different density case) in agreement with the analytical prediction. The viscous evolution studied with FLASH shows minor deviations from the analytical prediction. ; Comment: 16 pages, 17 figures Minimize

Year of Publication:

2010-04-12

Document Type:

text

Subjects:

Astrophysics - Galaxy Astrophysics

Astrophysics - Galaxy Astrophysics Minimize

DDC:

532 Fluid mechanics; liquid mechanics *(computed)*

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Title:

Modelling shear flows with smoothed particle hydrodynamics and grid-based methods

Author:

Publisher:

Wiley-Blackwell Publishing Inc

Year of Publication:

2010

Document Type:

text ; journal article

Language:

eng

Subjects:

Astronomical and space sciences (0201)

Astronomical and space sciences (0201) Minimize

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Monthly Notices Of The Royal Astronomical Society [P], vol. 407, no. 3, Wiley-Blackwell Publishing Inc, p. 1933-1945 ; urn:ISSN:0035-8711

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Title:

Modelling shear flows with smoothed particle hydrodynamics and grid-based methods

Author:

Description:

Given the importance of shear flows for astrophysical gas dynamics, we study the evolution of the Kelvin???Helmholtz instability (KHI) analytically and numerically. We derive the dispersion relation for the two-dimensional KHI including viscous dissipation. The resulting expression for the growth rate is then used to estimate the intrinsic visco...

Given the importance of shear flows for astrophysical gas dynamics, we study the evolution of the Kelvin???Helmholtz instability (KHI) analytically and numerically. We derive the dispersion relation for the two-dimensional KHI including viscous dissipation. The resulting expression for the growth rate is then used to estimate the intrinsic viscosity of four numerical schemes depending on code-specific as well as on physical parameters. Our set of numerical schemes includes the Tree-SPH code vine , an alternative smoothed particle hydrodynamics (SPH) formulation developed by Price and the finite-volume grid codes flash and pluto . In the first part, we explicitly demonstrate the effect of dissipation-inhibiting mechanisms such as the Balsara viscosity on the evolution of the KHI. With vine , increasing density contrasts lead to a continuously increasing suppression of the KHI (with complete suppression from a contrast of 6:1 or higher). The alternative SPH formulation including an artificial thermal conductivity reproduces the analytically expected growth rates up to a density contrast of 10:1. The second part addresses the shear flow evolution with flash and pluto . Both codes result in a consistent non-viscous evolution (in the equal as well as in the different density case) in agreement with the analytical prediction. The viscous evolution studied with flash shows minor deviations from the analytical prediction. Minimize

Publisher:

Blackwell Publishing Ltd

Contributors:

Department of Astronomy, University of Michigan, 500 Church St, Ann Arbor, MI 48109-1042, USA ; University Observatory Munich, Scheinerstrasse 1, 81679 Munich, Germany ; School of Physics and Astronomy, Cardiff University, The Parade, Roath, Cardiff CF24 3AA ; Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA ; Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, 85748 Garching, Germany ; School of Mathematical Sciences, Monash University, Clayton, VIC 3168, Australia

Year of Publication:

2010-09-21

DDC:

532 Fluid mechanics; liquid mechanics *(computed)*

Rights:

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