Coupled fermion and boson production in a strong background mean-field

We derive quantum kinetic equations for fermion and boson production starting from a phi^4 Lagrangian with minimal coupling to fermions. Decomposing the scalar field into a mean-field part and fluctuations we obtain spontaneous pair creation driven by a self-interacting strong background field. The produced fermion and boson pairs are self-consistently coupled. Consequently back reactions arise from fermion and boson currents determining the time dependent self-interacting background mean-field. We explore the numerical solution in flux tube geometry for the time evolution of the mean-field as well as for the number- and energy densities for fermions and bosons. We find that after a characteristic time all energy is converted from the background mean-field to particle creation. Applying this general approach to the production of ``quarks'' and ``gluons'' a typical time scale for the collapse of the flux tube is 1.5 fm/c.Comment: 9 pages, latex, epsfig, 7 figure

Mid-mantle deformation inferred from seismic anisotropy

With time, convective processes in the Earth's mantle will tend to align crystals, grains and inclusions. This mantle fabric is detectable seismologically, as it produces an anisotropy in material properties—in particular, a directional dependence in seismic-wave velocity. This alignment is enhanced at the boundaries of the mantle where there are rapid changes in the direction and magnitude of mantle flow, and therefore most observations of anisotropy are confined to the uppermost mantle or lithosphere and the lowermost-mantle analogue of the lithosphere, the D" region. Here we present evidence from shear-wave splitting measurements for mid-mantle anisotropy in the vicinity of the 660-km discontinuity, the boundary between the upper and lower mantle. Deep-focus earthquakes in the Tonga–Kermadec and New Hebrides subduction zones recorded at Australian seismograph stations record some of the largest values of shear-wave splitting hitherto reported. The results suggest that, at least locally, there may exist a mid-mantle boundary layer, which could indicate the impediment of flow between the upper and lower mantle in this region

Pair Creation and an X-ray Free Electron Laser

Using a quantum kinetic equation coupled to Maxwell's equation we study the possibility that focused beams at proposed X-ray free electron laser facilities can generate electric field strengths large enough to cause spontaneous electron-positron pair production from the QED vacuum. Our approach yields the time and momentum dependence of the single particle distribution function. Under conditions reckoned achievable at planned facilities, repeated cycles of particle creation and annihilation take place in tune with the laser frequency. However, the peak particle number density is insensitive to this frequency and one can anticipate the production of a few hundred particle pairs per laser period. Field-current feedback and quantum statistical effects are small and can be neglected in this application of non-equilibrium quantum mean field theory.Comment: 4 pages, LaTeX2

Momentum Spectra for Dynamically Assisted Schwinger Pair Production

Recently the dynamically assisted Schwinger mechanism, i.e., electron-positron pair production from vacuum by a combination of laser pulses with different time scales has been proposed. The corresponding results, which suggest that the rate of produced pairs is significantly enhanced by dynamical effects, are verified. Employing the framework of quantum kinetic theory intrinsically enables us to additionally provide momentum space information on the generated positron spectrum.Comment: 6 pages, 7 figure

Collective Deceleration of Ultrarelativistic Nuclei and Creation of Quark-Gluon Plasma

We propose a unified space-time picture of baryon stopping and quark-gluon plasma creation in ultrarelativistic heavy-ion collisions. It is assumed that the highly Lorentz contracted nuclei are decelerated by the coherent color field which is formed between them after they pass through each other. This process continues until the field is neutralized by the Schwinger mechanism. Conservation of energy and momentum allow us to calculate the energy losses of the nuclear slabs and the initial energy density of the quark-gluon plasma.Comment: 11 pages in revtex, 2 eps figure

A kinetic approach to eta' production from a CP-odd phase

The production of (eta,eta')- mesons during the decay of a CP-odd phase is studied within an evolution operator approach. We derive a quantum kinetic equation starting from the Witten-DiVecchia-Veneziano Lagrangian for pseudoscalar mesons containing a U_A(1) symmetry breaking term. The non-linear vacuum mean field for the flavour singlet pseudoscalar meson is treated as a classical, self-interacting background field with fluctuations assumed to be small. The numerical solution provides the time evolution of momentum distribution function of produced eta'- mesons after a quench at the deconfinement phase transition. We show that the time evolution of the momentum distribution of the produced mesons depend strongly on the shape of the effective potential at the end of the quench, exhibiting either parametric or tachyonic resonances. Quantum statistical effects are essential and lead to a pronounced Bose enhancement of the low momentum states.Comment: 10 pages, latex, epsfig, 6 figure

Pair creation: back-reactions and damping

We solve the quantum Vlasov equation for fermions and bosons, incorporating spontaneous pair creation in the presence of back-reactions and collisions. Pair creation is initiated by an external impulse field and the source term is non-Markovian. A simultaneous solution of Maxwell's equation in the presence of feedback yields an internal current and electric field that exhibit plasma oscillations with a period tau_pl. Allowing for collisions, these oscillations are damped on a time-scale, tau_r, determined by the collision frequency. Plasma oscillations cannot affect the early stages of the formation of a quark-gluon plasma unless tau_r >> tau_pl and tau_pl approx. 1/Lambda_QCD approx 1 fm/c.Comment: 16 pages, 6 figure, REVTEX, epsfig.st

Sub-lattice of Jahn-Teller centers in hexaferrite crystal

A novel type of sub-lattice of the Jahn-Teller (JT) centers was arranged in Ti-doped barium hexaferrite BaFe12O19. In the un-doped crystal all iron ions, sitting in five different crystallographic positions, are Fe3+ in the high-spin configuration (S = 5/2) and have a non-degenerate ground state. We show that the electron-donor Ti substitution converts the ions to Fe2+ predominantly in tetrahedral coordination, resulting in doubly-degenerate states subject to the E⊗ e problem of the JT effect. The arranged JT complexes, Fe2+O4, their adiabatic potential energy, non-linear and quantum dynamics, have been studied by means of ultrasound and terahertz-infrared spectroscopies. The JT complexes are sensitive to external stress and applied magnetic field. For that reason, the properties of the doped crystal can be controlled by the amount and state of the JT complexes. © 2020, The Author(s).Deutscher Akademischer Austauschdienst, DAADRussian Foundation for Basic Research, RFBR: 18–02–00332 aDeutscher Akademischer Austauschdienst, DAAD: 91728513Ministry of Education and Science of the Russian Federation, Minobrnauka: 19–53–0401019–72–00055Ministry of Education and Science of the Russian Federation, MinobrnaukaThe authors acknowledge fruitful discussions with A.S. Prokhorov. We acknowledge support of the HLD at HZDR, member of the European Magnetic Field Laboratory (EMFL). At Ural Federal University, the research was supported by the Russian Foundation for Basic Research (18–02–00332 a), UrFU Center of Excellence “Radiation and Nuclear Technologies” (Competitiveness Enhancement Program), the Ministry of Education and Science of the Russian Federation (Program 5–100). In M.N. Miheev Institute of Metal Physics, the research was carried out within the state assignment of the Ministry of Education and Science of the Russian Federation (theme “Electron” No. AAAA-A18–118020190098–5. At South Ural State University, the authors were generally supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0011. The single crystal growth part was supported by Russian Foundation for Basic Research (19–53–04010). At Moscow Institute of Physics and Technology, the work was supported by the Russian Ministry of Education and Science (Program 5–100) and by the German Academic Exchange Service (DAAD) Michael Lomonosov Programm Linie B, 91728513. Time-domain low temperature spectroscopic experiments were financially supported by the Russian Scientific Foundation (19–72–00055)