120 research outputs found
QCD Rescattering and High Energy Two-Body Photodisintegration of the Deuteron
Photon absorption by a quark in one nucleon followed by its high momentum
transfer interaction with a quark in the other may produce two final-state
nucleons with high relative momentum. We sum the relevant quark rescattering
diagrams, to show that the scattering amplitude depends on a convolution
between the large angle scattering amplitude, the hard photon-quark
interaction vertex and the low-momentum deuteron wave function. The computed
absolute values of the cross section are in reasonable agreement with the data.Comment: 4 pages, revised version to be published in Phys. Rev. Let
Universal Probability-Free Conformal Prediction
We construct universal prediction systems in the spirit of Popper's
falsifiability and Kolmogorov complexity and randomness. These prediction
systems do not depend on any statistical assumptions (but under the IID
assumption they dominate, to within the usual accuracy, conformal prediction).
Our constructions give rise to a theory of algorithmic complexity and
randomness of time containing analogues of several notions and results of the
classical theory of Kolmogorov complexity and randomness.Comment: 27 page
Selected Topics in High Energy Semi-Exclusive Electro-Nuclear Reactions
We review the present status of the theory of high energy reactions with
semi-exclusive nucleon electro-production from nuclear targets. We demonstrate
how the increase of transferred energies in these reactions opens a complete
new window in studying the microscopic nuclear structure at small distances.
The simplifications in theoretical descriptions associated with the increase of
the energies are discussed. The theoretical framework for calculation of high
energy nuclear reactions based on the effective Feynman diagram rules is
described in details. The result of this approach is the generalized eikonal
approximation (GEA), which is reduced to Glauber approximation when nucleon
recoil is neglected. The method of GEA is demonstrated in the calculation of
high energy electro-disintegration of the deuteron and A=3 targets.
Subsequently we generalize the obtained formulae for A>3 nuclei. The relation
of GEA to the Glauber theory is analyzed. Then based on the GEA framework we
discuss some of the phenomena which can be studied in exclusive reactions,
these are: nuclear transparency and short-range correlations in nuclei. We
illustrate how light-cone dynamics of high-energy scattering emerge naturally
in high energy electro-nuclear reactions.Comment: LaTex file with 51 pages and 23 eps figure
Hadronic properties of the S_{11}(1535) studied by electroproduction off the deuteron
Properties of excited baryonic states are investigated in the context of
electroproduction of baryon resonances off the deuteron. In particular, the
hadronic radii and the compositeness of baryon resonances are studied for
kinematic situations in which their hadronic reinteraction is the dominant
contribution. Specifically, we study the reaction at for kinematics in which the produced hadronic state reinteracts
predominantly with the spectator nucleon. A comparison of constituent quark
model and effective chiral Lagrangian calculations of the shows
substantial sensitivity to the structure of the produced resonance.Comment: 24 pages, 5 figure
Recent observation of short range nucleon correlations in nuclei and their implications for the structure of nuclei and neutron stars
Novel processes probing the decay of nucleus after removal of a nucleon with
momentum larger than Fermi momentum by hard probes finally proved unambiguously
the evidence for long sought presence of short-range correlations (SRCs) in
nuclei. In combination with the analysis of large , A(e,e')X processes at
they allow us to conclude that (i) practically all nucleons with momenta
300 MeV/c belong to SRCs, consisting mostly of two nucleons, ii)
probability of such SRCs in medium and heavy nuclei is , iii) a fast
removal of such nucleon practically always leads to emission of correlated
nucleon with approximately opposite momentum, iv) proton removal from
two-nucleon SRCs in 90% of cases is accompanied by a removal of a neutron and
only in 10% by a removal of another proton. We explain that observed absolute
probabilities and the isospin structure of two nucleon SRCs confirm the
important role that tensor forces play in internucleon interactions. We find
also that the presence of SRCs requires modifications of the Landau Fermi
liquid approach to highly asymmetric nuclear matter and leads to a
significantly faster cooling of cold neutron stars with neutrino cooling
operational even for . The effect is even stronger for the
hyperon stars. Theoretical challenges raised by the discovered dominance of
nucleon degrees of freedom in SRCs and important role of the spontaneously
broken chiral symmetry in quantum chromodynamics (QCD) in resolving them are
considered. We also outline directions for future theoretical and experimental
studies of the physics relevant for SRCs.Comment: 74 pages. Review article, updated version to be published in
International Journal of Modern Physics
Reciprocity as a foundation of financial economics
This paper argues that the subsistence of the fundamental theorem of contemporary financial mathematics is the ethical concept ‘reciprocity’. The argument is based on identifying an equivalence between the contemporary, and ostensibly ‘value neutral’, Fundamental Theory of Asset Pricing with theories of mathematical probability that emerged in the seventeenth century in the context of the ethical assessment of commercial contracts in a framework of Aristotelian ethics. This observation, the main claim of the paper, is justified on the basis of results from the Ultimatum Game and is analysed within a framework of Pragmatic philosophy. The analysis leads to the explanatory hypothesis that markets are centres of communicative action with reciprocity as a rule of discourse. The purpose of the paper is to reorientate financial economics to emphasise the objectives of cooperation and social cohesion and to this end, we offer specific policy advice
WriteSim TCExam - An open source text simulation environment for training novice researchers in scientific writing
BACKGROUND: The ability to write clearly and effectively is of central importance to the scientific enterprise. Encouraged by the success of simulation environments in other biomedical sciences, we developed WriteSim TCExam, an open-source, Web-based, textual simulation environment for teaching effective writing techniques to novice researchers. We shortlisted and modified an existing open source application - TCExam to serve as a textual simulation environment. After testing usability internally in our team, we conducted formal field usability studies with novice researchers. These were followed by formal surveys with researchers fitting the role of administrators and users (novice researchers) RESULTS: The development process was guided by feedback from usability tests within our research team. Online surveys and formal studies, involving members of the Research on Research group and selected novice researchers, show that the application is user-friendly. Additionally it has been used to train 25 novice researchers in scientific writing to date and has generated encouraging results. CONCLUSION: WriteSim TCExam is the first Web-based, open-source textual simulation environment designed to complement traditional scientific writing instruction. While initial reviews by students and educators have been positive, a formal study is needed to measure its benefits in comparison to standard instructional methods
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