Quantum theory of transition radiation and transition pair creation

Theory of the transition radiation and the transition pair creation is developed in the frame of QED. The spectral-angular distributions of probability of the transition radiation and of the transition pair creation are found. The total energy losses of and the total probability of pair creation are calculated and analyzed. Features of radiation and pair creation processes in a superdence medium (typical for white dwarfs) are discussed.Comment: LaTeX, 12 pages, 3 eps figure

Transition radiation as a source of quasi-monochromatic X-rays

Transition radiation (TR) from ultrarelativistic particles is considered. It is shown that performing collimation of the TR from the periodic N-foil stack (parameters of which are selected in a appropriate manner) one obtains the spectrum of the TR which has a form of a peak position of which $\omega_1$ depends on the plasma frequency and the thickness of the radiator foils. The height and width of the peak depend on the collimation angle $\vartheta_c$. The height of the peak for given $\vartheta_c$ is proportional to N. Selecting parameters one can have the source of X-rays of desired frequency with rather good monochromaticity.Comment: LaTeX 2.09, 12 pages, 3 eps figure

Large contribution of virtual Delbrueck scattering to the emission of photons by relativistic nuclei in nucleus-nucleus and electron-nucleus collisions

Delbrueck scattering is an elastic scattering of a photon in the Coulomb field of a nucleus via a virtual electron loop. The contribution of this virtual subprocess to the emission of a photon in the collision of ultra-relativistic nuclei Z_1 Z_2 -> Z_1 Z_2 gamma is considered. We identify the incoming virtual photon as being generated by one of the relativistic nuclei involved in the binary collision and the scattered photon as being emitted in the process. The energy and angular distributions of the photons are calculated. The discussed process has no infrared divergence. The total cross section obtained is 14 barn for Au-Au collisions at the RHIC collider and 50 barn for Pb-Pb collisions at the LHC collider. These cross sections are considerably larger than those for ordinary tree-level nuclear bremsstrahlung in the considered photon energy range m_e << E_\gamma << m_e gamma, where gamma is the Lorentz factor of the nucleus. Finally, photon emission in electron-nucleus collisions e Z -> e Z gamma is discussed in the context of the eRHIC option.Comment: 10 pages; 7 figure

Photon-Photon Luminosities in Relativistic Heavy Ion Collisions at LHC Energies

Effective photon-photon luminosities are calculated for various realistic hadron collider scenarios. The main characteristics of photon-photon processes at relativistic heavy-ion colliders are established and compared to the corresponding photon-photon luminosities at electron-positron and future Photon Linear Colliders (PLC). Higher order corrections as well as inelastic processes are discussed. It is concluded that feasible high luminosity Ca-Ca collisions at the Large Hadron Collider (LHC) are an interesting option for photon-photon physics up to about 100 GeV photon-photon CM energy.Comment: REVTeX, 13 pages, 10 figures (uuencoded,compressed postscript

Twin-photon techniques for photo-detector calibration

The aim of this review paper is to enlighten some recent progresses in quantum optical metrology in the part of quantum efficiency measurements of photo-detectors performed with bi-photon states. The intrinsic correlated nature of entangled photons from Spontaneous Parametric Down Conversion phenomenon has opened wide horizons to a new approach for the absolute measurement of photo-detector quantum efficiency, outgoing the requirement for conventional standards of optical radiation; in particular the simultaneous feature of the creation of conjugated photons led to a well known technique of coincidence measurement, deeply understood and implemented for standard uses. On the other hand, based on manipulation of entanglement developed for Quantum Information protocols implementations, a new method has been proposed for quantum efficiency measurement, exploiting polarisation entanglement in addition to energy-momentum and time ones, that is based on conditioned polarisation state manipulation. In this review, after a general discussion on absolute photo-detector calibration, we compare these different methods, in order to give an accurate operational sketch of the absolute quantum efficiency measurement state of the art

Hydrodynamic Approach to Vortex Lifetime in Trapped Bose Condensates

We study a vortex in a two-dimensional, harmonically trapped Bose-Einstein condensate at zero temperature. Through a variational calculation using a trial condensate wave function and a nonlinear Schroedinger Lagrangian, we obtain the effective potential experienced by a vortex at an arbitrary position in the condensate, and find that an off-center vortex will move in a circular trajectory around the trap center. We find the frequency of this precession to be smaller than the elementary excitation frequencies in the cloud. We also study the radiation of sound from a moving vortex in an infinite, uniform system, and discuss the validity of this as an approximation for the trapped case. Furthermore, we estimate the lifetime of a vortex due to imperfections in the trapping potential.Comment: 10 pages, 1 eps figure, submitted to PRA, adjustments in response to referee, one refernce adde

The Fourth Standard Model Family and the Competition in Standart Model Higgs Boson Search at Tevatron and LHC

The impact of the fourth Standard Model family on Higgs boson search at Tevatron and LHC is reviewed.Comment: 7 pages, 13 figure

Lepton flavor violating signals of a little Higgs model at the high energy linear e+e−e^{+}e^{-} colliders

Littlest Higgs $(LH)$ model predicts the existence of the doubly charged scalars $\Phi^{\pm\pm}$, which generally have large flavor changing couplings to leptons. We calculate the contributions of $\Phi^{\pm\pm}$ to the lepton flavor violating $(LFV)$ processes $l_{i}\to l_{j}\gamma$ and $l_{i}\to l_{j}l_{k}l_{k}$, and compare our numerical results with the current experimental upper limits on these processes. We find that some of these processes can give severe constraints on the coupling constant $Y_{ij}$ and the mass parameter $M_{\Phi}$. Taking into account the constraints on these free parameters, we further discuss the possible lepton flavor violating signals of $\Phi^{\pm\pm}$ at the high energy linear $e^{+}e^{-}$ collider $(ILC)$ experiments. Our numerical results show that the possible signals of $\Phi^{\pm\pm}$ might be detected via the subprocesses $e^{\pm}e^{\pm}\to l^{\pm}l^{\pm}$ in the future $ILC$ experiments.Comment: 16 pages, 7 figures. Discussions and references added, typos correcte

Vortex dynamics and states of artificially layered superconducting films with correlated defects

Linear resistances and $IV$-characteristics have been measured over a wide range in the parameter space of the mixed phase of multilayered a-TaGe/Ge films. Three films with varying interlayer coupling and correlated defects oriented at an angle $\approx 25$ from the film normal were investigated. Experimental data were analyzed within vortex glass models and a second order phase transition from a resistive vortex liquid to a pinned glass phase. Various vortex phases including changes from three to two dimensional behavior depending on anisotropy have been identified. Careful analysis of $IV$-characteristics in the glass phases revealed a distinctive $T$ and $H$-dependence of the glass exponent $\mu$. The vortex dynamics in the Bose-glass phase does not follow the predicted behavior for excitations of vortex kinks or loops.Comment: 16 pages, 10 figures, 3 table

Nonequilibrium relaxation in neutral BCS superconductors: Ginzburg-Landau approach with Landau damping in real time

We present a field-theoretical method to obtain consistently the equations of motion for small amplitude fluctuations of the order parameter directly in real time for a homogeneous, neutral BCS superconductor. This method allows to study the nonequilibrium relaxation of the order parameter as an initial value problem. We obtain the Ward identities and the effective actions for small phase the amplitude fluctuations to one-loop order. Focusing on the long-wavelength, low-frequency limit near the critical point, we obtain the time-dependent Ginzburg-Landau effective action to one-loop order, which is nonlocal as a consequence of Landau damping. The nonequilibrium relaxation of the phase and amplitude fluctuations is studied directly in real time. The long-wavelength phase fluctuation (Bogoliubov-Anderson-Goldstone mode) is overdamped by Landau damping and the relaxation time scale diverges at the critical point, revealing critical slowing down.Comment: 31 pages 14 figs, revised version, to appear in Phys. Rev.