423 research outputs found
A chromomagnetic mechanism for the X(3872) resonance
The chromomagnetic interaction, with proper account for flavour-symmetry
breaking, is shown to explain the mass and coupling properties of the X(3872)
resonance as a = 1 state consisting of a heavy quark-antiquark
pair and a light one. It is crucial to introduce all the spin-colour
configurations compatible with these quantum numbers and diagonalise the
chromomagnetic interaction in this basis. This approach thus differs from the
molecular picture and from the diquark-antidiquark picture.Comment: 4 pages - revtex4 - Typos corrected, refs. added, to be published in
Phys. Rev.
Facing the Spectator
We investigated the familiar phenomenon of the uncanny feeling that represented people in frontal pose invariably appear to ââface youââ from wherever you stand. We deploy two different methods. The stimuli include the conventional oneâa flat portrait rocking back and forth about a vertical axisâaugmented with two novel variations. In one alternative, the portrait frame rotates whereas the actual portrait stays motionless and fronto-parallel; in the other, we replace the (flat!) portrait with a volumetric object. These variations yield exactly the same optical stimulation in frontal view, but become grossly different in very oblique views. We also let participants sample their momentary awareness through ââgauge objectââ settings in static displays. From our results, we conclude that the psychogenesis of visual awareness maintains a numberâat least two, but most likely moreâof distinct spatial frameworks simultaneously involving ââcueâscission.ââ Cues may be effective in one of these spatial frameworks but ineffective or functionally different in other ones
The Single Photon Annihilation Contributions to the Positronium Hyperfine Splitting to Order
The single photon annihilation contributions for the positronium ground state
hyperfine splitting are calculated analytically to order using
NRQED. Based on intuitive physical arguments the same result can also be
determined by a trivial calculation using results from existing literature. Our
result completes the hyperfine splitting calculation to order . We
compare the theoretical prediction with the most recent experimental
measurement.Comment: 8 pages, latex, two eps figures include
Top Quark Pair Production at Threshold: Complete Next-to-next-to-leading Order Relativistic Corrections
The complete next-to-next-to-leading order (i.e. ,
and ) relativistic corrections to the total photon mediated
production cross section at threshold are presented in the framework
of nonrelativistic quantum chromodynamics. The results are obtained using
semi-analytic methods and ``direct matching''. The size of the
next-to-next-to-leading order relativistic corrections is found to be
comparable to the size of the next-to-leading order ones.Comment: 9 pages, latex, two postscript figures include
View From Outside the Viewing Sphere
The âviewing sphereâ, as defined by Euclid and explored by Gibson as the âoptic arrayâ, is generally thought of as wrapped around the eye. Can an observer step out of it? With currently popular photographic techniques, the spectator is forced to, because the viewing sphere is presented as a pictorial object. Then the question is whether human observers are able to use such pictorial representations in an intuitive manner. Can the spectator âmentally step into the interiorâ of the pictorial viewing sphere? We explore this issue in a short experiment. Perhaps unsurprisingly, because the eye cannot see itself, the short answer is no
The roots of "Western European societal evolution". A concept of Europe by JenĆ SzƱcs
JenĆ SzƱcs wrote his essay entitled Sketch on the three regions of Europe in the early 1980s in Hungary. During these years, a historically well-argued opinion emphasising a substantial difference between Central European and Eastern European societies was warmly received in various circles of the political opposition. In a wider European perspective SzƱcs used the old âliberty toposâ which claims that the history of Europe is no other than the fulfillment of liberty. In his Sketch, SzƱcs does not only concentrate on questions concerning the Middle Ages in Western Europe. Yet it is this stream of thought which brought a new perspective to explaining European history. His picture of the Middle Ages represents well that there is a way to integrate all typical Western motifs of post-war self-definition into a single theory. Mainly, the âliberty motifâ, as a sign of âEuropeanismâ â in the interpretation of BibĂłâs concept, Anglo-saxon Marxists and Weberâs social theory â, developed from medieval concepts of state and society and from an analysis of economic and social structures. SzƱcsâs historical aspect was a typical intellectual product of the 1980s: this was the time when a few Central European historians started to outline non-Marxist aspects of social theory and categories of modernisation theories, but concealing them with Marxist terminology
Local biases drive, but do not determine, the perception of illusory trajectories
When a dot moves horizontally across a set of tilted lines of alternating orientations, the dot appears to be moving up and down along its trajectory. This perceptual phenomenon, known as the slalom illusion, reveals a mismatch between the veridical motion signals and the subjective percept of the motion trajectory, which has not been comprehensively explained. In the present study, we investigated the empirical boundaries of the slalom illusion using psychophysical methods. The phenomenon was found to occur both under conditions of smooth pursuit eye movements and constant fixation, and to be consistently amplified by intermittently occluding the dot trajectory. When the motion direction of the dot was not constant, however, the stimulus display did not elicit the expected illusory percept. These findings confirm that a local bias towards perpendicularity at the intersection points between the dot trajectory and the tilted lines cause the illusion, but also highlight that higher-level cortical processes are involved in interpreting and amplifying the biased local motion signals into a global illusion of trajectory perception
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