Publications
118 results found
Autenrieth M, van Dyk D, Trotta R, et al., 2024, Stratified learning: a general-purpose statistical method for improved learning under covariate shift, Statistical Analysis and Data Mining, Vol: 17, ISSN: 1932-1864
We propose a simple, statistically principled, and theoretically justified method to improve supervised learning when the training set is not representative, a situation known as covariate shift. We build upon a well-established methodology in causal inference and show that the effects of covariate shift can be reduced or eliminated by conditioning on propensity scores. In practice, this is achieved by fitting learners within strata constructed by partitioning the data based on the estimated propensity scores, leading to approximately balanced covariates and much-improved target prediction. We refer to the overall method as Stratified Learning, or StratLearn. We demonstrate the effectiveness of this general-purpose method on two contemporary research questions in cosmology, outperforming state-of-the-art importance weighting methods. We obtain the best-reported AUC (0.958) on the updated “Supernovae photometric classification challenge,” and we improve upon existing conditional density estimation of galaxy redshift from Sloan Digital Sky Survey (SDSS) data.
Agostini F, Maouloud SEMA, Althueser L, et al., 2023, Erratum to: Sensitivity of the DARWIN observatory to the neutrinoless double beta decay of <sup>136</sup> Xe (The European Physical Journal C, (2020), 80, 9, (808), 10.1140/epjc/s10052-020-8196-z), European Physical Journal C, Vol: 83, ISSN: 1434-6044
Detailed MC simulation studies of muon-induced neutrons [1] revealed our initial overestimation of the (Formula presented.) Xe activation by neutron capture on (Formula presented.) Xe in the DARWIN TPC located at LNGS. The in-situ (Formula presented.) Xe production rate must be corrected to (0.82 ± 0.10) atoms/(t (Formula presented.) yr), a factor of 8.4 lower than the initially estimated value. This reduces the previously-dominant intrinsic background contribution from (Formula presented.) Xe to a level similar to the (Formula presented.) B neutrino background via (Formula presented.) - (Formula presented.) scattering. This increased importance of the formerly subdominant (Formula presented.) B background calls for a revision of its initially simplified calculation. The neutrino flux spectrum is now convolved with the energy-dependent electron neutrino survival probability (Formula presented.) , according to the MSW-LMA solution [2]. Accordingly, Table 3 and Figures 6, 7 and 8 of the initial manuscript are corrected. The DARWIN sensitivity to the (Formula presented.) decay of (Formula presented.) Xe is recalculated with the updated background rates. The figure-of-merit estimator (section 6.1 of the original manuscript) projects a half-life sensitivity at 90% confidence level (C.L.) of (Formula presented.) ((Formula presented.)) after 10 (4) years of exposure. The frequentist profile-likelihood analysis (section 6.2) yields a (Formula presented.) sensitivity limit of (Formula presented.) for a 10 year exposure with (Formula presented.) fiducial mass. The corresponding (Formula presented.) discovery potential after 10 years is (Formula presented.). (Table presented.) Expected background index averaged in the (Formula presented.) -ROI of [2435–2481] keV, the corresponding event rate in the (Formula presented.) FV and the relative uncertainty by origin Background source Background index Rate Rel. uncertainty [events/ (t (Formula presented.)
Heavens A, Trotta R, Mootoovaloo A, et al., 2023, Extreme data compression for Bayesian model comparison, Journal of Cosmology and Astroparticle Physics, Vol: 2023, ISSN: 1475-7516
We develop extreme data compression for use in Bayesian model comparison via the MOPED algorithm, as well as more general score compression. We find that Bayes Factors from data compressed with the MOPED algorithm are identical to those from their uncompressed datasets when the models are linear and the errors Gaussian. In other nonlinear cases, whether nested or not, we find negligible differences in the Bayes Factors, and show this explicitly for the Pantheon-SH0ES supernova dataset. We also investigate the sampling properties of the Bayesian Evidence as a frequentist statistic, and find that extreme data compression reduces the sampling variance of the Evidence, but has no impact on the sampling distribution of Bayes Factors. Since model comparison can be a very computationally-intensive task, MOPED extreme data compression may present significant advantages in computational time.
Crisostomi M, Dey K, Barausse E, et al., 2023, Neural posterior estimation with guaranteed exact coverage: The ringdown of GW150914, Physical Review D, Vol: 108, ISSN: 2470-0010
We analyze the ringdown phase of the first detected black-hole merger, GW150914, using a simulation-based inference pipeline based on masked autoregressive flows. We obtain approximate marginal posterior distributions for the ringdown parameters, namely the mass, spin, and the amplitude and phases of the dominant mode and its first overtone. Thanks to the locally amortized nature of our method, we are able to calibrate our posteriors with injected simulations, producing posterior regions with guaranteed (i.e., exact) frequentist coverage of the true values. For GW150914, our calibrated posteriors provide only mild evidence (∼2σ) for the presence of an overtone, even if the ringdown is assumed to start at the peak of the amplitude.
Karchev K, Trotta R, Weniger C, 2023, SICRET: Supernova Ia Cosmology with truncated marginal neural Ratio EsTimation, Monthly Notices of the Royal Astronomical Society, Vol: 520, Pages: 1056-1072, ISSN: 0035-8711
Type Ia supernovae (SNe Ia), standardizable candles that allow tracing the expansion history of the Universe, are instrumental in constraining cosmological parameters, particularly dark energy. State-of-the-art likelihood-based analyses scale poorly to future large data sets, are limited to simplified probabilistic descriptions, and must explicitly sample a high-dimensional latent posterior to infer the few parameters of interest, which makes them inefficient. Marginal likelihood-free inference, on the other hand, is based on forward simulations of data, and thus can fully account for complicated redshift uncertainties, contamination from non-SN Ia sources, selection effects, and a realistic instrumental model. All latent parameters, including instrumental and survey-related ones, per object and population-level properties, are implicitly marginalized, while the cosmological parameters of interest are inferred directly. As a proof of concept, we apply truncated marginal neural ratio estimation (TMNRE), a form of marginal likelihood-free inference, to BAHAMAS, a Bayesian hierarchical model for SALT parameters. We verify that TMNRE produces unbiased and precise posteriors for cosmological parameters from up to 100 000 SNe Ia. With minimal additional effort, we train a network to infer simultaneously the
Aalbers J, AbdusSalam SS, Abe K, et al., 2023, A next-generation liquid xenon observatory for dark matter and neutrino physics, Journal of Physics G: Nuclear and Particle Physics, Vol: 50, ISSN: 0954-3899
The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector.
Rahman W, Trotta R, Boruah SS, et al., 2022, New constraints on anisotropic expansion from supernovae type Ia, Monthly Notices of the Royal Astronomical Society, Vol: 514, Pages: 139-163, ISSN: 0035-8711
We re-examine the contentious question of constraints on anisotropic expansion from Type Ia supernovae (SNIa) in the light of a novel determination of peculiar velocities, which are crucial to test isotropy with SNe out to distances ⪝200h-1 Mpc. We re-analyse the Joint Light-Curve Analysis (JLA) Supernovae (SNe) data, improving on previous treatments of peculiar velocity corrections and their uncertainties (both statistical and systematic) by adopting state-of-the-art flow models constrained independently via the 2M++ galaxy redshift compilation. We also introduce a novel procedure to account for colour-based selection effects, and adjust the redshift of low-z SNe self-consistently in the light of our improved peculiar velocity model. We adopt the Bayesian hierarchical model BAHAMAS to constrain a dipole in the distance modulus in the context of the Lambda cold dark matter (ΛCDM) model and the deceleration parameter in a phenomenological Cosmographic expansion. We do not find any evidence for anisotropic expansion, and place a tight upper bound on the amplitude of a dipole, |Dμ| < 5.93 × 10−4 (95 per cent credible interval) in a ΛCDM setting, and |Dq0|<6.29×10−2 in the Cosmographic expansion approach. Using Bayesian model comparison, we obtain posterior odds in excess of 900:1 (640:1) against a constant-in-redshift dipole for ΛCDM (the Cosmographic expansion). In the isotropic case, an accelerating universe is favoured with odds of ∼1100:1 with respect to a decelerating one.
Althueser L, Antunovic B, Aprile E, et al., 2022, GPU-based optical simulation of the DARWIN detector, Journal of Instrumentation, Vol: 17, ISSN: 1748-0221
Understanding propagation of scintillation light is critical for maximizing the discovery potential of next-generation liquid xenon detectors that use dual-phase time projection chamber technology. This work describes a detailed optical simulation of the DARWIN detector implemented using Chroma, a GPU-based photon tracking framework. To evaluate the framework and to explore ways of maximizing efficiency and minimizing the time of light collection, we simulate several variations of the conventional detector design. Results of these selected studies are presented. More generally, we conclude that the approach used in this work allows one to investigate alternative designs faster and in more detail than using conventional Geant4 optical simulations, making it an attractive tool to guide the development of the ultimate liquid xenon observatory.
AbdusSalam SS, Agocs FJ, Allanach BC, et al., 2022, Simple and statistically sound recommendations for analysing physical theories, Reports on Progress in Physics, Vol: 85, ISSN: 0034-4885
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 sampling 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 examples can be reproduced with the code publicly available at Zenodo.
Aalbers J, Agostini F, Maouloud SEMA, et al., 2020, Solar Neutrino Detection Sensitivity in DARWIN via Electron Scattering, The European Physical Journal C - Particles and Fields, Vol: 80, ISSN: 1124-1861
We detail the sensitivity of the proposed liquid xenon DARWIN observatory to solar neutrinos via elastic electron scattering. We find that DARWIN will have the potential to measure the fluxes of five solar neutrino components: pp, 7Be, 13N, 15O and pep. The precision of the 13N, 15O and pep components is hindered by the double-beta decay of 136Xe and, thus, would benefit from a depleted target. A high-statistics observation of pp neutrinos would allow us to infer the values of the electroweak mixing angle, sin2θw, and the electron-type neutrino survival probability, Pee, in the electron recoil energy region from a few keV up to 200 keV for the first time, with relative precision of 5% and 4%, respectively, with 10 live years of data and a 30 tonne fiducial volume. An observation of pp and 7Be neutrinos would constrain the neutrino-inferred solar luminosity down to 0.2%. A combination of all flux measurements would distinguish between the high- (GS98) and low-metallicity (AGS09) solar models with 2.1–2.5σ significance, independent of external measurements from other experiments or a measurement of 8B neutrinos through coherent elastic neutrino-nucleus scattering in DARWIN. Finally, we demonstrate that with a depleted target DARWIN may be sensitive to the neutrino capture process of 131Xe.
Ando S, Geringer-Sameth A, Hiroshima N, et al., 2020, Structure formation models weaken limits on WIMP dark matter from dwarf spheroidal galaxies, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 102, Pages: 061302(R) – 1-061302(R) – 8, ISSN: 1550-2368
Dwarf spheroidal galaxies that form in halo substructures provide stringentconstraints on dark matter annihilation. Many ultrafaint dwarfs discovered withmodern surveys contribute significantly to these constraints. At present,because of the lack of abundant stellar kinematic data for the ultrafaints,non-informative prior assumptions are usually made for the parameters of thedensity profiles. Based on semi-analytic models of dark matter subhalos andtheir connection to satellite galaxies, we present more informative andrealistic satellite priors. We show that our satellite priors lead toconstraints on the annihilation rate that are between a factor of 2 and afactor of 7 weaker than under non-informative priors. As a result, the thermalrelic cross section can at best only be excluded (with 95% probability) fordark matter masses of $\lesssim 40$ GeV from dwarf spheroidal data, assumingannihilation into $b\bar{b}$.
Agostini F, Maouloud SEMA, Althueser L, et al., 2020, Sensitivity of the DARWIN observatory to the neutrinoless double beta decay of ¹³⁶Xe, European Physical Journal C: Particles and Fields, Vol: 80, ISSN: 1124-1861
The DARWIN observatory is a proposed next-generation experiment to search for particle dark matter and for the neutrinoless double beta decay of 136Xe. Out of its 50 t total natural xenon inventory, 40 t will be the active target of a time projection chamber which thus contains about 3.6 t of 136Xe. Here, we show that its projected half-life sensitivity is 2.4×1027year, using a fiducial volume of 5 t of natural xenon and 10 year of operation with a background rate of less than 0.2 events/(t ⋅ year) in the energy region of interest. This sensitivity is based on a detailed Monte Carlo simulation study of the background and event topologies in the large, homogeneous target. DARWIN will be comparable in its science reach to dedicated double beta decay experiments using xenon enriched in 136Xe.
Trotta R, Hajas D, Camargo-Molina JE, et al., 2020, Communicating cosmology with multisensory metaphorical experiences, JCOM : Journal of Science Communication, Vol: 19, Pages: 1-17, ISSN: 1824-2030
We present a novel approach to communicating abstract concepts in cosmology and astrophysics in a more accessible and inclusive manner. We describe an exhibit aiming at creating an immersive, multisensory metaphorical experience of an otherwise imperceptible physical phenomenon — dark matter. Human-Computer Interaction experts and physicists co-created a multisensory journey through dark matter by exploiting the latest advances in haptic and olfactory technology. We present the concept design of a pilot and a second, improved event, both held at the London Science Museum, including the practical setup of the multisensory dark matter experience, the delivery of sensory stimulation and preliminary insights from users' feedback.
Hoof S, Geringer-Sameth A, Trotta R, 2020, A global analysis of dark matter signals from 27 dwarf spheroidal galaxies using 11 years of Fermi-LAT observations, Journal of Cosmology and Astroparticle Physics, Vol: 2020, ISSN: 1475-7516
We search for a dark matter signal in 11 years of Fermi-LAT gamma-ray data from 27 Milky Way dwarf spheroidal galaxies with spectroscopically measured J-factors. Our analysis includes uncertainties in J-factors and background normalisations and compares results from a Bayesian and a frequentist perspective. We revisit the dwarf spheroidal galaxy Reticulum II, confirming that the purported gamma-ray excess seen in Pass 7 data is much weaker in Pass 8, independently of the statistical approach adopted. We introduce for the first time posterior predictive distributions to quantify the probability of a dark matter detection from another dwarf galaxy given a tentative excess. A global analysis including all 27 dwarfs shows no indication for a signal in nine annihilation channels. We present stringent new Bayesian and frequentist upper limits on the dark matter cross section as a function of dark matter mass. The best-fit dark matter parameters associated with the Galactic Centre excess are excluded by at least 95% confidence level/posterior probability in the frequentist/Bayesian framework in all cases. However, from a Bayesian model comparison perspective, dark matter annihilation within the dwarfs is not strongly disfavoured compared to a background-only model. These results constitute the highest exposure analysis on the most complete sample of dwarfs to date. Posterior samples and likelihood maps from this study are publicly available.
Karukes EV, Benito M, Iocco F, et al., 2019, A robust estimate of the Milky Way mass from rotation curve data, Publisher: arXiv
We present a new estimate of the mass of the Milky Way, inferred via aBayesian approach from tracers of the circular velocity in the disk plane andstars in the stellar halo. We use the rotation curve method to determine thedark matter density profile, together with the total stellar mass, which isconstrained by surface stellar density and microlensing measurements. We alsoinclude uncertainties on the baryonic morphology via Bayesian model averaging,thus converting a potential source of systematic error into a more manageablestatistical uncertainty. We evaluate the robustness of our result againstvarious possible systematics, including rotation curve data selection,uncertainty on the Sun's velocity $V_0$, dependence on the dark matter profileassumptions, and choice of priors. We find the Milky Way's virial mass to be$\log_{10}M_{200}/ {\rm M_\odot} =11.92^{+0.06}_{-0.05}{\rm(stat)}\pm{0.28}\pm0.27{\rm(syst)}$ and the total massto be $\log_{10}M_{\rm tot}/ {\rm M_\odot} =11.95^{+0.04}_{-0.04}{\rm(stat)}\pm{0.25}\pm0.25{\rm(syst)}$($M_{200}=8.3^{+1.2}_{-0.9}{\rm(stat)}\times10^{11}\,{\rm M_\odot}$ and $M_{\rmtot}=8.9^{+1.0}_{-0.8}{\rm(stat)}\times10^{11}\,{\rm M_\odot}$). We also applyour framework to Gaia DR2 rotation curve data and find good statisticalagreement with the above results.
Karukes E, Benito M, Iocco F, et al., 2019, Bayesian reconstruction of the Milky Way dark matter distribution, Journal of Cosmology and Astroparticle Physics, Vol: 2019, ISSN: 1475-7516
We develop a novel Bayesian methodology aimed at reliably and precisely inferring the distribution of dark matter within the Milky Way using rotation curve data. We identify a subset of the available rotation curve tracers that are mutually consistent with each other, thus eliminating data sets that might suffer from systematic bias. We investigate different models for the mass distribution of the luminous (baryonic) component that bracket the range of likely morphologies. We demonstrate the statistical performance of our method on simulated data in terms of coverage, fractional distance, and mean squared error. Applying it to Milky Way data we measure the local dark matter density at the solar circle ρ0 to be ρ0 = 0.43 ± 0.02(stat) ± 0.01(sys) GeV/cm3, with an accuracy ~ 6%. This result is robust to the assumed baryonic morphology. The scale radius and inner slope of the dark matter profile are degenerate and cannot be individually determined with high accuracy. We show that these results are robust to several possible residual systematic errors in the rotation curve data.
Hill R, Shariff H, Trotta R, et al., 2018, Projected distances to host galaxy reduce SNIa dispersion, Monthly Notices of the Royal Astronomical Society, Vol: 481, Pages: 2766-2777, ISSN: 0035-8711
We use multi-band imagery data from the Sloan Digital Sky Survey (SDSS) to measure projected distances of 302 supernova type Ia (SNIa) from the centre of their host galaxies, normalized to the galaxy's brightness scale length, with a Bayesian approach. We test the hypothesis that SNIas further away from the centre of their host galaxy are less subject to dust contamination (as the dust column density in their environment is maller) and/or come from a more homogeneous environment. Using the Mann-Whitney U test, we find a statistically significant difference in the observed colour correction distribution between SNIas that are near and those that are far from the centre of their host. The local p-value is 3 x 10^{-3}, which is significant at the 5 per cent level after look-elsewhere effect correction. We estimate the residual scatter of thetwo subgroups to be 0.073 +/- 0.018 for the far SNIas, compared to 0.114 +/-0.009 for the near SNIas -- an improvement of 30 per cent, albeit with a low statistical significance of 2sigma. This confirms the importance of host galaxy properties in correctly interpreting SNIa observations for cosmological inference.
Amendola L, Appleby S, Avgoustidis A, et al., 2018, Cosmology and fundamental physics with the Euclid satellite, Living Reviews in Relativity, Vol: 21, Pages: 1-345, ISSN: 1433-8351
Euclid is a European Space Agency medium-class mission selected for launch in 2020 within the cosmic vision 2015–2025 program. The main goal of Euclid is to understand the origin of the accelerated expansion of the universe. Euclid will explore the expansion history of the universe and the evolution of cosmic structures by measuring shapes and red-shifts of galaxies as well as the distribution of clusters of galaxies over a large fraction of the sky. Although the main driver for Euclid is the nature of dark energy, Euclid science covers a vast range of topics, from cosmology to galaxy evolution to planetary research. In this review we focus on cosmology and fundamental physics, with a strong emphasis on science beyond the current standard models. We discuss five broad topics: dark energy and modified gravity, dark matter, initial conditions, basic assumptions and questions of methodology in the data analysis. This review has been planned and carried out within Euclid’s Theory Working Group and is meant to provide a guide to the scientific themes that will underlie the activity of the group during the preparation of the Euclid mission.
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.
Trotta R, 2018, The Hands-On Universe: Making Sense of the Universe with All Your Senses, CAPJOURNAL, Pages: 20-25, ISSN: 1996-5621
For the past four years, the Hands-On Universe public engagement programme has explored unconventional, interactive and multi-sensorial ways of communicating complex ideas in cosmology and astrophysics to a wide variety of audiences. The programme lead, Roberto Trotta, has reached thousands of people through food-based workshops, art and science collaborations and a book written using only the 1000 most common words in the English language. In this article, Roberto reflects in first person on what has worked well in the programme, and what has not.
Trotta R, 2018, Bayesian Cosmology, Bayesian Astrophysics, Pages: 119-157, ISBN: 9781107102132
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Revsbech EA, Trotta R, van Dyk D, 2017, STACCATO: a novel solution to supernova photometric classification with biased training sets, Monthly Notices of the Royal Astronomical Society, Vol: 473, ISSN: 0035-8711
We present a new solution to the problem of classifying Type Ia supernovae from their light curves alone given a spectroscopically confirmed but biased training set, circumventing the need to obtain an observationally expensive unbiased training set. We use Gaussian processes (GPs) to model the supernovae's (SN's) light curves, and demonstrate that the choice of covariance function has only a small influence on the GPs ability to accurately classify SNe. We extend and improve the approach of Richards et al. – a diffusion map combined with a random forest classifier – to deal specifically with the case of biased training sets. We propose a novel method called Synthetically Augmented Light Curve Classification (STACCATO) that synthetically augments a biased training set by generating additional training data from the fitted GPs. Key to the success of the method is the partitioning of the observations into subgroups based on their propensity score of being included in the training set. Using simulated light curve data, we show that STACCATO increases performance, as measured by the area under the Receiver Operating Characteristic curve (AUC), from 0.93 to 0.96, close to the AUC of 0.977 obtained using the ‘gold standard’ of an unbiased training set and significantly improving on the previous best result of 0.88. STACCATO also increases the true positive rate for SNIa classification by up to a factor of 50 for high-redshift/low-brightness SNe.
Revsbech EA, Trotta R, van Dyk D, 2017, STACCATO: a novel solution to supernova photometric classification with biased training sets
R implementation of STACCATO method for supernova classification with biased training set. Accompanying paper: STACCATO: A Novel Solution to Supernova Photometric Classification with Biased Training Sets,E.A. Resvbech, R. Trotta & D.A. van Dyk, MNRAS 473, 3, 3969-3986 (2018), e-print archive: 1706.03811, doi
Oreshenko M, Lavie B, Grimm SL, et al., 2017, Retrieval analysis of the emission spectrum of WASP-12b: sensitivity of outcomes to prior assumptions and implications for formation history, Astrophysical Journal Letters, Vol: 847, ISSN: 2041-8205
We analyze the emission spectrum of the hot Jupiter WASP-12b using our HELIOS-R retrieval code and HELIOS-K opacity calculator. When interpreting Hubble and Spitzer data, the retrieval outcomes are found to be prior-dominated. When the prior distributions of the molecular abundances are assumed to be log-uniform, the volume mixing ratio of HCN is found to be implausibly high. A VULCAN chemical kinetics model of WASP-12b suggests that chemical equilibrium is a reasonable assumption even when atmospheric mixing is implausibly rigorous. Guided by (exo)planet formation theory, we set Gaussian priors on the elemental abundances of carbon, oxygen, and nitrogen with the Gaussian peaks being centered on the measured C/H, O/H, and N/H values of the star. By enforcing chemical equilibrium, we find substellar O/H and stellar to slightly superstellar C/H for the dayside atmosphere of WASP-12b. The superstellar carbon-to-oxygen ratio is just above unity, regardless of whether clouds are included in the retrieval analysis, consistent with Madhusudhan et al. Furthermore, whether a temperature inversion exists in the atmosphere depends on one's assumption for the Gaussian width of the priors. Our retrieved posterior distributions are consistent with the formation of WASP-12b in a solar-composition protoplanetary disk, beyond the water iceline, via gravitational instability or pebble accretion (without core erosion) and migration inward to its present orbital location via a disk-free mechanism, and are inconsistent with both in situ formation and core accretion with disk migration, as predicted by Madhusudhan et al. We predict that the interpretation of James Webb Space Telescope WASP-12b data will not be prior-dominated.
Aalbers J, Agostini F, Alfonsi M, et al., 2016, DARWIN: towards the ultimate dark matter detector, Journal of Cosmology and Astroparticle Physics, Vol: 2016, ISSN: 1475-7516
DARk matter WImp search with liquid xenoN (DARWIN) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until neutrino interactions with the target become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the xenon will be observed by VUV sensitive, ultra-low background photosensors. Besides its excellent sensitivity to WIMPs above a mass of 5 GeV/c2, such a detector with its large mass, low-energy threshold and ultra-low background level will also be sensitive to other rare interactions. It will search for solar axions, galactic axion-like particles and the neutrinoless double-beta decay of 136Xe, as well as measure the low-energy solar neutrino flux with < 1% precision, observe coherent neutrino-nucleus interactions, and detect galactic supernovae. We present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing detector design and R&D efforts.
Aaboud M, Aad G, Abbott B, et al., 2016, Dark matter interpretations of ATLAS searches for the electroweak production of supersymmetric particles in √ s=8 TeV proton-proton collisions, Journal of High Energy Physics, Vol: 2016, ISSN: 1126-6708
A selection of searches by the ATLAS experiment at the LHC for the electroweak production of SUSY particles are used to study their impact on the constraints on dark matter candidates. The searches use 20 fb−1 of proton-proton collision data at s√=8s=8 TeV. A likelihood-driven scan of a five-dimensional effective model focusing on the gaugino-higgsino and Higgs sector of the phenomenological minimal supersymmetric Standard Model is performed. This scan uses data from direct dark matter detection experiments, the relic dark matter density and precision flavour physics results. Further constraints from the ATLAS Higgs mass measurement and SUSY searches at LEP are also applied. A subset of models selected from this scan are used to assess the impact of the selected ATLAS searches in this five-dimensional parameter space. These ATLAS searches substantially impact those models for which the mass m(χ~01)m(χ~10) of the lightest neutralino is less than 65 GeV, excluding 86% of such models. The searches have limited impact on models with larger m(χ~01)m(χ~10) due to either heavy electroweakinos or compressed mass spectra where the mass splittings between the produced particles and the lightest supersymmetric particle is small.
Liem S, Bertone G, Calore F, et al., 2016, Effective field theory of dark matter: a global analysis, The Journal of High Energy Physics, Vol: 2016, ISSN: 1029-8479
We present global fits of an effective field theory description of real, and complex scalar dark matter candidates. We simultaneously take into account all possible dimension 6 operators consisting of dark matter bilinears and gauge invariant combinations of quark and gluon fields. We derive constraints on the free model parameters for both the real (five parameters) and complex (seven) scalar dark matter models obtained by combining Planck data on the cosmic microwave background, direct detection limits from LUX, and indirect detection limits from the Fermi Large Area Telescope. We find that for real scalars indirect dark matter searches disfavour a dark matter particle mass below 100 GeV. For the complex scalar dark matter particle current data have a limited impact due to the presence of operators that lead to p-wave annihilation, and also do not contribute to the spin-independent scattering cross-section. Although current data are not informative enough to strongly constrain the theory parameter space, we demonstrate the power of our formalism to reconstruct the theoretical parameters compatible with an actual dark matter detection, by assuming that the excess of gamma rays observed by the Fermi Large Area Telescope towards the Galactic centre is entirely due to dark matter annihilations. Please note that the excess can very well be due to astrophysical sources such as millisecond pulsars. We find that scalar dark matter interacting via effective field theory operators can in principle explain the Galactic centre excess, but that such interpretation is in strong tension with the non-detection of gamma rays from dwarf galaxies in the real scalar case. In the complex scalar case there is enough freedom to relieve the tension.
Shariff H, Dhawan S, Jiao X, et al., 2016, Standardizing type Ia supernovae optical brightness using near infrared rebrightening time, Monthly Notices of the Royal Astronomical Society, Vol: 463, Pages: 4311-4316, ISSN: 1365-2966
Accurate standardization of Type Ia supernovae (SNIa) is instrumental to theusage of SNIa as distance indicators. We analyse a homogeneous sample of 22 lowzSNIa, observed by the Carnegie Supernova Project (CSP) in the optical and nearinfra-red (NIR). We study the time of the second peak in the J-band, t2, as an alternativestandardization parameter of SNIa peak optical brightness, as measured by thestandard SALT2 parameter mB. We use BAHAMAS, a Bayesian hierarchical modelfor SNIa cosmology, to estimate the residual scatter in the Hubble diagram.We find that in the absence of a colour correction, t2 is a better standardizationparameter compared to stretch: t2 has a 1σ posterior interval for the Hubble residualscatter of σ∆µ = {0.250, 0.257} mag, compared to σ∆µ = {0.280, 0.287} mag whenstretch (x1) alone is used. We demonstrate that when employed together with a colourcorrection, t2 and stretch lead to similar residual scatter. Using colour, stretch andt2 jointly as standardization parameters does not result in any further reduction inscatter, suggesting that t2 carries redundant information with respect to stretch andcolour. With a much larger SNIa NIR sample at higher redshift in the future, t2 couldbe a useful quantity to perform robustness checks of the standardization procedure.
Shariff H, Jiao X, Trotta R, et al., 2016, Bahamas: new analysis of type Ia supernovae reveals inconsistencies with standard cosmology, The Astrophysical Journal, Vol: 827, ISSN: 1538-4357
We present results obtained by applying our BAyesian HierArchical Modeling for the Analysis of Supernova cosmology (BAHAMAS) software package to the 740 spectroscopically confirmed supernovae of type Ia (SNe Ia) from the "Joint Light-curve Analysis" (JLA) data set. We simultaneously determine cosmological parameters and standardization parameters, including corrections for host galaxy mass, residual scatter, and object-by-object intrinsic magnitudes. Combining JLA and Planck data on the cosmic microwave background, we find significant discrepancies in cosmological parameter constraints with respect to the standard analysis: we find ${{\rm{\Omega }}}_{{\rm{m}}}=0.399\pm 0.027$, $2.8\sigma $ higher than previously reported, and $w=-0.910\pm 0.045$, $1.6\sigma $ higher than the standard analysis. We determine the residual scatter to be ${\sigma }_{{\rm{res}}}=0.104\pm 0.005$. We confirm (at the 95% probability level) the existence of two subpopulations segregated by host galaxy mass, separated at ${\mathrm{log}}_{10}(M/{M}_{\odot })=10$, differing in mean intrinsic magnitude by 0.055 ± 0.022 mag, lower than previously reported. Cosmological parameter constraints, however, are unaffected by the inclusion of corrections for host galaxy mass. We find $\sim 4\sigma $ evidence for a sharp drop in the value of the color correction parameter, $\beta (z)$, at a redshift ${z}_{t}=0.662\pm 0.055$. We rule out some possible explanations for this behavior, which remains unexplained.
Johannesson G, de Austri RR, Vincent AC, et al., 2016, Bayesian analysis of cosmic ray propagation: evidence against homogeneous diffusion, Astrophysical Journal, Vol: 824, ISSN: 1538-4357
The American Astronomical Society, find out moreThe American Astronomical Society, find out moreThe Institute of Physics, find out moreThe Institute of Physics, find out moreBAYESIAN ANALYSIS OF COSMIC RAY PROPAGATION: EVIDENCE AGAINST HOMOGENEOUS DIFFUSIONG. Jóhannesson1, R. Ruiz de Austri2, A. C. Vincent3, I. V. Moskalenko4,5, E. Orlando4,5, T. A. Porter4,5, A. W. Strong6, R. Trotta7,8, F. Feroz9, P. Graff10,11Show full author listPublished 2016 June 3 • © 2016. The American Astronomical Society. All rights reserved.The Astrophysical Journal, Volume 824, Number 1 Citation G. Jóhannesson et al 2016 ApJ 824 16Download Article PDFFiguresTablesReferencesDownload PDF1482 Total downloads7070 total citations on Dimensions.Turn on MathJaxGet permission to re-use this articleShare this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on MendeleyArticle informationAbstractWe present the results of the most complete scan of the parameter space for cosmic ray (CR) injection and propagation. We perform a Bayesian search of the main GALPROP parameters, using the MultiNest nested sampling algorithm, augmented by the BAMBI neural network machine-learning package. This is the first study to separate out low-mass isotopes (p, $\bar{p}$, and He) from the usual light elements (Be, B, C, N, and O). We find that the propagation parameters that best-fit $p,\bar{p}$, and He data are significantly different from those that fit light elements, including the B/C and 10Be/9Be secondary-to-primary ratios normally used to calibrate propagation parameters. This suggests that each set of species is probing a very different interstellar medium, and that the standard approach of calibrating propagation parameters using B/C can lead to incorrect results. We present posterior distributions and best-fit parameters for propagation of both sets of nuclei, as well as for the injection abundances of elements from H to Si
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