Publications


Corrections to weighted opacities and energy exchange rate in 3-T radiation-hydrodynamics

High Energy Density Physics Elsevier BV 35 (2020) 100734

KW McLean, SJ Rose


Is there really a `Hubble tension'?

arXiv (2019)

M Rameez, SUBIR Sarkar

Errors in redshift measurements as small as $\Delta z \sim 0.0001$ can have significant impact on the value of inferred cosmological parameters such as $H_0$ (Davis et al. 2019). We have earlier reported that the redshifts of over 100 Type Ia supernovae (SNe Ia) which are in common between the SDSSII-SNLS3 Joint Lightcurve Analysis (JLA) catalogue (Betoule et al. 2014) and the subsequent Pantheon compilation (Scolnic et al. 2018) are discrepant - some by as much as $\Delta z \sim 0.1$ (Rameez 2019a). We study the impact of this on the inferred value of $H_0$ using calibrations of the supernova absolute magnitude via the 'local distance ladder' (Riess et al. 2016). For supernovae with $\Delta z > 0.025$, the JLA redshifts favour $H_0 \sim 72$~km~s$^{-1}$Mpc$^{-1}$, while the Pantheon redshifts favour $H_0 \sim 68$~km~s$^{-1}$Mpc$^{-1}$. For comparison the value inferred (assuming the flat $\Lambda$CDM model) from the Planck data on CMB anisotropies is $H_0 \sim 67.4 \pm 0.5$~km~s$^{-1}$Mpc$^{-1}$ (Aghanim et al. 2018). Thus the systematic uncertainties that apparently still plague the distance ladder measurement of $H_0$ undermine the significance of the discrepancy claimed by Riess et al. (2019).


Wakefields in a cluster plasma

Physical Review Special Topics: Accelerators and Beams American Physical Society 22 (2019) 113501

L Ceurvorst, N Bourgeois, R Pattathil, P Norreys, M Mayr, J Sadler, M Kasim, B Spiers, K Glize, A Savin, F Keeble, A Ross, R Wang, R Bingham, P Burrows, M Wing, D Symes, R Aboushelbaya, R Fonseca, J Holloway, N Ratan, R Trines

We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma.


Reply to: Reconsidering X-ray plasmons

NATURE PHOTONICS 13 (2019) 751-753

LB Fletcher, HJ Lee, T Doppner, E Galtier, B Nagler, P Heimann, C Fortmann, S LePape, T Ma, M Millot, A Pak, D Turnbull, DA Chapman, DO Gericke, J Vorberger, T White, G Gregori, M Wei, B Barbrel, RW Falcone, C-C Kao, H Nuhn, J Welch, U Zastrau, P Neumayer, JB Hastings, SH Glenzer


Validation of gyrokinetic simulations of a National Spherical Torus eXperiment H-mode plasma and comparisons with a high-k scattering synthetic diagnostic

Plasma Physics and Controlled Fusion IOP Publishing 61 (2019) 115015-115015

JR Ruiz, W Guttenfelder, AE White, NT Howard, J Candy, Y Ren, DR Smith, NF Loureiro, C Holland, CW Domier


Overview of recent TJ-II stellarator results

NUCLEAR FUSION 59 (2019) ARTN 112019

E Ascasibar, D Alba, D Alegre, A Alonso, J Alonso, F de Aragon, A Baciero, JM Barcala, E Blanco, J Botija, L Bueno, S Cabrera, E de la Cal, I Calvo, A Cappa, D Carralero, R Carrasco, B Carreras, F Castejon, R Castro, A de Castro, G Catalan, AA Chmyga, M Chamorro, AW Cooper, A Dinklage, L Eliseev, T Estrada, M Ezzat, F Fernandez-Marina, JM Fontdecaba, L Garcia, I Garcia-Cortes, R Garcia-Gomez, JM Garcia-Regana, A Gonzalez-Jerez, G Grenfell, J Guasp, J Hernandez-Sanchez, J Hernanz, C Hidalgo, E Hollmann, A Jimenez-Denche, P Khabanov, N Kharchev, I Kirpitchev, R Kleiber, AS Kozachek, L Krupnik, F Lapayese, M Liniers, B Liu, D Lopez-Bruna, A Lopez-Fraguas, B Lopez-Miranda, J Lopez-Razola, U Losada, E de la Luna, A Martin de Aguilera, F Martin-Diaz, M Martinez-Fuentes, G Martin-Gomez, AB Martin-Rojo, J Martinez-Fernandez, KJ McCarthy, F Medina, M Medrano, L Melon, AV Melnikov, P Mendez, R Merino, FJ Miguel, B van Milligen, A Molinero, B Momo, P Monreal, S Mulas, Y Narushima, M Navarro, M Ochando, S Ohshima, J Olivares, E Oyarzabal, JL de Pablos, L Pacios, N Panadero, F Parra, I Pastor, A de la Pena, A Pereira, JR Pinzon, AB Portas, E Poveda, JA Quintana, FJ Ramos, GA Ratta, M Redondo, E Rincon, L Rios, C Rodriguez-Fernandez, L Rodriguez-Rodrigo, B Rojo, A Ros, E Rosa, E Sanchez, J Sanchez, M Sanchez, E Sanchez-Sarabia, S Satake, JA Sebastian, R Sharma, C Silva, ER Solano, A Soleto, BJ Sun, FL Tabares, D Tafalla, H Takahashi, N Tamura, A Tolkachev, J Vega, G Velasco, JL Velasco, S Yamamoto, B Zurro, TJ-Team


Evidence for anisotropy of cosmic acceleration

Astronomy and Astrophysics: a European journal EDP Sciences (2019)

J Colin, R Mohayaee, M Rameez, S Sarkar

Observations reveal a `bulk flow' in the local Universe which is faster and extends to much larger scales than is expected around a typical observer in the standard $\Lambda$CDM cosmology. This is expected to result in a scale-dependent dipolar modulation of the acceleration of the expansion rate inferred from observations of objects within the bulk flow. From a maximum-likelihood analysis of the Joint Lightcurve Analysis (JLA) catalogue of Type Ia supernovae we find that the deceleration parameter, in addition to a small monopole, indeed has a much bigger dipole component aligned with the CMB dipole which falls exponentially with redshift $z$: $q_0 = q_\mathrm{m} + \vec{q}_\mathrm{d}.\hat{n}\exp(-z/S)$. The best fit to data yields $q_\mathrm{d} = -8.03$ and $S = 0.0262~(\Rightarrow d \sim 100~\mathrm{Mpc})$, rejecting isotropy ($q_\mathrm{d} = 0$) with $3.9\sigma$ statistical significance, while $q_\mathrm{m} = -0.157$ and consistent with no acceleration ($q_\mathrm{m} = 0$) at $1.4\sigma$. Thus the cosmic acceleration deduced from supernovae may be an artefact of our being non-Copernican observers, rather than evidence for a dominant component of `dark energy' in the Universe.


The SAMI Galaxy Survey: First detection of a transition in spin orientation with respect to cosmic filaments in the stellar kinematics of galaxies

Monthly Notices of the Royal Astronomical Society Oxford University Press (2019)

C Welker, P Elahi, J Bryant, C Pichon, L Cortese, M Goodwin, JS Lawrence, Y Dubois, J Devriendt, J Bland-Hawthorn, J Van de Sande, C Lagos, D Obreschkow, SM Croom, S Sweet, A Lopez-Sanchez, A Medling

We present the first detection of mass dependent galactic spin alignments with local cosmic filaments with >2σ confidence using IFS kinematics. The 3D network of cosmic filaments is reconstructed on Mpc scales across GAMA fields using the cosmic web extractor DisPerSe. We assign field galaxies from the SAMI survey to their nearest filament segment in 3D and estimate the degree of alignment between SAMI galaxies’ kinematic spin axis and their nearest filament in projection. Low-mass galaxies align their spin with their nearest filament while higher mass counterparts are more likely to display an orthogonal orientation. The stellar transition mass from the first trend to the second is bracketed between 1010.4 M⊙ and 1010.9 M⊙, with hints of an increase with filament scale. Consistent signals are found in the Horizon-AGN cosmological hydrodynamic simulation. This supports a scenario of early angular momentum build-up in vorticity rich quadrants around filaments at low stellar mass followed by progressive flip of spins orthogonal to the cosmic filaments through mergers at high stellar mass. Conversely, we show that dark-matter only simulations post-processed with a semi-analytic model treatment of galaxy formation struggles to reproduce this alignment signal. This suggests that gas physics is key in enhancing the galaxy-filament alignment.


Cosmic ray spectrum and composition from PeV to EeV using 3 years of data from IceTop and IceCube

PHYSICAL REVIEW D 100 (2019) ARTN 082002

MG Aartsen, M Ackermann, J Adams, JA Aguilar, M Ahlers, M Ahrens, C Alispach, K Andeen, T Anderson, I Ansseau, G Anton, C Arguelles, J Auffenberg, S Axani, P Backes, H Bagherpour, X Bai, A Barbano, SW Barwick, V Baum, S Baur, R Bay, JJ Beatty, K-H Becker, JB Tjus, S BenZvi, D Berley, E Bernardini, DZ Besson, G Binder, D Bindig, E Blaufuss, S Blot, C Bohm, M Boerner, S Boeser, O Botner, J Boettcher, E Bourbeau, J Bourbeau, F Bradascio, J Braun, H-P Bretz, S Bron, J Brostean-Kaiser, A Burgman, J Buscher, RS Busse, T Carver, C Chen, E Cheung, D Chirkin, K Clark, L Classen, GH Collin, JM Conrad, P Coppin, P Correa, DF Cowen, R Cross, P Dave, JPAM de Andre, C De Clercq, JJ DeLaunay, H Dembinski, K Deoskar, S De Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T DeYoung, A Diaz, JC Diaz-Velez, H Dujmovic, M Dunkman, E Dvorak, B Eberhardt, T Ehrhardt, P Eller, PA Evenson, S Fahey, AR Fazely, J Felde, T Feusels, K Filimonov, C Finley, A Franckowiak, E Friedman, A Fritz, TK Gaisser, J Gallagher, E Ganster, S Garrappa, L Gerhardt, K Ghorbani, T Glauch, T Gluesenkamp, A Goldschmidt, JG Gonzalez, D Grant, Z Griffith, M Guender, M Guenduez, C Haack, A Hallgren, L Halve, F Halzen, K Hanson, D Hebecker, D Heereman, P Heix, K Helbing, R Hellauer, F Henningsen, S Hickford, J Hignight, GC Hill, KD Hoffman, R Hoffmann, T Hoinka, B Hokanson-Fasig, K Hoshina, F Huang, M Huber, K Hultqvist, M Huennefeld, R Hussain, S In, N Iovine, A Ishihara, E Jacobi, GS Japaridze, M Jeong, K Jero, BJP Jones, F Jonske, R Joppe, W Kang, A Kappes, D Kappesser, T Karg, M Karl, A Karle, U Katz, M Kauer, JL Kelley, A Kheirandish, J Kim, T Kintscher, J Kiryluk, T Kittler, SR Klein, R Koirala, H Kolanoski, L Koepke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, K Krings, G Krueckl, N Kulacz, S Kunwar, N Kurahashi, A Kyriacou, M Labare, JL Lanfranchi, MJ Larson, F Lauber, JP Lazar, K Leonard, M Leuermann, QR Liu, E Lohfink, CJL Mariscal, L Lu, F Lucarelli, J Lunemann, W Luszczak, J Madsen, G Maggi, KBM Mahn, Y Makino, P Mallik, K Mallot, S Mancina, IC Mari, R Maruyama, K Mase, R Maunu, K Meagher, M Medici, A Medina, M Meier, S Meighen-Berger, T Menne, G Merino, T Meures, S Miarecki, J Micallef, G Momente, T Montaruli, RW Moore, R Morse, M Moulai, P Muth, R Nagai, R Nahnhauer, P Nakarmi, U Naumann, G Neer, H Niederhausen, SC Nowicki, DR Nygren, AO Pollmann, A Olivas, A O'Murchadha, E O'Sullivan, T Palczewski, H Pandya, DV Pankova, N Park, P Peiffer, CP de los Heros, S Philippen, D Pieloth, E Pinat, A Pizzuto, M Plum, A Porcelli, PB Price, GT Przybylski, C Raab, A Raissi, M Rameez, L Rauch, K Rawlins, IC Rea, R Reimann, B Relethford, G Renzi, E Resconi, W Rhode, M Richman, S Robertson, M Rongen, C Rott, T Ruhe, D Ryckbosch, D Rysewyk, I Safa, SES Herrera, A Sandrock, J Sandroos, M Santander, S Sarkar, K Satalecka, M Schaufel, P Schlunder, T Schmidt, A Schneider, J Schneider, L Schumacher, S Sclafani, D Seckel, S Seunarine, S Shefali, M Silva, R Snihur, J Soedingrekso, D Soldin, M Song, GM Spiczak, C Spiering, J Stachurska, M Stamatikos, T Stanev, A Stasik, R Stein, J Stettner, A Steuer, T Stezelberger, RG Stokstad, A Stossl, NL Strotjohann, T Stuerwald, T Stuttard, GW Sullivan, M Sutherland, I Taboada, F Tenholt, S Ter-Antonyan, A Terliuk, S Tilav, L Tomankova, C Tonnis, S Toscano, D Tosi, M Tselengidou, CF Tung, A Turcati, R Turcotte, CF Turley, B Ty, E Unger, MAU Elorrieta, M Usner, J Vandenbroucke, W Van Driessche, D van Eijk, N van Eijndhoven, S Vanheule, J van Santen, M Vraeghe, C Walck, A Wallace, M Wallraff, N Wandkowsky, TB Watson, C Weaver, MJ Weiss, J Weldert, C Wendt, J Werthebach, S Westerhoff, BJ Whelan, N Whitehorn, K Wiebe, CH Wiebusch, L Wille, DR Williams, L Wills, M Wolf, J Wood, TR Wood, K Woschnagg, G Wrede, DL Xu, XW Xu, Y Xu, JP Yanez, G Yodh, S Yoshida, T Yuan, M Zoecklein, I Collaboration


Efficient propagation of systematic uncertainties from calibration to analysis with the SnowStorm method in IceCube

Journal of Cosmology and Astroparticle Physics IOP Publishing 2019 (2019) 048-048

MG Aartsen, M Ackermann, J Adams, JA Aguilar, M Ahlers, C Alispach, BA Atoum, K Andeen, T Anderson, I Ansseau, G Anton, C Argüelles, J Auffenberg, S Axani, P Backes, H Bagherpour, X Bai, AB V., A Barbano, SW Barwick, B Bastian, V Baum, S Baur, R Bay, JJ Beatty, K-H Becker, JB Tjus, S BenZvi, D Berley, E Bernardini, DZ Besson, G Binder, D Bindig, E Blaufuss, S Blot, C Bohm, M Börner, S Böser, O Botner, J Böttcher, E Bourbeau, J Bourbeau, F Bradascio, J Braun, S Bron, J Brostean-Kaiser, A Burgman, J Buscher, RS Busse, T Carver, C Chen, E Cheung, D Chirkin, S Choi, K Clark, L Classen, A Coleman, GH Collin, JM Conrad, P Coppin, P Correa, DF Cowen, R Cross, P Dave, CD Clercq, JJ DeLaunay, H Dembinski, K Deoskar, SD Ridder, P Desiati, KD de Vries, G de Wasseige, M de With, T DeYoung, A Diaz, JC Díaz-Vélez, H Dujmovic, M Dunkman, E Dvorak, B Eberhardt, T Ehrhardt, P Eller, R Engel, PA Evenson, S Fahey, AR Fazely, J Felde, K Filimonov, C Finley, A Franckowiak, E Friedman, A Fritz, TK Gaisser, J Gallagher, E Ganster, S Garrappa, L Gerhardt, K Ghorbani, T Glauch, T Glüsenkamp, A Goldschmidt, JG Gonzalez, D Grant, Z Griffith, S Griswold, M Günder, M Gündüz, C Haack, A Hallgren, L Halve, F Halzen, K Hanson, A Haungs, D Hebecker, D Heereman, P Heix, K Helbing, R Hellauer, F Henningsen, S Hickford, J Hignight, GC Hill, KD Hoffman, R Hoffmann, T Hoinka, B Hokanson-Fasig, K Hoshina, F Huang, M Huber, T Huber, K Hultqvist, M Hünnefeld, R Hussain, S In, N Iovine, A Ishihara, GS Japaridze, M Jeong, K Jero, BJP Jones, F Jonske, R Joppe, D Kang, W Kang, A Kappes, D Kappesser, T Karg, M Karl, A Karle, U Katz, M Kauer, JL Kelley, A Kheirandish, J Kim, T Kintscher, J Kiryluk, T Kittler, SR Klein, R Koirala, H Kolanoski, L Köpke, C Kopper, S Kopper, DJ Koskinen, M Kowalski, K Krings, G Krückl, N Kulacz, N Kurahashi, A Kyriacou, M Labare, JL Lanfranchi, MJ Larson, F Lauber, JP Lazar, K Leonard, A Leszczyńska, M Leuermann, QR Liu, E Lohfink, CJL Mariscal, L Lu, F Lucarelli, J Lünemann, W Luszczak, Y Lyu, WY Ma, J Madsen, G Maggi, KBM Mahn, Y Makino, P Mallik, K Mallot, S Mancina, IC Mariş, R Maruyama, K Mase, R Maunu, F McNally, K Meagher, M Medici, A Medina, M Meier, S Meighen-Berger, T Menne, G Merino, T Meures, J Micallef, D Mockler, G Momenté, T Montaruli, RW Moore, R Morse, M Moulai, P Muth, R Nagai, U Naumann, G Neer, H Niederhausen, SC Nowicki, DR Nygren, AO Pollmann, M Oehler, A Olivas, A O'Murchadha, E O'Sullivan, T Palczewski, H Pandya, DV Pankova, N Park, P Peiffer, C Pérez de los Heros, S Philippen, D Pieloth, E Pinat, A Pizzuto, M Plum, A Porcelli, PB Price, GT Przybylski, C Raab, A Raissi, M Rameez, L Rauch, K Rawlins, IC Rea, R Reimann, B Relethford, M Renschler, G Renzi, E Resconi, W Rhode, M Richman, S Robertson, M Rongen, C Rott, T Ruhe, D Ryckbosch, D Rysewyk, I Safa, SES Herrera, A Sandrock, J Sandroos, M Santander, S Sarkar, S Sarkar, K Satalecka, M Schaufel, H Schieler, P Schlunder, T Schmidt, A Schneider, J Schneider, FG Schröder, L Schumacher, S Sclafani, D Seckel, S Seunarine, S Shefali, M Silva, R Snihur, J Soedingrekso, D Soldin, M Song, GM Spiczak, C Spiering, J Stachurska, M Stamatikos, T Stanev, R Stein, P Steinmüller, J Stettner, A Steuer, T Stezelberger, RG Stokstad, A Stößl, NL Strotjohann, T Stürwald, T Stuttard, GW Sullivan, I Taboada, F Tenholt, S Ter-Antonyan, A Terliuk, S Tilav, K Tollefson, L Tomankova, C Tönnis, S Toscano, D Tosi, A Trettin, M Tselengidou, CF Tung, A Turcati, R Turcotte, CF Turley, B Ty, E Unger, MAU Elorrieta, M Usner, J Vandenbroucke, WV Driessche, DV Eijk, NV Eijndhoven, S Vanheule, JV Santen, M Vraeghe, C Walck, A Wallace, M Wallraff, N Wandkowsky, TB Watson, C Weaver, A Weindl, MJ Weiss, J Weldert, C Wendt, J Werthebach, BJ Whelan, N Whitehorn, K Wiebe, CH Wiebusch, L Wille, DR Williams, L Wills, M Wolf, J Wood, TR Wood, K Woschnagg, G Wrede, DL Xu, XW Xu, Y Xu, JP Yanez, G Yodh, S Yoshida, T Yuan, M Zöcklein


Inverse problem instabilities in large-scale modelling of matter in extreme conditions

Physics of Plasmas AIP Publishing 26 (2019) 112706

MF Kasim, TP Galligan, J Topp-Mugglestone, G Gregori, S Vinko

Our understanding of physical systems often depends on our ability to match complex computational modeling with the measured experimental outcomes. However, simulations with large parameter spaces suffer from inverse problem instabilities, where similar simulated outputs can map back to very different sets of input parameters. While of fundamental importance, such instabilities are seldom resolved due to the intractably large number of simulations required to comprehensively explore parameter space. Here, we show how Bayesian inference can be used to address inverse problem instabilities in the interpretation of x-ray emission spectroscopy and inelastic x-ray scattering diagnostics. We find that the extraction of information from measurements on the basis of agreement with simulations alone is unreliable and leads to a significant underestimation of uncertainties. We describe how to statistically quantify the effect of unstable inverse models and describe an approach to experimental design that mitigates its impact.


Impact of main ion pressure anisotropy on stellarator impurity transport

Nuclear Fusion IOP Publishing (2019)

I Calvo, FI Parra, JL Velasco, JM García-Regaña

Main ions influence impurity dynamics through a variety of mechanisms; in particular, via impurity-ion collisions. To lowest order in an expansion in the main ion mass over the impurity mass, the impurity-ion collision operator only depends on the component of the main ion distribution that is odd in the parallel velocity. These lowest order terms give the parallel friction of the impurities with the main ions, which is typically assumed to be the main cause of collisional impurity transport. Next-order terms in the mass ratio expansion of the impurity-ion collision operator, proportional to the component of the main ion distribution that is even in the parallel velocity, are usually neglected. However, in stellarators, the even component of the main ion distribution can be very large. In this article, such next-order terms in the mass ratio expansion of the impurity-ion collision operator are retained, and analytical expressions for the neoclassical radial flux of trace impurities are calculated in the Pfirsch-Schl\"uter, plateau and $1/\nu$ regimes. The new terms provide a drive for impurity transport that is physically very different from parallel friction: they are associated to anisotropy in the pressure of the main ions, which translates into impurity pressure anisotropy. It is argued that main ion pressure anisotropy must be taken into account for a correct description of impurity transport in certain realistic stellarator plasmas. Examples are given by numerically evaluating the analytical expressions for the impurity flux.


Using sparse Gaussian processes for predicting robust inertial confinement fusion implosion yields

IEEE Transactions on Plasma Science IEEE (2019) 1-6

P Hatfield, I Almosallam, R Scott, S Rose, S Roberts, M Jarvis


Dependence on ion temperature of shallow-angle magnetic presheaths with adiabatic electrons

Journal of Plasma Physics Cambridge University Press 85 (2019) 795850601

A Geraldini, F Parra, F Militello


Design and Performance of the first IceAct Demonstrator at the South Pole

arXiv (2019)

GW Sullivan, I Taboada, A Taketa, S Ter-Antonyan, HKM Tanaka, F Tenholt, A Terliuk, S Tilav, K Tollefson, L Tomankova, C Tönnis, S Toscano, D Tosi, M Tselengidou, A Turcati, A Trettin, CF Tung, R Turcotte, CF Turley, MAU Elorrieta, B Ty, E Unger, J Vandenbroucke, M Usner, WV Driessche

In this paper we describe the first results of a compact imaging air-Cherenkov telescope, IceAct, operating in coincidence with the IceCube Neutrino Observatory (IceCube) at the geographic South Pole. An array of IceAct telescopes (referred to as the IceAct project) is under consideration as part of the IceCube-Gen2 extension to IceCube. Surface detectors in general will be a powerful tool in IceCube-Gen2 for distinguishing astrophysical neutrinos from the dominant backgrounds of cosmic-ray induced atmospheric muons and neutrinos: the IceTop array is already in place as part of IceCube, but has a high energy threshold. Although the duty cycle will be lower for the IceAct telescopes than the present IceTop tanks, the IceAct telescopes may prove to be more effective at lowering the detection threshold for air showers. Additionally, small imaging air-Cherenkov telescopes in combination with IceTop, the deep IceCube detector or other future detector systems might improve measurements of the composition of the cosmic ray energy spectrum. In this paper we present measurements of a first 7-pixel imaging air Cherenkov telescope demonstrator, proving the capability of this technology to measure air showers at the South Pole in coincidence with IceTop and the deep IceCube detector.


A response to Rubin & Heitlauf: "Is the expansion of the universe accelerating? All signs \emph{still} point to yes"

arXiv (2019)

R Mohayaee, J Colin, M Rameez, SUBIR Sarkar

We have shown (Colin et al. 2019) that the acceleration of the Hubble expansion rate inferred from Type Ia supernovae is essentially a dipole with 3.9$\sigma$ significance, approximately aligned with the CMB dipole, while its monopole component which may be interpreted as due to a Cosmological Constant (or more generally dark energy) is consistent with zero at 1.4$\sigma$. This is challenged by Rubin & Heitlauf (2019) who assert that we incorrectly assumed the supernova light-curve parameters to be independent of redshift, and erred further in considering their measured redshifts (in the heliocentric frame) rather than transforming them to the CMB frame (in which the universe supposedly looks isotropic). We emphasize that our procedure is justified and that their criticism serves only to highlight the rather "arbitrary corrections" that are made to the data in order to infer isotropic cosmic acceleration. This is a vivid illustration of the 'Cosmological Fitting Problem' faced by observers who live in an inhomogeneous universe but still use the maximally symmetric FLRW cosmolgy to interpret observations.


Constraints on Neutrino Emission from Nearby Galaxies Using the 2MASS Redshift Survey and IceCube

arXiv (2019)

M Ackermann, J Adams, JA Aguilar, M Ahlers, C Alispach, M Ahrens, K Andeen, T Anderson, I Ansseau, C Argüelles, G Anton, J Auffenberg, S Axani, P Backes, H Bagherpour, X Bai, A Barbano, SW Barwick, B Bastian, V Baum, S Baur, R Bay

The distribution of galaxies within the local universe is characterized by anisotropic features. Observatories searching for the production sites of astrophysical neutrinos can take advantage of these features to establish directional correlations between a neutrino dataset and overdensities in the galaxy distribution in the sky. The results of two correlation searches between a seven-year time-integrated neutrino dataset from the IceCube Neutrino Observatory, and the 2MASS Redshift Survey (2MRS) catalog are presented here. The first analysis searches for neutrinos produced via interactions between diffuse intergalactic Ultra-High Energy Cosmic Rays (UHECRs) and the matter contained within galaxies. The second analysis searches for low-luminosity sources within the local universe, which would produce subthreshold multiplets in the IceCube dataset that directionally correlate with galaxy distribution. No significant correlations were observed in either analyses. Constraints are presented on the flux of neutrinos originating within the local universe through diffuse intergalactic UHECR interactions, as well as on the density of standard candle sources of neutrinos at low luminosities.


Origins of Type Ibn SNe 2006jc/2015G in interacting binaries and implications for pre-SN eruptions

Monthly Notices of the Royal Astronomical Society Oxford University Press (2019)

N-C Sun, PA Crowther, P Podsiadlowski, R Hirai

Type Ibn supernovae (SNe Ibn) are intriguing stellar explosions whose spectra exhibit narrow helium lines with little hydrogen. They trace the presence of circumstellar material (CSM) formed via pre-SN eruptions of their stripped-envelope progenitors. Early work has generally assumed that SNe Ibn come from massive Wolf-Rayet (WR) stars via single star evolution. In this paper, we report ultraviolet (UV) and optical observations of two nearby Type Ibn SNe 2006jc and 2015G conducted with the Hubble Space Telescope (HST) at late times. A point source is detected at the position of SN 2006jc, and we confirm the conclusion of Maund et al. that it is the progenitor’s binary companion. Its position on the Hertzsprung-Russell (HR) diagram corresponds to a star that has evolved off the main sequence (MS); further analysis implies a low initial mass for the companion star (M2 ≤ 12.3+2.3−1.5 M⊙) and a secondary-to-primary initial mass ratio very close to unity (q = M2/M1 ∼ 1); the SN progenitor’s hydrogen envelope had been stripped through binary interaction. We do not detect the binary companion of SN 2015G. For both SNe, the surrounding stellar populations have relatively old ages and argue against any massive WR stars as their progenitors. These results suggest that SNe Ibn may have lower-mass origins in interacting binaries. As a result, they also provide evidence that the giant eruptions commonly seen in massive luminous blue variables (LBVs) can also occur in much lower-mass, stripped-envelope stars just before core collapse.


Deviations from normal distributions in artificial and real time series: a false positive prescription

Monthly Notices of the Royal Astronomical Society Oxford University Press 489 (2019) 2117–2129-

P Morris, N Chakraborty, G Cotter

<jats:title>ABSTRACT</jats:title> <jats:p>Time-series analysis allows for the determination of the Power Spectral Density (PSD) and Probability Density Function (PDF) for astrophysical sources. The former of these illustrates the distribution of power at various time-scales, typically taking a power-law form, while the latter characterizes the distribution of the underlying stochastic physical processes, with Gaussian and lognormal functional forms both physically motivated. In this paper, we use artificial time series generated using the prescription of Timmer &amp; Koenig to investigate connections between the PDF and PSD. PDFs calculated for these artificial light curves are less likely to be well described by a Gaussian functional form for steep (Γ⪆1) PSD indices due to weak non-stationarity. Using the Fermi LAT monthly light curve of the blazar PKS2155-304 as an example, we prescribe and calculate a false positive rate that indicates how likely the PDF is to be attributed an incorrect functional form. Here, we generate large numbers of artificial light curves with intrinsically normally distributed PDFs and with statistical properties consistent with observations. These are used to evaluate the probabilities that either Gaussian or lognormal functional forms better describe the PDF. We use this prescription to show that PKS2155-304 requires a high prior probability of having a normally distributed PDF, $P(\rm {G})~$ ≥ 0.82, for the calculated PDF to prefer a Gaussian functional form over a lognormal. We present possible choices of prior and evaluate the probability that PKS2155-304 has a lognormally distributed PDF for each.</jats:p>


Axion-like-particle decay in strong electromagnetic backgrounds

Journal of High Energy Physics Springer 2019 (2019) 162

B King, BM Dillon, K Beyer, G Gregori

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