Related papers: Exclusive two-photon annihilation at large energy …
Counterintuitive nature of quantum physics leads to a number of paradoxes. One of them is a "quantum vampire" effect [1] consisting in the fact, that photon annihilation in a part of a large beam doesn't change the shape of the beam profile…
The process of the muon (pion) pair production with small invariant mass in the electron--positron high--energy annihilation, accompanied by emission of hard photon at large angles, is considered. We find that the Drell--Yan picture for…
The theoretical analysis of the $\gamma\gamma \to \pi^0\eta$ process is presented within the energy range up to 1.4 GeV. The $S$-wave resonance $a_0(980)$ is described involving the coupled channel dispersive framework and the $D$-wave…
An $\omega$-meson in motion with respect to a nuclear medium can couple to a $\sigma$-meson through a particle-hole excitation. This coupling is large. We investigate its consequences for the width of $\omega$-mesons in matter and for the…
In this paper, a study of two-photon and two-gluon decays in the context of p-wave heavy quarkonia is presented. Within the covariant light-front framework, the annihilation rates of scalar and tensor quarkonium states are derived. In the…
Recent theoretical developments in electron-positron annihilation into fermion pairs are summarized. In particular, two-fermion production, DPA for WW signal, single-W production and ZZ signal
The scalar and vector meson exchange contributions to the doubly radiative decays $\eta^{(\prime)}\to\pi^0\gamma\gamma$ and $\eta^\prime\to\eta\gamma\gamma$ are analysed within the Linear Sigma Model and Vector Meson Dominance frameworks,…
Two-photon decay rates in simple atoms such as hydrogenlike systems represent rather interesting fundamental problems in atomic physics. The sum of the energies of the two emitted photons has to fulfill an energy conservation condition, the…
Previous representations of pion pair production amplitudes by two real photons at low energy, which combine dispersion theoretical constraints with elastic unitariy, chiral symmetry and soft photon constraints are generalized to the case…
Based on analyticity, unitarity, and Lorentz invariance the contribution from hadronic vacuum polarization to the anomalous magnetic moment of the muon is directly related to the cross section of e^+e^- --> hadrons. We review the main…
The amplitude of a Compton-like process nu_i gamma^* -> nu_j gamma^* with virtual photons is calculated in the standard GWS theory with lepton mixing. The contribution of this process to the high energy neutrino scattering on the nucleus…
We discuss a little-studied class of weak decay modes sensitive to only one quark topology at leading order in G_F: M --> m gamma, where M,m are mesons with completely distinct flavor quantum numbers. Specifically, they proceed via the…
The rare decay B -> X_s gamma gamma is studied in the Standard Model (SM) and in two different versions (Model I and Model II) of the Two Higgs Doublet Model (2HDM). In the SM the branching ratio into ``hard photons'' is about 10^(-7) and…
We present our studies on the neutrino pairs annihilation into electron-positron pairs ($\nu{\bar \nu}\to e^-e^+$) near the surface of a neutron star in the framework of extended theories of gravity. The latter modifies the maximum energy…
We discuss the theory and phenomenology of pair annihilation, within an ultra-short laser pulse, to a single photon. The signature of this process is the uni-directional emission of single photons with a fixed energy. We show that the cross…
Detecting the cosmic rays, in particular gamma-ray, coming from the dark matter annihilation or decay is an indirect way to survey the nature of the dark matter. In the commutative space-time, the annihilation of the dark matter candidates…
Process of muon (pion) pair production with small invariant mass in the electron-positron high-energy annihilation, accompanied by emission of hard photon at large angles, is considered. We find that the Dell-Yan picture for differential…
We investigate the exclusive photoproduction of a heavy timelike photon which decays into a lepton pair, gamma p -> l+ l- p. This can be seen as the analog of deeply virtual Compton scattering, and we argue that the two processes are…
We calculate in detail the annihilation of Muonium into two-neutrino final state and two-neutrino and a photon state.
We discuss the relevance of a dedicated measurement of exclusive production of a pair of neutral pions in a hard gamma* gamma scattering at small momentum transfer. In this case, the virtuality of one photon provides us with a hard scale in…