Imperial College London


Faculty of Natural SciencesDepartment of Physics

Professor of Astrostatistics



+44 (0)20 7594 7793r.trotta Website CV




Mrs Sheila Ekudo +44 (0)20 7594 2086




1009Blackett LaboratorySouth Kensington Campus





Publication Type

107 results found

Ando S, Geringer-Sameth A, Hiroshima N, Hoof S, Trotta R, Walker MGet 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 $b\bar{b}$.

Journal article

Agostini F, Maouloud SEMA, Althueser L, Amaro F, Antunovic B, Aprile E, Baudis L, Baur D, Biondi Y, Bismark A, Breur PA, Brown A, Bruno G, Budnik R, Capelli C, Cardoso J, Cichon D, Clark M, Colijn AP, Cuenca-García JJ, Cussonneau JP, Decowski MP, Depoian A, Dierle J, Gangi PD, Giovanni AD, Diglio S, Santos JMFD, Drexlin G, Eitel K, Engel R, Ferella AD, Fischer H, Galloway M, Gao F, Girard F, Glück F, Grandi L, Größle R, Gumbsheimer R, Hansmann-Menzemer S, Jörg F, Khundzakishvili G, Kopec A, Kuger F, Krauss LM, Landsman H, Lang RF, Lindemann S, Lindner M, Lopes JAM, Villalpando AL, Macolino C, Manfredini A, Undagoitia TM, Masbou J, Masson E, Meinhardt P, Milutinovic S, Molinario A, Monteiro CMB, Murra M, Oberlack UG, Pandurovic M, Peres R, Pienaar J, Pierre M, Pizzella V, Qin J, García DR, Reichard S, Rupp N, Sanchez-Lucas P, Sartorelli G, Schulte D, Schumann M, Lavina LS, Selvi M, Silva M, Simgen H, Steidl M, Terliuk A, Therreau C, Thers D, Thieme K, Trotta R, Tunnell CD, Valerius K, Volta G, Weinheimer C, Wittweg C, Wolf J, Zopounidis JP, Zuber Ket 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.

Journal article

Trotta R, Hajas D, Camargo-Molina JE, Cobden R, Maggioni E, Obrist Met 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.

Journal article

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.

Journal article

Karukes EV, Benito M, Iocco F, Trotta R, Geringer-Sameth Aet 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.

Working paper

Karukes E, Benito M, Iocco F, Trotta R, Geringer-Sameth Aet 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.

Journal article

Hill R, Shariff H, Trotta R, Ali-Khan S, Jiao X, Liu Y, Moon SK, Parker W, Paulus M, Dyk DAV, Lucy LBet 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.

Journal article

Amendola L, Appleby S, Avgoustidis A, Bacon D, Baker T, Baldi M, Bartolo N, Blanchard A, Bonvin C, Borgani S, Branchini E, Burrage C, Camera S, Carbone C, Casarini L, Cropper M, de Rham C, Dietrich JP, Di Porto C, Durrer R, Ealet A, Ferreira PG, Finelli F, Garcia-Bellido J, Giannantonio T, Guzzo L, Heavens A, Heisenberg L, Heymans C, Hoekstra H, Hollenstein L, Holmes R, Hwang Z, Jahnke K, Kitching TD, Koivisto T, Kunz M, La Vacca G, Linder E, March M, Marra V, Martins C, Majerotto E, Markovic D, Marsh D, Marulli F, Massey R, Mellier Y, Montanari F, Mota DF, Nunes NJ, Percival W, Pettorino V, Porciani C, Quercellini C, Read J, Rinaldi M, Sapone D, Sawicki I, Scaramella R, Skordis C, Simpson F, Taylor A, Thomas S, Trotta R, Verde L, Vernizzi F, Vollmer A, Wang Y, Weller J, Zlosnik Tet 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.

Journal article

Clark HA, Scott P, Trotta R, Lewis GFet 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.

Journal article

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.

Journal article

Revsbech EA, Trotta R, van Dyk DA, 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.

Journal article

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, Tsai S-M, Malik M, Demory B-O, Mordasini C, Alibert Y, Benz W, Quanz SP, Trotta R, Heng Ket 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.

Journal article

Aalbers J, Agostini F, Alfonsi M, Amaro FD, Amsler C, Aprile E, Arazi L, Arneodo F, Barrow P, Baudis L, Benabderrahmane ML, Berger T, Beskers B, Breskin A, Breur PA, Brown A, Brown E, Bruenner S, Bruno G, Budnik R, Butikofer L, Calven J, Cardoso JMR, Cichon D, Coderre D, Colijn AP, Conrad J, Cussonneau JP, Decowski MP, Diglio S, Drexlin G, Duchovni E, Erdal E, Eurin G, Ferella A, Fieguth A, Fulgione W, Rosso AG, Di Gangi P, Di Giovanni A, Galloway M, Garbini M, Geis C, Glueck F, Grandi L, Greene Z, Grignon C, Hasterok C, Hannen V, Hogenbirk E, Howlett J, Hilk D, Hils C, James A, Kaminsky B, Kazama S, Kilminster B, Kish A, Krauss LM, Landsman H, Lang RF, Lin Q, Linde FL, Lindemann S, Lindner M, Lopes JAM, Undagoitia TM, Masbou J, Massoli FV, Mayani D, Messina M, Micheneau K, Molinario A, Mora KD, Morteau E, Murra M, Naganoma J, Newstead JL, Ni K, Oberlack U, Pakarha P, Pelssers B, de Perio P, Persiani R, Piastra F, Piro MC, Plante G, Rauch L, Reichard S, Rizzo A, Rupp N, Dos Santos JMF, Sartorelli G, Scheibelhut M, Schindler S, Schumann M, Schreiner J, Lavina LS, Selvi M, Shagin P, Silva MC, Simgen H, Sissol P, von Sivers M, Thers D, Thum J, Tiseni A, Trotta R, Tunnell CD, Valerius K, Vargas MA, Wang H, Wei Y, Weinheimer C, Wester T, Wulf J, Zhang Y, Zhu T, Zuber Ket 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.

Journal article

Aaboud M, Aad G, Abbott B, Abdallah J, Abdinov O, Abeloos B, Aben R, AbouZeid OS, Abraham NL, Abramowicz H, Abreu H, Abreu R, Abulaiti Y, Acharya BS, Adachi S, Adamczyk L, Adams DL, Adelman J, Adomeit S, Adye T, Affolder AA, Agatonovic-Jovin T, Aguilar-Saavedra JA, Ahlen SP, Ahmadov F, Aielli G, Akerstedt H, Akesson TPA, Akimov AV, Alberghi GL, Albert J, Albrand S, Alconada Verzini MJ, Aleksa M, Aleksandrov IN, Alexa C, Alexander G, Alexopoulos T, Alhroob M, Ali B, Aliev M, Alimonti G, Alison J, Alkire SP, Allbrooke BMM, Allen BW, Allport PP, Aloisio A, Alonso A, Alonso F, Alpigiani C, Alshehri AA, Alstaty M, Gonzalez BA, Alvarez Piqueras D, Alviggi MG, Amadio BT, Amako K, Amaral Coutinho Y, Amelung C, Amidei D, Dos Santos SPA, Amorim A, Amoroso S, Amundsen G, Anastopoulos C, Ancu LS, Andari N, Andeen T, Anders CF, Anders G, Anders JK, Anderson KJ, Andreazza A, Andrei V, Angelidakis S, Angelozzi I, Angerami A, Anghinolfi F, Anisenkov AV, Anjos N, Annovi A, Antel C, Antonelli M, Antonov A, Anulli F, Aoki M, Bella LA, Arabidze G, Arai Y, Araque JP, Arce ATH, Arduh FA, Arguin J-F, Argyropoulos S, Arik M, Armbruster AJ, Armitage LJ, Arnaez O, Arnold H, Arratia M, Arslan O, Artamonov A, Artoni G, Artz S, Asai S, Asbah N, Ashkenazi A, Asman B, Asquith L, Assamagan K, Astalos R, Atkinson M, Atlay NB, Augsten K, Avolio G, Axen B, Ayoub MK, Azuelos G, Baak MA, Baas AE, Baca MJ, Bachacou H, Bachas K, Backes M, Backhaus M, Bagiacchi P, Bagnaia P, Bai Y, Baines JT, Baker OK, Baldin EM, Balek P, Balestri T, Balli F, Balunas WK, Banas E, Banerjee S, Bannoura AAE, Barak L, Barberio EL, Barberis D, Barbero M, Barillari T, Barisits M-S, Barklow T, Barlow N, Barnes SL, Barnett BM, Barnett RM, Barnovska-Blenessy Z, Baroncelli A, Barone G, Barr AJ, Barranco Navarro L, Barreiro F, da Costa JBG, Bartoldus R, Barton AE, Bartos P, Basalaev A, Bassalat A, Bates RL, Batista SJ, Batley JR, Battaglia M, Bauce M, Bauer F, Bawa HS, Beacham JB, Beattie MD, Beau T, Beauchemin PH, Bechtle P, Beck Het 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.

Journal article

Liem S, Bertone G, Calore F, Ruiz de Austri R, Tait TMP, Trotta R, Weniger Cet 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.

Journal article

Shariff H, Dhawan S, Jiao X, Leibundgut B, Trotta R, Van Dyk DAet 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.

Journal article

Shariff H, Jiao X, Trotta R, van Dyk DAet 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.

Journal article

Johannesson G, de Austri RR, Vincent AC, Moskalenko IV, Orlando E, Porter TA, Strong AW, Trotta R, Feroz F, Graff P, Hobson MPet al., 2016, Bayesian analysis of cosmic ray propagation: evidence against homogeneous diffusion, Astrophysical Journal, Vol: 824, ISSN: 1538-4357

Journal article

Bertone G, Calore F, Caron S, Austri RRD, Kim JS, Trotta R, Weniger Cet al., 2016, Global analysis of the pMSSM in light of the Fermi GeV excess: prospects for the LHC Run-II and astroparticle experiments, Journal of Cosmology and Astroparticle Physics, Vol: 2016, ISSN: 1475-7516

Journal article

Jóhannesson G, Ruiz De Austri R, Vincent AC, Moskalenko IV, Orlando E, Porter TA, Strong AW, Trotta Ret al., 2015, Bayesian approach to galactic cosmic ray propagation

The fully Bayesian approach to the problem of deriving constraints for cosmic ray (CR) model parameters has several advantages. These are: (i) an efficient global scan of the whole parameter space allowing us to explore and take into account parameter correlations and degeneracies, (ii) a best-fit point and statistically well-defined errors on the parameters, (iii) the ability to include and marginalize over 'nuisance' parameters (such as modulation potential and error rescaling parameters) making the analysis more robust. For this study, we use the latest version of the CR propagation code GALPROP together with the BAMBI code, the most efficient Bayesian analysis code available to date that combines MultiNest with Neural networks. The results of the analysis will be reported during the conference.

Conference paper

Strege C, Bertone G, Besjes GJ, Caron S, Ruiz de Austri R, Strubig A, Trotta Ret al., 2014, Profile likelihood maps of a 15-dimensional MSSM, Journal of High Energy Physics, Vol: 2014, ISSN: 1126-6708

We present statistically convergent profile likelihood maps obtained via globalfits of a phenomenological Minimal Supersymmetric Standard Model with 15 free parameters(the MSSM-15), based on over 250M points. We derive constraints on the modelparameters from direct detection limits on dark matter, the Planck relic density measurementand data from accelerator searches. We provide a detailed analysis of the richphenomenology of this model, and determine the SUSY mass spectrum and dark matterproperties that are preferred by current experimental constraints. We evaluate the impactof the measurement of the anomalous magnetic moment of the muon (g −2) on our results,and provide an analysis of scenarios in which the lightest neutralino is a subdominant componentof the dark matter. The MSSM-15 parameters are relatively weakly constrained bycurrent data sets, with the exception of the parameters related to dark matter phenomenology(M1, M2, µ), which are restricted to the sub-TeV regime, mainly due to the relic densityconstraint. The mass of the lightest neutralino is found to be < 1.5 TeV at 99% C.L., butcan extend up to 3 TeV when excluding the g − 2 constraint from the analysis. Low-massbino-like neutralinos are strongly favoured, with spin-independent scattering cross-sectionsextending to very small values, ∼ 10−20 pb. ATLAS SUSY null searches strongly impacton this mass range, and thus rule out a region of parameter space that is outside the reachof any current or future direct detection experiment. The best-fit point obtained after inclusionof all data corresponds to a squark mass of 2.3 TeV, a gluino mass of 2.1 TeV and a130 GeV neutralino with a spin-independent cross-section of 2.4×10−10 pb, which is withinthe reach of future multi-ton scale direct detection experiments and of the upcoming LHCrun at increased centre-of-mass energy.

Journal article

Martin J, Ringeval C, Trotta R, Vennin Vet al., 2014, Compatibility of Planck and BICEP2 results in light of inflation, PHYSICAL REVIEW D, Vol: 90, ISSN: 1550-7998

Journal article

Martin J, Ringeval C, Trotta R, Vennin Vet al., 2014, The best inflationary models after Planck, Journal of Cosmology and Astroparticle Physics, Vol: 2014, ISSN: 1475-7516

We compute the Bayesian evidence and complexity of 193 slow-roll single-field models of inflation using the Planck 2013 Cosmic Microwave Background data, with the aim of establishing which models are favoured from a Bayesian perspective. Our calculations employ a new numerical pipeline interfacing an inflationary effective likelihood with the slow-roll library ASPIC and the nested sampling algorithm MultiNest. The models considered represent a complete and systematic scan of the entire landscape of inflationary scenarios proposed so far. Our analysis singles out the most probable models (from an Occam's razor point of view) that are compatible with Planck data, while ruling out with very strong evidence 34% of the models considered. We identify 26% of the models that are favoured by the Bayesian evidence, corresponding to 15 different potential shapes. If the Bayesian complexity is included in the analysis, only 9% of the models are preferred, corresponding to only 9 different potential shapes. These shapes are all of the plateau type.

Journal article

Hilbe JM, Riggs J, Wandelt BD, de Souza RS, Ishida EEO, Cisewski J, Surdin V, Killedar M, Trotta R, Bassett B, Fantaye Y, Impey Cet al., 2014, Life, the universe, and everything, Significance, Vol: 11, Pages: 48-75, ISSN: 1740-9705

Journal article

Trotta R, 2013, Cosmological bayesian model selection: Recent advances and open challenges, Pages: 127-140

The cosmology community has been increasingly focusing on Bayesian model selection as a tool to discriminate between competing theories to explain a large amount of data about our Universe. In this paper, I summarize the conceptual underpinnings and the algorithmic implementations of Bayesian model comparison. I then discuss two representative applications of Bayesian model comparison to cosmological problems: determining whether the Universe is infinite and selecting the "best" model of inflation. I conclude by offering some reflections about open challenges and interpretational issues. Help and suggestions from the statistics community would be appreciated in further developing the field. © Springer Science+Business Media New York 2013.

Conference paper

Amendola L, Appleby S, Bacon D, Baker T, Baldi M, Bartolo N, Blanchard A, Bonvin C, Borgani S, Branchini E, Burrage C, Camera S, Carbone C, Casarini L, Cropper M, de Rham C, Di Porto C, Ealet A, Ferreira PG, Finelli F, Garcia-Bellido J, Giannantonio T, Guzzo L, Heavens A, Heisenberg L, Heymans C, Hoekstra H, Hollenstein L, Holmes R, Horst O, Jahnke K, Kitching TD, Koivisto T, Kunz M, La Vacca G, March M, Majerotto E, Markovic K, Marsh D, Marulli F, Massey R, Mellier Y, Mota DF, Nunes NJ, Percival W, Pettorino V, Porciani C, Quercellini C, Read J, Rinaldi M, Sapone D, Scaramella R, Skordis C, Simpson F, Taylor A, Thomas S, Trotta R, Verde L, Vernizzi F, Vollmer A, Wang Y, Weller J, Zlosnik Tet al., 2013, Cosmology and Fundamental Physics with the Euclid Satellite, Living Reviews in Relativity, Vol: 16, ISSN: 1433-8351

Euclid is a European Space Agency medium-class mission selected for launch in 2019 withinthe Cosmic Vision 2015 – 2025 program. The main goal of Euclid is to understand the originof the accelerated expansion of the universe. Euclid will explore the expansion history of theuniverse and the evolution of cosmic structures by measuring shapes and red-shifts of galaxiesas 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 avast range of topics, from cosmology to galaxy evolution to planetary research. In this reviewwe focus on cosmology and fundamental physics, with a strong emphasis on science beyondthe 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 dataanalysis.This review has been planned and carried out within Euclid’s Theory Working Group andis meant to provide a guide to the scientific themes that will underlie the activity of the groupduring the preparation of the Euclid mission.

Journal article

Strege C, Bertone G, Feroz F, Fornasa M, Ruiz de Austri R, Trotta Ret al., 2013, Global fits of the cMSSM and NUHM including the LHC Higgs discovery and new XENON100 constraints, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, Vol: 2013, ISSN: 1475-7516

We present global fits of the constrained Minimal Supersymmetric Standard Model (cMSSM) and the Non-Universal Higgs Model (NUHM), including the most recent CMS constraint on the Higgs boson mass, 5.8 fb−1 integrated luminosity null Supersymmetry searches by ATLAS, the new LHCb measurement of BR(bar Bs → μ+μ−) and the 7-year WMAP dark matter relic abundance determination. We include the latest dark matter constraints from the XENON100 experiment, marginalising over astrophysical and particle physics uncertainties. We present Bayesian posterior and profile likelihood maps of the highest resolution available today, obtained from up to 350M points. We find that the new constraint on the Higgs boson mass has a dramatic impact, ruling out large regions of previously favoured cMSSM and NUHM parameter space. In the cMSSM, light sparticles and predominantly gaugino-like dark matter with a mass of a few hundred GeV are favoured. The NUHM exhibits a strong preference for heavier sparticle masses and a Higgsino-like neutralino with a mass of 1 TeV. The future ton-scale XENON1T direct detection experiment will probe large portions of the currently favoured cMSSM and NUHM parameter space. The LHC operating at 14 TeV collision energy will explore the favoured regions in the cMSSM, while most of the regions favoured in the NUHM will remain inaccessible. Our best-fit points achieve a satisfactory quality-of-fit, with p-values ranging from 0.21 to 0.35, so that none of the two models studied can be presently excluded at any meaningful significance level.

Journal article

Pato M, Strigari LE, Trotta R, Bertone Get al., 2013, Taming astrophysical bias in direct dark matter searches, Journal of Cosmology and Astroparticle Physics, Vol: 2013, ISSN: 1475-7516

We explore systematic biases in the identification of dark matter in future direct detection experiments and compare the reconstructed dark matter properties when assuming a self-consistent dark matter distribution function and the standard Maxwellian velocity distribution. We find that the systematic bias on the dark matter mass and cross-section determination arising from wrong assumptions for its distribution function is of order ~ 1σ. A much larger systematic bias can arise if wrong assumptions are made on the underlying Milky Way mass model. However, in both cases the bias is substantially mitigated by marginalizing over galactic model parameters. We additionally show that the velocity distribution can be reconstructed in an unbiased manner for typical dark matter parameters. Our results highlight both the robustness of the dark matter mass and cross-section determination using the standard Maxwellian velocity distribution and the importance of accounting for astrophysical uncertainties in a statistically consistent fashion.

Journal article

Trotta R, Feroz F, Hobson M, de Austri RRet al., 2013, Recent advances in Bayesian inference in cosmology and astroparticle physics thanks to the multinest algorithm, Astrostatistical Challenges for the New Astronomy, Pages: 107-119, ISBN: 9781461435075

© Springer Science+Business Media New York 2013. All rights reserved. We present a new algorithm, called MultiNest, which is a highly efficient alternative to traditional Markov Chain Monte Carlo (MCMC) sampling of posterior distributions. MultiNest is more efficient than MCMC, can deal with highly multi-modal likelihoods and returns the Bayesian evidence (or model likelihood, the prime quantity for Bayesian model comparison) together with posterior samples. It can thus be used as an all-around Bayesian inference engine. When appropriately tuned, it also provides an exploration of the profile likelihood that is competitive with what can be obtained with dedicated algorithms. We demonstrate the power and flexibility of MultiNest for Bayesian inference for Bayesian model selection and l, multi-scale likelihoods. Applicapresented, including gravitational comparison and supersymmetric Abstract for profile likelihood evaluation for multi-moda for multi-dimensional, multimodal-likelihoods, tions in cosmology and astroparticle physics are waves astronomy, inflationary Bayesian model parameter spaces exploration.

Book chapter

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