The running mass of the t-quark
1 November 2019
The Standard Model predicts that the constantsof the interaction and mass of elementary particles can be “running”, i.e., can depend on the energy. This effect, which is explained by vacuum polarization and other processes, was actually observed in experiments, in particular, the running of b- and c-quark masses, as well the running of strong interaction constants were measured. A decrease in the t-quark mass with increasing energy was demonstrated for the first time by a CMS collaboration in a LHC experiment. The reaction product distribution in pp-collisions at a center-of-mass energy of 13 TeV was analyzed. The running of t-quark mass obtained from these data up to the energy of 1 TeV is well consistent with the predictions of the renormalization group equation in quantum chromodynamicscalculations, while the statistical hypothesis about the absence of mass running is excluded with 95 % reliability.
Source: arXiv:1909.09193 [hep-ex]
Direct measurement of a nonlocal quantum entanglement
1 November 2019
In 2011, J.S. Lundeen with colleagues measured directly the complex wave function of a single photon (both of the amplitude and the phase) using so-called weak measurements, perturbing little the system because of obtaining only limited information on the quantum state. This method is however inapplicable for measuring the general wave function of two spaced systems. Such a measurement is of great interest since it would allow tracking the relation between the general wave function and a nonlocal quantum entanglement. W.-W. Pan (the University of Science and Technology of China) with co-authors performed such a measurement for the first time using the new method developed by them. Instead of the weak values obtained in weak measurements, modular values were used. This helped in measuring the wave function of two spaced hyperentangled photons. The photon trajectories were used as a measurer. For large systems, the new method of measurement may appear to be simpler than quantum tomography as it does not require numerous copies of the system.
Source: Phys. Rev. Lett. 123 150402 (2019)
Quantum dependence on the observer
1 November 2019
In 1961, Wigner considered the thought experiment “Wigner’s friend paradox” (a modified “Schrödinger’s cat” experiment) in which for different observers the results of quantum measurements in laboratory are different: one particular state is chosen or a superposition of states remains. Later, an extended version of Wigner’s experiment with two laboratories was proposed and analogues of Bell’s inequalities were formulated that may serve to verify the dependence on the observer. A. Fedrizzi (Heriot-Watt University, United Kingdom) with colleagues verified experimentally the extended version of “Wigner’s friend paradox”. Using an interferometer they measured polarizationof photons in entangled state and recorded the results of measurements in photon memory cells that played the role of observers. They showed the violation of the indicated inequalitieswith fidelity of 5σ, which confirmed the dependence on the observer in this particular statement of the problem. It is not yet clear what result would be obtained in the case of classical (not quantum) observers more complicated than the photon memory cell. For the concept of consciousness in the context of quantum mechanics see the review by M.B. Menskii in Phys. Usp. 48 389 (2005). The fundamental questions of quantum mechanics were also elucidated in the book of B.B. Kadomtsev Dynamics and Information and in his review in Phys. Usp. 37 425 (1994).
Source: Science Advances 5 eaaw9832 (2019)
Non-Abelian gauge fields in a real space
1 November 2019
Synthetic Abelian (commutative) gauge fields modeling real fields have already been realized in a number of systems including cold atoms, photons, etc. It is more difficult to generate non-Abelian fields. Their noncommutativity implies importanceof the sequence in which the field is affected. Such fields have so far been only obtained in a momentum space or in an auxiliary synthetic space. M. Soljacic (Massachusetts Institute of Technology, USA) with colleagues demonstrated for the first time synthetic non-Abelian gauge fields in an ordinary spacegenerated by classical light waves with the use of the non-Abelian Aharonov-Bohm effect. Two types of non-Abelian gauge fields were obtained with the help of the Faraday effect and light modulation, and these fieldswere shown to produce interferential patterns depending on the light propagation direction in the Sagnac interferometer. This means that the fields are actually non-Abelian. The application of non-Abelian gauge fields is expected to allow observation of topological insulators in lattices, non-Abelian monopoles in superfluid liquids and other interesting phenomena.
Source: Science 365 1021 (2019)
New population of gamma-ray sources
1 November 2019
The observations on the high-sensitivity gamma-ray telescope HAWC with a wide field-of-view revealed a new population of unidentified cosmic gamma-ray sources.Nine discovered sources have fractions of a degree as angular dimensions and are observed at energies above 56 TeV, and the spectrum of three of them extends to energies exceeding 100 TeV. Eight sources are projected onto the Galactic disc, and therefore are probably Galactic in origin. At an angular distance of less than 0.5° from each source, young pulsars exist, and this coincidence may appear to be not accidental. Models of gamma-ray halo around pulsars were discussed, but the sizes of these halos must be much smaller than the observed distances between the sources and pulsars. It is not excluded that the gamma-ray emission from the new sources is generated in extended remnants that remained after supernova explosions in which pulsars had been born.
Source: arXiv:1909.08609 [astro-ph.HE]
The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.
Permanent editor is Yu.N. Eroshenko.
It is compiled from a multitude of Internet sources.