Abstracts of Interest
Selected by:
Abstract: 1911.02561
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Title:Neutrino astronomy with the next generation IceCube Neutrino Observatory
(Submitted on 6 Nov 2019)
Abstract: The past decade has welcomed the emergence of cosmic neutrinos as a new messenger to explore the most extreme environments of the universe. The discovery measurement of cosmic neutrinos, announced by IceCube in 2013, has opened a new window of observation that has already resulted in new fundamental information that holds the potential to answer key questions associated with the high-energy universe, including: what are the sources in the PeV sky and how do they drive particle acceleration; where are cosmic rays of extreme energies produced, and on which paths do they propagate through the universe; and are there signatures of new physics at TeV-PeV energies and above? The planned advancements in neutrino telescope arrays in the next decade, in conjunction with continued progress in broad multimessenger astrophysics, promise to elevate the cosmic neutrino field from the discovery to the precision era and to a survey of the sources in the neutrino sky. The planned detector upgrades to the IceCube Neutrino Observatory, culminating in IceCube-Gen2 (an envisaged $400M facility with anticipated operation in the next decade, described in this white paper) are the cornerstone that will drive the evolution of neutrino astrophysics measurements.
Abstract: 1911.02632
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Title:Pions in hot dense matter and their astrophysical implications
(Submitted on 6 Nov 2019)
Abstract: We study the role of pions in hot dense matter encountered in astrophysics. We find that strong interactions enhance the number density of negatively charged pions and that this enhancement can be calculated reliably for a relevant range of density and temperature using the virial expansion. We assess the influence of pions and muons on the equation of state (EOS) and weak interaction rates in hot dense matter. We find that thermal pions increase the proton fraction and soften the EOS. We also find that charged current weak reactions involving pions and muons $\bar{\nu}_\mu+\mu^- \rightarrow \pi$ and $\nu_\mu+\pi^- \rightarrow \mu^-$ make an important contribution to the opacity of muon neutrinos. This could influence the dynamics of core-collapse supernovae and neutron star mergers. Finally, we note that pion-nucleon reactions can alter the evolution of the proton fraction when weak interactions are not in equilibrium.
Abstract: 1911.02663
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Full Text: [ PostScript, PDF]
Title:Novel constraints on the particle nature of dark matter from stellar streams
(Submitted on 6 Nov 2019)
Abstract: We analyze the distribution of stars along the GD-1 stream with a combination of data from the ${\it Gaia}$ satellite and the Pan-STARRS survey, and we show that the population of subhalos predicted by the cold dark matter paradigm are necessary and sufficient to explain the perturbations observed in the linear density of stars. This allows us to set novel constraints on alternative dark matter scenarios that predict a suppression of the subhalo mass function on scales smaller than the mass of dwarf galaxies. A combined analysis of the density perturbations in the GD-1 and Pal 5 streams leads to a $95\%$ lower limit on the mass of warm dark matter thermal relics $m_{\rm WDM}>4.6$ keV; adding dwarf satellite counts strengthens this to $m_{\rm WDM}>6.3$ keV.
Abstract: 1911.02948
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Title:Optimizing neural network techniques in classifying Fermi-LAT gamma-ray sources
(Submitted on 7 Nov 2019)
Abstract: Machine learning is an automatic technique that is revolutionizing scientific research, with innovative applications and wide use in astrophysics. The aim of this study was to developed an optimized version of an Artificial Neural Network machine learning method for classifying blazar candidates of uncertain type detected by the Fermi Large Area Telescope gamma-ray instrument. The final result of this study increased the classification performance by about 80 per cent with respect to previous method, leaving only 15 unclassified blazars out of 573 blazar candidates of uncertain type listed in the LAT 4-year Source Catalog.
Abstract: 1911.03163
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Title:Extending and Calibrating the Velocity dependent One-Scale model for Cosmic Strings with One Thousand Field Theory Simulations
(Submitted on 8 Nov 2019)
Abstract: Understanding the evolution and cosmological consequences of topological defect networks requires a combination of analytic modeling and numerical simulations. The canonical analytic model for defect network evolution is the Velocity-dependent One-Scale (VOS) model. For the case of cosmic strings, this has so far been calibrated using small numbers of Goto-Nambu and field theory simulations, in the radiation and matter eras, as well as in Minkowski spacetime. But the model is only as good as the available simulations, and it should be extended as further simulations become available. In previous work we presented a General Purpose Graphics Processing Unit implementation of the evolution of cosmological domain wall networks, and used it to obtain an improved VOS model for domain walls. Here we continue this effort, exploiting a more recent analogous code for local Abelian-Higgs string networks. The significant gains in speed afforded by this code enabled us to carry out 1032 field theory simulations of $512^3$ size, with 43 different expansion rates. This detailed exploration of the effects of the expansion rate on the network properties in turn enables a statistical separation of various dynamical processes affecting the evolution of the network. We thus extend and accurately calibrate the VOS model for cosmic strings, including separate terms for energy losses due to loop production and scalar/gauge radiation. By comparing this newly calibrated VOS model with the analogous one for domain walls we quantitatively show that energy loss mechanisms are different for the two types of defects.
Abstract: 1911.03164
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Title:Absolute calibration of the polarisation angle for future CMB B-mode experiments from current and future measurements of the Crab nebula
(Submitted on 8 Nov 2019)
Abstract: A tremendous international effort is currently dedicated to observing the so-called primordial B modes of the Cosmic Microwave Background (CMB) polarisation. If measured, this faint signal imprinted by the primordial gravitational wave background, would be an evidence of the inflation epoch and quantify its energy scale, providing a rigorous test of fundamental physics far beyond the reach of accelerators. At the unprecedented sensitivity level that the new generation of CMB experiments aims to reach, every uncontrolled instrumental systematic effect will potentially result in an analysis bias that is larger than the much sought-after CMB B-mode signal. The absolute calibration of the polarisation angle is particularly important in this sense, as any associated error will end up in a leakage from the much larger E modes into B modes. The Crab nebula (Tau A), with its bright microwave synchrotron emission, is one of the few objects in the sky that can be used as absolute polarisation calibrators. In this communication, we review the best current constraints on its polarisation angle from 23 to 353 GHz, at typical angular scales for CMB observations, from WMAP, IRAM XPOL, Planck and NIKA data. We will show that these polarisation angle measurements are compatible with a constant angle and we will present a study of the uncertainty on this mean angle, making different considerations on how to combine the individual measurement errors. For each of the cases, the potential impact on the CMB B-mode spectrum will be explored.
Abstract: 1911.03250
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Title:Canada and the SKA from 2020-2030
(Submitted on 8 Nov 2019)
Abstract: This white paper submitted for the 2020 Canadian Long-Range Planning process (LRP2020) presents the prospects for Canada and the Square Kilometre Array (SKA) from 2020-2030, focussing on the first phase of the project (SKA1) scheduled to begin construction early in the next decade. SKA1 will make transformational advances in our understanding of the Universe across a wide range of fields, and Canadians are poised to play leadership roles in several. Canadian key SKA technologies will ensure a good return on capital investment in addition to strong scientific returns, positioning Canadian astronomy for future opportunities well beyond 2030. We therefore advocate for Canada's continued scientific and technological engagement in the SKA from 2020-2030 through participation in the construction and operations phases of SKA1.
Abstract: 1911.03294
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Title:Conspiracy of BSM physics and cosmology
(Submitted on 8 Nov 2019)
Abstract: The lack of experimental evidence at the LHC for physics beyond the Standard model (BSM) of elementary particles together with necessity of its existence to provide solutions of internal problems of the Standard model (SM) as well as of physical nature of the basic elements of the modern cosmology demonstrates the conspiracy of BSM physics. Simultaneously the data of precision cosmology only tighten the constraints on the deviations from the now standard LambdaCDM model and thus exhibit conspiracy of the nonstandard cosmological scenarios. We show that studying new physics in combination of its physical, astrophysical and cosmological probes, can not only unveil the conspiracy of BSM physics but will also inevitably reveal nonstandard features in the cosmological scenario.
Abstract: 1901.08040
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Full Text: [ PostScript, PDF]
Title:Data-driven estimation of the invisible energy of cosmic ray showers with the Pierre Auger Observatory
(Submitted on 23 Jan 2019 (v1), last revised 6 Nov 2019 (this version, v3))
Abstract: The determination of the primary energy of extensive air showers using the fluorescence detection technique requires an estimation of the energy carried away by particles that do not deposit all their energy in the atmosphere. This estimation is typically made using Monte Carlo simulations and thus depends on the assumed primary particle mass and on model predictions for neutrino and muon production. In this work we present a new method to obtain the invisible energy from events detected by the Pierre Auger Observatory. The method uses measurements of the muon number at ground level, and it allows us to reduce significantly the systematic uncertainties related to the mass composition and the high energy hadronic interaction models, and consequently to improve the estimation of the energy scale of the Observatory.
Abstract: 1903.11584
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Full Text: [ PostScript, PDF]
Title:The origin of Galactic cosmic rays: challenges to the standard paradigm
(Submitted on 27 Mar 2019 (v1), last revised 6 Nov 2019 (this version, v2))
Abstract: A critical review of the standard paradigm for the origin of Galactic cosmic rays is presented. Recent measurements of local and far-away cosmic rays reveal unexpected behaviours, which challenge the commonly accepted scenario. These recent findings are discussed, together with long-standing open issues. Despite the progress made thanks to ever-improving observational techniques and theoretical investigations, at present our understanding of the origin and of the behaviour of cosmic rays remains incomplete. We believe it is still unclear whether a modification of the standard paradigm, or rather a radical change of the paradigm itself is needed in order to interpret all the available data on cosmic rays within a self-consistent scenario.
Abstract: 1906.07419
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Title:Limits on point-like sources of ultra-high-energy neutrinos with the Pierre Auger Observatory
(Submitted on 18 Jun 2019 (v1), last revised 8 Nov 2019 (this version, v2))
Abstract: With the Surface Detector array (SD) of the Pierre Auger Observatory we can detect neutrinos with energy between $10^{17}\,$eV and $10^{20}\,$eV from point-like sources across the sky, from close to the Southern Celestial Pole up to $60^\circ$ in declination, with peak sensitivities at declinations around $\sim -53^\circ$ and $\sim+55^\circ$, and an unmatched sensitivity for arrival directions in the Northern hemisphere. A search has been performed for highly-inclined air showers induced by neutrinos of all flavours with no candidate events found in data taken between 1 Jan 2004 and 31 Aug 2018. Upper limits on the neutrino flux from point-like steady sources have been derived as a function of source declination. An unrivaled sensitivity is achieved in searches for transient sources with emission lasting over an hour or less, if they occur within the field of view corresponding to the zenith angle range between $60^\circ$ and $~95^\circ$ where the SD of the Pierre Auger Observatory is most sensitive to neutrinos.
Abstract: 1906.10090
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Full Text: [ PostScript, PDF]
Title:Holographic Principle, Cosmological Constant and Cyclic Cosmology
(Submitted on 24 Jun 2019 (v1), last revised 7 Nov 2019 (this version, v2))
Abstract: The holographic principle provides a deep insight into quantum gravity and resolves the fine-tuning crisis concerning the cosmological constant. Holographic dark energy introduces new ultra-violet (UV) and infra-red (IR) cutoffs into quantum gravity which are necessarily strongly related. The equation of state for dark energy $\omega = p/\rho$ is discussed from the holographic point of view. The phantom option of $\omega < -1$ is resurrected, as in an earlier cyclic cosmology. Such a cyclic model can, however, equally use the cosmological constant with $\omega = -1$.
Abstract: 1910.12953
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Full Text: [ PostScript, PDF]
Title:Cold Clouds as Cosmic-Ray Detectors
(Submitted on 28 Oct 2019 (v1), last revised 8 Nov 2019 (this version, v2))
Abstract: We show that the cosmic-ray ionization rate (CR, CRIR) may be constrained by observations of rovibrational H$_2$ lines in cold and dense molecular clouds. The H$_2$ is excited by penetrating electrons produced by CR ionization resulting in line emission that is proportional to the CRIR. The strongest CR excited lines are (1-0)O(2), S(0), Q(2) and O(4) in the 2-3 $\mu$m range. We derive an analytic framework for line formation by various pumping mechanisms: CR, ultraviolet (UV), and H$_2$-formation pumping, as functions of the CRIR and the UV field intensity. We obtain the required conditions for CRs to dominate line excitation, and find that the S(0) line may be detected with X-shooter instrument on the Very Large Telescope over one observation night. This new method, if successfully applied to a variety of clouds at different Galactic locations and with varying gas columns, will provide improved constraints on the spectrum of low energy CRs and their origins.
Abstract: 1911.02093
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Full Text: [ PostScript, PDF]
Title:Neutrino direction and energy resolution of Askaryan detectors
(Submitted on 5 Nov 2019)
Abstract: Detection of high-energy neutrinos via the radio technique allows for an exploration of the neutrino energy range from $\sim10^{16}$eV to $\sim10^{20}$eV with unprecedented precision. These Askaryan detectors have matured in two pilot arrays (ARA and ARIANNA) and the construction of a large-scale detector is actively discussed in the community. In this contribution, we present reconstruction techniques to determine the neutrino direction and energy from the observed few-nanoseconds short radio flashes and quantify the resolution of one of such detectors. The reconstruction of the neutrino direction requires a precise measurement of both the signal direction as well as the signal polarization. The reconstruction of the neutrino energy requires, in addition, the measurement of the vertex distance, obtainable from the time difference of two signal paths through the ice, and the viewing angle of the in-ice shower via the frequency spectrum. We discuss the required algorithms and quantify the resolution using a detailed Monte Carlo simulation study.
Abstract: 1911.02087
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Full Text: [ PostScript, PDF]
Title:Planck evidence for a closed Universe and a possible crisis for cosmology
(Submitted on 5 Nov 2019)
Abstract: The recent Planck Legacy 2018 release has confirmed the presence of an enhanced lensing amplitude in CMB power spectra compared to that predicted in the standard $\Lambda$CDM model. A closed universe can provide a physical explanation for this effect, with the Planck CMB spectra now preferring a positive curvature at more than $99 \%$ C.L. Here we further investigate the evidence for a closed universe from Planck, showing that positive curvature naturally explains the anomalous lensing amplitude and demonstrating that it also removes a well-known tension within the Planck data set concerning the values of cosmological parameters derived at different angular scales. We show that since the Planck power spectra prefer a closed universe, discordances higher than generally estimated arise for most of the local cosmological observables, including BAO. The assumption of a flat universe could, therefore, mask a cosmological crisis where disparate observed properties of the Universe appear to be mutually inconsistent. Future measurements are needed to clarify whether the observed discordances are due to undetected systematics, or to new physics, or simply are a statistical fluctuation.
Abstract: 1911.02016
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Full Text: [ PostScript, PDF]
Title:Calibration of the IceCube Neutrino Observatory
(Submitted on 5 Nov 2019)
Abstract: The IceCube Neutrino Observatory instruments roughly one cubic kilometer of deep, glacial ice below the geographic South Pole with 5160 optical sensors to register the Cherenkov light of passing relativistic, charged particles. Since its construction was completed in 2010, a wide range of analyses has been performed. Those include, among others, the discovery of a high energetic astrophysical neutrino flux, competitive measurements of neutrino oscillation parameters and world-leading limits on dark matter detection. With ever-increasing statistics the influence of insufficiently known aspects of the detector performance start to limit the potential gain of future analyses. This thesis presents calibration studies on both the hardware characteristics as well as the optical properties of the instrumented ice. Improving the knowledge of the detector systematics and the methods to study them does not only aid IceCube but also inform the design of potential future IceCube extensions.
Abstract: 1911.01813
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Title:Escaping from the herd of white elephants
(Submitted on 5 Nov 2019)
Abstract: About 60 ADASS participants discussed the evolving roles of users, developers, and managers of astronomical data reduction software. Special emphasis was placed on the role of the user in the era of Big Data. Is it really inevitable that the increasingly ignorant user will just have to be satisfied with the standard products from data processing centres?
Abstract: 1911.01719
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Full Text: [ PostScript, PDF]
Title:High-Energy Neutrino Astronomy: Current Status and Prospects
(Submitted on 5 Nov 2019)
Abstract: In the last decade, neutrino astronomy has taken off with two major breakthroughs, the first observation of high-energy astrophysical neutrinos in 2013 and the first evidence for gamma-rays and neutrinos from a single object published in summer 2018. In this talk, we will review these important milestones as well as the other noteworthy achievements reached by the community. We will emphasize the important role of neutrino searches in the multi-messenger era and describe the current efforts carried out in the large neutrino telescope community. We will conclude with an outlook for the coming decade.
Abstract: 1911.00656
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Full Text: [ PostScript, PDF]
Title:An ultra-wide bandwidth (704 to 4032 MHz) receiver for the Parkes radio telescope
(Submitted on 2 Nov 2019)
Abstract: We describe an ultra-wide-bandwidth, low-frequency receiver ("UWL") recently installed on the Parkes radio telescope. The receiver system provides continuous frequency coverage from 704 to 4032 MHz. For much of the band (~60%) the system temperature is approximately 22K and the receiver system remains in a linear regime even in the presence of strong mobile phone transmissions. We discuss the scientific and technical aspects of the new receiver including its astronomical objectives, as well as the feed, receiver, digitiser and signal-processor design. We describe the pipeline routines that form the archive-ready data products and how those data files can be accessed from the archives. The system performance is quantified including the system noise and linearity, beam shape, antenna efficiency, polarisation calibration and timing stability.
Abstract: 1911.00634
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Full Text: [ PostScript, PDF]
Title:Statistics of VHE gamma-Rays in Temporal Association with Radio Giant Pulses from the Crab Pulsar
(Submitted on 2 Nov 2019)
Abstract: The aim of this study is to search for evidence of a common emission engine between radio giant pulses (GPs) and very-high-energy (VHE, E>100 GeV) gamma-rays from the Crab pulsar. 16 hours of simultaneous observations of the Crab pulsar at 1.4 GHz with the Effelsberg radio telescope and the Westerbork Synthesis Radio Telescope (WSRT), and at energies above 60 GeV with the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes were performed. We searched for a statistical correlation between the radio and VHE gamma-ray emission with search windows of different lengths and different time lags to the arrival times of a radio GP. A dedicated search for an enhancement in the number of VHE gamma-rays correlated with the occurrence of radio GPs was carried out separately for the P1 and P2 phase ranges respectively. 99444 radio GPs have been detected in the radio data sample. We find no significant correlation between the GPs and VHE photons in any of the search windows. Depending on phase cuts and the chosen search windows we find upper limits at 95% confidence level on an increase in VHE gamma-ray events correlated with radio GPs between 7% and 61% of the average Crab pulsar VHE flux for the P1 and P2 phase ranges respectively. This puts upper limits on the flux increase during a radio GP of 12% to 2900% (depending on search window duration and phase cuts) of the pulsed VHE flux. This is the most stringent upper limit on a correlation between gamma-ray emission and radio GPs reported so far.}
Abstract: 1911.00057
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Full Text: [ PostScript, PDF]
Title:Primordial Black Holes from a tiny bump in the Inflaton potential
(Submitted on 31 Oct 2019)
Abstract: Scalar perturbations during inflation can be substantially amplified by tiny features in the inflaton potential. A bump-like feature behaves like a local speed-breaker and lowers the speed of the scalar field, thereby locally enhancing the scalar power spectrum. A bump-like feature emerges naturally if the base inflaton potential $V(\phi)$ contains a local correction term such as $V(\phi)\left[1+\varepsilon(\phi_0)\right]$. The presence of such a localised correction term at $\phi_0$ leads to a large peak in the curvature power spectrum and to an enhanced probability of black hole formation. Remarkably this does not significantly affect the scalar spectral index $n_{_S}$ and tensor to scalar ratio $r$ on CMB scales. Consequently such models can produce higher mass primordial black holes ($M_{\rm PBH}\geq 1 M_{\odot}$) in contrast to models with `near inflection-point potentials' in which generating higher mass black holes severely affects $n_{_S}$ and $r$. With a suitable choice of the base potential - such as the string theory based (KKLT) inflation or the $\alpha$-attractor models - the amplification of primordial scalar power spectrum can be as large as $10^7$ which leads to a significant contribution of primordial black holes (PBHs) to the dark matter density today, $f_{\rm PBH} = \Omega_{0,\rm PBH}/\Omega_{0,\rm DM} \sim O(1)$. We conclude that primordial black holes in the mass range $10^{-17} M_{\odot} \leq M_{\rm PBH} \leq 100\, M_{\odot}$ can easily form in single field inflation in the presence of small bump-like features in the inflaton potential.
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