An economic technique for calculation of polarized bremsstrahlung process is proposed, assuming typical atomic momentum transfer $q\ll m$. The adopted approach is based on the natural reduction of the matrix element to the form $V^αγ^α+A_{5}γ^{5}$. Polarization distribution in the fully differential cross-section is analyzed. It is found that at a given momentum transfer to the atom polarization in the plane of small radiation angles is oriented along circles passing through two common points. It is shown that with angular selection of radiated photons carried out, even with momentum transfers to the atom being integrated over, for particular radiation angles polarization may stay as high as 100%. Without angular selection of photons, only by control of the recoil, it is impossible to gain radiation polarization above 50%.
Helicity amplitudes and differential cross section of high-energy $e^+e^-$ photoproduction accompanied by bremsstrahlung in the electric field of a heavy atom are derived. The results are exact in the nuclear charge number and obtained in the leading quasiclassical approximation. They correspond to the leading high-energy small-angle asymptotics of the amplitude. It is shown that, in general, the Coulomb corrections essentially modify the differential cross section as compared to the Born result. When the initial photon is circularly polarized the Coulomb corrections lead to the asymmetry in t…
The polarization effects in the one-meson radiative decay of the polarized $τ$ lepton, $τ^-\toπ^-γν_τ$, are investigated. The inner bremsstrahlung and structural amplitudes are taken into account. The asymmetry of the differential decay width caused by the $τ$ lepton polarization and the Stokes parameters of the emitted photon itself, are calculated depending on the polarization of the decaying $τ$ lepton. The numerical estimation of these physical quantities was done for arbitrary direction of the $τ$ lepton polarization 3-vector in the rest frame. The vector and axial-vector form factors des…
The polarization effects in the one-meson radiative decay of the polarized $τ$ lepton, $τ^-\toπ^-γν_τ$, have been investigated. We present the analytical results for the $t-$distribution of the partial differential widths, which responsible for different polarization phenomena, in the case of the photon energy cut: $ω>X$. These quantities depend on the invariant mass squared $t$ of the pseudoscalar meson and photon and the photon energy cut $X.$ Our analytical formulae, in terms of the weak vector and axial-vector form factors, describing the structure-dependent part of the decay amplitude, ar…
Various distributions over the angles of the emitted photon, especially over the azimuthal angle, in the one-meson radiative decay of the polarized $τ$ lepton, $τ^-\toπ^-γν_τ$, have been investigated. In connection with this, the photon phase space is discussed in more detail since in the case of the polarized $τ$ lepton it is not trivial. The decay matrix element contains both the inner bremsstrahlung and the resonance (structural) contributions. The azimuthal dependence of some observables have been calculated. They are the asymmetry of the differential decay width caused by the $τ$ lepton p…
Recent theoretical studies have suggested that the suddenly recoiled atom struck by dark matter (DM) particle is much more likely to excite or lose its electrons than expected. Such Migdal effect provides a new avenue for exploring the sub-GeV DM particles. There have been various attempts to describe the Migdal effect in liquids and semiconductor targets. In this paper we incorporate the treatment of the bremsstrahlung process and the electronic many-body effects to give a full description of the Migdal effect in bulk semiconductor targets diamond and silicon. Compared with the results obtain…
The search for dark matter weakly interacting massive particles with noble liquids has probed masses down and below a GeV/c^2. The ultimate limit is represented by the experimental threshold on the energy transfer to the nuclear recoil. Currently, the experimental sensitivity has reached a threshold equivalent to a few ionization electrons. In these conditions, the contribution of a Bremsstrahlung photon or a so-called Migdal electron due to the sudden acceleration of a nucleus after a collision might be sizable. In the present work, we use a Bayesian approach to study how these effects can be…
The Polarized and Unpolarized Photon Content of the Nucleon
本文从理论上计算了在等效光子近似（EPA）下核子（质子、中子）$(Δ)γ^N$的极化和非极化光子分布，并论证了实验测定的可能性。它们都由两个部分组成：弹性部分$(Δ)γ^N_{\rm el}$（由$N\to γN $产生）和非弹性部分$(Δ)γ^N_{\rm inel}$（由$N\to γX$产生）和$X \neq N$。特别关注的是$e N \to e γN$和$e N \to e γX$中的QED康普顿过程，它是直接测量核子光子含量和检验EPA可靠性的最重要的反应之一。此外，它是如何讨论这样的测量可以提供额外的，独立的信息，通常的极化和非极化结构功能。
An expression for the Dalitz plot of the semileptonic decay of a charged kaon, including radiative corrections to order O[απ)(q/M_1)], where q is the four-momentum transfer and M_1 is the mass of the decaying kaon, is obtained. Contributions of both the three- and four-body regions are accounted for. Besides, the emitted muon is considered to be polarized so the analysis is also focused on evaluating the radiative corrections to the longitudinal, transverse, and normal polarization components of the muon. The final formulas, with the triple integration of the bremsstrahlung photon variables re…
CP-violation in K_{S,L}->π^{+}π^{-}γand K_{S,L}->π^{+}π^{-}e^{+}e^{-} decays
The dependence of K_{S,L} ->π^{+}π^{-}γdecay probabilities on photon polarization is calculated. The phases of terms of amplitude that arise from the pion-pion interaction are obtained by using a simple realistic model of pion-pion interaction via virtual ρ-meson, instead of the ChPT. The results are compared with those of other authors and the origin of slight discrepancies is explained. It is shown that the standard ChPT approach for K_{S,L} -> π^{+}π^{-}γdecays cannot reproduce the contribution of the ρ-meson to the P-wave ππinteraction. The departure of the photon spectrum from pure bremss…
The momentum spectrum and number density of created bosons for two types of arbitrarily polarized electric fields are calculated and compared with those of created fermions, employing the equal-time Feshbach-Villars-Heisenberg-Wigner formalism which is confirmed that for an uniform and time-varying electric field it is completely equivalent to the quantum Vlasov equation in scalar QED. For an elliptically polarized field, it is found that the number density of created bosons is a square root of the number density of spin-up electrons times that of spin-down ones for a circularly polarized mult…
