激光脉冲和电子束对撞准确度的测量方法

超强激光脉冲与相对论电子束相互对撞是当前主要的强场量子电动力学（QED）实验手段。如何测量超强激光脉冲和电子束对撞的准确度,进而实现微米精度的准确对撞,是目前限制实验发展的重要因素。利用蒙特卡罗数值模拟方法,系统研究了超强激光脉冲和相对论电子束相互对撞过程,重点关注了电子和辐射光子动力学信息与激光脉冲和电子束对撞偏移量之间的对应关系。研究发现:辐射光子的空间分布信息,可以有效反映出激光脉冲和电子束的对撞偏移量。基于该研究结果,实验中可利用光子空间分布的信息,实现对激光脉冲和电子束对撞准确度的调节,从而有望促进强场QED实验技术的发展。     

Ultrarelativistic electron-positron plasma

Ultrarelativistic electron-positron plasmas can be produced in high-intensity laser fields and play a role in various astrophysical situations. Their properties can be calculated using QED at finite temperature. Here we will use perturbative QED at finite temperature for calculating various important properties, such as the equation of state, dispersion relations of collective plasma modes of photons and electrons, Debye screening, damping rates, mean free paths, collision times, transport coefficients, and particle production rates, of ultrarelativistic electron-positron plasmas. In particular, we will focus on electron-positron plasmas produced with ultra-strong lasers.     

Theories of Variable Mass Particles and Low Energy Nuclear Phenomena

Variable particle masses have sometimes been invoked to explain observed anomalies in low energy nuclear reactions (LENR). Such behavior has never been observed directly, and is not considered possible in theoretical nuclear physics. Nevertheless, there are covariant off-mass-shell theories of relativistic particle dynamics, based on works by Fock, Stueckelberg, Feynman, Greenberger, Horwitz, and others. We review some of these and we also consider virtual particles that arise in conventional Feynman diagrams in relativistic field theories. Effective Lagrangian models incorporating variable mass particle theories might be useful in describing anomalous nuclear reactions by combining mass shifts together with resonant tunneling and other effects. A detailed model for resonant fusion in a deuterium molecule with off-shell deuterons and electrons is presented as an example. Experimental means of observing such off-shell behavior directly, if it exists, is proposed and described. Brief explanations for elemental transmutation and formation of micro-craters are also given, and an alternative mechanism for the mass shift in the Widom–Larsen theory is presented. If variable mass theories were to find experimental support from LENR, then they would undoubtedly have important implications for the foundations of quantum mechanics, and practical applications may arise.     

Laser energy deposition in relativistic interactions with underdense plasmas

It is well established that, at sub-relativistic intensities, the absorption of laser light by underdense plasmas decreases with increasing pulse intensity as interaction enters a non-linear regime. On the other hand, as the relativistic interaction regime is reached, further absorption mechanisms can be activated which can account for a substantial energy transfer. Using the particle code WAKE, we performed numerical simulations of the relativistic interaction of intense laser pulses with underdense plasmas in conditions that can be experimentally tested. Our simulations show that, while the relativistic laser intensity generates a population of fast electrons, a considerable fraction of the pulse energy goes into a population of thermal electrons. These findings open new possibilities for a direct observation of relativistic interaction processes using high resolution soft X-ray techniques.     

QED Theory of Transition Probabilities and Line Profiles in Highly Charged Ions

A rigorous QED theory of the spectral line profiles is applied to transition probabilities in few-electron highly charged ions. Interelectron interaction corrections are included as well as radiative corrections. Parity nonconserving (PNC) amplitudes with effective weak interactions between the electrons and nucleus are also considered. QED and interelectron interaction corrections to the PNC amplitudes are derived.     

Energy levels and transition data of 3p63d8 and 3p53d9 configurations in Fe-like ions (Z = 57, 60, 62, 64, 65)

Atomic data of highly charged ions (HCIs) offer an attractive means for plasma diagnostic and stars identification, and the investigations on atomic data are highly desirable. Herein, based on the fully relativistic multi-configuration Dirac-Hartree-Fock (MCDHF) method, we have performed calculations of the fine-structure energy levels, wavelengths, transition rates, oscillator strengths, and line strengths for the lowest 21 states of 3p⁶3d⁸-3p⁵3d⁹ electric dipole (E1) transitions configurations in Fe-like ions (Z = 57, 60, 62, 64, 65). The correlation effects of valence-valence (VV) and core-valence (CV) electrons were systematically considered. In addition, we have taken into account transverse-photon (Breit) interaction and quantum electrodynamics (QED) corrections to treat accurately the atomic state wave functions in the final relativistic configuration interaction (RCI) calculations. Our calculated energy levels and transition wavelengths are in excellent agreement with the available experimental and theoretical results. Most importantly, we predicted some new transition parameters that have not yet been reported. These data would further provide critical insights into better analyzing the physical processes of various astrophysical plasmas.     

Signatures of the Unruh effect from electrons accelerated by ultrastrong laser fields

We calculate the radiation resulting from the Unruh effect for strongly accelerated electrons and show that the photons are created in pairs whose polarizations are perfectly correlated. Apart from the photon statistics, this quantum radiation can further be discriminated from the classical (Larmor) radiation via the different spectral and angular distributions. The signatures of the Unruh effect become significant if the external electromagnetic field accelerating the electrons is not too far below the Schwinger limit and might be observable with future facilities. Finally, the corrections due to the birefringent nature of the QED vacuum at such ultrahigh fields are discussed.     

On refractive processes in strong laser field quantum electrodynamics

Refractive processes in strong-field QED are pure quantum processes, which involve only external photons and the background electromagnetic field. We show analytically that such processes occurring in a plane-wave field and involving external real photons are all characterized by a surprisingly modest net exchange of energy and momentum with the laser field, corresponding to a few laser photons, even in the limit of ultra-relativistic laser intensities. We obtain this result by a direct calculation of the transition matrix element of an arbitrary refractive QED process and accounting exactly for the background plane-wave field. A simple physical explanation of this modest net exchange of laser photons is provided, based on the fact that the laser field couples with the external photons only indirectly through virtual electron–positron pairs. For stronger and stronger laser fields, the pairs cover a shorter and shorter distance before they annihilate again, such that the laser can transfer to them an energy corresponding to only a few photons. These results can be relevant for the future experiments aiming to test strong-field QED at present and next-generation facilities.     

Relativistic study of electromagnetic electron cyclotron instability based on trapped electrons in kappa-Maxwellian auroral plasmas

The presence of relativistic electrons in the Earth's magnetosphere may excite EMEC waves via resonant interaction. The understanding of EMEC waves induced by such electrons requires relativistic treatment. Therefore, we present here the investigation of EMEC waves based on relativistic trapped electrons represented by kappa-Maxwellian distribution in auroral plasmas. The analytical expressions of real frequency and relativistic growth rate are derived. Our numerical outcomes report that relativistic approximation increases the wave growth and causes reduction in the threshold value of drift velocity of trapped electrons for instability. The wave frequency that corresponds to the maximum growth decreases as we go from nonrelativistic limit to relativistic. The maximum growth increases with the increment in plasma frequency, perpendicular thermal velocity, drift velocity of trapped electrons, and Lorentz factor γ. Moreover, the relativistic effects on maximum growth are more pronounced for smaller values of drift velocity and perpendicular thermal velocity.     

普朗克谱分布的辐射场对束缚电子布居的影响

研究了外加普朗克辐射场对不同温度和密度下的等离子体的主量子壳层束缚电子的布居数的分布以及随时间的演化规律的调制作用.结果表明：当具有普朗克谱分布的辐射场的辐射温度接近于等离子体的电子温度,且辐射场的强度等于等效温度下的黑体谱辐射强度时,随着等离子体的时间演化,等离子体中主壳层束缚电子布居数分布由non-LTE分布过渡到LTE分布. 关键词： 流体动力学 激光等离子体 布居数 普朗克辐射场     

The enhancement effect in K-shell radiative recombination of \mbox{\sffamily\bfseries U}^{\hbox{\sffamily\bfseries\fontsize{10}{12}\selectfont 92+}} ions with cooling electrons

We report the results of the x-ray radiative recombination (RR) experiment at the electron cooler of the ESR storage ring performed, for the first time, for detuned (off-cooling) electron energies. In this experiment the recombination of stored, decelerated bare uranium ions with electrons in the energy range 0–1000 meV was studied by observing K-RR x-ray photons emitted from direct radiative recombination to the lowest n=1 state. In this way the RR process was studied in a state selective manner for several off-cooling electron energies. The measured dependency of the recombination rate on the relative electron energies for K-shell RR x-ray photons are compared with the predictions of both nonrelativistic and fully relativistic calculations for the radiative recombination. A role of the relativistic effects, which contribute substantially for higher relative electron energies, are discussed. Strong enhancement of the recombination rate is observed for the the zero relative electron energy (cooling condition) for the K-shell.     

The stimulated Breit-Wheeler process as a source of background <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> pairs at the international linear collider

Passage of beamstrahlung photons through the bunch fields at the interaction point of the ILC determines background pair production. The number of background pairs per bunch crossing due to the Breit-Wheeler, Bethe-Heitler and Landau-Lifshitz processes is well-known. However, the Breit-Wheeler process also takes place in and is modified by the bunch fields. A full QED calculation of this stimulated Breit-Wheeler process reveals cross-section resonances due to the virtual particle reaching the mass shell. The one-loop electron self-energy in the bunch field is also calculated and included as a radiative correction. The bunch field is considered to be a constant crossed electromagnetic field with associated bunch field photons. Resonance is found to occur whenever the energy of contributed bunch field photons is equal to the beamstrahlung photon energy. The stimulated Breit-Wheeler cross-section exceeds the ordinary Breit-Wheeler cross-section by several orders of magnitude and a significantly different pair background may result.      

Index summation in real time statistical field theory

We have written a Mathematica program that calculates the integrand corresponding to any amplitude in the closed-time-path formulation of real time statistical field theory. The program is designed so that it can be used by someone with no previous experience with Mathematica. It performs the contractions over the tensor indices that appear in real time statistical field theory and gives the result in the 1-2, Keldysh or RA basis. The program treats all fields as scalars, but the result can be applied to theories with dirac and lorentz structure by making simple adjustments. As an example, we have used the program to calculate the ward identity for the QED 3-point function, the QED 4-point function for two photons and two fermions, and the QED 5-point function for three photons and two fermions. In real time statistical field theory, there are seven 3-point functions, 15 4-point functions and 31 5-point functions. We produce a table that gives the results for all of these functions. In addition, we give a simple general expression for the KMS conditions between n-point green functions and vertex functions, in both the Keldysh and RA bases. PACS 11.10.Wx; 11.15.-q     

Electron temperatures of intense electron-beam-produced plasmas

A method of estimating the electron temperatures in intense, relativistic, electron-beam-produced plasmas is presented. This method compares spectral line intensities obtained from visible emission spectroscopy to those expected from local thermodynamic equilibrium (LTE) plasmas. The line intensities, particularly those originating from highly excited states, are corrected for the effects of the fast-beam electrons     

Radiative corrections to the cross section for <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> + <Emphasis Type="Italic">p</Emphasis> → <Emphasis Type="Italic">v + n</Emphasis> and the crossed processes

The Born cross section and the radiative corrections to its lowest order are considered in the framework of QED with structureless nucleons including the emission of virtual and real photons. The result is generalized to take into account the radiative corrections in higher orders of the perturbation theory in the leading and next-to-leading logarithmic approximation. The crossing processes are considered in the leading approximation. The text was submitted by the authors in English.     

Gamma-ray lasing by free nuclei and bymatter-antimatter beams

I discuss the possibilities to induce the gamma-ray emission departing from attempts to use the Mössbauer effect. Three separate approaches are considered: (A) Stimulated radiative transitions in deeply cooled nuclear beams with hidden inversion; (B) external two-photon ignition of nuclear lasing accompanied by gamma-ray giant pulse emission; and (C) burst-like radiative annihilation of relativistic beams of electrons and positrons or parapositronium atoms ignited by an external beam of soft photons.     

Higher-Order Kinetic Term for Controlling Photon Mass in Off-Shell Electrodynamics

In relativistic classical and quantum mechanics with Poincaré-invariant parameter, particle worldlines are traced out by the evolution of spacetime events. The formulation of a covariant canonical framework for the evolving events leads to a dynamical theory in which mass conservation is demoted from a priori constraint to the status of conserved Noether current for a certain class of interactions. In pre-Maxwell electrodynamics—the local gauge theory associated with this framework —events induce five local off-shell fields, which mediate interactions between instantaneous events, not between the worldlines which represent entire particle histories. The fifth field, required to compensate for dependence of gauge transformations on the evolution parameter, enables the exchange of mass between particles and fields. In the equilibrium limit, these pre-Maxwell fields are pushed onto the zero-mass shell, but during interactions there is no mechanism regulating the mass that photons may acquire, even when event trajectories evolve far into the spacelike region. This feature of the off-shell formalism requires the application of some ad hoc mechanism for controlling the photon mass in two opposite physical domains: the low energy motion of a charged event in classical Coulomb scattering, and the renormalization of off-shell quantum electrodynamics. In this paper, we discuss a nonlocal, higher derivative correction to the photon kinetic term, which provides regulation of the photon mass in a manner which preserves the gauge invariance and Poincaré covariance of the original theory. We demonstrate that the inclusion of this term is equivalent to an earlier solution to the classical Coulomb problem, and that the resulting quantum field theory is renormalized.