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| Issue 12, 2024 |
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Extracts from the Internet | ||
Search for dark photons and dark Higgs bosons1 July 2015Belle Collaboration implemented search for hypothetic massive dark photons A' and Higgs dark bosons h' on KEK B accelerator in Japan. These particles were proposed as an extension of the Standard model, and A' can be carriers of the interaction between dark matter particles. If A' and h' decay immediately after production, they can in principle be registered by the products of decay into ordinary particles. The authors investigated possible e+e- → A'h', h' → A'A' channels with subsequent decays. All the data collected during the work of Belle were used in the analysis, but no statistically significant signal was detected above the background level. This negative result imposes restriction from above on the probability of A' and h' production and on the strength of the interaction of these particles with the ordinary particles of the Standard model. The restrictions obtained by Belle are more rigid than those obtained earlier in other experiments and cover wider ranges of A' and h' particle masses. Source: Phys. Rev. Lett. 114 211801 (2015) Delayed-choice experiment for the atom1 July 2015In 1978, J. Wheeler suggested the idea of a quantum interference experiment in which the decision to carry out measurements comes already after a particle has passed through the interferometer slits. This method excludes the possibility for the information on measurement to be somehow transferred to the particle before its passage. An experiment of this type was performed with photons in 2007 (see Phys. Usp. 50 329 (2007)). A.G. Truscott (Australian National University) and his colleagues were the first to conduct an analogous experiment with single atoms. Helium atoms fell one by one from an optical dipole trap filled with an ultracold gas and were exposed to laser pulses. The first two pulses changed the phase by π and π/2 playing the role of a mirror and a splitter in an analogous experiment with photons and brought the atom to a state of superposition of two motions in opposite directions. The third π/2 pulse emitted on the signal of a random-number quantum generator could induce interference of these states. In each experimental cycle, the interference for about 1000 atoms was examined. With a third pulse a clear interference pattern was observed. In this case the detection probability versus the phase difference of two atomic states had the form of a sinusoid. And in the absence of a third pulse no interference occurred. This experiment, the same as the delayed-choice experiment for photons confirmed the prediction of quantum mechanics and excluded the possibility of hidden parameter transfer to the atom before measurement. Source: Nature Physics 11 539 (2015) Volume-varying magnetostriction1 July 2015In 1842, J. Joule discovered the effect called “Joulian magnetostriction” consisting in the fact that upon switching on the external magnetic field magnetoactive substances are deformed anisotropically without changing their volume. This rule was met for all the substances studied till now. It is most often explained by the behavior of magnetic domains in a magnetic field. However, H.D. Chopra (Temple University, USA) and M. Wuttig (University of Maryland, USA) revealed for the first time that along with anisotropic deformation upon the magnetic field strengthening the iron-gallium alloy changes its volume expanding simultaneously in all directions. This unusual behavior was referred to as “non-Joulian magnetostriction”. H.D. Chopra and M. Wuttig investigated the magnetic structure of Fe-Ga samples by the fringe contrast method by depositing colloidal composition onto their surface. The magnetic structure turned out to have the form of a periodic two-dimensional body of microcells several µm in size. These microcells which have never been observed earlier are formed after sample quenching – its heating and then fast cooling. According to the authors, their occurrence is most likely due to charge waves. Source: Nature 521 340 (2015) Abraham force in a liquid1 July 2015H. Minkowski in 1908 and M. Abraham in 1909 proposed theories describing the interaction of light with a transparent medium (see, e.g., the review by V.L. Ginzburg and V.A. Ugarov in Sov. Phys. Usp. 19 94 (1976)). If light enters a liquid from the air, then according to Minkowski it affects the liquid with a force opposite to the beam direction, whereas the Abraham theory predicts the inverse direction of the force. In the former case, the surface of the liquid becomes convex and in the latter case concave. The shape of the surfaces was actually examined in a number of experiments to show agreement with the Minkowski theory. However, U. Leonhardt (Weizmann Institute in Rehovot, Israel) and his colleagues from Sun Yat-sen University in Guangzhou (China) performed a new experiment confirming the validity of the Abraham theory. Concavity of the surface was demonstrated for water and mineral oil. It was found that essential is the beam width and the depth of the liquid-filled vessel. If these are large enough, then the liquid, when affected by light, begins moving and a stationary vortex flow sets in with time. In the neighborhood of the beam inlet into the liquid the surface becomes concave and the effect of light on the liquid is described by the Abraham theory. And when U. Leonhardt with colleagues used a narrower focused beam in their experiment, no stationary motion of the liquid was observed and a convexity occurred on the surface, i.e., Minkowski’s theory held true. Source: New J. Phys. 17 053035 (2015) Measurement of ray velocities of a gravitational microlens1 July 2015Microlensing is an effect of star brightness amplification due to the gravitational focusing of their light by a star or another object passing through the line of sight. In 2012, a star from the galactic bulge was lensed, the lens being a binary system, OGLE-2011-BLG-0417, which is at a distance of ≈ 1 kpc from us. Using spectrograph of the VLT telescope at the European Southern Observatory I. Boisse (Aix-Marseille University, France) with colleagues measured with high accuracy the radial velocity of the bright star in the binary system OGLE-2011-BLG-0417 and compared the data obtained with the theoretical predictions. It turned out that the results of measurements at a level of 3.7 σ do not agree with the calculations: instead of increase with time (due to the orbital motion of the pair) the line-of-sight velocity was nearly constant. This difference can be explained by the fact that the main lens could be not the OGLE-2011-BLG-0417 system but the neighboring star which is occasionally located in the vicinity of the line of sight or rotates round the pair along a wide orbit. Source: arXiv:1506.02019 [astro-ph.EP] |
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. | |
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