As new concepts of sending interstellar spacecraft to the nearest stars are now being investigated by various research teams, crucial questions about the timing of such a vast financial and labor investment arise. If humanity could build high-speed interstellar lightsails and reach the alpha Centauri system 20 yr after launch, would it be better to wait a few years, then take advantage of further technology improvements to increase the speed, and arrive earlier despite waiting? The risk of being overtaken by a future, faster probe has been described earlier as the incentive trap. Based on 211 yr of historical data, we find that the speed growth of human-made vehicles, from steam-driven locomotives to Voyager 1, is much faster than previously believed, about 4.72 % annually or a doubling every 15 yr. We derive the mathematical framework to calculate the minimum of the wait time (t) plus travel time (tau(t)) and extend two exponential growth law models into the relativistic regime. We show that the minimum of t+tau(t) disappears for nearby targets. There is no use of waiting for speed improvements once we can reach an object within about 20 yr of travel, irrespective of the actual speed. In terms of speed, the t+tau(t) minimum for a travel to alpha Centauri will occur once 19.6 % the speed of light (c) become available, in agreement with the 20 % c proposed by the Breakthrough Starshot Initiative. If interstellar travel at 20 % c can be obtained within 45 yr from today and if the kinetic energy could be increased at a rate consistent with the historical record, then humans can reach the ten most nearby stars within 100 yr from today.
Read more at https://arxiv.org/pdf/1705.01481.pdf
Kevin J. Meagher on behalf of the IceCube Collaboration
The IceCube Neutrino Observatory is a cubic kilometer neutrino telescope located at the geographic South Pole. Cherenkov radiation emitted by charged secondary particles from neutrino interactions is observed by IceCube using an array of 5160 photomultiplier tubes embedded between a depth of 1.5 km to 2.5 km in the Antarctic glacial ice. The detection of astrophysical neutrinos is a primary goal of IceCube and has now been realized with the discovery of a diffuse, high-energy flux consisting of neutrino events from tens of TeV up to several PeV. Many analyses have been performed to identify the source of these neutrinos, including correlations with active galactic nuclei, gamma-ray bursts, and the Galactic plane. IceCube also conducts multi-messenger campaigns to alert other observatories of possible neutrino transients in real time. However, the source of these neutrinos remains elusive as no corresponding electromagnetic counterparts have been identified. This proceeding will give an overview of the detection principles of IceCube, the properties of the observed astrophysical neutrinos, the search for corresponding sources (including real-time searches), and plans for a next-generation neutrino detector, IceCube-Gen2.
Read more at https://arxiv.org/pdf/1705.00383.pdf
The answer to the question in the title is: in search of new physics beyond the Standard Model, for which there are many motivations, including the likely instability of the electroweak vacuum, dark matter, the origin of matter, the masses of neutrinos, the naturalness of the hierarchy of mass scales, cosmological inflation and the search for quantum gravity. So far, however, there are no clear indications about the theoretical solutions to these problems, nor the experimental strategies to resolve them. It makes sense now to prepare various projects for possible future accelerators, so as to be ready for decisions when the physics outlook becomes clearer. Paraphrasing George Harrison, “If you don’t yet know where you’re going, any road may take you there.”
Read more at https://arxiv.org/pdf/1704.02821.pdf
Joakim Edsjo, Jessica Elevant, Rikard Enberg, Carl Niblaeus
Cosmic rays hitting the solar atmosphere generate neutrinos that interact and oscillate in the Sun and oscillate on the way to Earth. These neutrinos could potentially be detected with neutrino telescopes and will be a background for searches for neutrinos from dark matter annihilation in the Sun. We calculate the flux of neutrinos from these cosmic ray interactions in the Sun and also investigate the interactions near a detector on Earth that give rise to muons. We compare this background with both regular Earth-atmospheric neutrinos and signals from dark matter annihilation in the Sun. Our calculation is performed with an event-based Monte Carlo approach that should be suitable as a simulation tool for experimental collaborations. Our program package is released publicly along with this paper.
Read more at https://arxiv.org/pdf/1704.02892.pdf
The construction of the Standard Model, which became gradually the Standard Theory of elementary particle physics, is, probably, the most remarkable achievement of modern theoretical physics. In this Chapter we shall deal mostly with the weak interactions. It may sound strange that a revolution in particle physics was initiated by the study of the weakest among them (the effects of the gravitational interactions are not measurable in high energy physics), but we shall see that the weak interactions triggered many such revolutions and we shall have the occasion to meditate on the fundamental significance of “tiny” effects. We shall outline the various steps, from the early days of the Fermi theory to the recent experimental discoveries, which confirmed all the fundamental predictions of the Theory. We shall follow a phenomenological approach, in which the introduction of every new concept is motivated by the search of a consistent theory which agrees with experiment. As we shall explain, this is only part of the story, the other part being the requirement of mathematical consistency… Read more at http://www.worldscientific.com/doi/pdf/10.1142/9789814733519_0002