Related papers: Exclusive two-photon annihilation at large energy …
We have studied the radiative decay of the 2s state of one-electron and one-muon ions, where the two-photon mechanism plays an important role. Due to the nuclear size corrections the radiative decay of the 2s state in the electron and muon…
This paper studies the decay of a large, closed domain wall in a closed universe. Such walls can form in the presence of a broken, discrete symmetry. We study a novel process of quantum decay for such a wall, in which the vacuum fluctuates…
A novel theory of radiative electron capture in second forbidden non-unique transition, is applied to reanalyze experimental data obtained previously for the decay of 59Ni. The measured gamma spectrum is shown to be distorted at the…
The two messenger results of the GeV gamma-ray excess at the Galactic center and a probable antiproton excess in the recent AMS-02 observation suggest that these two anomalies may be owing to the same origin --- the dark matter (DM)…
Recently published results from the PAMELA experiment have shown conclusive evidence for an excess of positrons at high (~ 10 - 100 GeV) energies, confirming earlier indications from HEAT and AMS-01. Such a signal is generally expected from…
An effective theory approach to heavy quarkonia decays based on the $1/m_Q$ expansion is introduced. Its application to decays in which the two heavy quarks annihilate is discussed.
Several recent studies have considered modifications to the standard weakly-interacting massive particle (WIMP) scenario in which the cross section (times relative velocity v) for pair annihilation is enhanced by a factor 1/v. Since…
Virtual corrections for electron--positron annihilation into one real and one off-shell photon of invariant mass Q^2 are evaluated. Special attention is paid to those configurations where the real photon is collinear with the beam…
We summarize the current theoretical and experimental status of the spectral changes of vector mesons ($\rho$, $\omega$, $\phi$) at finite baryon density. Various approaches including QCD sum rules, effective theory of hadrons and bag…
We investigate the gamma-ray spectrum in the MeV range arising from electron-positron pair annihilation in fireballs associated with magnetar giant flares (MGFs), motivated by the recent observation of a MeV gamma-ray line feature in a…
I review the parton picture at strong coupling emerging from the gauge/gravity duality together with its consequences for the energy loss and momentum broadening of a heavy quark moving through a strongly coupled plasma.
We calculate cross sections of a pair $B_c$ meson production on the basis of two-photon mechanism from electron-positron annihilation. We investigate the production cross sections in nonrelativistic approximation and with the account of…
We complement studies of the neutral pion transition form factor pi^0 --> gamma^(*) gamma^(*) with calculations for the electromagnetic decay widths of the processes pi^0 --> e^+ e^-, pi^0 --> e^+ e^- gamma and pi^0 --> e^+ e^- e^+ e^-.…
We present an analysis of the radiative decay $\phi \to \gamma \pi^0 \pi^0$ in a dispersive framework, where the two-pion subsystem undergoes strong final-state interactions that cover the $f_0(500)$ and $f_0(980)$ regions. We employ a…
We have calculated gamma-ray radiative transport in regions of high energy density, such as gamma-ray burst source regions, using a discrete ordinate, discrete energy group method. The calculations include two-photon pair production and…
We study in this paper the scenario where the dark matter is constituted by Majorana particles which couple to a light Standard Model fermion and an extra scalar via a Yukawa coupling. In this scenario, the annihilation rate into the light…
For Majorana dark matter, gauge boson bremsstrahlung plays an important role in enhancing an otherwise helicity-suppressed s-wave annihilation cross-section. This is well known for processes involving a radiated photon or gluon together…
Anomalous high energy photons, known as GRB221009A, with 18 TeV and 251 TeV were observed by LHAASO and Carpet-2 recently. Such observation of high energy gamma-ray bursts from distant source causes a mystery since high energy photons…
Two-photon decays of vector mesons and dilepton decays of scalar mesons which are forbidden in vacuum and can occur in dense baryonic matter due to the explicit violation of Lorentz symmetry are described within a quark model of the…
We calculate the medium modification of the pi-omega-rho vertex and analyze its significance for the pi^0 -> gamma gamma*, omega -> pi^0 gamma*, and rho -> pi gamma* decays in nuclear matter. We use a relativistic hadronic approach at zero…