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Copyright of Canadian Journal of Physics is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, we investigate the production process of a photon pair in a regime of quantum electrodynamics, considering the presence of a constant four-vector that defines a privileged direction in spacetime, resulting in Lorentz symmetry violation. We explore Lorentz violation in the context of vectorial nonminimal coupling, where we analyze the modifications introduced by this coupling in the scattering amplitude at the vertex. Moreover, we delve into Lorentz violation with axial-like nonminimal coupling. Both analyses are conducted by examining the constant four-vector of both time-like and space-like types. [ABSTRACT FROM AUTHOR]

The Doppler-shift spectra of the γ-rays from positron annihilation in molecules were determined by using the momentum distribution of the annihilation electron-positron pair. The effect of the positron wavefunction on spectra was analysed in a recent paper (Green et al 2012 New J. Phys. 14 035021). In this companion paper, we focus on the dominant contribution to the spectra, which arises from the momenta of the bound electrons. In particular, we use computational quantum chemistry models (Hartree-Fock with two basis sets and density functional theory (DFT)) to calculate the wavefunctions of the bound electrons. Numerical results are presented for noble gases and small molecules such as H2, N2, O2, CH4 and CF4. The calculations reveal relatively small effects on the Doppler-shift spectra from the level of inclusion of electron correlation energy in the models. For atoms, the difference in the full-width at half-maximum of the spectra obtained using the Hartree-Fock and DFT models does not exceed 2%. For molecules the difference can be much larger, reaching 8% for some molecular orbitals. These results indicate that the predicted positron annihilation spectra for molecules are generally more sensitive to inclusion of electron correlation energies in the quantum chemistry model than the spectra for atoms are. [ABSTRACT FROM AUTHOR]

Using the analytic scheme, three-loop contribution to the perturbative Coulomb-like part of the static color potential of a heavy quark–antiquark system, we obtain an analytic expression for the fourth-order -function in the gauge-invariant effective V scheme in the case of the generic simple gauge group. We also present the Adler function of electron–positron annihilation into hadrons and the coefficient function of the Bjorken polarized sum rule in the V scheme up to terms. We demonstrate that at this level of the perturbation theory in this effective scheme, the generalized Crewther relation, which connects the flavor nonsinglet contributions to the Adler and Bjorken polarized sum rule functions, is satisfied. Starting from the order, it contains a conformal symmetry breaking term that factors into the conformal anomaly and the polynomial in powers of . We prove that this relation also holds in other gauge-invariant renormalization schemes. The obtained results allows revealing the difference between the V-scheme -function in QED and the Gell-Mann–Low -function. This distinction arises due to the presence of the light-by-light type scattering corrections first appearing in the static potential at the three-loop level. [ABSTRACT FROM AUTHOR]

We demonstrate that in the mass-independent renormalization scheme, the renormalization group equations associated with the unphysical parameters that characterize the renormalization scheme and the mass scale leads to summation that results in a cancellation between the implicit and explicit dependence on these parameters. The resulting perturbative expansion is consequently independent of these arbitrary parameters. We illustrate this by considering R, the cross section for [e.sup.+][e.sup.-] [right arrow] hadrons. Key words: QCD, electron-positron annihilation, renormalization group, renormalization scheme independence, mass scale independence. Nous demontrons que, dans le schema de renormalisation independant de la masse, l'equation du groupe de renormalisation, associee aux parametres non physiques qui caracterisent la renormalisation et l'echelle de masse, mene a une sommation resultant en une annulation entre les dependances implicite et explicite sur ces parametres. Il en resulte une expansion perturbative qui est consequemment independante de ces parametres arbitraires. Nous illustrons ce phenomene en considerant R, la section efficace pour la reaction [e.sup.+][e.sup.-] [right arrow] hadrons. [Traduit par la Redaction] Mots-cles : CDQ/QCD, annihilation electron-positron, groupe de renormalization, independance du schema de renormalization, independance de l'echelle de masse., 1. Introduction When a perturbative calculation of the radiative effects contributing to R, the cross section for [e.sup.+][e.sup.-] [right arrow] hadrons, is carried out to some finite order, then the [...]

We describe in this paper the quantum chromodynamics prediction to calculate the strong coupling constant by using event shape variables as well as momentum spectra. By fitting the dispersive model and employing our parameters on event shape distribution, we obtain the perturbative value of [mathematical expression not reproducible] and also the non-perturbative value of [[alpha].sub.0] = 0.5246 [+ or -] 0.0516 GeV for electron-proton interactions. Next, by using momentum spectra for the same interactions, we obtain [[alpha].sub.s] = 0.1572 [+ or -] 0.029. Our values in both methods are consistent with those obtained from electron-positron annihilations measured previously. When we find coupling constant for different flavours, we observe that they do not affect our results considerably. This is in accordance with quantum chromodynamics theory. All these features will be explained in the main text. Key words: quantum chromodynamics, strong-coupling expansions, perturbative calculations, QCD properties, renormalization. Nous presentons ici la prediction de la chromodynamique quantique (CDQ) pour calculer la constante de couplage forte en utilisant les variables de forme des evenements ainsi que les spectres en impulsion. En ajustant le modele dispersif et en utilisant nos parametres sur les distributions de forme des evenements pour les interactions electron-proton, nous obtenons la valeur perturbatif de [mathematical expression not reproducible] et aussi la valeur non perturbatif de [[alpha].sub.0] = 0.5246 [+ or -] 0.0516 GeV. Par la suite, en utilisant les spectres en impulsion pour les memes interactions, nous obtenons [[alpha].sub.s] = 0.1572 [+ or -] 0.029. Nos valeurs dans ces deux approches sont coherentes avec celles deja mesurees dans des experiences d'annihilation electron-positron. Quand nous introduisons les constantes de couplage pour les differentes saveurs, nous observons qu'elles n'affectent pas nos resultats de facon importante. Ceci est en accord avec la prediction CDQ. Toutes ces caracteristiques sont expliquees dans le cadre de l'article. [Traduit par la Redaction] Mots-cles: chromodynamique quantique, expansion en couplage fort, calcul perturbative, proprietes de CDQ/QCD, renormalisation., 1. Introduction One of the most common and successful ways of testing quantum chromodynamics (QCD) is to investigate the distribution of event shapes in [e.sup.+][e.sup.-] hadrons, which have been measured [...]

Researches on the electron-positron pair production in the presence of the intense laser field are reviewed, motivated by the theoretical importance of the nonperturbative QED problem and the worldwide development of high power laser facilities. According to the distinct experimental requirements and theoretical methods, two types of pair production are elaborated, which are, respectively, pair production in the combination of a seed particle and the strong laser, and vacuum pair production without a seed particle. The origin of the nonperturbative problem caused by the strong field is analyzed. The main ideas, realisation, achievements, validity, challenges and bottleneck problems of the nonperturbative methods developed for each type of the pair production problem are discussed. [ABSTRACT FROM AUTHOR]

Defects in a silicon (Si) substrate induced by plasma exposure—plasma-induced damage (PID)—were investigated using various techniques. The authors performed a comprehensive characterization of plasma induced damages, which will be indispensable for suppressing PID, by precisely assigning the density profile of defects in the region to ∼1016 cm−3. In this study, the Si substrate was damaged using an electron cyclotron resonance plasma system. Cathodoluminescence analysis was used to detect the defects in the damaged Si substrates. The thickness of the damaged layer in the Si substrates was determined to be approximately 1–2 nm by transmission electron microscopy and spectroscopic ellipsometry, while time-of-flight secondary ion mass spectrometry identified the presence of interstitial atoms to a depth of ∼20 nm. Positron annihilation spectroscopy showed that the structural changes related to vacancies interacting with C and F atoms were distributed from the substrate surface to a depth of approximately 130 nm. The authors further verified this finding by a technique using the PID-enhanced dechanneling of As atoms implanted with a projection range of 10 nm. After plasma exposure, the difference between the plasma-damaged and the nondamaged samples in the injected As profiles was identified to a depth of ∼130 nm with a density of ∼1016 cm−3. The comprehensive defect profiling performed in this study provides key guidelines for the introduction mechanism of defects in plasma exposed Si before designing future electronic devices. [ABSTRACT FROM AUTHOR]

Recently, the Belle and BABAR collaborations published the single-inclusive electron-positron annihilation data at the center of mass energies ([square root of s]) of 10.52 and 10.54 GeV, respectively. These new data offer one the possibility to determine the nonperturbative initial conditions of fragmentation functions (FFs) much more accurately. Here, we extract the FFs of [π.sup.±] and [K.sup.±] particles at next-to-leading order (NLO) including these new data, which are in the regions of larger scaled-energy z and lower [square root of s]. However, the [π.sup.±] and [K.sup.±] FFs were calculated previously, but our new analysis shows that adding these new data, for instance, changes the (u, s) → [π.sup.+] FFs in the large-z region while the s → [π.sup.+] FF is also changed at low z. These new data also change the u → [K.sup.+] FF at low z (z 0.07. The FF of g → [K.sup.+] is decreased everywhere, for example, about 25% at z = 0.01. We also apply, for the first time, the extracted FFs to make our predictions for the scaled-energy distributions of [π.sup.±] and [K.sup.±] inclusively produced in top quark decays at NLO. Key words: fragmentation function, pion, kaon, Belle data, BABAR data, top decay. Recemment, les collaborations Belle et BABAR ont publie les donnees d'annihilation electron-positron inclusive simple a des energies dans le centre de masse ([square root of s]) de 10.52 et 10.54 GeV respectivement. Ces nouvelles donnees rendent possible la determination des conditions initiales non perturbatives des fonctions de fragmentation (FF) avec beaucoup plus de precision. Ici, nous extrayons les FF de [π.sup.[+ or -]] et de [K.sup.±] au premier ordre sous-dominant (NLO) suivant ces nouvelles donnees, qui sont dans des regions de plus grande valeur de l'energie fractionnaire z et de plus basse valeur de [square root of s]. Cependant, les valeurs des FF de [π.sup.±] et de [K.sup.±] ont deja ete calculees, mais notre analyse des nouvelles donnees change ces valeurs, par exemple, elle change la FF (u, s) → [π.sup.+] dans la region des grandes valeurs de z, et change aussi la FF s [right arrow] [π.sup.+] a basse valeur de z. Ces nouvelles donnees changent egalement la FF u → [K.sup.+] a basse valeur de z(z 0.07. La FF g → [K.sup.+] diminue partout, p.ex. environ 25% a z = 0.01. Pour la premiere fois, nous appliquons les FF extraites des experiences pour faire des predictions sur les distributions d'energie fractionnaire des [π.sup.±] et des [K.sup.±] produits inclusivement dans la desintegration du quark top au premier ordre sous-dominant. [Traduit par la Redaction] Mots-cles : fonction de fragmentation, pion et kaon, CDQnon perturbative, donnees Belle, donnees BABAR, desintegration du quark top., 1. Introduction Fragmentation functions (FFs) [D.sup.h.sub.i] (z, [μ.sup.2.sub.f]), which can be described as the probability for a parton i at the factorization scale [μ.sub.f] to fragment into a hadron h [...]

The reasons for the appearance of the angular distribution of photons formed upon electron-positron annihilation are considered. It is shown that the angular distribution of photons is a consequence of the Doppler effect in the reference system of the electron and positron center of mass. There is no angular distribution of photons in the reference system related to the electron; it is replaced with the Doppler variation of photon frequencies. The obtained results can be used to analyze the operation of positron-emission tomographs. [ABSTRACT FROM AUTHOR]

Copyright of Il Nuovo Cimento: A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Deals with the ability of a proposed esup+esup- collider to study the implications of various models of electroweak symmetry breaking. Background on the linear collider environment; Standard model and background processes at high energy esup+esup- colliders; Discussion on a proposed underlying symmetry that links bosons and fermions.

The modern state of gamma-ray astronomy is reviewed, the paper being mainly devoted to the theoretical models that describe generation of gamma-ray emission under astrophysical conditions. Basic information on the processes of generation and absorption of gamma-rays, as well as the results of observations for various gamma-ray photon energies are reported. In the region of soft gamma-ray emission (i.e., for energies less than tens of MeV), where emission in gamma-ray lines dominates, we also discuss the nature of gamma-ray bursts, the origin of gamma-ray emission from the galactic centre, etc. Discrete sources and, in particular, the mysterious source Cyg X-3 are discussed in the region of very high ( E > 10 eV) and ultra-high ( E > 10 eV) energy gamma-ray emission. A larger portion of the review is devoted to the analysis of cosmic-ray origin on the basis of the available gamma-ray data in the region from several tens of MeV to several GeV. The peculiarity of this energy range is, in particular, in the fact that the diffuse galactic emission was observed mainly there. We also discuss the problem of determination of the cosmic-ray density gradient from the gamma-ray data. The origin of high-latitude gamma-ray emission, the problem of galactic gamma-ray halo, etc., are discussed. The theoretical models explaining the nature of unidentified gamma-ray sources, as well as the results of measurements and theoretical estimations of a gamma-ray flux from SN1987A are analysed. [ABSTRACT FROM AUTHOR]

In this paper, we study the freeze-in production of fermionic dark matter with a pseudo scalar as the mediator between the dark sector and standard model (SM). While the fermionic DM is non-thermal, we will explain two scenarios in which the production of pseudo-scalar particles are either thermal or non thermal. We will present an elaborate discussion to derive yield quantity and relic density and illustrate these values for the different range of model parameters. We will investigate constraints on parameter space coming from invisible Higgs decay at LHC. For the case of extremely small couplings and zero mixing between the SM Higgs field with the pseudo scalar field, where the pseudo scalar boson can play the role of DM, we will justify recent observations of merging galaxies with a case of self-interacting DM. We will show that the influence of DM annihilation in this case would provide a better fit to the AMS-02 data of positron flux. [ABSTRACT FROM AUTHOR]