109 results found
Stoecker P, Balazs C, Bloor S, et al., 2021, Strengthening the bound on the mass of the lightest neutrino with terrestrial and cosmological experiments, PHYSICAL REVIEW D, Vol: 103, ISSN: 2470-0010
Athron P, Balazs C, Beniwal A, et al., 2021, Global fits of axion-like particles to XENON1T and astrophysical data, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
Balázs C, van Beekveld M, Caron S, et al., 2021, A comparison of optimisation algorithms for high-dimensional particle and astrophysics applications, Journal of High Energy Physics, Vol: 2021
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 sampling 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 example 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 sampling, 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.
Renk JJ, Stocker P, Bloor S, et al., 2021, CosmoBit: a GAMBIT module for computing cosmological observables and likelihoods, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
Abdallah W, AbdusSalam S, Ahmadov A, et al., 2020, Reinterpretation of LHC results for new physics: status and recommendations after run 2, SCIPOST PHYSICS, Vol: 9, ISSN: 2542-4653
Kvellestad A, Scott P, White M, 2020, GAMBIT and its application in the search for physics Beyond the Standard Model, PROGRESS IN PARTICLE AND NUCLEAR PHYSICS, Vol: 113, ISSN: 0146-6410
Hoof S, Kahlhoefer F, Scott P, et al., 2019, Axion global fits with Peccei-Quinn symmetry breaking before inflation using GAMBIT (vol 03, 191, 2019), JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
Camargo-Molina JE, Markkanen T, Scott P, 2019, Dark energy without fine tuning, The Journal of High Energy Physics, Vol: 44, Pages: 1-14, ISSN: 1029-8479
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.
Athron P, Balazs C, Buckley A, et al., 2019, Combined collider constraints on neutralinos and charginos, Publisher: SPRINGER
Hoof S, Kahlhoefer F, Scott P, et al., 2019, Axion global fits with Peccei-Quinn symmetry breaking before inflation using GAMBIT, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
Athron P, Balazs C, Beniwal A, et al., 2019, Global analyses of Higgs portal singlet dark matter models using GAMBIT, Publisher: SPRINGER
Athron P, Cornell JM, Kahlhoefer F, et al., 2018, Impact of vacuum stability, perturbativity and XENON1T on global fits of Z(2) and Z(3) scalar singlet dark matter, European Physical Journal C: Particles and Fields, Vol: 78, ISSN: 1434-6044
Scalar singlet dark matter is one of the simplest and most predictive realisations of the WIMP (weakly-interacting massive particle) idea. Although the model is constrained from all directions by the latest experimental data, it still has viable regions of parameter space. Another compelling aspect of scalar singlets is their ability to stabilise the electroweak vacuum. Indeed, models of scalar dark matter are not low-energy effective theories, but can be valid all the way to the Planck scale. Using the GAMBIT framework, we present the first global fit to include both the low-energy experimental constraints and the theoretical constraints from UV physics, considering models with a scalar singlet charged under either a Z2 or a Z3 symmetry. We show that if the model is to satisfy all experimental constraints, completely stabilise the electroweak vacuum up to high scales, and also remain perturbative to those scales, one is driven to a relatively small region of parameter space. This region has a Higgs-portal coupling slightly less than 1, a dark matter mass of 1–2 TeV and a spin-independent nuclear scattering cross-section around 10−45cm2 .
Clark HA, Scott P, Trotta R, et al., 2018, Dark matter substructure cannot explain properties of the Fermi Galactic Centre excess, Journal of Cosmology and Astroparticle Physics, Vol: 2018, ISSN: 1475-7516
An excess of gamma rays has been identified at the centre of the Milky Way, and annihilation of dark matter has been posited as a potential source. This hypothesis faces significant challenges: difficulty characterizing astrophysical backgrounds, the need for a non-trivial adiabatic contraction of the inner part of the Milky Way's dark matter halo, and recent observations of photon clustering, which suggest that the majority of the excess is due to unresolved point sources. Here we point out that the apparent point-like nature of the emission rules out the dark matter interpretation of the excess entirely. Attempting to model the emission with dark matter point sources either worsens the problem with the inner slope, requires an unrealistically large minihalo fraction toward the Galactic Centre, or overproduces the observed emission at higher latitudes.
McKay J, Scott P, 2018, Two-loop mass splittings in electroweak multiplets: Winos and minimal dark matter, Physical Review D, Vol: 97, ISSN: 2470-0010
© 2018 authors. The radiatively-induced splitting of masses in electroweak multiplets is relevant for both collider phenomenology and dark matter. Precision two-loop corrections of O(MeV) to the triplet mass splitting in the wino limit of the minimal supersymmetric standard model can affect particle lifetimes by up to 40%. We improve on previous two-loop self-energy calculations for the wino model by obtaining consistent input parameters to the calculation via two-loop renormalization-group running, and including the effect of finite light quark masses. We also present the first two-loop calculation of the mass splitting in an electroweak fermionic quintuplet, corresponding to the viable form of minimal dark matter (MDM). We place significant constraints on the lifetimes of the charged and doubly-charged fermions in this model. We find that the two-loop mass splittings in the MDM quintuplet are not constant in the large-mass limit, as might naively be expected from the triplet calculation. This is due to the influence of the additional heavy fermions in loop corrections to the gauge boson propagators.
McKay J, Scott P, 2018, Two-loop mass splittings in electroweak multiplets: Winos and minimal dark matter, PHYSICAL REVIEW D, Vol: 97, ISSN: 2470-0010
Athron P, Balazs C, Bringmann T, et al., 2018, GAMBIT: the global and modular beyond-the-standard-model inference tool, EUROPEAN PHYSICAL JOURNAL C, Vol: 78, ISSN: 1434-6044
In Ref. (GAMBIT Collaboration: Athron et. al., Eur. Phys. J. C. arXiv:1705.07908, 2017) we introduced the global-fitting framework GAMBIT. In this addendum, we describe a new minor version increment of this package. GAMBIT 1.1 includes full support for Mathematica backends, which we describe in some detail here. As an example, we backend SUSYHD (Vega and Villadoro, JHEP 07:159, 2015), which calculates the mass of the Higgs boson in the MSSM from effective field theory. We also describe updated likelihoods in PrecisionBit and DarkBit, and updated decay data included in DecayBit.
Athron P, Balazs C, Dal LA, et al., 2018, SpecBit, DecayBit and PrecisionBit: GAMBIT modules for computing mass spectra, particle decay rates and precision observables, European Physical Journal C: Particles and Fields, Vol: 78, ISSN: 1434-6044
We present the GAMBIT modules SpecBit, DecayBit and PrecisionBit. Together they provide a new framework for linking publicly available spectrum generators, decay codes and other precision observable calculations in a physically and statistically consistent manner. This allows users to automatically run various combinations of existing codes as if they are a single package. The modular design allows software packages fulfilling the same role to be exchanged freely at runtime, with the results presented in a common format that can easily be passed to downstream dark matter, collider and flavour codes. These modules constitute an essential part of the broader GAMBIT framework, a major new software package for performing global fits. In this paper we present the observable calculations, data, and likelihood functions implemented in the three modules, as well as the conventions and assumptions used in interfacing them with external codes. We also present 3-BIT-HIT, a command-line utility for computing mass spectra, couplings, decays and precision observables in the MSSM, which shows how the three modules can easily be used independently of GAMBIT.
Scott P, 2018, Global analyses of supersymmetry with GAMBIT, Proceedings of the 53rd Rencontres de Moriond - 2018 QCD and High Energy Interactions, Pages: 155-158
I provide a brief summary of the status of supersymmetric models with parameters defined at either the unification or weak scale, based on global fits using the GAMBIT framework.
We study the seven-dimensional Minimal Supersymmetric Standard Model (MSSM7) with the new GAMBIT software framework, with all parameters defined at the weak scale. Our analysis significantly extends previous weak-scale, phenomenological MSSM fits, by adding more and newer experimental analyses, improving the accuracy and detail of theoretical predictions, including dominant uncertainties from the Standard Model, the Galactic dark matter halo and the quark content of the nucleon, and employing novel and highly-efficient statistical sampling methods to scan the parameter space. We find regions of the MSSM7 that exhibit co-annihilation of neutralinos with charginos, stops and sbottoms, as well as models that undergo resonant annihilation via both light and heavy Higgs funnels. We find high-likelihood models with light charginos, stops and sbottoms that have the potential to be within the future reach of the LHC. Large parts of our preferred parameter regions will also be accessible to the next generation of direct and indirect dark matter searches, making prospects for discovery in the near future rather good.
Bringmann T, Conrad J, Cornell JM, et al., 2017, DarkBit: a GAMBIT module for computing dark matter observables and likelihoods, European Physical Journal C: Particles and Fields, Vol: 77, ISSN: 1434-6044
We introduce DarkBit, an advanced software code for computing dark matter constraints on various extensions to the Standard Model of particle physics, comprising both new native code and interfaces to external packages. This release includes a dedicated signal yield calculator for gamma-ray observations, which significantly extends current tools by implementing a cascade-decay Monte Carlo, as well as a dedicated likelihood calculator for current and future experiments (gamLike). This provides a general solution for studying complex particle physics models that predict dark matter annihilation to a multitude of final states. We also supply a direct detection package that models a large range of direct detection experiments (DDCalc), and that provides the corresponding likelihoods for arbitrary combinations of spin-independent and spin-dependent scattering processes. Finally, we provide custom relic density routines along with interfaces to DarkSUSY, micrOMEGAs, and the neutrino telescope likelihood package nulike. DarkBit is written in the framework of the Global And Modular Beyond the Standard Model Inference Tool (GAMBIT), providing seamless integration into a comprehensive statistical fitting framework that allows users to explore new models with both particle and astrophysics constraints, and a consistent treatment of systematic uncertainties. In this paper we describe its main functionality, provide a guide to getting started quickly, and show illustrative examples for results obtained with DarkBit (both as a stand-alone tool and as a GAMBIT module). This includes a quantitative comparison between two of the main dark matter codes (DarkSUSY and micrOMEGAs), and application of DarkBit ’s advanced direct and indirect detection routines to a simple effective dark matter model.
We present the most comprehensive global fits to date of three supersymmetricmodels motivated by grand unification: the Constrained Minimal SupersymmetricStandard Model (CMSSM), and its Non-Universal Higgs Mass generalisations NUHM1and NUHM2. We include likelihoods from a number of direct and indirect darkmatter searches, a large collection of electroweak precision and flavourobservables, direct searches for supersymmetry at LEP and Runs I and II of theLHC, and constraints from Higgs observables. Our analysis improves on existingresults not only in terms of the number of included observables, but also inthe level of detail with which we treat them, our sampling techniques forscanning the parameter space, and our treatment of nuisance parameters. We showthat stau co-annihilation is now ruled out in the CMSSM at more than 95\%confidence. Stop co-annihilation turns out to be one of the most promisingmechanisms for achieving an appropriate relic density of dark matter in allthree models, whilst avoiding all other constraints. We find high-likelihoodregions of parameter space featuring light stops and charginos, making thempotentially detectable in the near future at the LHC. We also show thattonne-scale direct detection will play a largely complementary role, probinglarge parts of the remaining viable parameter space, including essentially allmodels with multi-TeV neutralinos.
Balazs C, Buckley A, Dal LA, et al., 2017, ColliderBit: a GAMBIT module for the calculation of high-energy collider observables and likelihoods, European Physical Journal C: Particles and Fields, Vol: 77, ISSN: 1434-6044
We describe ColliderBit, a new code for the calculationof high energy collider observables in theories ofphysics beyond the Standard Model (BSM). ColliderBit featuresa generic interface to BSM models, a unique parallelisedMonte Carlo event generation scheme suitable for large-scalesupercomputer applications, and a number of LHC analyses,covering a reasonable range of the BSM signatures currentlysought by ATLAS and CMS. ColliderBit also calculates likelihoodsfor Higgs sector observables, and LEP searches forBSM particles. These features are provided by a combinationof new code unique to ColliderBit, and interfaces to existingstate-of-the-art public codes. ColliderBit is both an importantpart of the GAMBIT framework for BSM inference, anda standalone tool for efficiently applying collider constraintsto theories of new physics.
Bernlochner FU, Chrzaszcz M, Dal LA, et al., 2017, FlavBit: A GAMBIT module for computing flavour observables and likelihoods, European Physical Journal C: Particles and Fields, Vol: 77, ISSN: 1434-6044
Flavour physics observables are excellent probes of new physics up to veryhigh energy scales. Here we present FlavBit, the dedicated flavour physicsmodule of the global-fitting package GAMBIT. FlavBit includes customimplementations of various likelihood routines for a wide range of flavourobservables, including detailed uncertainties and correlations associated withLHCb measurements of rare, leptonic and semileptonic decays of B and D mesons,kaons and pions. It provides a generalised interface to external theory codessuch as SuperIso, allowing users to calculate flavour observables in and beyondthe Standard Model, and then test them in detail against all relevantexperimental data. We describe FlavBit and its constituent physics in somedetail, then give examples from supersymmetry and effective field theoryillustrating how it can be used both as a standalone library for flavourphysics, and within GAMBIT.
Collaboration TGAMBIT, Athron P, Balazs C, et al., 2017, GAMBIT: The Global and Modular Beyond-the-Standard-Model Inference Tool, The European Physical Journal C - Particles and Fields, Vol: 77, ISSN: 1434-6044
We describe the open-source global fitting package GAMBIT: the Global AndModular Beyond-the-Standard-Model Inference Tool. GAMBIT combines extensivecalculations of observables and likelihoods in particle and astroparticlephysics with a hierarchical model database, advanced tools for automaticallybuilding analyses of essentially any model, a flexible and powerful system forinterfacing to external codes, a suite of different statistical methods andparameter scanning algorithms, and a host of other utilities designed to makescans faster, safer and more easily-extendible than in the past. Here we give adetailed description of the framework, its design and motivation, and thecurrent models and other specific components presently implemented in GAMBIT.Accompanying papers deal with individual modules and present first GAMBITresults. GAMBIT can be downloaded from gambit.hepforge.org.
Martinez GD, McKay J, Farmer B, et al., 2017, Comparison of statistical sampling methods with ScannerBit, the GAMBIT scanning module, European Physical Journal C: Particles and Fields, Vol: 77, ISSN: 1434-6044
We introduce ScannerBit, the statistics and sampling module of the public, open-source global fitting framework GAMBIT. ScannerBit provides a standardised interface to different sampling algorithms, enabling the use and comparison of multiple computational methods for inferring profile likelihoods, Bayesian posteriors, and other statistical quantities. The current version offers random, grid, raster, nested sampling, differential evolution, Markov Chain Monte Carlo (MCMC) and ensemble Monte Carlo samplers. We also announce the release of a new standalone differential evolution sampler, Diver, and describe its design, usage and interface to ScannerBit. We subject Diver and three other samplers (the nested sampler MultiNest, the MCMC GreAT, and the native ScannerBit implementation of the ensemble Monte Carlo algorithm T-Walk) to a battery of statistical tests. For this we use a realistic physical likelihood function, based on the scalar singlet model of dark matter. We examine the performance of each sampler as a function of its adjustable settings, and the dimensionality of the sampling problem. We evaluate performance on four metrics: optimality of the best fit found, completeness in exploring the best-fit region, number of likelihood evaluations, and total runtime. For Bayesian posterior estimation at high resolution, T-Walk provides the most accurate and timely mapping of the full parameter space. For profile likelihood analysis in less than about ten dimensions, we find that Diver and MultiNest score similarly in terms of best fit and speed, outperforming GreAT and T-Walk; in ten or more dimensions, Diver substantially outperforms the other three samplers on all metrics.
Busoni G, De Simone A, Scott P, et al., 2017, Evaporation and scattering of momentum- and velocity-dependent dark matter in the Sun, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, Vol: 2017, ISSN: 1475-7516
Dark matter with momentum- or velocity-dependent interactions with nuclei has shown significant promise for explaining the so-called Solar Abundance Problem, a longstanding discrepancy between solar spectroscopy and helioseismology. The best-fit models are all rather light, typically with masses in the range of 3–5 GeV. This is exactly the mass range where dark matter evaporation from the Sun can be important, but to date no detailed calculation of the evaporation of such models has been performed. Here we carry out this calculation, for the first time including arbitrary velocity- and momentum-dependent interactions, thermal effects, and a completely general treatment valid from the optically thin limit all the way through to the optically thick regime. We find that depending on the dark matter mass, interaction strength and type, the mass below which evaporation is relevant can vary from 1 to 4 GeV. This has the effect of weakening some of the better-fitting solutions to the Solar Abundance Problem, but also improving a number of others. As a by-product, we also provide an improved derivation of the capture rate that takes into account thermal and optical depth effects, allowing the standard result to be smoothly matched to the well-known saturation limit.
Scott P, 2017, Dark matter theory: Implications and future prospects for Fermi, 7th Fermi Symposium 2017, Publisher: Proceedings of Science
I give a brief review of some of the implications of Fermi data for theoriesof the identity of dark matter, and their combination with data from othercomplementary probes. I also preview some of the prospects for probing suchmodels with future data.
McKay J, Scott P, Athron P, 2017, Pitfalls of iterative pole mass calculation in electroweak multiplets
One of the simplest viable models for dark matter is an additional neutral scalar, stabilised by a Z2Z2 symmetry. Using the GAMBIT package and combining results from four independent samplers, we present Bayesian and frequentist global fits of this model. We vary the singlet mass and coupling along with 13 nuisance parameters, including nuclear uncertainties relevant for direct detection, the local dark matter density, and selected quark masses and couplings. We include the dark matter relic density measured by Planck, direct searches with LUX, PandaX, SuperCDMS and XENON100, limits on invisible Higgs decays from the Large Hadron Collider, searches for high-energy neutrinos from dark matter annihilation in the Sun with IceCube, and searches for gamma rays from annihilation in dwarf galaxies with the Fermi-LAT. Viable solutions remain at couplings of order unity, for singlet masses between the Higgs mass and about 300 GeV, and at masses above ∼∼ 1 TeV. Only in the latter case can the scalar singlet constitute all of dark matter. Frequentist analysis shows that the low-mass resonance region, where the singlet is about half the mass of the Higgs, can also account for all of dark matter, and remains viable. However, Bayesian considerations show this region to be rather fine-tuned.
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