ORCID Profile
0000-0002-5866-0445
Current Organisations
University of Cambridge
,
Université de Fribourg
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Publisher: Springer Science and Business Media LLC
Date: 28-08-2017
Publisher: Springer Science and Business Media LLC
Date: 26-05-2022
Publisher: Oxford University Press (OUP)
Date: 03-03-2021
Abstract: It was recently emphasized that in the presence of plateaus in the likelihood function nested s ling (NS) produces faulty estimates of the evidence and posterior densities. After informally explaining the cause of the problem, we present a modified version of NS that handles plateaus and can be applied retrospectively to NS runs from popular NS software using anesthetic. In the modified NS, live points in a plateau are evicted one by one without replacement, with ordinary NS compression of the prior volume after each eviction but taking into account the dynamic number of live points. The live points are replenished once all points in the plateau are removed. We demonstrate it on a number of ex les. Since the modification is simple, we propose that it becomes the canonical version of Skilling’s NS algorithm.
Publisher: IOP Publishing
Date: 29-04-2022
Abstract: Physical theories that depend on many parameters or are tested against data from many different experiments pose unique challenges to statistical inference. Many models in particle physics, astrophysics and cosmology fall into one or both of these categories. These issues are often sidestepped with statistically unsound ad hoc methods, involving intersection of parameter intervals estimated by multiple experiments, and random or grid s ling of model parameters. Whilst these methods are easy to apply, they exhibit pathologies even in low-dimensional parameter spaces, and quickly become problematic to use and interpret in higher dimensions. In this article we give clear guidance for going beyond these procedures, suggesting where possible simple methods for performing statistically sound inference, and recommendations of readily-available software tools and standards that can assist in doing so. Our aim is to provide any physicists lacking comprehensive statistical training with recommendations for reaching correct scientific conclusions, with only a modest increase in analysis burden. Our ex les can be reproduced with the code publicly available at Zenodo.
Publisher: American Physical Society (APS)
Date: 10-01-2022
Publisher: IOP Publishing
Date: 12-2022
DOI: 10.1088/1475-7516/2022/12/027
Abstract: Axion-like particles (ALPs) decaying into photons are known to affect a wide range of astrophysical and cosmological observables. In this study we focus on ALPs with masses in the keV–MeV range and lifetimes between 10 4 and 10 13 seconds, corresponding to decays between the end of Big Bang Nucleosynthesis and the formation of the Cosmic Microwave Background (CMB). Using the CosmoBit module of the global fitting framework GAMBIT , we combine state-of-the-art calculations of the irreducible ALP freeze-in abundance, primordial element abundances (including photodisintegration through ALP decays), CMB spectral distortions and anisotropies, and constraints from supernovae and stellar cooling. This approach makes it possible for the first time to perform a global analysis of the ALP parameter space while varying the parameters of ΛCDM as well as several nuisance parameters. We find a lower bound on the ALP mass of around m a 300 keV, which can only be evaded if ALPs are stable on cosmological timescales. Future observations of CMB spectral distortions with a PIXIE-like mission are expected to improve this bound by two orders of magnitude.
Publisher: Springer Science and Business Media LLC
Date: 05-2021
Abstract: Models in which the Higgs boson is a composite pseudo-Nambu-Goldstone boson offer attractive solutions to the Higgs mass naturalness problem. We consider three such models based on the minimal SO (5) → SO (4) symmetry breaking pattern, and perform convergent global fits on the models under a Bayesian framework in order to find the regions of their parameter spaces that best fit a wide range of constraints, including recent Higgs measurements. We use a novel technique to analyse the fine-tuning of the models, quantifying the tuning as the Kullback-Leibler ergence from the prior to the posterior probability on the parameter space. Each model is found to be able to satisfy all constraints at the 3 σ level simultaneously. As a by-product of the fits, we analyse the collider phenomenology of our models in these viable regions. In two of the three models, we find that the gg → H → γγ cross section is less than ∼90% that predicted by the SM, which is already in slight tension with experiment and could potentially be ruled out in the future high-luminosity run of the LHC. In addition, the lightest fermions F arising from the new strong dynamics in these models are seen in general to lie above ∼1 . 1 TeV, with the F → tW + and F → $$ \\overline{b}{W}^{+} $$ b ¯ W + decays offering particularly promising channels for probing these models in future collider searches.
Publisher: Oxford University Press (OUP)
Date: 11-08-2020
Abstract: Nested s ling (NS) is an invaluable tool in data analysis in modern astrophysics, cosmology, gravitational wave astronomy, and particle physics. We identify a previously unused property of NS related to order statistics: the insertion indexes of new live points into the existing live points should be uniformly distributed. This observation enabled us to create a novel cross-check of single NS runs. The tests can detect when an NS run failed to s le new live points from the constrained prior and plateaus in the likelihood function, which break an assumption of NS and thus leads to unreliable results. We applied our cross-check to NS runs on toy functions with known analytic results in 2–50 dimensions, showing that our approach can detect problematic runs on a variety of likelihoods, settings, and dimensions. As an ex le of a realistic application, we cross-checked NS runs performed in the context of cosmological model selection. Since the cross-check is simple, we recommend that it become a mandatory test for every applicable NS run.
Publisher: Springer Science and Business Media LLC
Date: 05-2021
Abstract: Optimisation problems are ubiquitous in particle and astrophysics, and involve locating the optimum of a complicated function of many parameters that may be computationally expensive to evaluate. We describe a number of global optimisation algorithms that are not yet widely used in particle astrophysics, benchmark them against random s ling and existing techniques, and perform a detailed comparison of their performance on a range of test functions. These include four analytic test functions of varying dimensionality, and a realistic ex le derived from a recent global fit of weak-scale supersymmetry. Although the best algorithm to use depends on the function being investigated, we are able to present general conclusions about the relative merits of random s ling, Differential Evolution, Particle Swarm Optimisation, the Covariance Matrix Adaptation Evolution Strategy, Bayesian Optimisation, Grey Wolf Optimisation, and the PyGMO Artificial Bee Colony, Gaussian Particle Filter and Adaptive Memory Programming for Global Optimisation algorithms.
Publisher: American Physical Society (APS)
Date: 04-06-2021
Publisher: American Economic Association
Date: 06-2013
Abstract: Authority and power permeate political, social, and economic life, but empirical knowledge about the motivational origins and consequences of authority is limited. We study the motivation and incentive effects of authority experimentally in an authority-delegation game. In iduals often retain authority even when its delegation is in their material interest—suggesting that authority has nonpecuniary consequences for utility. Authority also leads to overprovision of effort by the controlling parties, while a large percentage of subordinates underprovide effort despite pecuniary incentives to the contrary. Authority thus has important motivational consequences that exacerbate the inefficiencies arising from suboptimal delegation choices. (JEL C92, D23, D82)
Location: United Kingdom of Great Britain and Northern Ireland
Location: No location found
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Will Handley.