ORCID Profile
0000-0002-3151-3701
Current Organisations
Imperial College London
,
Quantum Brilliance
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Atomic, Molecular, Nuclear, Particle and Plasma Physics | Particle Physics | Cosmology and Extragalactic Astronomy
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in the Information and Computing Sciences | Expanding Knowledge in the Mathematical Sciences |
Publisher: Springer Science and Business Media LLC
Date: 10-2019
Abstract: We present a two-field model that realises inflation and the observed density of dark energy today, whilst solving the fine-tuning problems inherent in quintessence models. One field acts as the inflaton, generically driving the other to a saddle-point of the potential, from which it acts as a quintessence field following electroweak symmetry breaking. The model exhibits essentially no sensitivity to the initial value of the quintessence field, naturally suppresses its interactions with other fields, and automatically endows it with a small effective mass in the late Universe. The magnitude of dark energy today is fixed by the height of the saddle point in the potential, which is dictated entirely by the scale of electroweak symmetry breaking.
Publisher: Springer Science and Business Media LLC
Date: 03-2019
Abstract: We present global fits of cosmologically stable axion-like particle and QCD axion models in the mass range 0.1 neV to 10 eV. We focus on the case where the Peccei-Quinn symmetry is broken before the end of inflation, such that the initial value of the axion field can be considered to be homogeneous throughout the visible Universe. We include detailed likelihood functions from light-shining-through-wall experiments, haloscopes, helioscopes, the axion relic density, horizontal branch stars, supernova 1987A, white dwarf cooling, and gamma-ray observations. We carry out both frequentist and Bayesian analyses, with and without the inclusion of white dwarf cooling. We explore the degree of fine-tuning present in different models and identify parameter regions where it is possible for QCD axion models to account for both the dark matter in the Universe and the cooling hints, comparing them to specific DFSZ- and KSVZ-type models. We find the most credible parameter regions, allowing us to set (prior-dependent) upper and lower bounds on the axion mass. Our analysis also suggests that QCD axions in this scenario most probably make up a non-negligible but sub-dominant component of the dark matter in the Universe.
Publisher: American Physical Society (APS)
Date: 27-09-2013
Publisher: American Physical Society (APS)
Date: 29-03-2018
Publisher: Springer Science and Business Media LLC
Date: 10-06-2023
DOI: 10.1140/EPJC/S10052-023-11574-Z
Abstract: Using the global fitting framework, we constrain the MSSM with an eV-scale gravitino as the lightest supersymmetric particle, and the six electroweakinos (neutralinos and charginos) as the only other light new states. We combine 15 ATLAS and 12 CMS searches at 13 TeV, along with a large collection of ATLAS and CMS measurements of Standard Model signatures. This model, which we refer to as the $${{\\tilde{G}}}$$ G ~ -EWMSSM, exhibits quite varied collider phenomenology due to its many permitted electroweakino production processes and decay modes. Characteristic $${{\\tilde{G}}}$$ G ~ -EWMSSM signal events have two or more Standard Model bosons and missing energy due to the escaping gravitinos. While much of the $${{\\tilde{G}}}$$ G ~ -EWMSSM parameter space is excluded, we find several viable parameter regions that predict phenomenologically rich scenarios with multiple neutralinos and charginos within the kinematic reach of the LHC during Run 3, or the High Luminosity LHC. In particular, we identify scenarios with Higgsino-dominated electroweakinos as light as 140 GeV that are consistent with our combined set of collider searches and measurements. The full set of $${{\\tilde{G}}}$$ G ~ -EWMSSM parameter s les and input files generated for this work is available via .
Publisher: American Physical Society (APS)
Date: 31-08-2015
Publisher: Sissa Medialab
Date: 12-12-2017
DOI: 10.22323/1.312.0167
Publisher: Sissa Medialab
Date: 24-08-2009
DOI: 10.22323/1.064.0073
Publisher: Springer Science and Business Media LLC
Date: 02-2018
Publisher: IOP Publishing
Date: 04-11-2016
Publisher: IOP Publishing
Date: 04-11-2011
Publisher: Springer Science and Business Media LLC
Date: 11-2017
Publisher: Springer Netherlands
Date: 2010
Publisher: Springer Science and Business Media LLC
Date: 2019
Publisher: Oxford University Press (OUP)
Date: 13-09-2016
Publisher: Annual Reviews
Date: 09-2009
DOI: 10.1146/ANNUREV.ASTRO.46.060407.145222
Abstract: The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential reference standard against which the elemental contents of other astronomical objects are compared. In this review, we evaluate the current understanding of the solar photospheric composition. In particular, we present a redetermination of the abundances of nearly all available elements, using a realistic new three-dimensional (3D), time-dependent hydrodynamical model of the solar atmosphere. We have carefully considered the atomic input data and selection of spectral lines, and accounted for departures from local thermodynamic equilibrium (LTE) whenever possible. The end result is a comprehensive and homogeneous compilation of the solar elemental abundances. Particularly noteworthy findings are significantly lower abundances of C, N, O, and Ne compared to the widely used values of a decade ago. The new solar chemical composition is supported by a high degree of internal consistency between available abundance indicators, and by agreement with values obtained in the Solar Neighborhood and from the most pristine meteorites. There is, however, a stark conflict with standard models of the solar interior according to helioseismology, a discrepancy that has yet to find a satisfactory resolution.
Publisher: American Physical Society (APS)
Date: 20-11-2009
Publisher: Springer Science and Business Media LLC
Date: 2018
Publisher: Springer Science and Business Media LLC
Date: 12-2017
Publisher: American Physical Society (APS)
Date: 26-02-2015
Publisher: IOP Publishing
Date: 21-03-2013
Publisher: IOP Publishing
Date: 07-05-2013
Publisher: IOP Publishing
Date: 13-03-2017
Publisher: Springer Science and Business Media LLC
Date: 11-2012
Publisher: Oxford University Press (OUP)
Date: 23-12-2015
Publisher: Springer Netherlands
Date: 10-12-2010
Publisher: American Physical Society (APS)
Date: 28-09-2016
Publisher: IOP Publishing
Date: 30-07-2012
Publisher: Springer Science and Business Media LLC
Date: 08-2017
Publisher: American Physical Society (APS)
Date: 13-06-2016
Publisher: Springer Science and Business Media LLC
Date: 12-2017
Publisher: Sissa Medialab
Date: 03-05-2011
DOI: 10.22323/1.121.0021
Publisher: Elsevier BV
Date: 06-2017
Publisher: Springer Science and Business Media LLC
Date: 10-2018
Publisher: IOP Publishing
Date: 30-03-2015
Publisher: Springer Science and Business Media LLC
Date: 10-2018
Publisher: IOP Publishing
Date: 13-04-2011
Publisher: IOP Publishing
Date: 23-10-2017
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: Sissa Medialab
Date: 03-05-2011
DOI: 10.22323/1.121.0026
Publisher: IOP Publishing
Date: 04-2022
DOI: 10.1088/1475-7516/2022/04/002
Abstract: Asymmetric dark matter (ADM) that is captured in stars can act as an efficient conductor of heat. Small ADM-induced changes in a star's temperature gradient are known to alter neutrino fluxes and asteroseismological signatures, erase convective cores and modify a star's main sequence lifetime. The Sun's proximity to us makes it an ideal laboratory for studying these effects. However, the two formalisms commonly used to parametrize such heat transport were developed over 30 years ago, and calibrated with a single set of simulations. What's more, both are based on assumptions that break down at the Knudsen transition, where heat transport is maximized. We construct a Monte Carlo simulation to exactly solve the Boltzmann collision equation, determining the steady-state distribution and luminosity carried in stars by ADM with cross sections that depend on velocity and momentum. We find that, although the established (Gould & Raffelt) formalism based on local thermal equilibrium does well for constant cross sections, the isothermal (Spergel & Press) method actually performs better across all models with a simple, universal rescaling function. Based on simulation results, we provide recommendations on the parametrization of DM heat transport in stellar evolution models.
Publisher: IOP Publishing
Date: 12-04-2016
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: RWTH Aachen University
Date: 2018
Publisher: Springer Science and Business Media LLC
Date: 04-08-2023
DOI: 10.1140/EPJC/S10052-023-11859-3
Abstract: Global fits explore different parameter regions of a given model and apply constraints obtained at many energy scales. This makes it challenging to perform global fits of simplified models, which may not be valid at high energies. In this study, we derive a unitarity bound for a simplified vector dark matter model with an s -channel vector mediator and apply it to global fits of this model with in order to correctly interpret missing energy searches at the LHC. Two parameter space regions emerge as consistent with all experimental constraints, corresponding to different annihilation modes of the dark matter. We show that although these models are subject to strong validity constraints, they are currently most strongly constrained by measurements less sensitive to the high-energy behaviour of the theory. Understanding when these models cannot be consistently studied will become increasingly relevant as they are applied to LHC Run 3 data.
Publisher: American Physical Society (APS)
Date: 03-07-2012
Publisher: IOP Publishing
Date: 28-03-2013
Publisher: IOP Publishing
Date: 26-01-2010
Publisher: Springer Science and Business Media LLC
Date: 05-2021
Abstract: The excess of electron recoil events seen by the XENON1T experiment has been interpreted as a potential signal of axion-like particles (ALPs), either produced in the Sun, or constituting part of the dark matter halo of the Milky Way. It has also been explained as a consequence of trace amounts of tritium in the experiment. We consider the evidence for the solar and dark-matter ALP hypotheses from the combination of XENON1T data and multiple astrophysical probes, including horizontal branch stars, red giants, and white dwarfs. We briefly address the influence of ALP decays and supernova cooling. While the different datasets are in clear tension for the case of solar ALPs, all measurements can be simultaneously accommodated for the case of a sub-dominant fraction of dark-matter ALPs. Nevertheless, this solution requires the tuning of several a priori unknown parameters, such that for our choices of priors a Bayesian analysis shows no strong preference for the ALP interpretation of the XENON1T excess over the background hypothesis.
Publisher: American Physical Society (APS)
Date: 08-11-2013
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: 11-2019
Abstract: Ex le for the effect of wrongly defining the axion-photon coupling. The colour map and black lines are for the corrected figure using GAMBIT 1.3.1, while dashed blue lines indicate the previous erroneous exclusion lines from GAMBIT 13 0.
Publisher: EDP Sciences
Date: 11-12-2015
Publisher: EDP Sciences
Date: 11-12-2014
Publisher: Oxford University Press (OUP)
Date: 04-08-2016
Publisher: EDP Sciences
Date: 11-12-2014
Publisher: Springer Science and Business Media LLC
Date: 11-02-2010
Publisher: Springer Science and Business Media LLC
Date: 12-2020
DOI: 10.1140/EPJC/S10052-020-08635-Y
Abstract: The evaluation of higher-order cross-sections is an important component in the search for new physics, both at hadron colliders and elsewhere. For most new physics processes of interest, total cross-sections are known at next-to-leading order (NLO) in the strong coupling $$\\alpha _s$$ α s , and often beyond, via either higher-order terms at fixed powers of $$\\alpha _s$$ α s , or multi-emission resummation. However, the computation time for such higher-order cross-sections is prohibitively expensive, and precludes efficient evaluation in parameter-space scans beyond two dimensions. Here we describe the software tool , which allows for fast evaluation of cross-sections based on the use of machine-learning regression, using distributed Gaussian processes trained on a pre-generated s le of parameter points. This first version of the code provides all NLO Minimal Supersymmetric Standard Model strong-production cross-sections at the LHC, for in idual flavour final states, evaluated in a fraction of a second. Moreover, it calculates regression errors, as well as estimates of errors from higher-order contributions, from uncertainties in the parton distribution functions, and from the value of $$\\alpha _s$$ α s . While we focus on a specific phenomenological model of supersymmetry, the method readily generalises to any process where it is possible to generate a sufficient training s le.
Publisher: WORLD SCIENTIFIC
Date: 12-2009
Publisher: Informa UK Limited
Date: 18-03-2014
Publisher: Springer Science and Business Media LLC
Date: 24-03-2023
DOI: 10.1140/EPJC/S10052-023-11399-W
Abstract: Simplified models provide a useful way to study the impacts of a small number of new particles on experimental observables and the interplay of those observables, without the need to construct an underlying theory. In this study, we perform global fits of simplified dark matter models with using an up-to-date set of likelihoods for indirect detection, direct detection and collider searches. We investigate models in which a scalar or fermionic dark matter candidate couples to quarks via an s -channel vector mediator. Large parts of parameter space survive for each model. In the case of Dirac or Majorana fermion dark matter, excesses in LHC monojet searches and relic density limits tend to prefer the resonance region, where the dark matter has approximately half the mass of the mediator. A combination of vector and axial-vector couplings to the Dirac candidate also leads to competing constraints from direct detection and unitarity violation.
Publisher: IOP Publishing
Date: 22-04-2014
Publisher: IOP Publishing
Date: 26-07-2018
Publisher: Oxford University Press (OUP)
Date: 16-05-2013
DOI: 10.1093/MNRAS/STT683
Publisher: Springer Science and Business Media LLC
Date: 12-2017
Publisher: IOP Publishing
Date: 30-10-2014
Publisher: Oxford University Press (OUP)
Date: 23-12-2015
Publisher: Oxford University Press (OUP)
Date: 30-11-2010
Publisher: Oxford University Press (OUP)
Date: 08-10-2016
Publisher: American Physical Society (APS)
Date: 19-06-2012
Publisher: Oxford University Press (OUP)
Date: 21-12-2009
Publisher: Sissa Medialab
Date: 08-02-2021
DOI: 10.22323/1.360.0027
Publisher: Stichting SciPost
Date: 21-08-2020
DOI: 10.21468/SCIPOSTPHYS.9.2.022
Abstract: We report on the status of efforts to improve the reinterpretation of searches and measurements at the LHC in terms of models for new physics, in the context of the LHC Reinterpretation Forum. We detail current experimental offerings in direct searches for new particles, measurements, technical implementations and Open Data, and provide a set of recommendations for further improving the presentation of LHC results in order to better enable reinterpretation in the future. We also provide a brief description of existing software reinterpretation frameworks and recent global analyses of new physics that make use of the current data.
Publisher: EDP Sciences
Date: 2013
Publisher: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Date: 2017
Publisher: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Date: 2018
Publisher: Springer
Date: 2017
DOI: 10.5167/UZH-148663
Publisher: Elsevier BV
Date: 07-2020
Publisher: EDP Sciences
Date: 31-08-2006
Publisher: Springer Science and Business Media LLC
Date: 06-2021
DOI: 10.1007/S10686-021-09781-1
Abstract: Sky survey telescopes and powerful targeted telescopes play complementary roles in astronomy. In order to investigate the nature and characteristics of the motions of very faint objects, a flexibly-pointed instrument capable of high astrometric accuracy is an ideal complement to current astrometric surveys and a unique tool for precision astrophysics. Such a space-based mission will push the frontier of precision astrometry from evidence of Earth-mass habitable worlds around the nearest stars, to distant Milky Way objects, and out to the Local Group of galaxies. As we enter the era of the James Webb Space Telescope and the new ground-based, adaptive-optics-enabled giant telescopes, by obtaining these high precision measurements on key objects that Gaia could not reach, a mission that focuses on high precision astrometry science can consolidate our theoretical understanding of the local Universe, enable extrapolation of physical processes to remote redshifts, and derive a much more consistent picture of cosmological evolution and the likely fate of our cosmos. Already several missions have been proposed to address the science case of faint objects in motion using high precision astrometry missions: NEAT proposed for the ESA M3 opportunity, micro-NEAT for the S1 opportunity, and Theia for the M4 and M5 opportunities. Additional new mission configurations adapted with technological innovations could be envisioned to pursue accurate measurements of these extremely small motions. The goal of this White Paper is to address the fundamental science questions that are at stake when we focus on the motions of faint sky objects and to briefly review instrumentation and mission profiles.
Publisher: Springer Science and Business Media LLC
Date: 11-2017
Publisher: American Physical Society (APS)
Date: 08-09-2010
Publisher: American Physical Society (APS)
Date: 15-03-2018
Publisher: Canadian Science Publishing
Date: 04-2011
DOI: 10.1139/P10-119
Abstract: We have very recently re-determined the abundances of nearly all the available chemical elements in the solar photosphere, from lithium to thorium (Asplund et al. Annu. Rev. Astron. Astrophys. 47, 481 (2009)). This new complete and homogeneous analysis results from a very careful selection of spectral lines of all the indicators of the abundances present in the solar photospheric spectrum, from a discussion of the atomic and molecular data, and from an analysis of these lines based on a new 3D model of the solar outer layers, taking non-LTE effects into account when possible. We present these new results, compare them with other recent solar data as well as with recent results for the solar neighborhood, and discuss some of their most important implications as well as some of the atomic data we still urgently need.
Publisher: Springer Science and Business Media LLC
Date: 11-2017
Publisher: IOP Publishing
Date: 19-08-2015
Publisher: IOP Publishing
Date: 04-07-2011
Publisher: Springer Science and Business Media LLC
Date: 11-2017
Publisher: IOP Publishing
Date: 25-05-2017
Publisher: American Astronomical Society
Date: 13-01-2009
Publisher: WORLD SCIENTIFIC
Date: 05-2008
Publisher: Springer Science and Business Media LLC
Date: 05-2018
Publisher: IOP Publishing
Date: 11-06-2014
Publisher: Oxford University Press (OUP)
Date: 21-03-2009
Publisher: American Physical Society (APS)
Date: 04-02-2008
Publisher: American Physical Society (APS)
Date: 04-06-2021
Publisher: Deutsches Elektronen-Synchrotron, DESY, Hamburg
Date: 2018
Publisher: American Astronomical Society
Date: 15-11-2011
Publisher: Springer Science and Business Media LLC
Date: 04-2010
Publisher: American Physical Society (APS)
Date: 15-07-2015
Publisher: IOP Publishing
Date: 03-2017
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2014
End Date: 2019
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2016
End Date: 2019
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2017
End Date: 2020
Funder: Science and Technology Facilities Council
View Funded ActivityStart Date: 2019
End Date: 2022
Funder: Australian Research Council
View Funded ActivityStart Date: 05-2020
End Date: 06-2022
Amount: $871,533.00
Funder: Australian Research Council
View Funded ActivityStart Date: 07-2023
End Date: 06-2026
Amount: $644,249.00
Funder: Australian Research Council
View Funded Activity