The JWST High Redshift Observations and Primordial Non-Gaussianity

Several bright and massive galaxy candidates at high redshifts have been recently observed by the James Webb Space Telescope. Such early massive galaxies seem difficult to reconcile with standard $\Lambda$ Cold Dark Matter model predictions. We discuss under which circumstances such observed massive galaxy candidates can be explained by introducing primordial non-Gaussianity in the initial conditions of the cosmological perturbations.Comment: 10 pages, 4 figure

Primordial black holes from inflation and quantum diffusion

Primordial black holes as dark matter may be generated in single-field models of inflation thanks to the enhancement at small scales of the comoving curvature perturbation. This mechanism requires leaving the slow-roll phase to enter a non-attractor phase during which the inflaton travels across a plateau and its velocity drops down exponentially. We argue that quantum diffusion has a significant impact on the primordial black hole mass fraction making the classical standard prediction not trustable.Comment: 25+12 pages, 12 figures. v3: Appendix added with comments in response to arXiv:1807.0905

Nonlinear Dynamic System Identification in the Spectral Domain Using Particle-Bernstein Polynomials

System identification (SI) is the discipline of inferring mathematical models from unknown dynamic systems using the input/output observations of such systems with or without prior knowledge of some of the system parameters. Many valid algorithms are available in the literature, including Volterra series expansion, Hammerstein–Wiener models, nonlinear auto-regressive moving average model with exogenous inputs (NARMAX) and its derivatives (NARX, NARMA). Different nonlinear estimators can be used for those algorithms, such as polynomials, neural networks or wavelet networks. This paper uses a different approach, named particle-Bernstein polynomials, as an estimator for SI. Moreover, unlike the mentioned algorithms, this approach does not operate in the time domain but rather in the spectral components of the signals through the use of the discrete Karhunen–Loève transform (DKLT). Some experiments are performed to validate this approach using a publicly available dataset based on ground vibration tests recorded from a real F-16 aircraft. The experiments show better results when compared with some of the traditional algorithms, especially for large, heterogeneous datasets such as the one used. In particular, the absolute error obtained with the prosed method is 63% smaller with respect to NARX and from 42% to 62% smaller with respect to various artificial neural network-based approaches

Testing Multi-Field Inflation with Galaxy Bias

Multi-field models of inflation predict an inequality between the amplitude tauNL of the collapsed limit of the four-point correlator of the primordial curvature perturbation and the amplitude fNL of the squeezed limit of its three-point correlator. While a convincing detection of non-Gaussianity through the squeezed limit of the three-point correlator would rule out all single-field models, a robust confirmation or disproval of the inequality between tauNL and fNL would provide crucial information about the validity of multi-field models of inflation. In this paper, we discuss to which extent future measurements of the scale-dependence of galaxy bias can test multi-field inflationary scenarios. The strong degeneracy between the effect of a non-vanishing fNL and tauNL on halo bias can be broken by considering multiple tracer populations of the same surveyed volume. If halos down to 1e13 Msun/h are resolved in a survey of volume 25(Gpc/h)^3, then testing multi-field models of inflation at the 3-\sigma level would require, for instance, a detection of tauNL at the level of tauNL~1e5 given a measurement of a local bispectrum with amplitude fNL~10. However, we find that disproving multi-field models of inflation with measurements of the non-Gaussian bias only will be very challenging, unless |fNL| > 80 and one can achieve a halo mass resolution of 1e10 Msun/h.Comment: 8 pages, 4 figure