scholarly journals Scalar and tensor perturbations in DHOST bounce cosmology

2021 ◽  
Vol 2021 (11) ◽  
pp. 045
Author(s):  
Mian Zhu ◽  
Amara Ilyas ◽  
Yunlong Zheng ◽  
Yi-Fu Cai ◽  
Emmanuel N. Saridakis
Keyword(s):  
Scale Invariance ◽  
Initial Conditions ◽  
Power Spectra ◽  
Thermal Fluctuations ◽  
Spectral Indices ◽  
Vacuum Fluctuations ◽  
Perfect Agreement ◽  
Expansion Phase ◽  
Contraction Phase ◽  
Tensor Perturbations

Abstract We investigate the bounce realization in the framework of DHOST cosmology, focusing on the relation with observables. We perform a detailed analysis of the scalar and tensor perturbations during the Ekpyrotic contraction phase, the bounce phase, and the fast-roll expansion phase, calculating the power spectra, the spectral indices and the tensor-to-scalar ratio. Furthermore, we study the initial conditions, incorporating perturbations generated by Ekpyrotic vacuum fluctuations, by matter vacuum fluctuations, and by thermal fluctuations. The scale invariance of the scalar power spectrum can be acquired introducing a matter contraction phase before the Ekpyrotic phase, or invoking a thermal gas as the source. The DHOST bounce scenario with cosmological perturbations generated by thermal fluctuations proves to be the most efficient one, and the corresponding predictions are in perfect agreement with observational bounds. Especially the tensor-to-scalar ratio is many orders of magnitude within the allowed region, since it is suppressed by the Hubble parameter at the beginning of the bounce phase.

scholarly journals Inflationary perturbation spectra at next-to-leading slow-roll order in effective field theory of inflation

2019 ◽  
Vol 79 (11) ◽  
Author(s):  
Guang-Hua Ding ◽  
Jin Qiao ◽  
Qiang Wu ◽  
Tao Zhu ◽  
Anzhong Wang
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
High Energy Physics ◽  
Power Spectra ◽  
High Energy ◽  
Effective Field ◽  
Spectral Indices ◽  
Leading Order ◽  
Slow Roll ◽  
Tensor Perturbations

AbstractThe effective field theory (EFT) of inflation provides an essential picture to explore the effects of the unknown high energy physics in the single scalar field inflation models. For a generic EFT of inflation, possible high energy corrections to simple slow-roll inflation can modify both the propagating speed and dispersion relations of the cosmological scalar and tensor perturbations. With the arrival of the era of precision cosmology, it is expected that these high energy corrections become more important and have to be taken into account in the analysis with future precise observational data. In this paper we study the observational predictions of the EFT of inflation by using the third-order uniform asymptotic approximation method. We calculate explicitly the primordial power spectra, spectral indices, running of the spectral indices for both scalar and tensor perturbations, and the ratio between tensor and scalar spectra. These expressions are all written in terms of the Hubble flow parameters and the flow of four new slow-roll parameters and expanded up to the next-to-leading order in the slow-roll expansions so they represent the most accurate results obtained so far in the literature. The flow of the four new slow-roll parameters, which arise from the four new operators introduced in the action of the EFT of inflation, can affect the primordial perturbation spectra at the leading-order and the corresponding spectral indices at the next-to-leading order.

Evolution of cosmological perturbations

2018 ◽  
Author(s):  
Michele Maggiore
Keyword(s):  
Numerical Solutions ◽  
Transfer Functions ◽  
Initial Conditions ◽  
Power Spectra ◽  
Single Component ◽  
Cosmological Perturbations ◽  
Tensor Perturbations

Evolutions equations for cosmological perturbations. Single-component and multi-component fluids. Super-horizon and sub-horizon limits. Adiabatic and isocurvature initial conditions. Analytic and numerical solutions. Power spectra and transfer functions for scalar and tensor perturbations. GW damping from neutrino free-streaming.

scholarly journals The anisotropy of the power spectrum in periodic cosmological simulations

2021 ◽  
Vol 503 (4) ◽  
pp. 5638-5645
Author(s):  
Gábor Rácz ◽  
István Szapudi ◽  
István Csabai ◽  
László Dobos
Keyword(s):  
Dark Matter ◽  
Power Spectrum ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Initial Conditions ◽  
Power Spectra ◽  
Cosmological Simulations ◽  
Spherical Collapse ◽  
Lower Amplitude ◽  
Hydrodynamical Simulations

ABSTRACT The classical gravitational force on a torus is anisotropic and always lower than Newton’s 1/r2 law. We demonstrate the effects of periodicity in dark matter only N-body simulations of spherical collapse and standard Lambda cold dark matter (ΛCDM) initial conditions. Periodic boundary conditions cause an overall negative and anisotropic bias in cosmological simulations of cosmic structure formation. The lower amplitude of power spectra of small periodic simulations is a consequence of the missing large-scale modes and the equally important smaller periodic forces. The effect is most significant when the largest mildly non-linear scales are comparable to the linear size of the simulation box, as often is the case for high-resolution hydrodynamical simulations. Spherical collapse morphs into a shape similar to an octahedron. The anisotropic growth distorts the large-scale ΛCDM dark matter structures. We introduce the direction-dependent power spectrum invariant under the octahedral group of the simulation volume and show that the results break spherical symmetry.

scholarly journals Phenomenological Implications of Modified Loop Cosmologies: An Overview

2021 ◽  
Vol 8 ◽  
Author(s):  
Bao-Fei Li ◽  
Parampreet Singh ◽  
Anzhong Wang
Keyword(s):  
Initial Conditions ◽  
Scale Effects ◽  
Hybrid Approach ◽  
Planck Scale ◽  
Power Spectra ◽  
Big Bang ◽  
Hamiltonian Constraint ◽  
Hybrid Approaches ◽  
Effective Dynamics ◽  
The Big Bang

In this paper, we first provide a brief review of the effective dynamics of two recently well-studied models of modified loop quantum cosmologies (mLQCs), which arise from different regularizations of the Hamiltonian constraint and show the robustness of a generic resolution of the big bang singularity, replaced by a quantum bounce due to non-perturbative Planck scale effects. As in loop quantum cosmology (LQC), in these modified models the slow-roll inflation happens generically. We consider the cosmological perturbations following the dressed and hybrid approaches and clarify some subtle issues regarding the ambiguity of the extension of the effective potential of the scalar perturbations across the quantum bounce, and the choice of initial conditions. Both of the modified regularizations yield primordial power spectra that are consistent with current observations for the Starobinsky potential within the framework of either the dressed or the hybrid approach. But differences in primordial power spectra are identified among the mLQCs and LQC. In addition, for mLQC-I, striking differences arise between the dressed and hybrid approaches in the infrared and oscillatory regimes. While the differences between the two modified models can be attributed to differences in the Planck scale physics, the permissible choices of the initial conditions and the differences between the two perturbation approaches have been reported for the first time. All these differences, due to either the different regularizations or the different perturbation approaches in principle can be observed in terms of non-Gaussianities.

scholarly journals Testing the reliability of fast methods for weak lensing simulations: wl-moka on pinocchio

2020 ◽  
Vol 496 (2) ◽  
pp. 1307-1324
Author(s):  
Carlo Giocoli ◽  
Pierluigi Monaco ◽  
Lauro Moscardini ◽  
Tiago Castro ◽  
Massimo Meneghetti ◽  
...  
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Mass Density ◽  
Cosmological Parameters ◽  
Power Spectra ◽  
Mass Function ◽  
Parametric Models ◽  
Weak Lensing ◽  
Approximate Methods ◽  
Percent Accuracy

ABSTRACT The generation of simulated convergence maps is of key importance in fully exploiting weak lensing by large-scale structure (LSS) from which cosmological parameters can be derived. In this paper, we present an extension of the pinocchio code that produces catalogues of dark matter haloes so that it is capable of simulating weak lensing by Modify LSS into Large Scale Structures (LSS). Like wl-moka, the method starts with a random realization of cosmological initial conditions, creates a halo catalogue and projects it on to the past light-cone, and paints in haloes assuming parametric models for the mass density distribution within them. Large-scale modes that are not accounted for by the haloes are constructed using linear theory. We discuss the systematic errors affecting the convergence power spectra when Lagrangian perturbation theory at increasing order is used to displace the haloes within pinocchio, and how they depend on the grid resolution. Our approximate method is shown to be very fast when compared to full ray-tracing simulations from an N-body run and able to recover the weak lensing signal, at different redshifts, with a few percent accuracy. It also allows for quickly constructing weak lensing covariance matrices, complementing pinocchio’s ability of generating the cluster mass function and galaxy clustering covariances and thus paving the way for calculating cross-covariances between the different probes. This work advances these approximate methods as tools for simulating and analysing survey data for cosmological purposes.

scholarly journals l = 1: Weinberg’s weakly damped mode in an N-body model of a spherical stellar system

2020 ◽  
Author(s):  
Douglas C Heggie ◽  
Philip G Breen ◽  
Anna Lisa Varri
Keyword(s):  
Distribution Function ◽  
Initial Conditions ◽  
Stellar System ◽  
Power Spectra ◽  
Monte Carlo Sampling ◽  
Stellar Systems ◽  
Prominent Feature ◽  
Body Model ◽  
Perturbative Solution ◽  
The Matrix

Abstract Spherical stellar systems such as King models, in which the distribution function is a decreasing function of energy and depends on no other invariant, are stable in the sense of collisionless dynamics. But Weinberg showed, by a clever application of the matrix method of linear stability, that they may be nearly unstable, in the sense of possessing weakly damped modes of oscillation. He also demonstrated the presence of such a mode in an N-body model by endowing it with initial conditions generated from his perturbative solution. In the present paper we provide evidence for the presence of this same mode in N-body simulations of the King W0 = 5 model, in which the initial conditions are generated by the usual Monte Carlo sampling of the King distribution function. It is shown that the oscillation of the density centre correlates with variations in the structure of the system out to a radius of about 1 virial radius, but anticorrelates with variations beyond that radius. Though the oscillations appear to be continually reexcited (presumably by the motions of the particles) we show by calculation of power spectra that Weinberg’s estimate of the period (strictly, 2π divided by the real part of the eigenfrequency) lies within the range where the power is largest. In addition, however, the power spectrum displays another very prominent feature at shorter periods, around 5 crossing times.

scholarly journals Hybrid Simulation of Solar-Wind-Like Turbulence

Solar Physics ◽  
2019 ◽  
Vol 294 (11) ◽  
Author(s):  
D. Aaron Roberts ◽  
Leon Ofman
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
High Speed ◽  
Radial Flow ◽  
Initial Conditions ◽  
Thermal Fluctuations ◽  
Flow Speed ◽  
Initial State ◽  
Simplifying Assumptions ◽  
The Magnetic Field

Abstract We present 2.5D hybrid simulations of the spectral and thermodynamic evolution of an initial state of magnetic field and plasma variables that in many ways represents solar wind fluctuations. In accordance with Helios near-Sun high-speed stream observations, we start with Alfvénic fluctuations along a mean magnetic field in which the fluctuations in the magnitude of the magnetic field are minimized. Since fluctuations in the radial flow speed are the dominant free energy in the observed fluctuations, we include a field-aligned $v_{\|}(k_{\perp })$v∥(k⊥) with an $k^{ -1}$k−1 spectrum of velocity fluctuations to drive the turbulent evolution. The flow rapidly distorts the Alfvénic fluctuations, yielding spectra (determined by spacecraft-like cuts) transverse to the field that become comparable to the $k_{\|}$k∥ fluctuations, as in spacecraft observations. The initial near constancy of the magnetic field is lost during the evolution; we show this also takes place observationally. We find some evolution in the anisotropy of the thermal fluctuations, consistent with expectations based on Helios data. We present 2D spectra of the fluctuations, showing the evolution of the power spectrum and cross-helicity. Despite simplifying assumptions, many aspects of simulations and observations agree. The greatly faster evolution in the simulations is at least in part due to the small scales being simulated, but also to the non-equilibrium initial conditions and the relatively low overall Alfvénicity of the initial fluctuations.

scholarly journals On the road to per cent accuracy – II. Calibration of the non-linear matter power spectrum for arbitrary cosmologies

2019 ◽  
Vol 490 (4) ◽  
pp. 4826-4840 ◽  
Author(s):  
Benjamin Giblin ◽  
Matteo Cataneo ◽  
Ben Moews ◽  
Catherine Heymans
Keyword(s):  
Power Spectrum ◽  
Initial Conditions ◽  
Power Spectra ◽  
Linear Regime ◽  
The Road ◽  
Matter Power Spectrum ◽  
Non Linear ◽  
Standard Cosmological Model ◽  
Massive Neutrinos ◽  
On The Road

ABSTRACT We introduce an emulator approach to predict the non-linear matter power spectrum for broad classes of beyond-ΛCDM cosmologies, using only a suite of ΛCDM N-body simulations. By including a range of suitably modified initial conditions in the simulations, and rescaling the resulting emulator predictions with analytical ‘halo model reactions’, accurate non-linear matter power spectra for general extensions to the standard ΛCDM model can be calculated. We optimize the emulator design by substituting the simulation suite with non-linear predictions from the standard halofit tool. We review the performance of the emulator for artificially generated departures from the standard cosmology as well as for theoretically motivated models, such as f(R) gravity and massive neutrinos. For the majority of cosmologies we have tested, the emulator can reproduce the matter power spectrum with errors ${\lesssim}1{{\ \rm per\ cent}}$ deep into the highly non-linear regime. This work demonstrates that with a well-designed suite of ΛCDM simulations, extensions to the standard cosmological model can be tested in the non-linear regime without any reliance on expensive beyond-ΛCDM simulations.

Deterministic Chaos in the Dynamics of a Freely Jointed Chain with Three Degrees of Freedom

1993 ◽  
Vol 48 (4) ◽  
pp. 584-594
Author(s):  
Georg R. Siegert ◽  
Roland G. Winkler ◽  
Peter Reineker
Keyword(s):  
Degrees Of Freedom ◽  
Chaotic Behavior ◽  
Initial Conditions ◽  
Deterministic Chaos ◽  
Power Spectra ◽  
Constrained System ◽  
Rigid Rods ◽  
End Distance ◽  
Poincaré Surfaces Of Section ◽  
Three Degrees Of Freedom

Abstract The dynamics of a short freely jointed chain of three segments is investigated numerically. The chain consists of mass points connected by massless rigid rods, its initial and final points being fixed. Thus the chain represents a holonomically constrained system with three degrees of freedom. It is shown that the motion of the mass points can be chaotic; the occurrence of chaos depends on the initial conditions of the motion, the end-to-end distance of the chain, and the angular momentum about the axis of the stretching direction. Moreover, the chain more likely exhibits regular than chaotic behavior. The numerical results are presented in the form of Poincare surfaces of section, including the use of a slice technique, as well as in the form of power spectra.

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