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Category: particle physics – Page 136

Physicists in Konstanz (Germany) have discovered a way to imprint a previously unseen geometrical form of chirality onto electrons. The electrons are shaped into chiral coils of mass and charge. Such engineered elementary particles may open new research avenues in fundamental physics and electron microscopy.

Have you ever placed the palm of your left hand on the back of your right hand, in such a way that all fingers point in the same direction? If you have, then you probably know that your left thumb will not touch its right counterpart. Neither rotations nor translations nor their combinations can turn a left hand into a right hand and vice versa. This feature is called chirality.

Scientists at the University of Konstanz have now succeeded to imprint such a three-dimensional chirality onto the wave function of a single electron. They used laser light to shape the electron’s matter wave into left-handed or right-handed coils of mass and charge. Such engineered elementary particles with chiral geometries other than their intrinsic spin have implications for fundamental physics but may also be useful for a range of applications, such as quantum optics, particle physics or electron microscopy.

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The Standard Model of Particle Physics encapsulates nearly everything we know about the tiny quantum-scale particles that make up our everyday world. It is a remarkable achievement, but it’s also incomplete — rife with unanswered questions. To fill the gaps in our knowledge, and discover new laws of physics beyond the Standard Model, we must study the exotic phenomena and states of matter that don’t exist in our everyday world. These include the high-energy collisions of particles and nuclei that take place in the fiery heart of stars, in cosmic ray events occurring all across earth’s upper atmosphere, and in particle accelerators like the Large Hadron Collider (LHC) at CERN or the Relativistic Heavy Ion Collider at Brookhaven National Laboratory.

Computer simulations of fundamental physics processes play an essential role in this research, but many important questions require simulations that are much too complex for even the most powerful classical supercomputers. Now that utility-scale quantum computers have demonstrated the ability to simulate quantum systems at a scale beyond exact or “brute force” classical methods, researchers are exploring how these devices might help us run simulations and answer scientific questions that are inaccessible to classical computation. In two recent papers published in PRX Quantum (PRX)1 and Physical Review D (PRD)2, our research group did just that, developing scalable techniques for simulating the real-time dynamics of quantum-scale particles using the IBM® fleet of utility-scale, superconducting quantum computers.

The techniques we’ve developed could very well serve as the building blocks for future quantum computer simulations that are completely inaccessible to both exact and even approximate classical methods — simulations that would demonstrate what we call “quantum advantage” over all known classical techniques. Our results provide clear evidence that such simulations are potentially within reach of the quantum hardware we have today.

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A new superconducting compound offers a bridge to more practicals with a potentially attractive range of applications, according to new research. And the new material’s strange magnetic behavior recalls classics of decades ago—but this time in a material that’s already demonstrated its near-room-temperature bona fides.

Lanthanum hydrides—which combine atoms of the rare earth metal lanthanum with atoms of hydrogen—contain a range of superconducting materials of varying properties. One noteworthy material is lanthanum decahydride (LaH10), which boasts the world’s highest accepted superconducting transition temperature, at −23 °C. (The catch is that to achieve this feat, lanthanum decahydride must be subjected to 200 billion pascals of pressure.)

Now a different lanthanum hydride (La4H23) has revealed similar if not quite equally impressive superconductivity stats. (Its transition temperature is −168 °C at 122 billion Pa.) However, the new lanthanum hydride also has revealingly peculiar magnetic properties that suggest an unexpected family resemblance to the superstar of the superconductivity world, cuprates.

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The Belle II experiment is a large research effort aimed at precisely measuring weak-interaction parameters, studying exotic hadrons (i.e., a class of subatomic particles) and searching for new physical phenomena. This effort primarily relies on the analysis of data collected by the Belle II detector (i.e., a general purpose spectrometer) and delivered by the SuperKEKB, a particle collider, both located at the High Energy Accelerator Research Organization (KEK) in Tsukuba, Japan.

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Life’s evolutionary timescale is typically calibrated to the oldest fossil occurrences. However, the veracity of fossil discoveries from the early Archaean period has been contested11,12. Relaxed Bayesian node-calibrated molecular clock approaches provide a means of integrating the sparse fossil and geochemical record of early life with the information provided by molecular data; however, constraining LUCA’s age is challenging due to limited prokaryote fossil calibrations and the uncertainty in their placement on the phylogeny. Molecular clock estimates of LUCA13,14,15 have relied on conserved universal single-copy marker genes within phylogenies for which LUCA represented the root. Dating the root of a tree is difficult because errors propagate from the tips to the root of the dated phylogeny and information is not available to estimate the rate of evolution for the branch incident on the root node. Therefore, we analysed genes that duplicated before LUCA with two (or more) copies in LUCA’s genome16. The root in these gene trees represents this duplication preceding LUCA, whereas LUCA is represented by two descendant nodes. Use of these universal paralogues also has the advantage that the same calibrations can be applied at least twice. After duplication, the same species divergences are represented on both sides of the gene tree17,18 and thus can be assumed to have the same age. This considerably reduces the uncertainty when genetic distance (branch length) is resolved into absolute time and rate. When a shared node is assigned a fossil calibration, such cross-bracing also serves to double the number of calibrations on the phylogeny, improving divergence time estimates. We calibrated our molecular clock analyses using 13 calibrations (see ‘Fossil calibrations’ in Supplementary Information). The calibration on the root of the tree of life is of particular importance. Some previous studies have placed a younger maximum constraint on the age of LUCA based on the assumption that life could not have survived Late Heavy Bombardment (LHB) (~3.7–3.9 billion years ago (Ga))19. However, the LHB hypothesis is extrapolated and scaled from the Moon’s impact record, the interpretation of which has been questioned in terms of the intensity, duration and even the veracity of an LHB episode20,21,22,23. Thus, the LHB hypothesis should not be considered a credible maximum constraint on the age of LUCA. We used soft-uniform bounds, with the maximum-age bound based on the time of the Moon-forming impact (4,510 million years ago (Ma) ± 10 Myr), which would have effectively sterilized Earth’s precursors, Tellus and Theia13. Our minimum bound on the age of LUCA is based on low δ98 Mo isotope values indicative of Mn oxidation compatible with oxygenic photosynthesis and, therefore, total-group Oxyphotobacteria in the Mozaan Group, Pongola Supergroup, South Africa24,25, dated minimally to 2,954 Ma ± 9 Myr (ref. 26).

Our estimates for the age of LUCA are inferred with a concatenated and a partitioned dataset, both consisting of five pre-LUCA paralogues: catalytic and non-catalytic subunits from ATP synthases, elongation factor Tu and G, signal recognition protein and signal recognition particle receptor, tyrosyl-tRNA and tryptophanyl-tRNA synthetases, and leucyl-and valyl-tRNA synthetases27. Marginal densities (commonly referred to as effective priors) fall within calibration densities (that is, user-specified priors) when topologically adjacent calibrations do not overlap temporally, but may differ when they overlap, to ensure the relative age relationships between ancestor-descendant nodes. We consider the marginal densities a reasonable interpretation of the calibration evidence given the phylogeny; we are not attempting to test the hypothesis that the fossil record is an accurate temporal archive of evolutionary history because it is not28.

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Neutrinos have a quantum mechanical property called “flavor.” This flavor can transform as neutrinos move through space. A major challenge is to keep track of both the physical movement of the neutrinos and their change of flavor in astrophysical systems such as core-collapse supernovae and neutron star mergers. The complicated arrangement and large number of neutrinos in these systems make it nearly impossible to follow all or even a subset of the neutrinos.

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You can think of our atmosphere as a big chemistry set, a global churn of gaseous molecules and particles that constantly bounce off and change each other in complicated ways. While the particles are very small, often less than 1% of the thickness of human hair, they have outsized impacts. For example, particles are the seeds of cloud droplets, and the abundance of the particles changes the reflectivity and the amount of clouds, rainfall and climate.

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However, a paper just published in Physical Review D by physicists from the University of Warsaw and the University of Oxford has shown that many of these prejudices were unfounded. Tachyons are not only not ruled out by the theory, but allow us to understand its causal structure better.

Motion at speeds beyond the of light is one of the most controversial issues in physics. Hypothetical particles that could move at superluminal speeds, called tachyons (from the Greek tachýs—fast, quick), are the “enfant terrible” of modern physics. Until recently, they were widely regarded as creations that do not fit into the .

At least three reasons for the non-existence of tachyons within were known so far. The first: the ground state of the tachyon field was supposed to be unstable, which would mean that such superluminal particles would form “avalanches.” The second: a change in the inertial observer was supposed to lead to a change in the number of particles observed in his reference system, yet the existence of, say, seven particles cannot depend on who is looking at them. The third reason: the energy of the superluminal particles could take on negative values.

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We evaluate the top-bottom interference contribution to the fully inclusive Higgs production cross section at next-to-next-to-leading order in QCD. Although bottom-quark-mass effects are power suppressed, the accuracy of state-of-the-art theory predictions makes an exact determination of this effect indispensable. The total effect of the interference at 13 TeV is −1.99_-0.15^+0.30 pb, while the pure mathcalO(alpha_s^4)$ correction is 0.43 pb. With this result, we address one of the leading theory uncertainties of the cross section.

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