The Experts below are selected from a list of 43125 Experts worldwide ranked by ideXlab platform
Takahiko Matsubara - One of the best experts on this subject based on the ideXlab platform.
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velocity bias and the Nonlinear Perturbation theory of peaks
Physical Review D, 2019Co-Authors: Takahiko MatsubaraAbstract:The biasing in the large-scale structure of the universe is a crucial problem in cosmological applications. The peaks model of biasing predicts a linear velocity bias of halos, which is not present in a simple model of local bias. We investigate the origin of the velocity bias in the peaks model from the viewpoint of the integrated Perturbation theory, which is a Nonlinear Perturbation theory in the presence of general Lagrangian bias. The presence of the velocity bias in the peaks model is a consequence of the "flat constraint," ${\nabla}\delta = 0$; i.e., all the first spatial derivatives should vanish at the locations of peaks. We show that the velocity bias in the peaks model is systematically derived in the framework of the integrated Perturbation theory, and then develop a formal theory to perturbatively trace the Nonlinear evolution of biased objects with the flat constraint. A formula for the Nonlinear velocity dispersion of peaks with the one-loop approximation is also derived.
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Nonlinear Perturbation theory integrated with nonlocal bias redshift space distortions and primordial non gaussianity
Physical Review D, 2011Co-Authors: Takahiko MatsubaraAbstract:The standard Nonlinear Perturbation theory of the gravitational instability is extended to incorporate the nonlocal bias, redshift-space distortions, and primordial non-Gaussianity. We show that local Eulerian bias is not generally compatible with local Lagrangian bias in the Nonlinear regime. The Eulerian and Lagrangian biases are nonlocally related order by order in the general Perturbation theory. The relation between Eulerian and Lagrangian kernels of density Perturbations with biasing is derived. The effects of primordial non-Gaussianity and redshift-space distortions are also incorporated in our general formalism, and diagrammatic methods are introduced. Vertex resummations of higher-order Perturbations in the presence of bias are considered. Resummations of Lagrangian bias are shown to be essential to handle biasing schemes in a general framework.
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Nonlinear Perturbation theory with halo bias and redshift space distortions via the lagrangian picture
Physical Review D, 2008Co-Authors: Takahiko MatsubaraAbstract:The Nonlinear Perturbation theory of gravitational instability is extended to include effects of both biasing and redshift-space distortions, which are inevitable in predicting observable quantities in galaxy surveys. Weakly Nonlinear effects in galaxy clustering on large scales recently attracted great interest, since the precise determination of scales of baryon acoustic oscillations is crucial to investigate the nature of dark energy by galaxy surveys. We find that a local Lagrangian bias and redshift-space distortions are naturally incorporated in our formalism of Perturbation theory with a resummation technique via the Lagrangian picture. Our formalism is applicable to any biasing scheme which is local in Lagrangian space, including the halo bias as a special case. Weakly Nonlinear effects on halo clustering in redshift space are analytically given. We assume only a fundamental idea of the halo model: haloes form according to the extended Press-Schechter theory, and the spatial distributions are locally biased in Lagrangian space. There is no need for assuming the spherical collapse model to follow the dynamical evolution, which is additionally assumed in standard halo prescriptions. One-loop corrections to the power spectrum and correlation function of haloes in redshift space are explicitly derived and presented. Instead of relying on expensive numerical simulations, our approach provides an analytic way of investigating the weakly Nonlinear effects, simultaneously including the Nonlinear biasing and Nonlinear redshift-space distortions. Nonlinearity introduces a weak scale dependence in the halo bias. The scale dependence is a smooth function in Fourier space, and the bias does not critically change the feature of baryon acoustic oscillations in the power spectrum. The same feature in the correlation function is less affected by Nonlinear effects of biasing.
Hiroaki Isobe - One of the best experts on this subject based on the ideXlab platform.
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large amplitude oscillation of a polar crown filament in the pre eruption phase
Astronomy and Astrophysics, 2006Co-Authors: Hiroaki Isobe, Durgesh TripathiAbstract:Aims. We report observation of a large-amplitude filament oscillation followed by an eruption. This is used to probe the pre-eruption condition and the trigger mechanism of solar eruptions. Methods. We used the EUV images from the Extreme-Ultraviolet Imaging Telescope on board SOHO satellite and the H α images from the Flare Monitoring Telescope at Hida Observatory. The observed event is a polar crown filament that erupted on 15 Oct. 2002. Results. The filament clearly exhibited oscillatory motion in the slow-rising, pre-eruption phase. The amplitude of the oscillation was larger than 20 km s -1 , and the motion was predominantly horizontal. The period was about 2 h and seemed to increase during the oscillation, indicating weakening of restoring force. Conclusions. Even in the slow-rise phase before the eruption, the filament retained equilibrium and behaved as an oscillator, and the equilibrium is stable to Nonlinear Perturbation. The transition from such Nonlinear stability to either instabilities or a loss of equilibrium that leads to the eruption occurred in the Alfven time scale (~1 h). This suggests that the onset of the eruption was triggered by a fast magnetic reconnection that destabilized the pre-eruption magnetic configuration, rather than by the slow shearing motion at the photosphere.
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large amplitude oscillation of a polar crown filament in the pre eruption phase
arXiv: Astrophysics, 2006Co-Authors: Hiroaki Isobe, Durgesh TripathiAbstract:We report observation of a large-amplitude filament oscillation followed by an eruption. This is used to probe the pre-eruption condition and the trigger mechanism of solar eruptions. We used the EUV images from the Extreme-Ultraviolet Imaging Telescope on board SOHO satellite and the H-alpha images from the Flare Monitoring Telescope at Hida Observatory. The observed event is a polar crown filament that erupted on 15 Oct. 2002. The filament clearly exhibited oscillatory motion in the slow-rising, pre-eruption phase. The amplitude of the oscillation was larger than 20 km/s, and the motion was predominantly horizontal. The period was about 2 hours and seemed to increase during the oscillation, indicating weakening of restoring force. These results strongly indicate that, even in the slow-rise phase before the eruption, the filament retained equilibrium and behaved as an oscillator, and the equilibrium is stable to Nonlinear Perturbation. Moreover, the transition from such Nonlinear stability to either instabilities or a loss of equilibrium that leads to the eruption occurred in the Alfven time scale. This suggests that the onset of the eruption was triggered by a fast magnetic reconnection that stabilized the pre-eruption magnetic configuration, rather than by the slow shearing motion at the photosphere.
Durgesh Tripathi - One of the best experts on this subject based on the ideXlab platform.
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large amplitude oscillation of a polar crown filament in the pre eruption phase
Astronomy and Astrophysics, 2006Co-Authors: Hiroaki Isobe, Durgesh TripathiAbstract:Aims. We report observation of a large-amplitude filament oscillation followed by an eruption. This is used to probe the pre-eruption condition and the trigger mechanism of solar eruptions. Methods. We used the EUV images from the Extreme-Ultraviolet Imaging Telescope on board SOHO satellite and the H α images from the Flare Monitoring Telescope at Hida Observatory. The observed event is a polar crown filament that erupted on 15 Oct. 2002. Results. The filament clearly exhibited oscillatory motion in the slow-rising, pre-eruption phase. The amplitude of the oscillation was larger than 20 km s -1 , and the motion was predominantly horizontal. The period was about 2 h and seemed to increase during the oscillation, indicating weakening of restoring force. Conclusions. Even in the slow-rise phase before the eruption, the filament retained equilibrium and behaved as an oscillator, and the equilibrium is stable to Nonlinear Perturbation. The transition from such Nonlinear stability to either instabilities or a loss of equilibrium that leads to the eruption occurred in the Alfven time scale (~1 h). This suggests that the onset of the eruption was triggered by a fast magnetic reconnection that destabilized the pre-eruption magnetic configuration, rather than by the slow shearing motion at the photosphere.
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large amplitude oscillation of a polar crown filament in the pre eruption phase
arXiv: Astrophysics, 2006Co-Authors: Hiroaki Isobe, Durgesh TripathiAbstract:We report observation of a large-amplitude filament oscillation followed by an eruption. This is used to probe the pre-eruption condition and the trigger mechanism of solar eruptions. We used the EUV images from the Extreme-Ultraviolet Imaging Telescope on board SOHO satellite and the H-alpha images from the Flare Monitoring Telescope at Hida Observatory. The observed event is a polar crown filament that erupted on 15 Oct. 2002. The filament clearly exhibited oscillatory motion in the slow-rising, pre-eruption phase. The amplitude of the oscillation was larger than 20 km/s, and the motion was predominantly horizontal. The period was about 2 hours and seemed to increase during the oscillation, indicating weakening of restoring force. These results strongly indicate that, even in the slow-rise phase before the eruption, the filament retained equilibrium and behaved as an oscillator, and the equilibrium is stable to Nonlinear Perturbation. Moreover, the transition from such Nonlinear stability to either instabilities or a loss of equilibrium that leads to the eruption occurred in the Alfven time scale. This suggests that the onset of the eruption was triggered by a fast magnetic reconnection that stabilized the pre-eruption magnetic configuration, rather than by the slow shearing motion at the photosphere.
Marko Simonovic - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Perturbation theory extension of the boltzmann code class
Physical Review D, 2020Co-Authors: Anton Chudaykin, Mikhail M Ivanov, Oliver H E Philcox, Marko SimonovicAbstract:We present a new open-source code that calculates one-loop power auto- and cross-power spectra for matter fields and biased tracers in real and redshift space. These spectra incorporate all ingredients required for a direct application to data: non-linear bias, redshift-space distortions, infra-red resummation, counterterms, and the Alcock-Paczynski effect. Our code is based on the Boltzmann solver CLASS and inherits its advantage: user friendliness, ease of modification, high speed, and simple interface with other software. We present detailed descriptions of the theoretical model, the code structure, approximations, and accuracy tests. A typical end-to-end run for one cosmology takes $\sim 0.3$ seconds, which is sufficient for Markov Chain Monte Carlo parameter extraction. As an example, we apply the code to data from the Baryon Oscillation Spectroscopic Survey (BOSS) and infer cosmological parameters from the shape of the galaxy power spectrum.
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Nonlinear Perturbation theory extension of the boltzmann code class
Physical Review D, 2020Co-Authors: Anton Chudaykin, Mikhail M Ivanov, Oliver H E Philcox, Marko SimonovicAbstract:We present a new open-source code that calculates one-loop power spectra and cross spectra for matter fields and biased tracers in real and redshift space. These spectra incorporate all ingredients required for a direct application to data: Nonlinear bias and redshift-space distortions, infrared resummation, counterterms, and the Alcock-Paczynski effect. Our code is based on the Boltzmann solver class and inherits its advantageous properties: user friendliness, ease of modification, high speed, and simple interface with other software. We present detailed descriptions of the theoretical model, the code structure, approximations, and accuracy tests. A typical end-to-end run for one cosmology takes 0.3 seconds, which is sufficient for Markov chain Monte Carlo parameter extraction. As an example, we apply the code to the Baryon Oscillation Spectroscopic Survey (BOSS) data and infer cosmological parameters from the shape of the galaxy power spectrum.
Anton Chudaykin - One of the best experts on this subject based on the ideXlab platform.
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Nonlinear Perturbation theory extension of the boltzmann code class
Physical Review D, 2020Co-Authors: Anton Chudaykin, Mikhail M Ivanov, Oliver H E Philcox, Marko SimonovicAbstract:We present a new open-source code that calculates one-loop power auto- and cross-power spectra for matter fields and biased tracers in real and redshift space. These spectra incorporate all ingredients required for a direct application to data: non-linear bias, redshift-space distortions, infra-red resummation, counterterms, and the Alcock-Paczynski effect. Our code is based on the Boltzmann solver CLASS and inherits its advantage: user friendliness, ease of modification, high speed, and simple interface with other software. We present detailed descriptions of the theoretical model, the code structure, approximations, and accuracy tests. A typical end-to-end run for one cosmology takes $\sim 0.3$ seconds, which is sufficient for Markov Chain Monte Carlo parameter extraction. As an example, we apply the code to data from the Baryon Oscillation Spectroscopic Survey (BOSS) and infer cosmological parameters from the shape of the galaxy power spectrum.
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Nonlinear Perturbation theory extension of the boltzmann code class
Physical Review D, 2020Co-Authors: Anton Chudaykin, Mikhail M Ivanov, Oliver H E Philcox, Marko SimonovicAbstract:We present a new open-source code that calculates one-loop power spectra and cross spectra for matter fields and biased tracers in real and redshift space. These spectra incorporate all ingredients required for a direct application to data: Nonlinear bias and redshift-space distortions, infrared resummation, counterterms, and the Alcock-Paczynski effect. Our code is based on the Boltzmann solver class and inherits its advantageous properties: user friendliness, ease of modification, high speed, and simple interface with other software. We present detailed descriptions of the theoretical model, the code structure, approximations, and accuracy tests. A typical end-to-end run for one cosmology takes 0.3 seconds, which is sufficient for Markov chain Monte Carlo parameter extraction. As an example, we apply the code to the Baryon Oscillation Spectroscopic Survey (BOSS) data and infer cosmological parameters from the shape of the galaxy power spectrum.
