scholarly journals Cosmic expansion and structure formation in running vacuum cosmologies

2015 ◽  
Vol 30 (22) ◽  
pp. 1540031 ◽  
Author(s):  
Spyros Basilakos
Keyword(s):  
Large Scale ◽  
Cold Dark Matter ◽  
Vacuum Energy ◽  
Dynamical Evolution ◽  
Quantum Field ◽  
Cluster Number ◽  
Energy Behavior ◽  
Collapse Model ◽  
Number Counts ◽  
Structure Properties

We investigate the dynamics of the Friedmann–Lemaître–Robertson–Walker (FLRW) flat cosmological models in which the vacuum energy varies with redshift. A particularly well-motivated model of this type is the so-called quantum field vacuum, in which both kind of terms [Formula: see text] and constant appear in the effective dark energy (DE) density affecting the evolution of the main cosmological functions at the background and perturbation levels. Specifically, it turns out that the functional form of the quantum vacuum endows the vacuum energy of a mild dynamical evolution which could be observed nowadays and appears as dynamical DE. Interestingly, the low-energy behavior is very close to the usual Lambda cold dark matter (ΛCDM) model, but it is by no means identical. Finally, within the framework of the quantum field vacuum we generalize the large scale structure properties, namely growth of matter perturbations, cluster number counts and spherical collapse model.

scholarly journals Combining cosmological constraints from cluster counts and galaxy clustering

2014 ◽  
Vol 10 (S306) ◽  
pp. 216-218 ◽  
Author(s):  
F. Lacasa
Keyword(s):  
Large Scale ◽  
Harmonic Space ◽  
Cluster Number ◽  
Dark Energy Survey ◽  
Ongoing Work ◽  
Cross Covariance ◽  
Diagrammatic Method ◽  
Non Gaussian ◽  
Number Counts ◽  
Halo Occupation Distribution

AbstractPresent and future large scale surveys offer promising probes of cosmology. For example the Dark Energy Survey (DES) is forecast to detect ~300 millions galaxies and thousands clusters up to redshift ~1.3. I here show ongoing work to combine two probes of large scale structure : cluster number counts and galaxy 2-point function (in real or harmonic space). The halo model (coupled to a Halo Occupation Distribution) can be used to model the cross-covariance between these probes, and I introduce a diagrammatic method to compute easily the different terms involved. Furthermore, I compute the joint non-Gaussian likelihood, using the Gram-Charlier series. Then I show how to extend the methods of Bayesian hyperparameters to Poissonian distributions, in a first step to include them in this joint likelihood.

scholarly journals Non-linear description of massive neutrinos in the framework of large-scale structure formation

2014 ◽  
Vol 11 (S308) ◽  
pp. 121-124
Author(s):  
Hélène Dupuy
Keyword(s):  
Large Scale ◽  
Cold Dark Matter ◽  
Dynamical Evolution ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Linear Regime ◽  
Non Linear ◽  
Massive Neutrinos ◽  
Single Flow ◽  
The Universe

AbstractThere is now no doubt that neutrinos are massive particles fully involved in the non-linear growth of the large-scale structure of the universe. A problem is that they are particularly difficult to include in cosmological models because the equations describing their behavior in the non-linear regime are cumbersome and difficult to handle. In this manuscript I present a new method allowing to deal with massive neutrinos in a very simple way, based on basic conservation laws. This method is still valid in the non-linear regime. The key idea is to describe neutrinos as a collection of single-flow fluids instead of seeing them as a single hot multi-flow fluid. In this framework, the time evolution of neutrinos is encoded in fluid equations describing macroscopic fields, just as what is done for cold dark matter. Although valid up to shell-crossing only, this approach is a further step towards a fully non-linear treatment of the dynamical evolution of neutrinos in the framework of large-scale structure growth.

scholarly journals The large-scale structure of vacuum

2014 ◽  
Vol 23 (12) ◽  
pp. 1442019 ◽  
Author(s):  
Franco D. Albareti ◽  
Jose A. R. Cembranos ◽  
Antonio L. Maroto
Keyword(s):  
Large Scale ◽  
Cold Dark Matter ◽  
Vacuum Energy ◽  
Vacuum State ◽  
Large Scale Structure ◽  
Momentum Tensor ◽  
Scale Structure ◽  
Cosmological Observations ◽  
Spacetime Structure ◽  
Physical Features

The vacuum state in quantum field theory is known to exhibit an important number of fundamental physical features. In this work we explore the possibility that this state could also present a nontrivial spacetime structure on large scales. In particular, we will show that by imposing the renormalized vacuum energy–momentum tensor to be conserved and compatible with cosmological observations, the vacuum energy of sufficiently heavy fields behaves at late times as nonrelativistic matter rather than as a cosmological constant. In this limit, the vacuum state supports perturbations whose speed of sound is negligible and accordingly allows the growth of structures in the vacuum energy itself. This large-scale structure of vacuum could seed the formation of galaxies and clusters very much in the same way as cold dark matter does.

scholarly journals A Monte Carlo study of cosmological parameter estimators from galaxy cluster number counts

2014 ◽  
Vol 10 (S306) ◽  
pp. 262-265
Author(s):  
Mariana Penna-Lima ◽  
Martín Makler ◽  
Carlos A. Wuensche
Keyword(s):  
Monte Carlo ◽  
Dark Energy ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Monte Carlo Study ◽  
Density Parameter ◽  
Cluster Number ◽  
Number Counts

AbstractModels for galaxy clusters abundance and their spatial distribution are sensitive to cosmological parameters. Present and future surveys will provide high-redshift sample of clusters, such as Dark Energy Survey (z ⩽ 1.3), making cluster number counts one of the most promising cosmological probes. In the literature, some cosmological analyses are carried out using small cluster catalogs (tens to hundreds), like in Sunyaev-Zel'dovich (SZ) surveys. However, it is not guaranteed that maximum likelihood estimators of cosmological parameters are unbiased in this scenario. In this work we study different estimators of the cold dark matter density parameter Ωc, σ8 and the dark energy equation of state parameter w0 obtained from cluster abundance. Using an unbinned likelihood for cluster number counts and the Monte Carlo approach, we determine the presence of bias and how it varies with the size of the sample. Our fiducial models are based on the South Pole Telescope (SPT). We show that the biases from SZ estimators do not go away with increasing sample sizes and they may become the dominant source of error for an all sky survey at the SPT sensitivity.

scholarly journals Constraints from thermal Sunyaev-Zel’dovich cluster counts and power spectrum combined with CMB

2018 ◽  
Vol 614 ◽  
pp. A13 ◽  
Author(s):  
Laura Salvati ◽  
Marian Douspis ◽  
Nabila Aghanim
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Power Spectrum ◽  
Large Scale ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Cluster Number ◽  
Number Count ◽  
First Case ◽  
Number Counts

The thermal Sunyaev-Zel’dovich (tSZ) effect is one of the recent probes of cosmology and large-scale structures. We update constraints on cosmological parameters from galaxy clusters observed by the Planck satellite in a first attempt to combine cluster number counts and the power spectrum of hot gas; we used a new value of the optical depth and, at the same time, sampling on cosmological and scaling-relation parameters. We find that in the ΛCDM model, the addition of a tSZ power spectrum provides small improvements with respect to number counts alone, leading to the 68% c.l. constraints Ωm = 0.32  ± 0.02, σ8 = 0.76  ± 0.03, and σ8(Ωm/0.3)1/3 = 0.78  ± 0.03 and lowering the discrepancy with results for cosmic microwave background (CMB) primary anisotropies (updated with the new value of τ) to ≃1.8σ on σ8. We analysed extensions to the standard model, considering the effect of massive neutrinos and varying the equation of state parameter for dark energy. In the first case, we find that the addition of the tSZ power spectrum helps in improving cosmological constraints with respect to number count alone results, leading to the 95% upper limit ∑ mν < 1.88 eV. For the varying dark energy equation of state scenario, we find no important improvements when adding tSZ power spectrum, but still the combination of tSZ probes is able to provide constraints, producing w = −1.0 ± 0.2. In all cosmological scenarios, the mass bias to reconcile CMB and tSZ probes remains low at (1 − b) ≲ 0.67 as compared to estimates from weak lensing and X-ray mass estimate comparisons or numerical simulations.

scholarly journals Constraints on the Matter Fluctuation Spectrum from X-Ray Cluster Number Counts

1998 ◽  
Vol 188 ◽  
pp. 314-314
Author(s):  
Tetsu Kitayama ◽  
Yasushi Suto
Keyword(s):  
Cold Dark Matter ◽  
Theoretical Modelling ◽  
Density Parameter ◽  
Cluster Number ◽  
New Approach ◽  
X Ray ◽  
Fluctuation Amplitude ◽  
Number Counts ◽  
Cosmological Constants ◽  
Best Fit

We find that the observed logN-logS relation of X-ray clusters (Ebeling et al. 1997; Rosati et al. 1997) can be reproduced remarkably well with a certain range of values for the fluctuation amplitude σ8 and the cosmological density parameter Ω0 in cold dark matter (CDM) universes (Kitayama & Suto 1997). The 1σ confidence limits on σ8 in the CDM models with n = 1 and h = 0.7 are expressed as (0.54 ± 0.02)Ω−0.35-0.82Ω0+0.55Ω200 (λ0 = 1 - Ω0) and (0.54 ± 0.02) Ω−0.28-0.91Ω0+0.68Ω200 (λ0 = 0), where n is the primordial spectral index, and h and λ0 are the dimensionless Hubble and cosmological constants. The errors quoted above indicate the statistical ones from the observed logN-logS only, and the systematic uncertainty from our theoretical modelling of X-ray flux in the best-fit value of σ8 is about 15%. In the case of n = 1, we find that the CDM models with (Ω0, λ0, h, σ8) ≃ (0.3, 0.7, 0.7, 1) and (0.45, 0, 0.7, 0.8) simultaneously account for the cluster logN-logS, X-ray temperature functions, and the normalization from the COBE 4 year data. The derived values assume the observations are without systematic errors, and we discuss in details other theoretical uncertainties which may change the limits on Ω0 and σ8 from the logN-logS relation. We have shown the power of this new approach which will become a strong tool as the observations attain more precision.

scholarly journals Shell-crossing in a ΛCDM Universe

2020 ◽  
Vol 501 (1) ◽  
pp. L71-L75
Author(s):  
Cornelius Rampf ◽  
Oliver Hahn
Keyword(s):  
Dark Matter ◽  
Perturbation Theory ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Three Dimensional ◽  
Random Initial Data ◽  
Recursion Relations ◽  
Indispensable Tool ◽  
First Time ◽  
Very High

ABSTRACT Perturbation theory is an indispensable tool for studying the cosmic large-scale structure, and establishing its limits is therefore of utmost importance. One crucial limitation of perturbation theory is shell-crossing, which is the instance when cold-dark-matter trajectories intersect for the first time. We investigate Lagrangian perturbation theory (LPT) at very high orders in the vicinity of the first shell-crossing for random initial data in a realistic three-dimensional Universe. For this, we have numerically implemented the all-order recursion relations for the matter trajectories, from which the convergence of the LPT series at shell-crossing is established. Convergence studies performed at large orders reveal the nature of the convergence-limiting singularities. These singularities are not the well-known density singularities at shell-crossing but occur at later times when LPT already ceased to provide physically meaningful results.

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 How low can vacuum energy go when your fields are finite-dimensional?

2019 ◽  
Vol 28 (14) ◽  
pp. 1944006
Author(s):  
ChunJun Cao ◽  
Aidan Chatwin-Davies ◽  
Ashmeet Singh
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Degrees Of Freedom ◽  
Vacuum Energy ◽  
Quantum Field ◽  
Locally Finite ◽  
Finite Dimensional ◽  
Finite Dimensionality ◽  
Klein Gordon ◽  
Dimensional Version

According to the holographic bound, there is only a finite density of degrees of freedom in space when gravity is taken into account. Conventional quantum field theory does not conform to this bound, since in this framework, infinitely many degrees of freedom may be localized to any given region of space. In this paper, we explore the viewpoint that quantum field theory may emerge from an underlying theory that is locally finite-dimensional, and we construct a locally finite-dimensional version of a Klein–Gordon scalar field using generalized Clifford algebras. Demanding that the finite-dimensional field operators obey a suitable version of the canonical commutation relations makes this construction essentially unique. We then find that enforcing local finite dimensionality in a holographically consistent way leads to a huge suppression of the quantum contribution to vacuum energy, to the point that the theoretical prediction becomes plausibly consistent with observations.

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