Relativistic effects in the production of pseudoscalar and vector doubly heavy mesons from e^+e^- annihilation

On the basis of the perturbative QCD and the relativistic quark model we investigate the relativistic and bound state effects in the production processes of a pair of $S$-wave doubly heavy mesons with opposite charge conjugation consisting of $b$ and $c$ quarks. All possible relativistic corrections in the production amplitude including the terms connected with the transformation law of the bound state wave function to the reference frame of the moving pseudoscalar ${\cal P}-$ and vector ${\cal V}-$ mesons are taken into account. We obtain a growth of the cross section for the reaction $e^++e^-\to J/\Psi+ \eta_c$ due to considered effects by a factor $2\div 2.5$ in the range of the center-of-mass energy $\sqrt{s}=6\div 12$ GeV.Comment: 18 pages, 4 figure

Pion condensation in quark matter with finite baryon density

The phase structure of the Nambu -- Jona-Lasinio model at zero temperature and in the presence of baryon- and isospin chemical potentials is investigated. It is shown that in the chiral limit and for a wide range of model parameters there exist two different phases with pion condensation. In the first, ordinary phase, quarks are gapped particles. In the second, gapless pion condensation phase, there is no energy cost for creating only $u$- or both $u$ and $d$ quarks, and the density of baryons is nonzero.Comment: 7 pages, 6 figures; two references adde

Spontaneous Branching of Anode-Directed Streamers between Planar Electrodes

Non-ionized media subject to strong fields can become locally ionized by penetration of finger-shaped streamers. We study negative streamers between planar electrodes in a simple deterministic continuum approximation. We observe that for sufficiently large fields, the streamer tip can split. This happens close to Firsov's limit of `ideal conductivity'. Qualitatively the tip splitting is due to a Laplacian instability quite like in viscous fingering. For future quantitative analytical progress, our stability analysis of planar fronts identifies the screening length as a regularization mechanism.Comment: 4 pages, 6 figures, submitted to PRL on Nov. 16, 2001, revised version of March 10, 200

Dynamical Symmetry Breaking in Models with the Yukawa Interaction

We discuss models with a massless fermion and a self-interacting massive scalar field with the Yukawa interaction. The chiral condensate and the fermion mass are calculated analytically. It is shown that the models have a phase transition as a function of the squared mass of the scalar field.Comment: 7 pages, no figures, in Eqs. (7) and (11) one coefficient was change

Chiral phase transitions in strong chromomagnetic fields at finite temperature and dimensional reduction

Dynamical fermion mass generation in external chromomagnetic fields is considered at non--zero temperature. The general features of dynamical chiral symmetry breaking ($D\chi SB$) are investigated for several field configurations in relation to their symmetry properties and the form of the quark spectrum. According to the fields, there arises dimensional reduction by one or two units. In all cases there exists $D\chi SB$ even at weak quark attraction, confirming the idea about the dimensional insensitivity of this mechanism in a chromomagnetic field.Comment: LATEX file, 12 pages, no figure

A Heavy-Light Chiral Quark Model

We present a new chiral quark model for mesons involving a heavy and a light (anti-) quark. The model relates various combinations of a quark - meson coupling constant and loop integrals to physical quantities. Then, some quantities may be predicted and some used as input. The extension from other similar models is that the present model includes the lowest order gluon condensate of the order (300 MeV)^4 determined by the mass splitting of the 0^- and the 1^- heavy meson states. Within the model, we find a reasonable description of parameters such as the decay constants f_B and f_D, the Isgur-Wise function and the axial vector coupling g_A in chiral perturbation theory for light and heavy mesons.Comment: 31 pages, 13 figures, RevTex4.

Chromomagnetic Catalysis of Color Superconductivity in a (2+1)-dimensional NJL Model

The influence of a constant uniform external chromomagnetic field $H$ on the formation of color superconductivity has been investigated. The consideration was performed in the framework of a (2+1)-dimensional Nambu--Jona-Lasinio model with two different four-fermionic structures responsible for $$and diquark$$ condensates. In particular, it was shown that there exists a critical value $H_c$ of the external chromomagnetic field such that at $H>H_c$ a nonvanishing diquark condensate is dynamically created (the so-called chromomagnetic catalysis effect of color superconductivity). Moreover, external chromomagnetic fields may in some cases enhance the diquark condensate of color superconductivity.Comment: 32 pages, 2 figures, revte

Theory of superfast fronts of impact ionization in semiconductor structures

We present an analytical theory for impact ionization fronts in reversely biased p^{+}-n-n^{+} structures. The front propagates into a depleted n base with a velocity that exceeds the saturated drift velocity. The front passage generates a dense electron-hole plasma and in this way switches the structure from low to high conductivity. For a planar front we determine the concentration of the generated plasma, the maximum electric field, the front width and the voltage over the n base as functions of front velocity and doping of the n base. Theory takes into account that drift velocities and impact ionization coefficients differ between electrons and holes, and it makes quantitative predictions for any semiconductor material possible.Comment: 18 pagers, 10 figure

D₂ Dopamine Receptors Colocalize Regulator of G-Protein Signaling 9-2 (RGS9-2) via the RGS9 DEP Domain, and RGS9 Knock-Out Mice Develop Dyskinesias Associated with Dopamine Pathways

Regulator of G-protein signaling 9-2 (RGS9-2), a member of the RGS family of Gα GTPase accelerating proteins, is expressed specifically in the striatum, which participates in antipsychotic-induced tardive dyskinesia and in levodopa-induced dyskinesia. We report that RGS9 knock-out mice develop abnormal involuntary movements when inhibition of dopaminergic transmission is followed by activation of D₂-like dopamine receptors (DRs). These abnormal movements resemble drug-induced dyskinesia more closely than other rodent models. Recordings from striatal neurons of these mice establish that activation of D₂-like DRs abnormally inhibits glutamate-elicited currents. We show that RGS9-2, via its DEP domain (for Disheveled, EGL-10, Pleckstrin homology), colocalizes with D₂DRs when coexpressed in mammalian cells. Recordings from oocytes coexpressing D₂DR or the m2 muscarinic receptor and G-protein-gated inward rectifier potassium channels show that RGS9-2, via its DEP domain, preferentially accelerates the termination of D₂DR signals. Thus, alterations in RGS9-2 may be a key factor in the pathway leading from D₂DRs to the side effects associated with the treatment both of psychoses and Parkinson's disease

The Universal Gaussian in Soliton Tails

We show that in a large class of equations, solitons formed from generic initial conditions do not have infinitely long exponential tails, but are truncated by a region of Gaussian decay. This phenomenon makes it possible to treat solitons as localized, individual objects. For the case of the KdV equation, we show how the Gaussian decay emerges in the inverse scattering formalism.Comment: 4 pages, 2 figures, revtex with eps