Annihilation Effects Research Articles

Study of virtual annihilation and retardation effects in relativistic two-, four-, and six-body wave equations in scalar QFT

The variational method within the Hamiltonian formalism of QFT using Darewych reformulated model has been used for scalar particles and antiparticles interacting through a scalar mediating field. We have investigated the relativistic effects such as virtual annihilation interactions and retardation effects for relativistic two-, four-, and six-body wave equations in scalar QFT. Approximate ground-state solutions have been studied for different strengths of coupling, for both massive and massless mediating fields where the virtual annihilation terms or retardation effects in the wave equations have been included or eliminated.

Ga-doped ZnO films by magnetron sputtering at ultralow discharge voltages: Effects of defect annihilation

Preparation of high quality transparent conductive oxide (TCO) films by sputter deposition involves an intricate balance of defect generation by the highly energetic negative oxygen ions (depending on the discharge voltage) and the concomitant annihilation of these defects during film growth. Ga-doped ZnO films with a low Ga content (1.7at.%) were deposited to investigate the effects of defect annihilation on the microstructure evolutions as well as the optical and electrical properties. To achieve this aim, we prepared the GZO films by magnetron sputtering at ultralow discharge voltages (~70V) to minimize the defect generation, and varied the substrate temperature (from 130°C to 380°C) to adjust the annihilation rates. The microstructure was systematically characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Raman Spectroscopy. The electrical and optical properties were obtained by a Hall-effect measurement system and Spectroscopic Ellipsometry (SE), respectively. It was found that (i) even under the condition of highly controlled defect generation from the bombardment of negative oxygen ions, a sufficient annihilation of the defects cannot be realized without externally heating the substrate; and (ii) there existed a threshold temperature, above which both the structural quality and the electrical properties were improved with the increased temperature over the temperature range we examined. These results reveal that the growth temperature during the GZO film deposition has played an important role in effective annihilation of the irradiation-induced structural defects, which may be due to the higher diffusion barrier of Ga atoms in our GZO films.

Analysis of Effect of Singlet-Triplet Annihilation in a Low-Threshold Optically Pumped Organic Semiconductor Laser

We investigate the impact of optical excitation in a low-threshold organic semiconductor vertical-cavity surface-emitting laser (OVCSEL) to achieve lasing. We study the threshold behavior and the dynamics of the optimized OVCSEL structure when pumped by both picosecond and nanosecond pulses. The boundary between pulsed and continuous wave lasing is analyzed for the study of annihilation quenching losses in the proposed OVCSEL. Results from numerical simulation show that, for the picosecond pulses excitation case, the singlet–triplet annihilation is not effective and a lasing threshold of about 0.75 μJ cm−2 can be obtained. We show that for the nanosecond pulses pumping case, triplet excitons largely quench singlet excitons and lasing is sustained for a short time following turn-on of the pump.

Magnetic annihilation of the dark mode in a strongly coupled bright-dark terahertz metamaterial.

Dark mode in metamaterials has become a vital component in determining the merit of the Fano type of interference in the system. Its strength dictates the enhancement and suppression in the amplitude and Q-factors of resulting resonance features. In this work, we experimentally probe the effect of strong near-field coupling on the strength of the dark mode in a concentrically aligned bright resonator and a dark split ring resonator (SRR) system exhibiting the classical analog of the electromagnetically induced transparency effect. An enhanced strong magnetic field between the bright-dark resonators destructively interferes with the inherent magnetic field of the dark mode to completely annihilate its effect in the coupled system. Moreover, the observed annihilation effect in the dark mode has a direct consequence on the disappearance of the SRR effect in the proposed system, wherein under the strong magnetic interactions, the LC resonance feature of the split ring resonator becomes invisible to the incident terahertz wave.

Erratum to: Radiative Processes in Graphene and similar Nanostructures in Strong Electric Fields

Low-energy single-electron dynamics in graphene monolayers and similar nanostructures is described by the Dirac model, being a 2+1 dimensional version of massless QED with the speed of light replaced by the Fermi velocity v_{F}=c/300. Methods of strong-field QFT are relevant for the Dirac model, since any low-frequency electric field requires a nonperturbative treatment of massless carriers in case it remains unchanged for a sufficiently long time interval. In this case, the effects of creation and annihilation of electron-hole pairs produced from vacuum by a slowly varying and small-gradient electric field are relevant, thereby substantially affecting the radiation pattern. For this reason, the standard QED text-book theory of photon emission cannot be of help. We construct the Fock-space representation of the Dirac model, which takes exact accounts of the effects of vacuum instability caused by external electric fields, and in which the interaction between electrons and photons is taken into account perturbatively, following the general theory (the generalized Furry representation). We consider the effective theory of photon emission in the first-order approximation and construct the corresponding total probabilities, taking into account the unitarity relation.

Radiative Processes in Graphene and Similar Nanostructures in Strong Electric Fields

Low-energy single-electron dynamics in graphene monolayers and similar nanostructures is described by the Dirac model, being a 2+1 dimensional version of massless QED with the speed of light replaced by the Fermi velocity vF ≃ c/300. Methods of strong-field QFT are relevant for the Dirac model, since any low-frequency electric field requires a nonperturbative treatment of massless carriers in the case it remains unchanged for a sufficiently long time interval. In this case, the effects of creation and annihilation of electron-hole pairs produced from vacuum by a slowly varying and small-gradient electric field are relevant, thereby substantially affecting the radiation pattern. For this reason, the standard QED text-book theory of photon emission cannot be of help. We construct the Fock-space representation of the Dirac model, which takes exact accounts of the effects of vacuum instability caused by external electric fields, and in which the interaction between electrons and photons is taken into account perturbatively, following the general theory (the generalized Furry representation). We consider the effective theory of photon emission in the first-order approximation and construct the corresponding total probabilities, taking into account the unitarity relation.

P -wave coupled channel effects in electron-positron annihilation

$P$-wave coupled channel effects arising from the $D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, and ${D}^{*}{\overline{D}}^{*}$ thresholds in ${e}^{+}{e}^{\ensuremath{-}}$ annihilations are systematically studied. We provide an exploratory study by solving the Lippmann-Schwinger equation with short-ranged contact potentials obtained in the heavy quark limit. These contact potentials can be extracted from the $P$-wave interactions in the ${e}^{+}{e}^{\ensuremath{-}}$ annihilations, and then be employed to investigate possible isosinglet $P$-wave hadronic molecules. In particular, such an investigation may provide information about exotic candidates with quantum numbers ${J}^{\mathrm{PC}}={1}^{\ensuremath{-}+}$. In the mass region of the $D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, and ${D}^{*}{\overline{D}}^{*}$ thresholds, there are two quark model bare states, i.e. the $\ensuremath{\psi}(3770)$ and $\ensuremath{\psi}(4040)$, which are assigned as $({1}^{3}{D}_{1})$ and $({3}^{1}{S}_{1})$ states, respectively. By an overall fit of the cross sections of ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}D\overline{D}$, $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$, ${D}^{*}{\overline{D}}^{*}$, we determine the physical coupling constants to each channel and extract the pole positions of the $\ensuremath{\psi}(3770)$ and $\ensuremath{\psi}(4040)$. The deviation of the ratios from that in the heavy quark spin symmetry (HQSS) limit reflects the HQSS breaking effect due to the mass splitting between the $D$ and the ${D}^{*}$. Besides the two poles, we also find a pole a few MeV above the $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}.$ threshold which can be related to the so-called $G(3900)$ observed earlier by BABAR and Belle. This scenario can be further scrutinized by measuring the angular distribution in the ${D}^{*}{\overline{D}}^{*}$ channel with high luminosity experiments.

Searching for singlino-Higgsino dark matter in the NMSSM

We study a simplified scenario in the next-to-minimal supersymmetric standard model with a split electroweak spectrum, in which only the singlino and higgsinos are light and other superpartners are decoupled. Serving as a dark matter candidate, a singlino-dominated neutralino $\tilde{\chi}_1^0$ should have either resonant annihilation effects or sizable higgsino components to satisfy the observed relic abundance. The sensitivities of LHC searches and dark matter detection experiments are investigated. With an integrated luminosity of $30 (300) \mathrm{fb}^{-1}$, $3l + E_\mathrm{T} \!\!\!\!\!\!\!/ \;\;\;$and $2l + E_\mathrm{T} \!\!\!\!\!\!\!/ \;\;\;$ searches at the 13 (14) TeV LHC are expected to reach up to $m_{\tilde{\chi}_1^0}\sim 150 (230) \mathrm{GeV}$ and $m_{\tilde{\chi}_2^0,\tilde{\chi}_1^{\pm}}\sim 320 (480) \mathrm{GeV}$. Near future dark matter direct and indirect detection experiments can cover some parameter regions where collider searches lose their sensitivities.

Size effects in Cu50Zr50 metallic glass films revealed by molecular dynamics simulations

The mechanical behavior of metallic glasses shows similar size dependences as fine grained crystals, yet the strengthening mechanism is quite different. Tensile deformations of Cu50Zr50 metallic glass thin films by molecular dynamics simulation reveal that surface effects play an important role in affecting the deformation mode and ductility of the films. The presence of surfaces promotes the activation of shear transformation zones upon deformation, facilitating homogeneous plastic flow. While surface relaxation helps to annihilate the excess free volume generated in the film, and in turn retards the nucleation and/or propagation of shear bands, and consequently enhances the ductility of the films. The surface area to volume ratio is larger for thinner films and therefore the annihilation effect overwhelms the generation effect due to deformation, enabling the “smaller is stronger” phenomenon. Meanwhile, a transition of deformation mode from shear fracture dominated to mixed mode and then to homogeneous deformation is observed with the decreasing of film thickness. The findings suggest that the ductility and strength of metallic glass samples could be improved effectively by reducing the sample size or increasing its surface area to volume ratio.

Weak annihilation cusp inside the dark matter spike about a black hole.

We reinvestigate the effect of annihilations on the distribution of collisionless dark matter (DM) in a spherical density spike around a massive black hole. We first construct a very simple, pedagogic, analytic model for an isotropic phase space distribution function that accounts for annihilation and reproduces the "weak cusp" found by Vasiliev for DM deep within the spike and away from its boundaries. The DM density in the cusp varies as r-1/2 for s-wave annihilation, where r is the distance from the central black hole, and is not a flat "plateau" profile. We then extend this model by incorporating a loss cone that accounts for the capture of DM particles by the hole. The loss cone is implemented by a boundary condition that removes capture orbits, resulting in an anisotropic distribution function. Finally, we evolve an initial spike distribution function by integrating the Boltzmann equation to show how the weak cusp grows and its density decreases with time. We treat two cases, one for s-wave and the other for p-wave DM annihilation, adopting parameters characteristic of the Milky Way nuclear core and typical WIMP models for DM. The cusp density profile for p-wave annihilation is weaker, varying like ~r-0.34, but is still not a flat plateau.

24-4: Investigation of Effect of Triplet-Triplet Annihilation and Molecular Orientation on External Quantum Efficiency of Ultrahigh-Efficiency Blue Fluorescent Device

The effects of triplet-triplet annihilation (TTA) and molecular orientation were quantitatively investigated for a high-efficiency blue fluorescent organic light-emitting diode. Both the efficient TTA generation by improving carrier balance and the horizontal orientation of the transition dipole moment of the blue dopant realized ultrahigh external quantum efficiency (approximately 12%).

Auger-Assisted Ultrafast Fluorescence Measurement of Semiconductor Single-Walled Carbon Nanotubes

In the Auger process of a semiconductor nanostructure, the recombination energy of higher-order excitons would be nonradiatively transferred to the lower-order ones, and only the last exciton left could emit a photon. Here we show that this exciton–exciton annihilation effect can be positively employed to develop a novel optical technique for ultrafast fluorescence measurement. Upon excitation with two laser pulse trains continuously delayed in time, the fluorescence intensity of semiconductor single-walled carbon nanotubes increases accordingly, with two lifetime components of several and tens to hundreds of picoseconds being clearly resolved.

Light dark matter and dark radiation

Light dark-matter ($M\leq20$ MeV) particles freeze out after neutrino decoupling. If the dark-matter particle couples to a neutrino or an electromagnetic plasma, the late time entropy production from dark-matter annihilation can change the neutrino-to-photon temperature ratio, and equally the effective number of neutrinos $N_{eff}$. We study the non-equilibrium effects of dark-matter annihilation on the $N_{eff}$ and the effects by using a thermal equilibrium approximation. Both results are constrained with Planck observations. We demonstrate that the lower bounds of the dark-matter mass and the possibilities of the existence of additional radiation particles are more strongly constrained for dark-matter annihilation process in non-equilibrium.

The Radiation Control with the Different Energy Resources in the Engineering Industry

This paper concerns the problem of gamma radiation in the engineering industry. Distinctive features of the high energy resources in use are the short time of the product control. The research is devoted to problems of the small thickness about 30-40mm. This investigation denoted to radioactive resources of high radiation and high energy range. In this case the photo effect plays insignificant role at this value of the energy, but others effects enter: Compton Effect and effect of annihilations. The type of the energy is influence on the quality of the results for the thickness 30-40mm of the steel. Questions of personal dose measurement are urgent for radiation securities in the all enterprises of measuring system are considered. The results have shown that is possible to use selenium resource for the small thickness. The application of modern system of radiation control allows conduct the complex monitoring system with wide range or safe security.

Interpreting the Fermi-LAT gamma ray excess in the simplified framework

We test the plausibility that a Majorana fermion dark matter candidate with a scalar mediator explains the gamma ray excess from the Galactic center. Assuming that the mediator couples to all third generation fermions we calculate observables for dark matter abundance and scattering on nuclei, gamma, positron, and anti-proton cosmic ray fluxes, radio emission from dark matter annihilation, and the effect of dark matter annihilations on the CMB. After discarding the controversial radio observation the rest of the data prefers a dark matter (mediator) mass in the 10-100 (3-1000) GeV region and weakly correlated couplings to bottom quarks and tau leptons with values of 10^{-3}-1 at the 68\% credibility level.

Dark Matter annihilations in halos and high-redshift sources of reionization of the universe

It is well known that annihilations in the homogeneous fluid of dark matter (DM) can leave imprints in the cosmic microwave background (CMB) anisotropy power spectrum. However, the relevance of DM annihilations in halos for cosmological observables is still subject to debate, with previous works reaching different conclusions on this point. Also, all previous studies used a single type of parameterization for the astrophysical reionization, and included no astrophysical source for the heating of the intergalactic medium. In this work, we revisit these problems. When standard approaches are adopted, we find that the ionization fraction does exhibit a very particular (and potentially constraining) pattern, but the currently measurable τreio is left almost unchanged: in agreement with most of the previous literature, for plausible halo models we find that the modification of the signal with respect to the one coming from annihilations in the smooth background is tiny, below cosmic variance within currently allowed parameter space. However, if different and probably more realistic treatments of the astrophysical sources of reionization and heating are adopted, a more pronounced effect of the DM annihilation in halos is possible. We thus conclude that within currently adopted baseline models the impact of the virialised DM structures cannot be uncovered by CMB power spectra measurements, but a larger impact is possible if peculiar models are invoked for the redshift evolution of the DM annihilation signal or different assumptions are made for the astrophysical contributions. A better understanding (both theoretical and observational) of the reionization and temperature history of the universe, notably via the 21 cm signal, seems the most promising way for using halo formation as a tool in DM searches, improving over the sensitivity of current cosmological probes.

Revisiting big-bang nucleosynthesis constraints on dark-matter annihilation

We study the effects of dark-matter annihilation during the epoch of big-bang nucleosynthesis on the primordial abundances of light elements. We improve the calculation of the light-element abundances by taking into account the effects of anti-nucleons emitted by the annihilation of dark matter and the interconversion reactions of neutron and proton at inelastic scatterings of energetic nucleons. Comparing the theoretical prediction of the primordial light-element abundances with the latest observational constraints, we derive upper bounds on the dark-matter pair-annihilation cross section. Implication to some of particle-physics models are also discussed.

Weak annihilation and new physics in charmless [Formula: see text] decays.

We use currently available data of nonleptonic charmless 2-body Brightarrow MM decays (MM !=! PP, PV, VV) that are mediated by brightarrow (d, s) QCD- and QED-penguin operators to study weak annihilation and new-physics effects in the framework of QCD factorization. In particular we introduce one weak-annihilation parameter for decays related by (uleftrightarrow d) quark interchange and test this universality assumption. Within the standard model, the data supports this assumption with the only exceptions in the Brightarrow K pi system, which exhibits the well-known “{varDelta } {mathcal{A}_mathrm{CP}} puzzle”, and some tensions in B rightarrow K^* phi . Beyond the standard model, we simultaneously determine weak-annihilation and new-physics parameters from data, employing model-independent scenarios that address the “{varDelta } {mathcal{A}_mathrm{CP}} puzzle”, such as QED-penguins and brightarrow s, bar{u}u current-current operators. We discuss also possibilities that allow further tests of our assumption once improved measurements from LHCb and Belle II become available.

Recent Advances in Solution‐Processable Dendrimers for Highly Efficient Phosphorescent Organic Light‐Emitting Diodes (PHOLEDs)

AbstractPhosphorescent dendrimers together with dendritic host materials have inherent advantages in achieving highly efficient phosphorescent organic light‐emitting diodes (PHOLEDs) with low‐cost, solution‐processed device fabrication. Recently, much research effort has been devoted to developing these dendritic materials in the field of electroluminescence (EL). In this Focus Review, the major advances in this line of research are summarized and discussed. The crucial roles played by these dendritic organic electronic materials in coping with the key issues in the field of PHOLEDs have been specially emphasized. These include alleviating the triplet‐triplet annihilation effect through the site‐isolation effect associated with the dendritic structures, promoting charge‐carrier injection/transporting ability and ambipolar properties through functionalized dendrons, fulfilling simple PHOLEDs with high EL efficiencies, obtaining self‐hosting phosphorescent emitters, and avoiding undesired energy transfer process from phosphorescent cores to the dendrons. In addition, the future perspectives and ongoing challenges of this research frontier are also highlighted.

Resonant instability of the surface dust-acoustic wave in electron–positron–ion dusty plasmas including pair annihilation effects

Abstract The influence of electron–positron pair annihilations on the resonant instability of surface dust-acoustic wave is investigated in semi-bounded electron–positron–ion dusty plasmas. The dispersion relation and the temporal growth rate of the surface dust-acoustic wave including the pair annihilation effect are obtained by the specular reflection boundary condition. It is found that the electron–positron annihilation effect suppresses the temporal growth rate of the surface dust-acoustic instability and, however, increases the domain of the resonant instability. It is also shown that the pair annihilation effect on the growth rate decreases with increasing wave number and dust plasma frequency. The variation of the domain and magnitude of temporal growth rate is also discussed.