New strings for old Veneziano amplitudes II. Group-theoretic treatment

In this part of our four parts work (e.g see Part I, hep-th/0410242) we use the theory of polynomial invariants of finite pseudo-reflection groups in order to reconstruct both the Veneziano and Veneziano-like (tachyon-free) amplitudes and the generating function reproducing these amplitudes. We demonstrate that such generating function can be recovered with help of the finite dimensional exactly solvable N=2 supersymmetric quantum mechanical model known earlier from works by Witten, Stone and others. Using the Lefschetz isomorphisms theorem we replace traditional supersymmetric calculations by the group-theoretic thus solving the Veneziano model exactly using standard methods of representation theory. Mathematical correctness of our arguments relies on important theorems by Shepard and Todd, Serre and Solomon proven respectively in early fifties and sixties and documented in the monograph by Bourbaki. Based on these theorems we explain why the developed formalism leaves all known results of conformal field theories unchanged. We also explain why these theorems impose stringent requirements connecting analytical properties of scattering amplitudes with symmetries of space-time in which such amplitudes act.Comment: 57 pages J.Geom.Phys.(in press, available on line

Transport Properties of the Quark-Gluon Plasma -- A Lattice QCD Perspective

Transport properties of a thermal medium determine how its conserved charge densities (for instance the electric charge, energy or momentum) evolve as a function of time and eventually relax back to their equilibrium values. Here the transport properties of the quark-gluon plasma are reviewed from a theoretical perspective. The latter play a key role in the description of heavy-ion collisions, and are an important ingredient in constraining particle production processes in the early universe. We place particular emphasis on lattice QCD calculations of conserved current correlators. These Euclidean correlators are related by an integral transform to spectral functions, whose small-frequency form determines the transport properties via Kubo formulae. The universal hydrodynamic predictions for the small-frequency pole structure of spectral functions are summarized. The viability of a quasiparticle description implies the presence of additional characteristic features in the spectral functions. These features are in stark contrast with the functional form that is found in strongly coupled plasmas via the gauge/gravity duality. A central goal is therefore to determine which of these dynamical regimes the quark-gluon plasma is qualitatively closer to as a function of temperature. We review the analysis of lattice correlators in relation to transport properties, and tentatively estimate what computational effort is required to make decisive progress in this field.Comment: 54 pages, 37 figures, review written for EPJA and APPN; one parag. added end of section 3.4, and one at the end of section 3.2.2; some Refs. added, and some other minor change

COVID-19 and thrombotic microangiopathy [COVID-19 и тромботическая микроангиопатия]

As shown by numerous studies conducted during the pandemic, the severe course of COVID-19 is accompanied by multiple organ failure. Cytokine storm, hypercoagulation, complement hyperactivation and other arms comprise the overall picture of the pathogenesis of the severe disease course. The frequent diagnosis of multiple microvascular thrombosis in lung, heart, and kidneys, as well as the presence of platelet-fibrin thrombi there and signs of terminal organ damage, suggest a possible involvement of thrombotic microangiopathy (TMA) in the development of multiple organ failure. In this regard, it is especially important to timely diagnose TMA and start pathogenetic therapy. These measures can significantly reduce mortality due to the novel disease. Heparins and direct oral anticoagulants are the mainstay for prevention and treatment of venous thromboembolism in patients with COVID-19, but their effectiveness in the presence of TMA is questionable. It has been proven that anticoagulants use in critically ill patients with COVID-19 for prevention of large vessel thrombosis is effective, but their role in the prevention of microthrombosis is not clear. Here we review the currently available information on thrombotic microangiopathy, as well as a review of literature data describing TMA-like conditions in COVID-19, discuss potential pathophysiology of the condition development and proposed therapeutic approaches. © Obstetrics, Gynecology and Reproduction 2021