Astrophysical limitations to the identification of dark matter: indirect neutrino signals vis-a-vis direct detection recoil rates

A convincing identification of dark matter (DM) particles can probably be achieved only through a combined analysis of different detections strategies, which provides an effective way of removing degeneracies in the parameter space of DM models. In practice, however, this program is made complicated by the fact that different strategies depend on different physical quantities, or on the same quantities but in a different way, making the treatment of systematic errors rather tricky. We discuss here the uncertainties on the recoil rate in direct detection experiments and on the muon rate induced by neutrinos from dark matter annihilations in the Sun, and we show that, contrarily to the local DM density or overall cross section scale, irreducible astrophysical uncertainties affect the two rates in a different fashion, therefore limiting our ability to reconstruct the parameters of the dark matter particle. By varying within their respective errors astrophysical parameters such as the escape velocity and the velocity dispersion of dark matter particles, we show that the uncertainty on the relative strength of the neutrino and direct-detection signal is as large as a factor of two for typical values of the parameters, but can be even larger in some circumstances.Comment: 12 pages, 3 figures. Improved presentation and Fig.3; clarifications, references and an appendix added; conclusions unchanged. Matches version published in PR

Dark Stars: A New Study of the FIrst Stars in the Universe

We have proposed that the first phase of stellar evolution in the history of the Universe may be Dark Stars (DS), powered by dark matter heating rather than by nuclear fusion. Weakly Interacting Massive Particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a Dark Star, powered by dark matter annihilation as long as there is dark matter fuel, with lifetimes from millions to billions of years. We find that the first stars are very bright ($\sim 10^6 L_\odot$) and cool ($T_{surf} < 10,000$K) during the DS phase, and grow to be very massive (500-1000 times as massive as the Sun). These results differ markedly from the standard picture in the absence of DM heating, in which the maximum mass is about 140$M_\odot$ and the temperatures are much hotter ($T_{surf} > 50,000$K); hence DS should be observationally distinct from standard Pop III stars. Once the dark matter fuel is exhausted, the DS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate black holes.Comment: article to be published in special issue on Dark Matter and Particle Physics in New Journal of Physic

(Mis-)Interpreting supernovae observations in a lumpy universe

Light from `point sources' such as supernovae is observed with a beam width of order of the sources' size - typically less than 1 AU. Such a beam probes matter and curvature distributions that are very different from coarse-grained representations in N-body simulations or perturbation theory, which are smoothed on scales much larger than 1 AU. The beam typically travels through unclustered dark matter and hydrogen with a mean density much less than the cosmic mean, and through dark matter halos and hydrogen clouds. Using N-body simulations, as well as a Press-Schechter approach, we quantify the density probability distribution as a function of beam width and show that, even for Gpc-length beams of 500 kpc diameter, most lines of sight are significantly under-dense. From this we argue that modelling the probability distribution for AU-diameter beams is absolutely critical. Standard analyses predict a huge variance for such tiny beam sizes, and nonlinear corrections appear to be non-trivial. It is not even clear whether under-dense regions lead to dimming or brightening of sources, owing to the uncertainty in modelling the expansion rate which we show is the dominant contribution. By considering different reasonable approximations which yield very different cosmologies we argue that modelling ultra-narrow beams accurately remains a critical problem for precision cosmology. This could appear as a discordance between angular diameter and luminosity distances when comparing SN observations to BAO or CMB distances.Comment: 20 pages and 6 figures. v3 is a substantially revised version, now including detailed analysis of N-body and Press-Schechter predictions which indicate that even for 1Gpc/h length beams, the mean density sampled is significantly below the cosmic mea

The Reality of Pervasive Transcription

Despite recent controversies, the evidence that the majority of the human genome is transcribed into RNA remains strong

EUSO-SPB1 mission and science

The Extreme Universe Space Observatory on a Super Pressure Balloon 1 (EUSO-SPB1) was launched in 2017 April from Wanaka, New Zealand. The plan of this mission of opportunity on a NASA super pressure balloon test flight was to circle the southern hemisphere. The primary scientific goal was to make the first observations of ultra-high-energy cosmic-ray extensive air showers (EASs) by looking down on the atmosphere with an ultraviolet (UV) fluorescence telescope from suborbital altitude (33 km). After 12 days and 4 h aloft, the flight was terminated prematurely in the Pacific Ocean. Before the flight, the instrument was tested extensively in the West Desert of Utah, USA, with UV point sources and lasers. The test results indicated that the instrument had sensitivity to EASs of ⪆ 3 EeV. Simulations of the telescope system, telescope on time, and realized flight trajectory predicted an observation of about 1 event assuming clear sky conditions. The effects of high clouds were estimated to reduce this value by approximately a factor of 2. A manual search and a machine-learning-based search did not find any EAS signals in these data. Here we review the EUSO-SPB1 instrument and flight and the EAS search

Neutrino Target-of-Opportunity Observations with Space-based and Suborbital Optical Cherenkov Detectors

Cosmic-ray accelerators capable of reaching ultra-high energies are expected to also produce very-high energy neutrinos via hadronic interactions within the source or its surrounding environment. Many of the candidate astrophysical source classes are either transient in nature or exhibit flaring activity. Using the Earth as a neutrino converter, suborbital and space-based optical Cherenkov detectors, such as EUSO-SPB2 and POEMMA, will be able to detect upward-moving extensive air showers induced by decay tau-leptons generated from cosmic tau neutrinos with energies ∼10 PeV and above. Both EUSO-SPB2 and POEMMA will be able to quickly repoint, enabling rapid response to astrophysical transient events. we calculate the transient sensitivity and sky coverage for both EUSO-SPB2 and POEMMA, accounting for constraints imposed by the Sun and the Moon on the observation time. We also calculate both detectors\u27 neutrino horizons for a variety of modeled astrophysical neutrino fluences. We find that both EUSO-SPB2 and POEMMA will achieve transient sensitivities at the level of modeled neutrino fluences for nearby sources. We conclude with a discussion of the prospects of each mission detecting at least one transient event for various modeled astrophysical neutrino sources

Neutrino Target-of-Opportunity Observations with Space-based and Suborbital Optical Cherenkov Detectors

Cosmic-ray accelerators capable of reaching ultra-high energies are expected to also produce very-high energy neutrinos via hadronic interactions within the source or its surrounding environment. Many of the candidate astrophysical source classes are either transient in nature or exhibit flaring activity. Using the Earth as a neutrino converter, suborbital and space-based optical Cherenkov detectors, such as POEMMA and EUSO-SPB2, will be able to detect upward-moving extensive air showers induced by decaying tau-leptons generated from cosmic tau neutrinos with energies ∼10 PeV and above. Both EUSO-SPB2 and POEMMA will be able to quickly repoint, enabling rapid response to astrophysical transient events. We calculate the transient sensitivity and sky coverage for both EUSO-SPB2 and POEMMA, accounting for constraints imposed by the Sun and the Moon on the observation time. We also calculate both detectors\u27 neutrino horizons for a variety of modeled astrophysical neutrino fluences. We find that both EUSO-SPB2 and POEMMA will achieve transient sensitivities at the level of modeled neutrino fluences for nearby sources. We conclude with a discussion of the prospects of each mission detecting at least one transient event for various modeled astrophysical neutrino sources

Estimation of the exposure of the TUS space-based cosmic ray observatory

The TUS observatory was the first orbital detector aimed at the detection of ultra-high energy cosmic rays (UHECRs). It was launched on April 28, 2016, from the Vostochny cosmodrome in Russia and operated until December 2017. It collected ∼80,000 events with a time resolution of 0.8~μs. A fundamental parameter to be determined for cosmic ray studies is the exposure of an experiment. This parameter is important to estimate the average expected event rate as a function of energy and to calculate the absolute flux in case of event detection. Here we present results of a study aimed to calculate the exposure that TUS accumulated during its mission. The role of clouds, detector dead time, artificial sources, storms, lightning discharges, airglow and moon phases is studied in detail. An exposure estimate with its geographical distribution is presented. We report on the applied technique and on the perspectives of this study in view of the future missions of the JEM-EUSO program

Measurement of UV light emission of the nighttime Earth by Mini-EUSO for space-based UHECR observations

The JEM-EUSO (Joint Experiment Missions for Extreme Universe Space Observatory) program aims at the realization of the ultra-high energy cosmic ray (UHECR) observation using wide field of view fluorescence detectors in orbit. Ultra-violet (UV) light emission from the atmosphere such as airglow and anthropogenic light on the Earth\u27s surface are the main background for the space-based UHECR observations. The Mini-EUSO mission has been operated on the International Space Station (ISS) since 2019 which is the first space-based experiment for the program. The Mini-EUSO instrument consists of a 25 cm refractive optics and the photo-detector module with the 2304-pixel array of the multi-anode photomultiplier tubes. On the nadir-looking window of the ISS, the instrument is capable of continuously monitoring a ~300 km x 300 km area. In the present work, we report the preliminary result of the measurement of the UV light in the nighttime Earth using the Mini-EUSO data downlinked to the ground. We mapped UV light distribution both locally and globally below the ISS obit. Simulations were also made to characterize the instrument response to diffuse background light. We discuss the impact of such light on space-based UHECR observations and the Mini-EUSO science objectives