arXiv subjects

Lerh Feng Low

Publications and source records attributed to Lerh Feng Low.

3 recordsLinked to original sources

arXiv2023

Commuter Count: Inferring Travel Patterns from Location Data

In this Working Paper we analyse computational strategies for using aggregated spatio-temporal population data acquired from telecommunications networks to infer travel and movement patterns between geographical regions. Specifically, we focus on hour-by-hour cellphone counts for the SA-2 geographical regions covering the whole of New Zealand. This Working Paper describes the implementation of the inference algorithms, their ability to produce models of travel patterns during the day, and lays out opportunities for future development.

stat.AP↗

arXiv2021

Inflation in a Gaussian Random Landscape

Random, multifield functions can set generic expectations for landscape-style cosmologies. We consider the inflationary implications of a landscape defined by a Gaussian random function, which is perhaps the simplest such scenario. Many key properties of this landscape, including the distribution of saddles as a function of height in the potential, depend only on its dimensionality, $N$, and a single parameter, $γ$, which is set by the power spectrum of the random function. We show that for saddles with a single downhill direction the negative mass term grows smaller, relative to the average mass, as $N$ increases, a result with potential implications for the $η$-problem in landscape scenarios. For some power spectra Planck-scale saddles have $η \sim 1$ and eternal, topological inflation would be common in these scenarios. Lower-lying saddles typically have large $η$, but the fraction of these saddles which would support inflation is computable, allowing us to identify which scenarios can deliver a universe that resembles ours. Finally, by drawing inferences about the relative viability of different multiverse proposals we also illustrate ways in which quantitative analyses of multiverse scenarios are feasible.

hep-th↗

arXiv2020

The Distribution of Vacua in Random Landscape Potentials

Landscape cosmology posits the existence of a convoluted, multidimensional, scalar potential -- the "landscape" -- with vast numbers of metastable minima. Random matrices and random functions in many dimensions provide toy models of the landscape, allowing the exploration of conceptual issues associated with these scenarios. We compute the relative number and slopes of minima as a function of the vacuum energy $Λ$ in an $N$-dimensional Gaussian random potential, quantifying the associated probability density, $p(Λ)$. After normalisations $p(Λ)$ depends only on the dimensionality $N$ and a single free parameter $γ$, which is related to the power spectrum of the random function. For a Gaussian landscape with a Gaussian power spectrum, the fraction of positive minima shrinks super-exponentially with $N$; at $N=100$, $p(Λ>0) \approx 10^{-1197}$. Likewise, typical eigenvalues of the Hessian matrices reveal that the flattest approaches to typical minima grow flatter with $N$, while the ratio of the slopes of the two flattest directions grows with $N$. We discuss the implications of these results for both swampland and conventional anthropic constraints on landscape cosmologies. In particular, for parameter values when positive minima are extremely rare, the flattest approaches to minima where $Λ\approx 0$ are much flatter than for typical minima, increasingly the viability of quintessence solutions.

hep-th↗