Related papers: Implications of automatic photon quenching on comp…
Electrons at the surface of a plasma that is irradiated by a laser with intensity in excess of $10^{23}~\mathrm{W}\mathrm{cm}^{-2}$ are accelerated so strongly that they emit bursts of synchrotron radiation. Although the combination of high…
We study the effects of a finite mass for the photon on its propagation in a weak gravitational field. In particular, we analyse the gravitational time delay, also known as the Shapiro effect. We work in isotropic coordinates in the…
We present a model of gamma-ray emission through neutral pion production and decay in two-temperature accretion flows around supermassive black holes. We refine previous studies of such a hadronic gamma-ray emission by taking into account…
Weak gravitational lensing from large-scale structure enhances and reduces the fluxes from extragalactic point sources with an rms amplitude of order 15%. In cosmic microwave background (CMB) experiments, sources exceeding some flux…
We review the theory for photon-photon scattering in vacuum, and some of the proposals for its experimental search, including the results of our recent works on the subject. We then describe a very simple and sensitive proposal of an…
The recent association of soft gamma repeaters (SGRs) with counterparts in other wavebands has sparked much interest in these sources. One of the recent models for these objects is that they originate in the environs of neutron stars with…
We study Klein-Nishina (KN) effects in the spectrum produced by a steady state, non-thermal source where rapidly accelerated electrons cool by emitting synchrotron radiation and Compton upscattering ambient photons produced outside the…
We show that electron betatron resonance acceleration by an ultra-intense ultra-short laser pulse in a near critical density plasma works as a high-brightness gamma-ray source. Compared with laser plasma X-ray sources in under-dense plasma,…
Colliding winds of massive binaries have long been considered as potential sites of non-thermal high-energy photon production. This is motivated by the detection of non-thermal spectra in the radio band, as well as by correlation studies of…
In the past decade, gamma-ray observations and radio observations put strong constraints on the parameters of dark matter annihilation. In this article, we suggest another robust way to constrain the parameters of dark matter annihilation.…
Monochromatic photons could be produced in the annihilation or decay of dark matter particles. At high energies, the search for such line features in the cosmic gamma-ray spectrum is essentially background free because plausible…
We reassess the importance of photon splitting to spectral formation in cosmic X-ray and $\gamma$-ray sources with magnetic fields of several $10^{12}$ gauss. Our analysis is based on the recent numerically accurate evaluation of the full…
We re-examine scattering of photons near the Lyman-alpha resonance in the intergalactic medium (IGM). We first derive a general integral solution for the radiation field around resonance when spin diffusivity is ignored. Our solution shows…
Single-photon sources are subjected to a fundamental limitation in the speed of operation dictated by the spontaneous emission rate of quantum emitters (QEs). The current paradigm of the rate acceleration suggests coupling of a QE to a…
Gravitational microlensing within the Galaxy offers the prospect of probing the details of distant stellar sources, as well as revealing the distribution of compact (and potentially non-luminous) masses along the line-of-sight. Recently, it…
The Large High Altitude Air Shower Observatory (LHAASO) has reported the measurement of photons with high energy up to 1.42 PeV from twelve gamma-ray sources. We are concerned with the implications of LHAASO data on the fate of Lorenz…
We investigate potential $\gamma-\gamma$ absorption of gamma-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess…
We quantitatively investigate the non-classicality and non-locality of a whole new class of mixed disparate quantum and semiquantum photon sources at the quantum-classical boundary. The latter include photon added thermal and photon added…
If the present dark matter in the Universe annihilates into Standard Model particles, it must contribute to the gamma ray fluxes detected on the Earth. Here we briefly review the present constraints for the detection of gamma ray photons…
Nearby sources of cosmic rays up to a ZeV(=10^21 eV) could be observed with a multi-messenger approach including secondary gamma-rays and neutrinos. If cosmic rays above ~10^18 eV are produced in magnetized environments such as galaxy…