Cherenkov Process Research Articles

Comment on ``Čerenkov Radiation by Neutrinos in a Supernova Core''

Mohanty and Samal have shown that the magnetic-moment interaction with nucleons contributes significantly to the photon dispersion relation in a supernova core, and with an opposite sign relative to the usual plasma effect. Because of a numerical error they overestimated the magnetic-moment term by two orders of magnitude, but it is still of the same order as the plasma effect. It appears that the Cherenkov processes gamma+nu -> nu and nu -> nu+gamma remain forbidden, but a final verdict depends on a more detailed investigation of the dynamical magnetic susceptibility of a hot nuclear medium.

Cherenkov radiation by massless neutrinos in a magnetic field

We calculate the Cherenkov process $\ensuremath{\nu}\ensuremath{\rightarrow}\ensuremath{\nu}\ensuremath{\gamma}$ in the presence of a homogeneous magnetic field. The neutrinos are taken to be massless with only standard-model couplings. The magnetic field satisfies the dual purpose of inducing an effective neutrino-photon vertex and of modifying the photon dispersion relation such that the Cherenkov condition $\ensuremath{\omega}<|\mathbf{k}|$ is satisfied. Our effect is closely related to photon splitting that occurs in magnetic fields and that may be astrophysically important in the strong magnetic fields of pulsars. It is also closely related to magnetic-field enhanced radiative decays $\ensuremath{\nu}\ensuremath{\rightarrow}{\ensuremath{\nu}}^{\ensuremath{'}}\ensuremath{\gamma}$ that have been extensively discussed in the recent literature. In the appropriate limits we agree with these results, but we disagree with earlier explicit calculations of the Cherenkov process. For a field strength ${B}_{\mathrm{crit}}{=m}_{e}^{2}/e=4.41\ifmmode\times\else\texttimes\fi{}{10}^{13}$ G and for ${E=2m}_{e}$ the Cherenkov rate is about $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}{\mathrm{ }\mathrm{s}}^{\ensuremath{-}1}$ and thus too small to be of practical importance for pulsar physics.

Stimulated phenomena in the surface Cherenkov process by unmagnetized electron beam

The operability of the surface Cherenkov laser with unmagnetized electron beam is considered. The small-signal gain of the surface Cherenkov laser for various regimes is calculated. The dependence of the gain on the electron beam angular spread is analyzed. The quantum mechanical consideration shows the possibility of the electron-beam quantum modulation after the interaction.

Preface

The probability to detect a twisted photon produced by a cold relativistic particle bunch of charged particles is derived. The radiation of twisted photons by such particle bunches in stationary electromagnetic fields and in propagating electromagnetic waves is investigated. Several general properties of both incoherent and coherent contributions to the radiation probability of twisted photons are established. It is shown that the incoherent radiation by bunches of particles traversing normally an isotropic dispersive medium (the edge, transition, and Vavilov–Cherenkov radiations) and by bunches moving in a helical undulator does not depend on the azimuthal distribution of particles in the bunch and is the same as for round bunches. As for planar undulators, the incoherent radiation by particle bunches is the same as for the bunches symmetric under reflection with respect to the axis of a twisted photon detector. At high energies of detected twisted photons, this property is universal and holds for the forward incoherent radiation by any cold relativistic particle bunch. The coherent radiation of twisted photons by such particle bunches obeys the property that we call the addition rule. This rule provides a simple means to describe the properties of coherent radiation of twisted photons. Furthermore, the strong addition rule is established for the coherent radiation by sufficiently long helical bunches. The use of this rule allows one to elaborate superradiant pure sources of twisted photons. The coherent radiation by helical bunches is considered for the edge, transition, and Vavilov–Cherenkov processes and for particles moving in undulators and plane laser waves with circular polarization. In these cases, the sum rules are deduced for the total probability to detect a twisted photon and for the projection of the total angular momentum per photon. The explicit expressions for both incoherent and coherent interference factors are derived for several simple bunch profiles.

Laser Beat Accelerator

Parallel intense photon (laser, microwave, etc.) beams &#x003C9;₀,k₀ and &#x003C9;₁,k₁ shone on a plasma with frequency separation equal to the plasma frequency &#x003C9;_p is capable of accelerating plasma electrons to high energies in large flux. The photon beat excites through the forward Raman scattering large amplitude plasmons whose phase velocity is equal to (&#x003C9;<sub0</sub>-&#x003C9;₁)/(k₀-k₁), close to c in an underdense plasma. The plasmon electrostatic fields trap electrons and carry them to high energies: Maximum electron energy ^max = 2mc²[1-(&#x003C9;₀-&#x003C9;₁)²/c²(k₀-k₁)²]^-1~2mc²(&#x003C9;₀/&#x003C9;_p)². The multiple forward Raman instability produces smaller and smaller frequency and group velocity of photons; thus the photons slow down in the plasma by emitting accelerated electrons (inverse Cherenkov process).