Seed and vacuum pair production in strong laser field

Researches on the electron-positron pair production in the presence of the intense laser field are reviewed, motivated by the theoretical importance of the nonperturbative QED problem and the worldwide development of high power laser facilities. According to the distinct experimental requirements and theoretical methods, two types of pair production are elaborated, which are, respectively, pair production in the combination of a seed particle and the strong laser, and vacuum pair production without a seed particle. The origin of the nonperturbative problem caused by the strong field is analyzed. The main ideas, realisation, achievements, validity, challenges and bottleneck problems of the nonperturbative methods developed for each type of the pair production problem are discussed.     

强场下真空中粒子对产生的研究进展

随着激光技术的飞快发展,激光强度不断提高,超强外场下真空中正负电子对产生的过程,即能量向质量转化过程,已经成为一个研究热点。主要综述了近几年量子Vlasov方程方法和计算量子场论(数值求解Dirac方程)方法在研究强场下真空中正负电子对产生方面的进展,分别介绍了空间均匀场和空间不均匀场下的粒子对产生的情况。第一种情况主要介绍双脉冲结构振荡电场中电子-正电子对的产生、强双频振荡电场中非微扰电子-正电子对的产生、频率调制的激光场中电子-正电子对的产生和Dirac真空对啁啾外场的快速分辨。第二种情况主要介绍优化空间局域电场提高粒子对的产生率、多个势阱-垒结构的振荡场对粒子对产生的增强、振荡 Sauter 电势中正负电子对产生的问题、操纵Dirac真空以控制其在场诱导下的衰变、作为信息传输介质的Dirac真空还有正负电子对产生中的相干和非相干啁啾机制的转变。     

Electron-Positron Pair Production in a Strong Laser Field Enhanced by an Assisted High Frequency Weak Field

Electron-positron pair production in a strong laser field enhanced by an assisted high frequency weak field is investigated by solving the quantum Vlasov equation.The average and residual pair number densities are obtained for sinusoid electric field and it is found that the high frequency assisted weak field will enhance pair production significantly.There exists an optimal frequency of assisted field that makes the pair production number density get a maximum one,which is a few orders of higher than that without assisted field.We also discuss the other possible assisted fields.     

Monopole pair production in a magnetic field

The rate of monopole pair production in a weak external magnetic field is computed by a semiclassical method. The result is analogous to that for electron-positron pair production in an electric field.     

Polarized triplet production by circularly polarized photons

A process of pair production by a circularly polarized photon in the field of an unpolarized atomic electron was considered in the Weizaecker-Williams approximation. The degree of longitudinal polarization of a positron and an electron was calculated. An exclusive cross section, as well as a spectral distribution, were obtained. We estimate the accuracy of our calculations at the level of a few percent. We show the identity of the positron polarization for the considered process and for the process of pair production in the screened Coulomb field of a nucleus.     

Pair production at strong coupling in weak external fields

The rate of electron-positron pair production in a weak external electric field at large values of e is computed. The method is extended to compute the rate of monopole-antimonopole pair production in a weak external magnetic field at large magnetic charge.     

Electron-positron pair production by photons in nonuniform strong fields

A probability of electron-positron pair production by photons in strong nonuniform fields is derived by applying a model trajectory method in the frame of a semiclassical approach. In addition to the well known invariant field parameter chi, a new invariant parameter nu is introduced to characterize the nonuniformity of the field. For nu>1, the obtained expression is reduced to the uniform-field approximation while it approaches the Bethe-Heitler formula for nu<1. The pair production is predicted for relatively weak external fields where the uniform-field approximation gives no effect. The theory agrees well with the experimental results of crystal-assisted pair production.     

Analytical Study of Pair Production Rate from Vacuum in an Elliptic Polarized Field by a Two-Level Transition Technique

Electron-positron pair production rate created from vacuum in the presence of an elliptically polarized laser field is investigated.By applying the technique of two level transition amplitude,a routine for obtaining pair production rate is presented,and approximate analytical expressions are given both for the low frequency strong field regime and the high frequency weak field regime.We found that for an elliptically polarized field,the electron-positron pair production rate decrease when the elliptic eccentricity increase in the high frequency weak field regime,however,in the low frequency strong field regime,there is almost the same electron-positron pair production rate as in the constant electric field case.     

Investigation of the production of electron-positron pairs in nucleon-nucleon interactions with the HADES detector

The inclusive production of electron-positron pairs in proton-proton and deuteron-proton collisions at a beam kinetic energy of 1.25 GeV per nucleon was studied with the HADES (High Acceptance Dielectron Spectrometer) detector. The main objective of the deuteron-proton experiment was to investigate pair production in quasifree neutron-proton collisions. In the invariant-mass region M > 140 MeV/c ², the invariant-mass spectrum determined in this channel shows a significant enhancement of the pair yield in relation to that in the case of proton-proton collisions.     

A new possible mechanism of lepton-pair radiation from quark-gluon plasmas

The lepton-pair production mechanism resulting from escaping quarks interacting with a collective confining colour field is discussed. The pair production rate is estimated and the spectrum of pair invariant mass is calculated. It is suggested that measuring the angle asymmetry of radiated lepton-pairs could indicate quark-gluon plasma formation.     

Monolithic source of photon pairs

The creation of monolithically integratable sources of single and entangled photons is a top research priority with formidable challenges: The production, manipulation, and measurement of the photons should all occur in the same material platform, thereby fostering stability and scalability. Here we demonstrate efficient photon pair production in a semiconductor platform, gallium arsenide. Our results show type-I spontaneous parametric down-conversion of laser light from a 2.2 mm long Bragg-reflection waveguide, and we estimate its internal pair production efficiency to be 2.0×10(-8) (pairs/pump photon). This is the first time that significant pair production has been demonstrated in a structure that can be electrically self-pumped and which can form the basis for passive optical circuitry, bringing us markedly closer to complete integration of quantum optical technologies.     

Nonresonant muon pair production in electron-positron annihilation in the field of light wave

In the frame of the Born approximation it was theoretically investigated nonresonant muon pair production in e ⁺ e ⁻ collision in the field of elliptically polarized electromagnetic wave in the general relativistic case. It was analyzed in detail the reaction kinematics. It was derived the expressions for the amplitude and the cross section of the nonresonant muon pair production in e ⁺ e ⁻ annihilation in the moderately strong field. It was demonstrated that the partial cross-section is factorized as a product of the cross section of the muon pair production from e ⁺ e ⁻ pair in the absence of the external field and the probability of emission and absorption of photons from the wave. Original Text ? Astro, Ltd., 2009. The article is published in the original.     

Top pair production in the littlest Higgs model with T-parity

In the framework of the littlest Higgs model with T-parity,we study the top pair production at the next generation colliders like LHC and ILC.We find that the order O(αs) corrections to the standard model top pair production cross section at LHC can be very small and the magnitude is below 1%.However,the magnitude of corrections to the standard model top pair production rate at ILC may be over 5% for reasonable values'of the parameters.Besides this,the corrections to the asymmetry ALR(tt) may be more sizable. Therefore,the top pair production at ILC may serve as a probe of the littlest Higgs model with T-parity,especially the asymmetry ALR(tt).     

Processes with heavy ion collisions

Some Coulomb effects in heavy ion collisions are considered. Among them the process of muon and lepton pair creation, Coulomb and unitary corrections, statistics of multiple pair production. Effects of multiple photon exchange in process of lepton pair production by linearly polarized photon on nuclei are considered. This process is used for measuring the polarization of initial photon. Relativistic muon energy loss due to the light lepton pair production in the Coulomb field are calculated. Also we consider the effects of multiple photon exchange in elastic lepton scattering on unscreened atomic field and discuss the possible experimental testing.     

Anisotropy of Thermal Dileptons

The meaningful specific anisotropy in the angle distribution of leptons with respect to the three-momentum of pair is predicted as a feasibility signature of synchrotron-like mechanism resulting from the quarks interacting with a collective confining color field in the heavy ion collisions. The lepton pair production rate and the spectrum of pair invariant mass are presented for this new dilepton source that is apparently not taken into consideration in the available phenomenological estimates.     

Effect of symmetrical frequency chirp on pair production

By using Dirac–Heisenberg–Wigner formalism we study electron–positron pair production for linear, elliptic, nearly circular, and circular polarizations of electric fields with symmetrical frequency chirp, and we obtain momentum spectra and pair yield. The difference of results among polarized fields is obvious for the small chirp. When the chirp parameter increases, the momentum spectra tend to exhibit the multiphoton pair generation that is characterized by the multi-concentric ring structure. The increase of the number density is also remarkable compared to the case of asymmetrical frequency chirp. Note that the dynamically assisted Schwinger mechanism plays an important role for the enhanced pair production in the symmetrical frequency chirp.     

Electron-positron pair creation and Oleinik resonances

We consider the process of electron-positron pair creation by an impact of ultra-intense laser beam on a highly relativistic nucleus, with an exact account for its finite mass. It is shown that the probability rates of pair production increase tremendously due to the nuclear recoil. Numerical calculations also show the existence of very narrow resonances in differential probability rates of pair production, which are recognized to be Oleinik resonances, as they originate from poles of the photon propagator. Using our exact treatment of the colliding nucleus, we analyze also the effect of dressing it by the laser field on the process of pair creation.     

Dynamically assisted pair production for scalar QED by two fields

By solving the quantum Vlasov equation, the dynamically assisted pair production for scalar quantum electrodynamics (QED) is investigated. It is verified that this mechanism still holds true for boson pair production. Two combinations of two electric fields having different time scales under various time delays are considered; it is found that the oscillations of the momentum spectrum and the number density of created bosons decrease with increasing time delay, and the latter has a maximum value when the time delay equals zero. Furthermore, the differences in vacuum pair production between bosons and fermions are also studied, and they are helpful for distinguishing the created bosons from fermions.