Primordial Anisotropy Research Articles

The kinematic richness of star clusters – I. Isolated spherical models with primordial anisotropy

We investigate the dynamical evolution of isolated equal-mass star cluster models by means of direct N-body simulations, primarily focusing on the effects of the presence of primordial anisotropy in the velocity space. We found evidence of the existence of a monotonic relationship between the moment of core collapse and the amount and flavour of anisotropy in the stellar system. Specifically, equilibria characterised by the same initial structural properties (Plummer density profile) and with different degrees of tangentially-biased (radially-biased) anisotropy, reach core collapse earlier (later) than isotropic models. We interpret this result in light of an accelerated (delayed) phase of the early evolution of collisional stellar systems "anisotropic-response"), which we have characterised both in terms of the evolution of the velocity moments and of a fluid model of two-body relaxation. For the case of the most tangentially anisotropic model the initial phase of evolution involves a catastrophic collapse of the inner part of the system which continues until an isotropic velocity distribution is reached. This study represents a first step towards a comprehensive investigation of the role played by kinematic richness in the long-term dynamical evolution of collisional systems.

Isotropization of the universe during inflation

A primordial inflationary phase allows one to erase any possible anisotropic expansion thanks to the cosmic no-hair theorem. If there is no global anisotropic stress, then the anisotropic expansion rate tends to decrease. What are the observational consequences of a possible early anisotropic phase? We first review the dynamics of anisotropic universes and report analytic approximations. We then discuss the structure of dynamical equations for perturbations and the statistical properties of observables, as well as the implication of a primordial anisotropy on the quantization of these perturbations during inflation. Finally we review briefly models based on primordial vector field that evade the cosmic no-hair theorem. Une phase d'inflation primordiale permet d'effacer une possible expansion anisotrope grâce au théorème de calvitie cosmique. S'il n'y a pas de tenseur des contraintes global, alors le taux d'expansion anisotrope tend à décroître. Quelles sont les conséquences observationnelles de cette possible phase anisotrope ? Nous passons d'abord en revue la dynamique des univers anisotropes et donnons des approximations analytiques. Nous discutons ensuite la structure des équations dynamiques régissant l'évolution des perturbations et les propriétés statistiques des observables, ainsi que l'implication d'une phase anisotrope primordiale sur la quantification de ces perturbations pendant l'inflation. Pour terminer, nous examinons brièvement des modèles basés sur des champs vectoriels primordiaux qui permettent de contourner le théorème de calvitie.

Some Problems of Relativistic Thermodynamics Allowing for Primordial Substance Anisotropy

Some processes of heat and electrical charge transfer under relativistic conditions have been studied allowing for primordial substance anisotropy. In particular, electrical charge convection and conductivity were examined in the framework of 3-D and 4-D formalisms. Dependences were obtained in which the left-hand-sides and right-hand-sides transformed identically as v , с → where v was the velocity of the object under study, c was the speed of light. Dependences were also obtained for the heat transfer in the framework of 4-D formalism under relativistic conditions when the substance in the system was primordially anisotropic. The above dependences for the charge transfer are correct for systems where charges, e.g., electrons, can move more quickly than photons (Cherenkov's case). A consistent relativistic thermodynamics was also to be obtainable only if H.Ott's temperature transformation under relativistic conditions takes place. Range of Considered Symbols. α J and α

Implications of the primordial anisotropy for a scalar field with nonminimal kinetic coupling

We consider a scalar field with a kinetic term non-minimally coupled to gravity in an anisotropic background. Various potentials for the scalar field are considered. By explicit examples, we show that how the anisotropy can change the dynamics of the scalar field compared with the isotropic background.

Inflation in the generalized inverse power law scenario

We propose a single field inflationary model by generalizing the inverse power law potential from the intermediate model.We study the implication of our model on the primordial anisotropy of cosmological microwave background radiation.Specifically, we apply the slow-roll approximation to calculate the scalar spectral tilt ns and the tensor-to-scalar ratio r.The results are compared with the recent data measured by the Planck satellite. We find that by choosing proper values for the parameters, our model can well describe the Planck data.

Large scale anisotropic bias from primordial non-Gaussianity

In this work we study the large scale structure bias in models of anisotropic inflation. We use the Peak Background Splitting method in Excursion Set Theory to find the scale-dependent bias. We show that the amplitude of the bias is modified by a direction-dependent factor. In the specific anisotropic inflation model which we study, the scale-dependent bias vanishes at leading order when the long wavelength mode in squeezed limit is aligned with the anisotropic direction in the sky. We also extend the scale-dependent bias formulation to the general situations with primordial anisotropy. We find some selection rules indicating that some specific parts of a generic anisotropic bispectrum is picked up by the bias parameter. We argue that the anisotropic bias is mainly sourced by the angle between the anisotropic direction and the long wavelength mode in the squeezed limit.

Non-Gaussianities in the cosmological perturbation spectrum due to primordial anisotropy II

We continue to investigate possible signatures of a pre-inflationary anisotropic phase in two-point and three point correlation functions of the curvature perturbation for high-momentum modes which exit the horizon well after isotropization. The late time dynamics of these modes is characterized by a non-Bunch Davies vacuum state which encodes all the information about initial anisotropy in the background space-time. We observe that, unlike the non-planar momenta, there exist regimes of planar momenta for which scale invariance of the power spectrum is strongly broken. This regime of planar momenta gives rise to enhanced non-Gaussianity in certain squeezed triangle configurations, although the enhancement of the fNL parameter is limited by the breakdown of linear perturbation theory at ``exact planarity". Finally, we demonstrate that for the range of planar modes for which scale invariance of the power spectrum is preserved, non-Gaussianity in the curvature perturbation spectrum is naturally constrained to be extremely small.

Higher order spectra from an initially anisotropic universe

In this paper, we present the higher order spectra of a scalar field produced through the higher derivative interactions in the initially anisotropic universe. Although we ignore the backreaction of the scalar field on the geometry, our analysis should have much overlap with the quantum fluctuations of the inflaton field in the anisotropic universe. We also include the planar modes whose momenta are along the plane which is perpendicular to the primordial preferred direction, for which effects of the initial anisotropy are not suppressed. The presence of a negative frequency mode produces features distinguishable from the case of the de Sitter inflation. We also show that richer features appear in the trispectra due to the primordial anisotropy.

Non-gaussianities in the cosmological perturbation spectrum due to primordial anisotropy

We investigate possible signatures of a pre-inflationary anisotropic phase in two-point and three-point correlation functions of the curvature perturbation for high-momentum modes which exit the horizon well after isotropization. In this momentum regime, the early time dynamics admits a WKB description and the late time dynamics can be described in terms of a non-Bunch Davies vacuum state which encodes the information of initial anisotropy in the background spacetime. We compute the bi-spectrum for curvature perturbation in a canonical single-field action with and without higher derivative operators. We show that the bi-spectrum at late times, in either case, is enhanced for a flattened triangle configuration as well as a squeezed triangle configuration and compute the corresponding fNL parameters. The angular dependence and the particular momentum dependence of the fNL parameter appear as distinctive features of background anisotropy at early times.

Space-dependent step features: Transient breakdown of slow-roll, homogeneity, and isotropy during inflation

A step feature in the inflaton potential can model a transient breakdown of slow-roll inflation. Here we generalize the step feature to include space-dependence, allowing it also to model a breakdown of homogeneity and isotropy. The space-dependent inflaton potential generates a classical curvature perturbation mode characterized by the wave number of the step inhomogeneity. For inhomogeneities small compared with the horizon at the step, space-dependence has a small effect on the curvature perturbation. Therefore, the smoothly oscillating quantum power spectrum predicted by the homogeneous step is robust with respect to subhorizon space-dependence. For inhomogeneities equal to or greater than the horizon at the step, the space-dependent classical mode can dominate, producing a curvature perturbation in which modes of wave number determined by the step inhomogeneity are superimposed on the oscillating power spectrum. Generation of a space-dependent step feature may therefore provide a mechanism to introduce primordial anisotropy into the curvature perturbation. Space-dependence also modifies the quantum fluctuations, in particular, via resonancelike features coming from mode coupling to amplified superhorizon modes. However, these effects are small relative to the classical modes.

Theory of cosmological perturbations in an anisotropic universe

This paper describes the theory of cosmological perturbations around a homogeneous andanisotropic universe of the Bianchi I type. Starting from a general parametrization of theperturbed spacetime à la Bardeen, a complete set of gauge invariant variables isconstructed. Three physical degrees of freedom are identified and it is shownthat, in the case where matter is described by a scalar field, they generalize theMukhanov–Sasaki variables. In order to show that they are canonical variables, the actionfor the cosmological perturbations at second order is derived. Two major physicalimprints of the primordial anisotropy are identified: (1) a scalar–tensor ‘seesaw’mechanism arising from the fact that scalar, vector and tensor modes do notdecouple and (2) an explicit dependence of the statistical properties of the densityperturbations and gravity waves on the wavevector instead of its norm. Thisanalysis extends, but also sheds some light on, the quantization procedure that wasdeveloped under the assumption of a Friedmann–Lemaître background spacetime,and allows one to investigate the robustness of the predictions of the standardinflationary scenario with respect to the hypothesis on the symmetries of thebackground spacetime. These effects of a primordial anisotropy may be related to someanomalies of the cosmic microwave background anisotropies on large angularscales.

The Validity of the Cosmic String Pattern Search with the Cosmic Microwave Background

We introduce a new technique to detect the discrete temperature steps that cosmic strings might have left in the cosmic microwave background (CMB) anisotropy map. The technique provides a validity test on the pattern search of cosmic strings that could serve as the groundwork for future pattern searches. The detecting power of the technique is only constrained by two unavoidable features of CMB data: (1) the finite pixelization of the sky map and (2) the Gaussian fluctuation from instrumental noise and primordial anisotropy. We set the upper limit on the cosmic string parameter as Gμ 1.6 × 10-5 at the 95% confidence level (CL) and find that the amplitude of the temperature step has to be greater than 44 μK in order to be detected for the Wilkinson Microwave Anisotropy Probe (WMAP) 3 year data.

Building blocks for a polarimeter-on-a-chip

For the “Primordial Anisotropy Polarization Pathfinder Array (PAPPA)” balloon flight project, we have designed and made thin-film niobium microstrip circuits as building blocks for a “polarimeter-on-a-chip” in which superconducting transmission lines are used to couple millimeter wave signals from planar antennas to superconducting transition edge sensor (TES) detectors. Our goal is to demonstrate technology for precision measurements of the polarization of the cosmic microwave background. To enable characterization and verification of our microstrip components, we have incorporated waveguide probes on each chip that can bring millimeter wave signals from a room temperature vector network analyzer to the superconducting circuits on the chip and back again for S-parameter measurements. We have designed a planar antenna and RF choke on the probes to efficiently couple radiation between waveguide and thin-film microstrip. To support the probe antennas in waveguides, we sculpted thin silicon cantilevers that extend from an edge of each silicon chip into a pair of waveguides within a specially designed split-block mount. This technique will allow us to make calibrated measurements at low temperatures of the velocity, impedance, and loss properties of our niobium transmission lines, the frequency response of microstrip filters, hybrid couplers, or terminations, and the performance of integrated detectors.

Polarization Signatures of Clusters in the Microwave Background

Compton scattering of photons from ionised gas in galaxy clusters along the line of sight leaves an imprint in the polarization of the cosmic microwave background. We investigate this process taking account of the effects of relativistic electron velocity dispersion and primordial anisotropy on the frequency spectrum of the generated polarization. We also discuss the prospects of detecting such effects with the Planck survey.

Very Small Array observations of the Sunyaev-Zel'dovich effect in nearby galaxy clusters

We present Very Small Array (VSA) observations (centred on � 34GHz) on scales � 20 arcmin towards a complete, X-ray–flux–limited sample of seven clusters at redshift z < 0.1. Four of the clusters have significant Sunyaev-Zel’dovich (SZ) detections in the presence of CMB primordial anisotropy. For all seven, we use a Bayesian MarkovChain-Monte-Carlo (MCMC) method for inference from the VSA data, with X-ray priors on cluster positions and temperatures, and radio priors on sources. In this context, the CMB primordial fluctuations are an additional source of Gaussian noise, and are included in the model as a non–diagonal covariance matrix derived from the known angular power spectrum. In addition, we make assumptions of �–model gas distributions and of hydrostatic equilibrium, to evaluate probability densities for the gas mass (Mgas) and total mass (Mr) out to r200, the radius at which the average density enclosed is 200 times the critical density at the redshift of the cluster. This is further than has been done before and close to the classical value for a collapsed cluster. Our combined estimate of the gas fraction (fgas = Mgas/Mr) is 0.08 +0.06 0.04 h 1 . The random errors are poor (note however that the errors are higher than would have been obtained with the usual chi-squared method on the same data) but the control of bias is good. We have described the MCMC analysis method specifically in terms of SZ but hope the description will be of more general use. We find that the effects of primordial CMB contamination tend to be similar in the estimates of both Mgas and Mr over the narrow range of angular scales we are dealing with, so that there is little effect of primordials on fgas determination. Using our Mr estimates we find a normalisation of the mass – temperature relation based on the profiles from the VSA cluster pressure maps that is in good agreement with recent M T determinations from X-ray cluster measurements.

How Anisotropic is Our Universe?

Large-scale cosmic microwave background anisotropies in homogeneous, globally anisotropic cosmologies are investigated. We perform a statistical analysis in which the 4-yr data from the Cosmic Background Explorer satellite is searched for the specific anisotropy patterns predicted by these models and thereby set definitive upper limits on the amount of shear, $(\ensuremath{\sigma}/H{)}_{0}$, and vorticity, $(\ensuremath{\omega}/H{)}_{0}$, which are orders of magnitude stronger than previous constraints. We find that primordial anisotropy should have been fine tuned to be less than ${10}^{\ensuremath{-}3}$ of its natural value in the Planck era.

COBE anisotropy from supercluster gas

It is suggested that the microwave background anisotropy detected by the COBE DMR might be dominated not by the direct gravitational effect of primordial fluctuations in the last scattering surface, but by scattering off of moving electrons in optically thin, nearby superclusters. Hot diffuse clouds of ionized gas created during supercluster collapse produce Sunyaev-Zel'dovich and Doppler background anisotropy whose properties may closely mimic those of primordial anisotropy in current data. Strategies for and difficulties in separating the effects are discussed, based on the anisotropy spectrum, autocorrelation, correlation with galaxy catalogs, X-ray emission, and integrated spectral distortions.

Inflation in a Bianchi-IX cosmological model. The roles of primordial shear and gauge fields

The role played by primordial anisotropy and gauge field configurations is investigated in the context of a model with an inflationary stage driven by a self-interacting complex scalar field. We find that, in general, both the anisotropy and the gauge field aid inflation and we try to understand, qualitatively, the reasons for such behaviour. Asymptotic inflationary solutions and their stability are investigated.