Nl Parameter Research Articles

Taming assembly bias for primordial non-Gaussianity

Primordial non-Gaussianity of the local type induces a strong scale-dependent bias on the clustering of halos in the late-time Universe. This signature is particularly promising to provide constraints on the non-Gaussianity parameter f NL from galaxy surveys, as the bias amplitude grows with scale and becomes important on large, linear scales. However, there is a well-known degeneracy between the real prize, the f NL parameter, and the (non-Gaussian) assembly bias i.e., the halo formation history-dependent contribution to the amplitude of the signal, which could seriously compromise the ability of large-scale structure surveys to constrain f NL. We show how the assembly bias can be modeled and constrained, thus almost completely recovering the power of galaxy surveys to competitively constrain primordial non-Gaussianity. In particular, studying hydrodynamical simulations, we find that a proxy for the halo properties that determine assembly bias can be constructed from photometric properties of galaxies. Using a prior on the assembly bias guided by this proxy degrades the statistical errors on f NL only mildly compared to an ideal case where the assembly bias is perfectly known. The systematic error on f NL that the proxy induces can be safely kept under control.

Quijote-PNG: The Information Content of the Halo Mass Function

We study signatures of primordial non-Gaussianity (PNG) in the redshift-space halo field on nonlinear scales using a combination of three summary statistics, namely, the halo mass function (HMF), power spectrum, and bispectrum. The choice of adding the HMF to our previous joint analysis of the power spectrum and bispectrum is driven by a preliminary field-level analysis, in which we train graph neural networks on halo catalogs to infer the PNG f NL parameter. The covariance matrix and the responses of our summaries to changes in model parameters are extracted from a suite of halo catalogs constructed from the Quijote-png N-body simulations. We consider the three main types of PNG: local, equilateral, and orthogonal. Adding the HMF to our previous joint analysis of the power spectrum and bispectrum produces two main effects. First, it reduces the equilateral f NL predicted errors by roughly a factor of 2 while also producing notable, although smaller, improvements for orthogonal PNG. Second, it helps break the degeneracy between the local PNG amplitude, , and assembly bias, b ϕ , without relying on any external prior assumption. Our final forecasts for the PNG parameters are , , , on a cubic volume of , with a halo number density of , at z = 1, and considering scales up to .

Hydrodynamical simulations of galaxy formation with non-Gaussian initial conditions

Collisionless simulations of structure formation with significant local primordial non-Gaussianities at Mpc scales have shown that a non-Gaussian tail favouring underdensities, with a negative f NL parameter, can significantly change the merging history of galaxy-sized dark matter halos, which then typically assemble later than in vanilla ΛCDM. Moreover, such a small-scale negative f NL could have interesting consequences for the cosmological S 8 tension. Here, we complement our previous work on collisionless simulations with new hydrodynamical simulations of galaxy formation in boxes of 30 Mpc/h, using the RAMSES code. In particular, we show that all feedback prescriptions being otherwise identical, simulations with a negative f NL ∼ -1000 on small scales, hence forming galaxies a bit later than in vanilla ΛCDM, allow to form simulated galaxies with more disky kinematics than in the vanilla case. Therefore, such small-scale primordial non-Gaussianities could potentially help alleviate, simultaneously, tensions in cosmology and galaxy formation. These hydrodynamical simulations on small scales will need to be complemented with larger box simulations with scale-dependent non-Gaussianities, to statistically confirm these trends and explore their observational consequences in further detail.

Non-Gaussianity effects on the primordial black hole abundance for sharply-peaked primordial spectrum

We perturbatively study the effect of non-Gaussianities on the mass fraction of primordial black holes (PBHs) at the time of formation by systematically taking its effect into account in the one-point probability distribution function of the primordial curvature perturbation. We focus on the bispectrum and trispectrum and derive formulas that describe their effects on the skewness and kurtosis of the distribution function. Then considering the case of narrowly peaked spectra, we obtain simple formulas that concisely express the effect of the bi- and trispectra. In particular, together with the g NL and τ NL parameters of the trispectrum, we find that non-Gaussianity parameters for various types of the bispectrum are linearly combined to give an effective parameter, f NL eff, that determines the PBH mass fraction in the narrow spectral shape limit.

Contributions from primordial non-Gaussianity and general relativity to the galaxy power spectrum

We compute the real space galaxy power spectrum, including the leading order effects of General Relativity and primordial non-Gaussianity from the f NL and g NL parameters. Such contributions come from the one-loop matter power spectrum terms dominant at large scales, and from the factors of the non-linear bias parameter b NL (akin to the Newtonian b ϕ). We assess the detectability of these contributions in Stage-IV surveys. In particular, we note that specific values of the bias parameter may erase the primordial and relativistic contributions to the configuration space power spectrum.

Ultrafast nonlinear optical properties of orthorhombic YbFeO3 thin film

Tuning magnetization in rare-earth orthoferrites ( R F e O 3 ) by ultrashort laser pulses is one of the emerging interests of new technologies. It subsequently revitalized the interest in light intensity-dependent nonlinear optical (NLO) properties of orthoferrites. The present work reports the results from femtosecond (fs) NLO characterization of Y b F e O 3 thin film by the standard Z-scan technique in open- and closed-aperture configurations. The thin film sample of Y b F e O 3 deposited on quartz substrate is irradiated with ∼ 50 f s laser pulses of varying input powers. Y b F e O 3 exhibited reverse saturable absorption characteristics at the excitation wavelengths of 600 and 800 nm. The observed NL absorption characteristics are associated with the electronic excitation between F e 3 + 3d-orbitals and charge transfer transition from O 2p-orbital to F e 3 + 3d-orbitals, respectively. The NL parameters are estimated using the coupled-type absorption model for simultaneous linear and two-photon absorption (2PA) developed previously by our group and found comparable to that of the many other mixed oxide materials such as ( B a , S r ) T i O 3 . The NL coefficients are correlated with linear absorption characteristics at 2PA wavelengths and with the theoretical 2PA model based on parabolic and nonparabolic band structures reported in the literature.

Probing non-Gaussianities with the high frequency tail of induced gravitational waves

We investigate in detail the spectrum of gravitational waves induced by a peaked primordial curvature power spectrum generated in single-field inflationary models. We argue that the f NL parameter can be inferred by measuring the high frequency spectral tilt of the induced gravitational waves. We also show that the intrinsically non-Gaussian impact of f NL in ΩGW is to broaden its peak, although at a negligible level in order not to overproduce primordial black holes. We discuss possible degeneracies in the high frequency spectral tilt between f NL and a general equation of state of the universe w. Finally, we discuss the constraints on the amplitude, peak and slope (or equivalently, f NL) of the primordial power spectrum by combining current and future gravitational wave experiments with limits on μ distortions from the cosmic microwave background.

Single-Carrier and Multi-Carrier 400 Gbps Transmission With Multi-Rate Multi-Format Real-Time Transceiver Prototypes

New customer usages such as on-demand high-definition videos, business analytics, and cloud services stress more and more optical transport networks. While 100 Gbps WDM systems have been widely adopted by operators to cope with the capacity growth of the past 6–7 years, a new generation of the optical transmission system is required to respond to the exponential traffic demands coming from mobile, fixed, and data center networks. Equipment manufacturers recently planned to enhance to 400 Gbps the data rate carried by WDM channels to meet this ever-increasing traffic requirement. Various trends are in competition to achieve this objective. Single-carrier and multi-carrier techniques operating at different symbol rates (i.e., 32, 45, > 60 Gbaud) and with diverse modulation formats (DP-QPSK, DP-8QAM, DP-16QAM) are proposed depending on whether transmission distance, spectral efficiency, or cost is the predominant driver. In this paper, we investigate the potential of these various 400 Gbps solutions by using real-time transceiver prototypes generating 32/64 Gbaud DP-QPSK, 45 Gbaud DP-8QAM, 32/61 Gbaud DP-16QAM formats over various fiber types (i.e., G.652, G.654, G.655 fibers). In particular, we demonstrate 400 Gbps WDM transmission with 61 Gbaud DP-16QAM channels using bandwidth-limited DAC/ADC (i.e., A NL parameter and quantify non-linear interference affecting optical channels after fiber propagation.

High optical nonlinearity of nematic liquid crystal doped with graphen oxide

Colloidal suspensions of nematic liquid crystal (NLC) doped with graphene oxide (GO) were prepared and their third-order nonlinear optical (NLO) response χ(3), nonlinear refractive index (NLR), and nonlinear absorption coefficient (NLA) were investigated using Z-scan technique employing He: Ne laser at 632.8nm. GO doped system exhibits a significantly different nonlinear optical response compared to pure NLC and the highest nonlinearity was observed at the system including 0.75% GO.The results of GO doped NLC show that the external field changes the NL parameter are dependent upon the electrical field direction since it affects the director axis, n→, compared to their initial orientation. The external field is applied perpendicular to the cell surface. The χ(3) change value was measured as the applied electrical filed varies. The mentioned studies were carried out without and under the electric field effect using different AC voltages. The value of NLO, NLA and χ(3) in present of electric field were more significant compare without of electric field. Additionally, the optical limiting (OL) behavior of colloidal suspensions was investigated. The obtained results provide new useful information about the NLO properties of NLC's nanocomposite in particular to design optical limiting devices and also other photonic applications.

Non-Gaussianities and curvature perturbations from hybrid inflation

For the original hybrid inflation as well as the supersymmetric F-term and D-term hybrid models, we calculate the level of non-gaussianities and the power spectrum of curvature perturbations generated during the waterfall, taking into account the contribution of entropic modes. We focus on the regime of mild waterfall, in which inflation continues for more than about 60 e-folds N during the waterfall. We find that the associated f_nl parameter goes typically from f_nl \simeq -1 / N_exit in the regime with N >> 60, where N_exit is the number of e-folds between the time of Hubble exit of a pivot scale and the end of inflation, down to f_nl ~-0.3 when N \gtrsim 60, i.e. much smaller in magnitude than the current bound from Planck. Considering only the adiabatic perturbations, the power spectrum is red, with a spectral index n_s = 1 - 4 / N_exit, in the case N >> 60, whereas in the case N \gtrsim 60, it increases up to unity. Including the contribution of entropic modes does not change the observable predictions in the first case. However, in the second case, they are a relevant source for the power spectrum of curvature perturbations, of which the amplitude increases by several orders of magnitudes and can lead to black hole formation. We conclude that due to the important contribution of entropic modes, the parameter space leading to a mild waterfall phase is excluded by CMB observations for all the considered models.

Voxel-based lesion-parameter mapping: Identifying the neural correlates of a computational model of word production

The dual-route interactive two-step model explains the variation in the error patterns of aphasic speakers in picture naming, and word and nonword repetition tasks. The model has three parameters that can vary across individuals: the efficiency of the connections between semantic and lexical representations (s-weight), between lexical and phonological representations (p-weight), and between representations of auditory input and phonological representations (nl-weight). We determined these parameter values in 103 participants with chronic aphasia from left hemisphere stroke whose lesion locations had been determined. Then, using voxel-based lesion-parameter mapping, we mapped the parameters onto the brain, thus determining the neural correlates of the model’s mechanisms. The maps and the behavioral findings supported the model’s central claim that word repetition is affected by both the p and nl parameters. We propose that these two parameters constitute the model’s analogue of the “dorsal stream” component of neurocognitive models of language processing.

Scale-dependent non-Gaussianities in the CMB data identified with Minkowski functionals and scaling indices

In order to test for non-Gaussianities with respect to scale-dependencies we use so-called surrogate maps, in which possible phase correlations of the Fourier phases of the original WMAP data and simulations, respectively, are destroyed by applying a shuffling scheme to the maps. A statistical comparison of the original maps with the surrogate maps then allows to test for the existence of higher order correlations in the original maps, also and especially on well-defined Fourier modes. Using Minkowski functionals as an image analysis technique we calculate the deviation between the original data and 500 surrogates for different hemispheres in the sky and find ecliptic hemispherical asymmetries between northern and southern ecliptic sky. We find strong deviations from Gaussianity in the WMAP data when considering the low-l range with l = [2,20]. The analysis technique of the scaling indices leads to a slightly lower deviation. Although the underlying foreground reduction methods of the maps differ from each other, we find similar results for the WMAP 7yr ILC map and the WMAP 7yr (needlet-based) NILC map in the low-l range. Our results point once more to a cosmological nature of the signal. For a higher l range with l = [120,300] the results differ between the two image analysis techniques and between the two maps which makes an intrinsic nature of the signal on this l range less likely. When we decrease the size of the analysed sky regions for the low-l study, we do not find signatures of NG in the northern sky. In the south we find individual spots which show deviations from Gaussianity. In addition, we investigate non-Gaussian CMB simulations that depend on the f_NL parameter of the local type. These simulations cannot account for the detected signatures on the low-l range.

The potential of X-ray cluster surveys to constrain primordial non-Gaussianity

We present forecasts for constraints on deviations from Gaussian distribution of primordial density perturbations from future X-ray surveys of galaxy clusters. Our analysis is based on computing the Fisher-Matrix for number counts and large-scale power spectrum of clusters. We consider a survey with high-sensitivity and wide-area to detect about 2.5 x 10^5 extended sources. Based on the self-calibration approach, and including Planck priors in our analysis, we constrain 9 cosmological parameters and 4 nuisance parameters, which define the relation between cluster mass and X-ray flux. Because of the scale dependence of large-scale bias induced by local-shape non-Gaussianity, we find that the power spectrum provides strong constraints on the non-Gaussianity f_nl parameter, which complement the stringent constraints on the power spectrum normalization, \sigma_8, from the number counts. To quantify the joint constraints on theese two parameters, that specify the timing of structure formation for a fixed background expansion, we define the figure-of-merit FoM_SFT = (det[Cov(sigma_8,f_nl)])^{-1/2}. We find that our surveys constrain deviations from Gaussianity with a precision of \Delta f_nl~10 at 1 \sigma confidence level, with FoM_SFT~39. We point out that constraints on f_nl are weakly sensitive to the uncertainties in the knowledge of nuisance parameters. As an application of non-Gaussian constraints from available data, we analyse the impact of positive skewness on the occurrence of XMMU-J2235, a massive distant cluster discovered at z~1.4. We confirm that in a WMAP-7 Gaussian Lambda CDM cosmology, within the survey volume, ~5x10^{-3} objects like this are expected to be found: to increase this probability by a factor of at least 10, one needs to evade either the available constraints on f_nl or sigma_8.

IMPROVED CONSTRAINTS ON PRIMORDIAL NON-GAUSSIANITY FOR THEWILKINSON MICROWAVE ANISOTROPY PROBE5-YEAR DATA

We present constraints on the nonlinear coupling parameter f nl with the Wilkinson Microwave Anisotropy Probe (WMAP) data. We use an updated method based on the spherical Mexican hat wavelet (SMHW) which provides improved constraints on the f nl parameter. This paper is a continuation of a previous work by Curto et al., where several third-order statistics based on the SMHW were considered. In this paper, we use all the possible third-order statistics computed from the wavelet coefficient maps evaluated at 12 angular scales. The scales are logarithmically distributed from 6.9 arcmin to 500 arcmin. Our analysis indicates that f nl is constrained to –18 < f nl < +80 at 95% confidence level (CL) for the combined V+W WMAP map. This value has been corrected by the presence of undetected point sources, which adds a positive contribution of Δf nl = 6 ± 5. Our result excludes at ~99% CL the best-fitting value f nl = 87 reported by Yadav & Wandelt. We have also constrained f nl for the Q, V, and W frequency bands separately, finding compatibility with zero at 95% CL for the Q and V bands but not for the W band. We have performed some further tests to understand the cause of this deviation which indicate that systematics associated with the W radiometers could be responsible for this result. Finally, we have performed a Galactic north-south analysis for f nl. We have not found any asymmetry, i.e., the best-fitting f nl for the northern pixels is compatible with the best-fitting f nl for the southern pixels.

Influence of water and aqueous carboxylic acids on properties of epoxide polymer materials

The possibility of biodegradation in model media is investigated. The relative changes in weight Δm/m0, electric permeability Δɛ/ɛ0, tangent of dielectric losses angle Δtanδ/tanδ0, and numeric values of physicomechanical HR, σtensile, and ɛp, adhesive τshear and structural nL parameters for epoxide polymers solidified by amine, anhydride, or catalytic agents upon exposure for a long period (up to 60 days) in water and aqueous carboxylic acids were determined. The changes in the specified parameters were found to depend on the nature of the solidifying agent. The validation of the model was performed by comparing data obtained under model conditions with those obtained during in-field tests using air and methane tanks.