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  • 1. Barack, Leor
    et al.
    Cardoso, Vitor
    Nissanke, Samaya
    Sotiriou, Thomas P.
    Askar, Abbas
    Belczynski, Chris
    Bertone, Gianfranco
    Bon, Edi
    Blas, Diego
    Brito, Richard
    Bulik, Tomasz
    Burrage, Clare
    Byrnes, Christian T.
    Caprini, Chiara
    Chernyakova, Masha
    Chruściel, Piotr
    Colpi, Monica
    Ferrari, Valeria
    Gaggero, Daniele
    Gair, Jonathan
    García-Bellido, Juan
    Hassan, Sayed Fawad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Heisenberg, Lavinia
    Hendry, Martin
    Heng, Ik Siong
    Herdeiro, Carlos
    Hinderer, Tanja
    Horesh, Assaf
    Kavanagh, Bradley J.
    Kocsis, Bence
    Kramer, Michael
    Le Tiec, Alexandre
    Mingarelli, Chiara
    Nardini, Germano
    Nelemans, Gijs
    Palenzuela, Carlos
    Pani, Paolo
    Perego, Albino
    Porter, Edward K.
    Rossi, Elena M.
    Schmidt, Patricia
    Sesana, Alberto
    Sperhake, Ulrich
    Stamerra, Antonio
    Stein, Leo C.
    Tamanini, Nicola
    Tauris, Thomas M.
    Arturo Urena-López, L.
    Vincent, Frederic
    Volonteri, Marta
    Wardell, Barry
    Wex, Norbert
    Yagi, Kent
    Abdelsalhin, Tiziano
    Ángel Aloy, Miguel
    Amaro-Seoane, Pau
    Annulli, Lorenzo
    Arca-Sedda, Manuel
    Bah, Ibrahima
    Barausse, Enrico
    Barakovic, Elvis
    Benkel, Robert
    Bennett, Charles L.
    Bernard, Laura
    Bernuzzi, Sebastiano
    Berry, Christopher P. L.
    Berti, Emanuele
    Bezares, Miguel
    Juan Blanco-Pillado, Jose
    Blázquez-Salcedo, Jose Luis
    Bonetti, Matteo
    Bošković, Mateja
    Bosnjak, Zeljka
    Bricman, Katja
    Brügmann, Bernd
    Capelo, Pedro R.
    Carloni, Sante
    Cerdá-Durán, Pablo
    Charmousis, Christos
    Chaty, Sylvain
    Clerici, Aurora
    Coates, Andrew
    Colleoni, Marta
    Collodel, Lucas G.
    Compère, Geoffrey
    Cook, William
    Cordero-Carríon, Isabel
    Correia, Miguel
    de la Cruz-Dombriz, Álvaro
    Czinner, Viktor G.
    Destounis, Kyriakos
    Dialektopoulos, Kostas
    Doneva, Daniela
    Dotti, Massimo
    Drew, Amelia
    Eckner, Christopher
    Edholm, James
    Emparan, Roberto
    Erdem, Recai
    Ferreira, Miguel
    Ferreira, Pedro G.
    Finch, Andrew
    Font, Jose A.
    Franchini, Nicola
    Fransen, Kwinten
    Gal'tsov, Dmitry
    Ganguly, Apratim
    Gerosa, Davide
    Glampedakis, Kostas
    Gomboc, Andreja
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gualtieri, Leonardo
    Guendelman, Eduardo
    Haardt, Francesco
    Harmark, Troels
    Hejda, Filip
    Hertog, Thomas
    Hopper, Seth
    Husa, Sascha
    Ihanec, Nada
    Ikeda, Taishi
    Jaodand, Amruta
    Jetzer, Philippe
    Jimenez-Forteza, Xisco
    Kamionkowski, Marc
    Kaplan, David E.
    Kazantzidis, Stelios
    Kimura, Masashi
    Kobayashi, Shiho
    Kokkotas, Kostas
    Krolik, Julian
    Kunz, Jutta
    Lämmerzahl, Claus
    Lasky, Paul
    Lemos, José P. S.
    Said, Jackson Levi
    Liberati, Stefano
    Lopes, Jorge
    Luna, Raimon
    Ma, Yin-Zhe
    Maggio, Elisa
    Mangiagli, Alberto
    Montero, Marina Martinez
    Maselli, Andrea
    Mayer, Lucio
    Mazumdar, Anupam
    Messenger, Christopher
    Ménard, Brice
    Minamitsuji, Masato
    Moore, Christopher J.
    Mota, David
    Nampalliwar, Sourabh
    Nerozzi, Andrea
    Nichols, David
    Nissimov, Emil
    Obergaulinger, Martin
    Obers, Niels A.
    Oliveri, Roberto
    Pappas, George
    Pasic, Vedad
    Peiris, Hiranya
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Petrushevska, Tanja
    Pollney, Denis
    Pratten, Geraint
    Rakic, Nemanja
    Racz, Istvan
    Radia, Miren
    Ramazanoglu, Fethi M.
    Ramos-Buades, Antoni
    Raposo, Guilherme
    Rogatko, Marek
    Rosca-Mead, Roxana
    Rosinska, Dorota
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ruiz-Morales, Ester
    Sakellariadou, Mairi
    Sanchis-Gual, Nicolás
    Salafia, Om Sharan
    Samajdar, Anuradha
    Sintes, Alicia
    Smole, Majda
    Sopuerta, Carlos
    Souza-Lima, Rafael
    Stalevski, Marko
    Stergioulas, Nikolaos
    Stevens, Chris
    Tamfal, Tomas
    Torres-Forne, Alejandro
    Tsygankov, Sergey
    Ünlütürk, Kivanç I.
    Valiante, Rosa
    van de Meent, Maarten
    Velhinho, José
    Verbin, Yosef
    Vercnocke, Bert
    Vernieri, Daniele
    Vicente, Rodrigo
    Vitagliano, Vincenzo
    Weltman, Amanda
    Whiting, Bernard
    Williamson, Andrew
    Witek, Helvi
    Wojnar, Aneta
    Yakut, Kadri
    Yan, Haopeng
    Yazadjiev, Stoycho
    Zaharijas, Gabrijela
    Zilhão, Miguel
    Black holes, gravitational waves and fundamental physics: a roadmap2019In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 36, no 14, article id 143001Article, review/survey (Refereed)
    Abstract [en]

    The grand challenges of contemporary fundamental physics dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'.

  • 2. Bird, Simeon
    et al.
    Rogers, Keir K.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Verde, Licia
    Font-Ribera, Andreu
    Pontzen, Andrew
    An emulator for the Lyman-alpha forest2019In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 2, article id 050Article in journal (Refereed)
    Abstract [en]

    We present methods for interpolating between the 1-D flux power spectrum of the Lyman-alpha forest, as output by cosmological hydrodynamic simulations. Interpolation is necessary for cosmological parameter estimation due to the limited number of simulations possible. We construct an emulator for the Lyman-alpha forest flux power spectrum from 21 small simulations using Latin hypercube sampling and Gaussian process interpolation. We show that this emulator has a typical accuracy of 1 : 5% and a worst-case accuracy of 4%, which compares well to the current statistical error of 3-5% at z < 3 from BOSS DR9. We compare to the previous state of the art, quadratic polynomial interpolation. The Latin hypercube samples the entire volume of parameter space, while quadratic polynomial emulation samples only lower-dimensional subspaces. The Gaussian process provides an estimate of the emulation error and we show using test simulations that this estimate is reasonable. We construct a likelihood function and use it to show that the posterior constraints generated using the emulator are unbiased. We show that our Gaussian process emulator has lower emulation error than quadratic polynomial interpolation and thus produces tighter posterior confidence intervals, which will be essential for future Lyman-alpha surveys such as DESI.

  • 3. Braden, Jonathan
    et al.
    Johnson, Matthew C.
    Peiris, Hiranya
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, United Kingdom.
    Pontzen, Andrew
    Weinfurtner, Silke
    New Semiclassical Picture of Vacuum Decay2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 123, no 3, article id 031601Article in journal (Refereed)
    Abstract [en]

    We introduce a new picture of vacuum decay which, in contrast to existing semiclassical techniques, provides a real-time description and does not rely on classically forbidden tunneling paths. Using lattice simulations, we observe vacuum decay via bubble formation by generating realizations of vacuum fluctuations and evolving with the classical equations of motion. The decay rate obtained from an ensemble of simulations is in excellent agreement with existing techniques. Future applications include bubble correlation functions, fast decay rates, and decay of nonvacuum states.

  • 4. Braden, Jonathan
    et al.
    Johnson, Matthew C.
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, United Kingdom.
    Aguirre, Anthony
    Constraining cosmological ultralarge scale structure using numerical relativity2017In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 96, no 2, article id 023541Article in journal (Refereed)
    Abstract [en]

    Cosmic inflation, a period of accelerated expansion in the early universe, can give rise to large amplitude ultralarge scale inhomogeneities on distance scales comparable to or larger than the observable universe. The cosmic microwave background (CMB) anisotropy on the largest angular scales is sensitive to such inhomogeneities and can be used to constrain the presence of ultralarge scale structure (ULSS). We numerically evolve nonlinear inhomogeneities present at the beginning of inflation in full general relativity to assess the CMB quadrupole constraint on the amplitude of the initial fluctuations and the size of the observable universe relative to a length scale characterizing the ULSS. To obtain a statistically meaningful ensemble of simulations, we adopt a toy model in which inhomogeneities are injected along a preferred direction. We compute the likelihood function for the CMB quadrupole including both ULSS and the standard quantum fluctuations produced during inflation. We compute the posterior given the observed CMB quadrupole, finding that when including gravitational nonlinearities, ULSS curvature perturbations of order unity are allowed by the data, even on length scales not too much larger than the size of the observable universe. To demonstrate the robustness of our conclusions, we also explore a semianalytic model for the ULSS which reproduces our numerical results for the case of planar symmetry, and which can be extended to ULSS with a three-dimensional inhomogeneity structure. Our results illustrate the utility and importance of numerical relativity for constraining early universe cosmology.

  • 5. Braden, Jonathan
    et al.
    Johnson, Matthew C.
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, U.K..
    Weinfurtner, Silke
    Towards the cold atom analog false vacuum2018In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, article id 014Article in journal (Refereed)
    Abstract [en]

    Analog condensed matter systems present an exciting opportunity to simulate early Universe models in table-top experiments. We consider a recent proposal for an analog condensed matter experiment to simulate the relativistic quantum decay of the false vacuum. In the proposed experiment, two ultra-cold condensates are coupled via a time-varying radio-frequency field. The relative phase of the two condensates in this system is approximately described by a relativistic scalar field with a potential possessing a series of false and true vacuum local minima. If the system is set up in a false vacuum, it would then decay to a true vacuum via quantum mechanical tunnelling. Should such an experiment be realized, it would be possible to answer a number of open questions regarding non-perturbative phenomena in quantum field theory and early Universe cosmology. In this paper, we illustrate a possible obstruction: the time-varying coupling that is invoked to create a false vacuum for the long-wavelength modes of the condensate leads to a destabilization of shorter wavelength modes within the system via parametric resonance. We focus on an idealized setup in which the two condensates have identical properties and identical background densities. Describing the system by the coupled Gross-Pitaevskii equations (GPE), we use the machinery of Floquet theory to perform a linear stability analysis, calculating the wavenumber associated with the first instability band for a variety of experimental parameters. However, we demonstrate that, by tuning the frequency of the time-varying coupling, it may be possible to push the first instability band outside the validity of the GPE, where dissipative effects are expected to damp any instabilities. This provides a viable range of experimental parameters to perform analog experiments of false vacuum decay.

  • 6. Elsner, Franz
    et al.
    Leistedt, Boris
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Univesity College London, UK.
    Unbiased pseudo-C-l power spectrum estimation with mode projection2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 465, no 2, p. 1847-1855Article in journal (Refereed)
    Abstract [en]

    With the steadily improving sensitivity afforded by current and future galaxy surveys, a robust extraction of two-point correlation function measurements may become increasingly hampered by the presence of astrophysical foregrounds or observational systematics. The concept of mode projection has been introduced as a means to remove contaminants for which it is possible to construct a spatialmap, reflecting the expected signal contribution. Owing to its computational efficiency compared to minimum-variance methods, the sub-optimal pseudo-C-l (PCL) power spectrum estimator is a popular tool for the analysis of high-resolution data sets. Here, we integrate mode projection into the framework of PCL power spectrum estimation. In contrast to results obtained with optimal estimators, we show that the uncorrected projection of template maps leads to biased power spectra. Based on analytical calculations, we find exact closed-form expressions for the expectation value of the bias and demonstrate that they can be recast in a form which allows a numerically efficient evaluation, preserving the favourable O(l(max)(3)) time complexity of PCL estimator algorithms. Using simulated data sets, we assess the scaling of the bias with various analysis parameters and demonstrate that it can be reliably removed. We conclude that in combination with mode projection, PCL estimators allow for a fast and robust computation of power spectra in the presence of systematic effects - properties in high demand for the analysis of ongoing and future large-scale structure surveys.

  • 7. Feeney, Stephen M.
    et al.
    Gudmundsson, Jón E.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Verde, Licia
    Errard, Josquin
    Cosmic microwave background science at commercial airline altitudes2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, no 1, p. l6-L10Article in journal (Refereed)
    Abstract [en]

    Obtaining high-sensitivity measurements of degree-scale cosmic microwave background (CMB) polarization is the most direct path to detecting primordial gravitational waves. Robustly recovering any primordial signal from the dominant foreground emission will require high-fidelity observations at multiple frequencies, with excellent control of systematics. We explore the potential for a new platform for CMB observations, the Airlander 10 hybrid air vehicle, to perform this task. We show that the Airlander 10 platform, operating at commercial airline altitudes, is well suited to mapping frequencies above 220 GHz, which are critical for cleaning CMB maps of dust emission. Optimizing the distribution of detectors across frequencies, we forecast the ability of Airlander 10 to clean foregrounds of varying complexity as a function of altitude, demonstrating its complementarity with both existing (Planck) and ongoing (C-BASS) foreground observations. This novel platform could play a key role in defining our ultimate view of the polarized microwave sky.

  • 8. Feeney, Stephen M.
    et al.
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, United Kingdom.
    Williamson, Andrew R.
    Nissanke, Samaya M.
    Mortlock, Daniel J.
    Stockholm University, Faculty of Science, Department of Astronomy. Imperial College London, United Kingdom.
    Alsing, Justin
    Scolnic, Dan
    Prospects for Resolving the Hubble Constant Tension with Standard Sirens2019In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 122, no 6, article id 061105Article in journal (Refereed)
    Abstract [en]

    The Hubble constant (H-0) estimated from the local Cepheid-supernova distance ladder is in 3-sigma tension with the value extrapolated from cosmic microwave background (CMB) data assuming the standard cosmological model. Whether this tension represents newphysics or systematic effects is the subject of intense debate. Here, we investigate how new, independent H-0 estimates can arbitrate this tension, assessing whether the measurements are consistent with being derived from the same model using the posterior predictive distribution (PPD). We show that, with existing data, the inverse distance ladder formed from BOSS baryon acoustic oscillation measurements and the Pantheon supernova sample yields an H-0 posterior near identical to the Planck CMB measurement. The observed local distance ladder value is a very unlikely draw from the resulting PPD. Turning to the future, we find that a sample of similar to 50 binary neutron star standard sirens (detectable within the next decade) will be able to adjudicate between the local and CMB estimates.

  • 9. Lockhart, K. E.
    et al.
    Lu, J. R.
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Rich, R. M.
    Bouchez, A.
    Ghez, A. M.
    A Slowly Precessing Disk in the Nucleus of M31 as the Feeding Mechanism for a Central Starburst2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 854, no 2, article id 121Article in journal (Refereed)
    Abstract [en]

    We present a kinematic study of the nuclear stellar disk in M31 at infrared wavelengths using high spatial resolution integral field spectroscopy. The spatial resolution achieved, FWHM = 0.'' 12 (0.45 pc at the distance of M31), has only previously been equaled in spectroscopic studies by space-based long-slit observations. Using adaptive optics-corrected integral field spectroscopy from the OSIRIS instrument at the W. M. Keck Observatory, we map the line-of-sight kinematics over the entire old stellar eccentric disk orbiting the supermassive black hole (SMBH) at a distance of r<4 pc. The peak velocity dispersion is 381 +/- 55 km/s(-1), offset by 0.'' 13 +/- 0.'' 03 from the SMBH, consistent with previous high-resolution long-slit observations. There is a lack of near-infrared (NIR) emission at the position of the SMBH and young nuclear cluster, suggesting a spatial separation between the young and old stellar populations within the nucleus. We compare the observed kinematics with dynamical models from Peiris & Tremaine (2003). The best-fit disk orientation to the NIR flux is [theta(l), theta(i), theta(a)] = [-33 +/- 4 degrees, 44 +/- 2 degrees, -15 +/- 15 degrees}], which is tilted with respect to both the larger-scale galactic disk and the best-fit orientation derived from optical observations. The precession rate of the old disk is Omega(P) = 0.0 +/- 3.9 km/s(-1)pc(-1), lower than the majority of previous observations. This slow precession rate suggests that stellar winds from the disk will collide and shock, driving rapid gas inflows and fueling an episodic central starburst as suggested in Chang et al.

  • 10. Lucie-Smith, Luisa
    et al.
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Pontzen, Andrew
    Lochner, Michelle
    Machine learning cosmological structure formation2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 479, no 3, p. 3405-3414Article in journal (Refereed)
    Abstract [en]

    We train a machine learning algorithm to learn cosmological structure formation from N-body simulations. The algorithm infers the relationship between the initial conditions and the final dark matter haloes, without the need to introduce approximate halo collapse models. We gain insights into the physics driving halo formation by evaluating the predictive performance of the algorithm when provided with different types of information about the local environment around dark matter particles. The algorithm learns to predict whether or not dark matter particles will end up in haloes of a given mass range, based on spherical overdensities. We show that the resulting predictions match those of spherical collapse approximations such as extended Press-Schechter theory. Additional information on the shape of the local gravitational potential is not able to improve halo collapse predictions; the linear density field contains sufficient information for the algorithm to also reproduce ellipsoidal collapse predictions based on the Sheth-Tormen model. We investigate the algorithm's performance in terms of halo mass and radial position and perform blind analyses on independent initial conditions realizations to demonstrate the generality of our results.

  • 11. McEwen, J. D.
    et al.
    Feeney, S. M.
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Wiaux, Y.
    Ringeval, C.
    Bouchet, F. R.
    Wavelet-Bayesian inference of cosmic strings embedded in the cosmic microwave background2017In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 472, no 4, p. 4081-4098Article in journal (Refereed)
    Abstract [en]

    Cosmic strings are a well-motivated extension to the standard cosmological model and could induce a subdominant component in the anisotropies of the cosmic microwave background (CMB), in addition to the standard inflationary component. The detection of strings, while observationally challenging, would provide a direct probe of physics at very high-energy scales. We develop a framework for cosmic string inference from observations of the CMB made over the celestial sphere, performing a Bayesian analysis in wavelet space where the string-induced CMB component has distinct statistical properties to the standard inflationary component. Our wavelet-Bayesian framework provides a principled approach to compute the posterior distribution of the string tension G mu and the Bayesian evidence ratio comparing the string model to the standard inflationary model. Furthermore, we present a technique to recover an estimate of any string-induced CMB map embedded in observational data. Using Planck-like simulations, we demonstrate the application of our framework and evaluate its performance. The method is sensitive to G mu similar to 5 x 10(-7) for Nambu-Goto string simulations that include an integrated Sachs-Wolfe contribution only and do not include any recombination effects, before any parameters of the analysis are optimized. The sensitivity of the method compares favourably with other techniques applied to the same simulations.

  • 12. Pyne, Susan
    et al.
    Joachimi, Benjamin
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, U.K..
    Weak lensing deflection of three-point correlation functions2017In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 12, article id 043Article in journal (Refereed)
    Abstract [en]

    Weak gravitational lensing alters the apparent separations between observed sources, potentially affecting clustering statistics. We derive a general expression for the lensing deflection which is valid for any three-point statistic, and investigate its effect on the three-point clustering correlation function. We find that deflection of the clustering correlation function is greatest at around z = 2. It is most prominent in regions where the correlation function varies rapidly, in particular at the baryon acoustic oscillation scale where it smooths out the peaks and troughs, reducing the peak-to-trough difference by about 0.1 percent at z = 1 and around 2.3 percent at z = 10. The modification due to lensing deflection is typically at the per cent level of the expected errors in a Euclid-like survey and therefore undetectable.

  • 13.
    Rogers, Keir K.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Bird, Simeon
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Pontzen, Andrew
    Font-Ribera, Andreu
    Leistedt, Boris
    Correlations in the three-dimensional Lyman-alpha forest contaminated by high column density absorbers2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 476, no 3, p. 3716-3728Article in journal (Refereed)
    Abstract [en]

    Correlations measured in three dimensions in the Lyman-alpha forest are contaminated by the presence of the damping wings of high column density (HCD) absorbing systems of neutral hydrogen (H I; having column densities N(H I) > 1.6 x 10(17) atoms cm(-2)), which extend significantly beyond the redshift-space location of the absorber. We measure this effect as a function of the column density of the HCD absorbers and redshift by measuring threedimensional (3D) flux power spectra in cosmological hydrodynamical simulations from the Illustris project. Survey pipelines exclude regions containing the largest damping wings. We find that, even after this procedure, there is a scale-dependent correction to the 3D Lyman alpha forest flux power spectrum from residual contamination. We model this residual using a simple physical model of the HCD absorbers as linearly biased tracers of the matter density distribution, convolved with their Voigt profiles and integrated over the column density distribution function. We recommend the use of this model over existing models used in data analysis, which approximate the damping wings as top-hats and so miss shape information in the extended wings. The simple 'linear Voigt model' is statistically consistent with our simulation results for a mock residual contamination up to small scales (vertical bar k vertical bar < 1 h Mpc(-1)). It does not account for the effect of the highest column density absorbers on the smallest scales (e.g. vertical bar k vertical bar > 0.4 h Mpc(-1) for small damped Lyman-alpha absorbers; HCD absorbers with N(H-I) similar to 10(21) atoms cm(-2)). However, these systems are in any case preferentially removed from survey data. Our model is appropriate for an accurate analysis of the baryon acoustic oscillations feature. It is additionally essential for reconstructing the full shape of the 3D flux power spectrum.

  • 14. Rogers, Keir K.
    et al.
    Bird, Simeon
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Pontzen, Andrew
    Font-Ribera, Andreu
    Leistedt, Boris
    Simulating the effect of high column density absorbers on the one-dimensional Lyman alpha forest flux power spectrum2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 474, no 3, p. 3032-3042Article in journal (Refereed)
    Abstract [en]

    We measure the effect of high column density absorbing systems of neutral hydrogen (H I) on the one-dimensional (1D) Lyman alpha forest flux power spectrum using cosmological hydrodynamical simulations from the Illustris project. High column density absorbers (which we define to be those with HI column densities N(H I) > 1.6 x 10(17) atoms cm(-2)) cause broadened absorption lines with characteristic damping wings. These damping wings bias the 1D Lyman alpha forest flux power spectrum by causing absorption in quasar spectra away from the location of the absorber itself. We investigate the effect of high column density absorbers on the Lyman alpha forest using hydrodynamical simulations for the first time. We provide templates as a function of column density and redshift, allowing the flexibility to accurately model residual contamination, i.e. if an analysis selectively clips out the largest damping wings. This flexibility will improve cosmological parameter estimation, for example, allowing more accurate measurement of the shape of the power spectrum, with implications for cosmological models containing massive neutrinos or a running of the spectral index. We provide fitting functions to reproduce these results so that they can be incorporated straightforwardly into a data analysis pipeline.

  • 15.
    Rogers, Keir K.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, U.K.
    Pontzen, Andrew
    Bird, Simeon
    Verde, Licia
    Font-Ribera, Andreu
    Bayesian emulator optimisation for cosmology: application to the Lyman-alpha forest2019In: Journal of Cosmology and Astroparticle Physics, ISSN 1475-7516, E-ISSN 1475-7516, no 2, article id 031Article in journal (Refereed)
    Abstract [en]

    The Lyman-alpha forest provides strong constraints on both cosmological parameters and intergalactic medium astrophysics, which are forecast to improve further with the next generation of surveys including eBOSS and DESI. As is generic in cosmological inference, extracting this information requires a likelihood to be computed throughout a high-dimensional parameter space. Evaluating the likelihood requires a robust and accurate mapping between the parameters and observables, in this case the 1D flux power spectrum. Cosmological simulations enable such a mapping, but due to computational time constraints can only be evaluated at a handful of sample points; emulators are designed to interpolate between these. The problem then reduces to placing the sample points such that an accurate mapping is obtained while minimising the number of expensive simulations required. To address this, we introduce an emulation procedure that employs Bayesian optimisation of the training set for a Gaussian process interpolation scheme. Starting with a Latin hypercube sampling (other schemes with good space-filling properties can be used), we iteratively augment the training set with extra simulations at new parameter positions which balance the need to reduce interpolation error while focussing on regions of high likelihood. We show that smaller emulator error from the Bayesian optimisation propagates to smaller widths on the posterior distribution. Even with fewer simulations than a Latin hypercube, Bayesian optimisation shrinks the 95% credible volume by 90% and, e.g., the 1 sigma error on the amplitude of small-scale primordial fluctuations by 38%. This is the first demonstration of Bayesian optimisation applied to large-scale structure emulation, and we anticipate the technique will generalise to many other probes such as galaxy clustering, weak lensing and 21cm.

  • 16.
    Setzer, Christian N.
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Biswas, Rahul
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Korobkin, Oleg
    Wollaeger, Ryan T.
    Serendipitous discoveries of kilonovae in the LSST main survey: maximizing detections of sub-threshold gravitational wave events2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, no 3, p. 4260-4273Article in journal (Refereed)
    Abstract [en]

    We investigate the ability of the Large Synoptic Survey Telescope (LSST) to discover kilonovae (kNe) from binary neutron star (BNS) and neutron star-black hole (NSBH) mergers, focusing on serendipitous detections in the Wide-Fast-Deep (WFD) survey. We simulate observations of kNe with proposed LSST survey strategies, focusing on cadence choices that are compatible with the broader LSST cosmology programme. If all kNe are identical to GW170817, we find the baseline survey strategy will yield 58 kNe over the survey lifetime. If we instead assume a representative population model of BNS kNe, we expect to detect only 27 kNe. However, we find the choice of survey strategy significantly impacts these numbers and can increase them to 254 and 82 kNe over the survey lifetime, respectively. This improvement arises from an increased cadence of observations between different filters with respect to the baseline. We then consider the detectability of these BNS mergers by the Advanced LIGO/Virgo (ALV) detector network. If the optimal survey strategy is adopted, 202 of the GW170817-like kNe and 56 of the BNS population model kNe are detected with LSST but are below the threshold for detection by the ALV network. This represents, for both models, an increase by a factor greater than 4.5 in the number of detected sub-threshold events over the baseline strategy. These subthreshold events would provide an opportunity to conduct electromagnetic-triggered searches for signals in gravitational-wave data and assess selection effects in measurements of the Hubble constant from standard sirens, e.g. viewing angle effects.

  • 17. Traykova, Dina
    et al.
    Braden, Jonathan
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    Accretion of a symmetry-breaking scalar field by a Schwarzschild black hole2018In: Philosophical Transactions. Series A: Mathematical, physical, and engineering science, ISSN 1364-503X, E-ISSN 1471-2962, Vol. 376, no 2114, article id 20170122Article in journal (Refereed)
    Abstract [en]

    We simulate the behaviour of a Higgs-like field in the vicinity of a Schwarzschild black hole using a highly accurate numerical framework. We consider both the limit of the zero-temperature Higgs potential and a toy model for the time-dependent evolution of the potential when immersed in a slowly cooling radiation bath. Through these numerical investigations, we aim to improve our understanding of the non-equilibrium dynamics of a symmetry-breaking field (such as the Higgs) in the vicinity of a compact object such as a black hole. Understanding this dynamics may suggest new approaches for studying properties of scalar fields using black holes as a laboratory. This article is part of the Theo Murphy meeting issue 'Higgs Cosmology'.

  • 18.
    Widmark, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mortlock, Daniel J.
    Stockholm University, Faculty of Science, Department of Astronomy. Imperial College London, UK.
    Peiris, Hiranya V.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University College London, UK.
    A Bayesian model for inferring properties of the local white dwarf population in astrometric and photometric surveys2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, no 1, p. 179-188Article in journal (Refereed)
    Abstract [en]

    The Gaia mission is providing precise astrometry for an unprecedented number of white dwarfs (WDs), encoding information on stellar evolution, Type Ia supernovae progenitor scenarios, and the star formation and dynamical history of the Milky Way. With such a large data set, it is possible to infer properties of the WD population using only astrometric and photometric informations. We demonstrate a framework to accomplish this using a mock data set with Sloan Digital Sky Survey ugriz photometry and Gaia astrometric information. Our technique utilizes a Bayesian hierarchical model for inferring properties of a WD population while also taking into account all observational errors of individual objects, as well as selection and incompleteness effects. We demonstrate that photometry alone can constrain the WD population's distributions of temperature, surface gravity, and atmospheric composition, and that astrometric information significantly improves determination of the WD surface gravity distribution. We also discuss the possibility of identifying unresolved binary WDs using only photometric and astrometric informations.

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