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We revise the π + π − and qq annihilation mechanisms of dilepton production during relativistic heavy-ion collisions. We focus on the modifications caused by the specific features of intramedium pion states rather than by medium modification of the ρ-meson spectral density. The main ingredient emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, "connects" the 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the dilepton production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant mass below two masses of the annihilating particles.Since leptons do not interact practically with the highly excited nuclear matter, they leave the reaction zone after their creation in a relativistic nucleus-nucleus collision without further rescattering. That is why, the dileptons (e + e − and µ + µ − pairs) observed in high-energy heavy ion collisions secure an excellent opportunity for obtaining information on the initial state and the evolution of the system created in a collision. The enhancement with an invariant mass of 200 ÷ 800 MeV observed by the CERES collaboration [1,2] in the production of dileptons has received recently a considerable attention and has been studied in the framework of various theoretical models (for the review, see Ref.[3]). It was found that a large part of the observed enhancement is due to the medium effects (see Refs. [4,5] and references therein). Meanwhile, pion annihilation is the main source of dileptons which come from the hadron matter [6,7]. That is why, the proper analysis of the dilepton spectra obtained experimentally gives important observables which probe the pion dynamics in the dense nuclear matter that exists at the early stage of the collision. The purpose of the present letter is to look once more on the π + π − annihilation mechanism of dilepton production from the hadron plasma by accounting the medium-induced modifications of the dilepton spectrum. In order to do this, we concentrate on the modifications which are due rather to intramedium pion states, than on the discussion of a modification of the ρ-meson spectral density. In accordance with our suggestions, the main features of a pion wave function follow from the fact that pions live a finite time in the *

It is shown that subcritical phase-separation nuclei (domains of decomposition) arising spontaneously in a supersaturated He3–He4 mixture can become centers of hydrodynamic vortex generation in the presence of a local nonzero or global vorticity of the liquid. The acceleration of the “rigid-body” vortex rotation of an incompressible fluid within a domain is due to the joint action of convective and Coriolis forces in the presence of a convergent radial flow whose velocity is linked by the continuity equation to the velocity of an ascending vertical flow, which increases with height. Such flows, which arise on account of the chemical and dynamical equilibrium between the domains of decomposition and the surrounding metastable He3–He4 mixture, compensate the escape of the light He3 component from the volume of the domain to the surface of the liquid on account of its buoyancy in the Earth’s gravity. Depending on the conditions of the decomposition of the solution inside the domains, acceleration of the vortices can occur according to an exponential law or by a scenario of nonlinear “explosive” instability. The formation and growth of such hydrodynamic vortices in decomposing He3–He4 mixtures gives rise to quantum vortices in the superfluid component and, as a consequence, leads to acceleration of the process of heterogeneous decomposition (phase separation) in comparison with homogeneous decomposition.

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It is shown that unstable hydrodynamic vortices can form inside subcritical domains in the normal component of a supersaturated decomposing He3–4He solution. A mechanism for the entrainment of the superfluid component by the normal component of the He3–4He solution into “rigid-body” rotation due to Hall–Vinen–Bekarevich–Khalatnikov forces in the equations of two-fluid hydrodynamics, which leads to the creation of quantized vortices, is considered. An increase of the average density of quantized vortices can increase the rate of heterogeneous decomposition of the He3–4He solution.