Aside

Is the expansion of the universe accelerating? All signs still point to yes

David Rubin, Jessica Heitlauf
Type Ia supernovae (SNe Ia) provided the first strong evidence that the expansion of the universe is accelerating. With SN samples now more than ten times larger than those used for the original discovery and joined by other cosmological probes, this discovery is on even firmer ground. Two recent, related studies (Nielsen et al. 2016 and Colin et al. 2019, hereafter N16 and C19, respectively) have claimed to undermine the statistical significance of the SN Ia constraints. Rubin & Hayden (2016) (hereafter RH16) showed N16 made an incorrect assumption about the distributions of SN Ia light-curve parameters, while C19 also fails to remove the impact of the motion of the solar system from the SN redshifts, interpreting the resulting errors as evidence of a dipole in the deceleration parameter. Building on RH16, we outline the errors C19 makes in their treatment of the data and inference on cosmological parameters. Reproducing the C19 analysis with our proposed fixes, we find that the dipole parameters have little effect on the inferred cosmological parameters. We thus affirm the conclusion of RH16: the evidence for acceleration is secure.

Read more at https://arxiv.org/abs/1912.02191

Read also: “No Dark Energy? No Chance, Cosmologists Contend

FASER’s new detector expected to catch first collider neutrino

The first-of-its-kind detector could initiate a new era in neutrino physics at particle colliders

Illustration of the FASER experiment. The new FASERν detector, which is just 25 cm wide, 25 cm tall and 1.35 m long, will be located at the front of FASER’s main detector in a narrow trench (yellow block in the bottom right of the image). (Image: FASER/CERN)

No neutrino produced at a particle collider has ever been detected, even though colliders create them in huge numbers. This could now change with the approval of a new detector for the FASER experiment at CERN. The small and inexpensive detector, called FASERν, will be placed at the front of the FASER experiment’s main detector, and could launch a new era in neutrino physics at particle colliders.

Ever since they were first observed at a nuclear reactor in 1956, neutrinos have been detected from many sources, such as the sun, cosmic-ray interactions in the atmosphere, and the Earth, yet never at a particle collider. That’s unfortunate, because most collider neutrinos are produced at very high energies, at which neutrino interactions have not been well studied. Neutrinos produced at colliders could therefore shed new light on neutrinos, which remain the most enigmatic of the fundamental particles that make up matter.

The main reasons why collider neutrinos haven’t been detected are that, firstly, neutrinos interact very weakly with other matter and, secondly, collider detectors miss them. The highest-energy collider neutrinos, which are more likely to interact with the detector material, are mostly produced along the beamline – the line travelled by particle beams in a collider. However, typical collider detectors have holes along the beamline to let the beams through, so they can’t detect these neutrinos.

Enter FASER, which was approved earlier this year to search for light and weakly interacting particles such as dark photons – hypothetical particles that could mediate an unknown force that would link visible matter with dark matter. FASER, supported by the Heising-Simons and Simons Foundations, will be located along the beamline of the Large Hadron Collider (LHC), about 480 metres downstream of the ATLAS experiment, so it will be ideally positioned to detect neutrinos. However, the detection can’t be done with the experiment’s main detector.

“Since neutrinos interact very weakly with matter, you need a target with a lot of material in it to successfully detect them. The main FASER detector doesn’t have such a target, and is therefore unable to detect neutrinos, despite the huge number that will traverse the detector from the LHC collisions,” explains Jamie Boyd, co-spokesperson for the FASER experiment. “This is where FASERν comes in. It is made up of emulsion films and tungsten plates, and acts both as the target and the detector to see the neutrino interactions.”

FASERν is only 25 cm wide, 25 cm tall and 1.35 m long, but weighs 1.2 tonnes. Current neutrino detectors are generally much bigger, for example Super-Kamiokande, an underground neutrino detector in Japan, weighs 50 000 tonnes, and the IceCube detector in the South Pole has a volume of a cubic kilometre.

After studying FASER’s ability to detect neutrinos and doing preliminary studies using pilot detectors in 2018, the FASER collaboration estimated that FASERν could detect more than 20 000 neutrinos. These neutrinos would have a mean energy of between 600 GeV and 1 TeV, depending on the type of neutrino produced. Indeed there are three types of neutrinos – electron neutrino, muon neutrino and tau neutrino – and the collaboration expects to detect 1300 electron neutrinos, 20 000 muon neutrinos and 20 tau neutrinos.

“These neutrinos will have the highest energies yet of man-made neutrinos, and their detection and study at the LHC will be a milestone in particle physics, allowing researchers to make highly complementary measurements in neutrino physics,” says Boyd. “What’s more, FASERν may also pave the way for neutrino programmes at future colliders, and the results of these programmes could feed into discussions of proposals for much larger neutrino detectors.”

The FASERν detector will be installed before the next LHC run, which will start in 2021, and it will collect data throughout this run.

https://home.cern/news/news/physics/fasers-new-detector-expected-catch-first-collider-neutrino

Etude des effets non linéaires observés sur les oscillations d’un pendule simple

Thomas Gibaud, Alain Gibaud
In this paper we present a study of the non-linear effects of anharmonicity of the potential of the simple pendulum. In a theoretical reminder we highlight that anharmonicity of the potential generates additional harmonics and the non-isochronism of oscillations. These phenomena are all the more important as we move away from the oscillations at small angles, which represent the domain of validity of the harmonic approximation. The measurement is apprehended by means of the acquisition box SYSAM-SP5 coupled with the Latis pro software and the Eurosmart pendulum. We show that only a detailed analysis by fitting the recorded curve can provide sufficient accuracy to describe the quadratic evolution of the period as a function of the amplitude of the oscillations. We we can detect the additional harmonics in the oscillations when the amplitude becomes very high.
read more at https://arxiv.org/ftp/arxiv/papers/1911/1911.11594.pdf

Will recent advances in AI result in a paradigm shift in Astrobiology and SETI?

Time line for the evolution of life on Earth. Data from Lyon et al, 2014 and
elsewhere

Joe Gale, Amri Wandel, Hugh Hill
The steady advances in computer performance and in programming raise the concern that the ability of computers would overtake that of the human brain, an occurrence termed “the Singularity”. While comparing the size of the human brain and the advance in computer capacity, the Singularity has been estimated to occur within a few decades although the capacity of conventional computers may reach its limits in the near future. However, in the last few years, there have been rapid advances in Artificial Intelligence (AI). There are already programs that carry out pattern recognition and self-learning which, at least in limited fields such as chess and other games, are superior to the best human players. Furthermore, the quantum computing revolution, which is expected to vastly increase computer capacities, is already on our doorstep. It now seems inevitable that the Singularity will arrive within the foreseeable future. Biological life, on Earth and on extraterrestrial planets and their satellites, may continue as before, but humanity could be ‘replaced’ by computers. Older and more advanced intelligent life forms, possibly evolved elsewhere in the universe, may have passed their Singularity a long time ago. Post Singularity life would probably be based not on biochemical reactions but on electronics. Their communication may use effects such as quantum entanglement and be undetectable to us. This may explain the Fermi paradox or at least the “Big Silence” problem in SETI.
Read more at https://arxiv.org/ftp/arxiv/papers/1910/1910.03944.pdf

The Mechanism of Nuclear Fission

The potential energy associated with any arbitrary deformation of the nuclear form may be plotted as a function of the parameters which specify the deformation, thus giving a contour surface which is represented schematically in the left-hand portion of the figure.<br /> The pass or saddle point corresponds to the critical deformation of unstable equilibrium. To the extent to which we may use classical terms, the course of the fission process may be symboiized by a ball lying in the hollow at the origin of coordinates (spherical form) which receives an impulse (neutron capture) which sets it to executing a complicated Lissajous figure of oscillation about equilibrium. If its energy is sufficient, it will in the course of time happen to move in the proper direction to pass over the saddle point (after which fission will occur), unless it loses its energy (radiation or neutron re-emission). At the right is a cross section taken through the fission barrier, illustrating the calculation in the text of the probability per unit time of fission occurring.

Niels Bohr and John Archibald Wheeler
On the basis of the liquid drop model of atomic nuclei, an account is given of the mechanism of nuclear fission. In particular, conclusions are drawn regarding the variation from nucleus to nucleus of the critical energy required for fission, and regarding the dependence of fission cross section fo’r a given nucleus on energy of the exciting agency. A detailed discussion of the observations is presented on the basis of the theoretical considerations. Theory and experiment fit together in a reasonable way to give a satisfactory picture of nuclear fission.
Read more at https://journals.aps.org/pr/pdf/10.1103/PhysRev.56.426
Phys. Rev. 56, 426 – Published 1 September 1939

Nonconservation of Energy and Loss of Determinism

I. Infinitely Many Balls
David Atkinson, Porter Johnson
An infinite number of elastically colliding balls is considered in a classical, and then in a relativistic setting. Energy and momentum are not necessarily conserved globally, even though each collision does separately conserve them. This result holds in particular when the total mass of all the balls is finite, and even when the spatial extent and temporal duration of the process are also finite. Further, the process is shown to be indeterministic: there is an arbitrary parameter in the general solution that corresponds to the injection of an arbitrary amount of energy (classically), or energy-momentum (relativistically), into the system at the point of accumulation of the locations of the balls. Specific examples are given that illustrate these counter-intuitive results, including one in which all the balls move with the same velocity after every collision has taken place.
Read more at https://arxiv.org/pdf/1908.10458.pdf

II: Colliding with an Open Set
An actual infinity of colliding balls can be in a configuration in which the laws of mechanics lead to logical inconsistency. It is argued that one should therefore limit the domain of these laws to a finite, or only a potentially infinite number of elements. With this restriction indeterminism, energy non-conservation and (creatio ex nihilo) no longer occur. A numerical analysis of finite systems of colliding balls is given, and the asymptotic behavior that corresponds to the potentially infinite system is inferred.
Read more at https://arxiv.org/pdf/1908.09865.pdf