Enhanced Pair Production Research Articles

Enhanced vacuum pair production by combination of two spatially separated electric fields

The effective enhancement of the pair production rate using a subcritical electromagnetic field is an active area of interest in quantum electrodynamics. Enhanced pair production was investigated using the Dirac–Heisenberg–Wigner (DHW) formalism with spatially separated electric fields. Symmetric and asymmetric combinations of two separate electric fields with the same temporal shape were considered. The interplay and dynamical assistance between the fields were examined from a numerical perspective to elucidate the effects of the spatial distance and asymmetry of the field on the pair production efficiency. For the symmetric combination, the total particle number was reduced with an increase in the distance between the two fields up to one Compton length and then remained constant with distance. For the asymmetric combination, the total number of created pairs increased significantly up to a distance of one Compton length. It was also determined that not only was the separation distance crucial for enhancing pair production, but the spatial field asymmetries were also important, both of which had nontrivial effects on the particle momentum distribution. Finally, we have studied the validity of the DHW and analytical approximation in the spatially separated two electric fields. We found that the analytical approximation could almost estimate the DHW results.

Effect of symmetrical frequency chirp on pair production* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11875007, 11935008, and 11965020).

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.

Electric and magnetic axion quark nuggets, their stability and their detection

The present work studies the dynamics of axion quark nuggets introduced in Zhitnitsky (JCAP 0310:010, 2003) and developed further in the works (Zhitnitsky in Phys Rev D 74:043515, 2006; Lawson and Zhitnitsky in Phys Lett B 724, 17, 2013; Lawson and Zhitnitsky in Phys Rev D 95:063521, 2017; Liang and Zhitnitsky in Phys Rev D 94:083502, 2016; Ge et al. in Phys Rev D 97:043008, 2018; Zhitnitsky in Phys Dark Univ 22:1, 2018; Lawson and Zhitnitsky in Phys Dark Univ 100295, 2019; Raza et al. in Phys Rev D 98:103527, 2018; Fischer et al. in Phys Rev D 98:043013, 2018; van Waerbeke and Zhitnitsky in Phys Rev D 99:043535, 2019; Flambaum and Zhitnitsky in Phys Rev D 99:043535, 2019; Lawson and Zhitnitsky in JCAP 02:049, 2017; Ge et al. in Phys Rev D 99:116017, 2019). The new feature considered here is the possibility that these nuggets become ferromagnetic. This possibility was pointed out in Tatsumi (Phys Lett B 489:280 2000) for ordinary quark nuggets, although ferromagnetism may also take place due some anomaly terms found in Son and Zhitnitsky (Phys Rev D 70:074018, 2004), Son and Stephanov (Phys Rev D 77:014021, 2008) and Melitski and Zhitnitsky (Phys Rev D 72:045011, 2005). The purpose of the present letter however, is not to give evidence in favor or against these statements. Instead, it is focused in some direct consequences of this ferromagnetic behavior, if it exists. The first is that the nugget magnetic field induces an electric field due to the axion wall, which may induce pair production by Schwinger effect. Depending on the value of the magnetic field, the pair production can be quite large. A critical value for such magnetic field at the surface of the nugget is obtained, and it is argued that the value of the magnetic field of Tatsumi (2000) is at the verge of stability and may induce large pair production. The consequences of this enhanced pair production may be unclear. It may indicate that the the nugget evaporates, but on the other hand it may be just an indication that the intrinsic magnetic field disappears and the nuggets evolves to a non magnetized state such as in Zhitnitsky (2003), Oaknin and Zhitnitsky (Phys. Rev. D 71:023519, 2005), Zhitnitsky (2006), Lawson and Zhitnitsky (2013), Lawson and Zhitnitsky (2017), Liang and Zhitnitsky (2016), Ge et al. (2018), Zhitnitsky (2018), Lawson and Zhitnitsky (2019), Raza et al. (2018), Fischer et al. (2018), van Waerbeke and Zhitnitsky (2019), Flambaum and Zhitnitsky (2019), Lawson and Zhitnitsky (2017), and Ge et al. (2019). The interaction of such magnetic and electric nugget with the troposphere of the earth is also analyzed. It is suggested that the cross section with the troposphere is enhanced in comparison with a non magnetic nugget but still, it does not violate the dark matter collision bounds. Consequently, these nuggets may be detected by impacts on water or by holes in the mountain craters (Pace VanDevender et al. in Sci Rep 7:8758, 2017). However, if the magnetic field does not decay before the actual universe, then this would lead to high energy electron flux due to its interaction with the electron gases of the Milky Way. This suggests that these magnetized quarks may be a considerably part of dark matter, but only if their hypothetical magnetic and electric fields are evaporated.

Enhanced pair production in collisions of intense pulsed lasers with a high-energy electron beam

Production of electron-positron pairs by a relativistic electron beam propagating through an intense laser field is reconsidered by use of the Monte Carlo method within the quantum electrodynamics theory. The scenario of the SLAC experiment is analyzed [D. Burke et al., Phys. Rev. Lett. 79, 1626 (1997)], on the basis of which a scheme for pair production by a high-energy electron beam colliding with a composed laser field is proposed. The laser field consists of two components with different frequencies. We show that this composed laser field can facilitate pair creation by the double-photon Breit-Wheeler process and could significantly amplify the production probability. Our predictions can be tested by utilizing presently available high-energy electron accelerators and high-intensity laser facilities.

Enhanced pair production of heavy Majorana neutrinos at the LHC

Towards experimental confirmations of the type-I seesaw mechanism, we explore a prospect of discovering the heavy Majorana right-handed neutrinos (RHNs) from a resonant production of a new massive gauge boson ($Z^{\prime}$) and its subsequent decay into a pair of RHNs ($Z^{\prime}\to NN$) at the future LHC. Recent simulation studies have shown that the discovery of the RHNs through this process is promising in the future. However, the current LHC data very severely constrains the production cross section of the $Z^{\prime}$ boson into a dilepton final states, $pp \to Z^{\prime}\to \ell^{+}\ell^{-} $ ($\ell=e$ or $\mu$). Extrapolating the current bound to the future, we find that a significant enhancement of the branching ratio ${\rm BR}(Z^{\prime}\to NN$) over ${\rm BR}(Z^{\prime}\to \ell^{+}\ell^{-}$) is necessary for the future discovery of RHNs. As a well-motivated simple extension of the Standard Model (SM) to incorporate the $Z^\prime$ boson and the type-I seesaw mechanism, we consider the minimal U(1)$_X$ model. We point out that this model can yield a significant enhancement up to ${\rm BR}(Z^{\prime}\to NN)/{\rm BR}(Z^{\prime}\to \ell^{+}\ell^{-}) \simeq 5$ (per generation). This is in sharp contrast with the minimal $B-L$ model, a benchmark scenario commonly used in simulation studies, which predicts ${\rm BR}(Z^{\prime}\to NN)/{\rm BR}(Z^{\prime}\to \ell^{+}\ell^{-}) \simeq 0.5$ (per generation). With such an enhancement and a realistic model-parameter choice to reproduce the neutrino oscillation data, we conclude that the possibility of discovering RHNs with a $300 \; {\rm fb}^{-1}$ luminosity implies that the $Z^\prime$ boson will be discovered with a luminosity of $170.5 \;{\rm fb}^{-1}$ ($125 \; {\rm fb}^{-1}$) for the normal (inverted) hierarchy of the light neutrino mass pattern.

Enhanced pair production in strong fields by multiple-slit interference effect with dynamically assisted Schwinger mechanism

In the quantum kinetic framework, we investigate the momentum spectrum and the number density of created electron-positron pairs from vacuum in the combined electric fields composed of two sets of alternating-sign electric field pulse trains, a strong but slowly varying one and a weak but rapidly changing one. It is found that the pair production can be strongly enhanced by combining the multiple-slit interference effect with the dynamically assisted Schwinger mechanism. By considering the contribution of the transverse momentum, we find that the number density of created particles depends linearly on the electric field pulse number, i.e., a power law with index 1. Moreover, we study the effect of interpulse time delay on pair production and find that the number density is very sensitive to the interpulse time delay. The symmetry of the momentum spectrum for an $N$-pulse electric field and the difference of the multiple-slit interference effect between the nonperturbative Schwinger mechanism and the perturbative multiphoton electron-positron pair creation are also studied. Some possible explanations for observed results of momentum spectrum and number density are also given and discussed.

Enhanced Pair Production in Multicenter Systems by SuperIntense Lasers

Enhanced Pair Production in Multicenter Systems by SuperIntense Lasers

Strongly enhanced pair production in combined high- and low-frequency laser fields

Production of particle-antiparticle pairs by a high-energy probe photon propagating through a high-intensity laser field is considered in the nonperturbative interaction regime. The laser field consists of a strong low-frequency and a weak high-frequency component. While for each component alone photoproduction of pairs is strongly suppressed, we show that their combination can largely amplify the pair production probability by facilitating to bridge the energetic barrier of the process. Our predictions can be tested by utilizing presently available high-intensity laser devices.

Enhanced Schwinger pair production in many-centre systems

Electron–positron pair production is considered for many-centre systems with multiple bare nuclei immersed in a constant electric field. It is shown that there are two distinct regimes where the pair production rate is enhanced. At small interatomic distance, the effective charge of the nuclei approaches the critical charge where the ground state dives into the negative continuum. This facilitates the transition from the negative to the positive energy states, which in turn increases the pair production rate. At larger atomic distance, the enhancement is due to the crossing of resonances and the pair production proceeds by the resonantly enhanced pair production mechanism. These processes are studied within a simple one-dimensional model. A numerical method is developed to evaluate the transmission coefficient in relativistic quantum mechanics, which is required in the calculation of the pair production rate. The latter is evaluated for systems with many (up to five) nuclei. It is shown that the production rate for many-centre systems can reach a few orders of magnitude above Schwinger’s tunnelling result in a static field.

New mechanism for the generation of electron-positron pairs in Laser-Matter Interaction: Resonantly Enhanced Pair Production in a molecular system

A new mechanism for pair production from the interaction of a laser with two nuclei is presented. The latter takes advantage of the Stark effect in diatomic molecules and the presence of molecular resonances in the negative and positive energy continua. Both move in the complex energy plane as the interatomic distance and the electric field strength are varied. We demonstrate that there is an enhancement of pair production at the crossing of these resonances. This mechanism is studied in a very simple one-dimensional model where the nuclei are modeled by delta function potential wells and the laser by a constant electric field. The position of resonances is evaluated by using the Weyl-Titchmarch-Kodaira theory, which allows to treat singular boundary value problems and to compute the spectral density. The rate of producing pairs is also computed. It is shown that this process yields a positron production rate which is approximately an order of magnitude higher than in the single nucleus case and a few orders of magnitudes higher than Schwinger's tunneling result in a static field.

Resonantly Enhanced Pair Production in a Simple Diatomic Model

A new mechanism for the production of electron-positron pairs from the interaction of a laser field and a fully ionized diatomic molecule in the tunneling regime is presented. When the laser field is turned off, the Dirac operator has resonances in both the positive and the negative energy continua while bound states are in the mass gap. When this system is immersed in a strong laser field, the resonances move in the complex energy plane: the negative energy resonances are pushed to higher energies while the bound states are Stark shifted [F. Fillion-Gourdeau et al., J. Phys. A 45, 215304 (2012)]. It is argued here that there is a pair production enhancement at the crossing of resonances by looking at a simple one-dimensional model: the nuclei are modeled simply by Dirac delta potential wells while the laser field is assumed to be static and of finite spatial extent. The average rate for the number of electron-positron pairs produced is evaluated and the results are compared to the one and zero nucleus cases. It is shown that positrons are produced by the resonantly enhanced pair production mechanism, which is analogous to the resonantly enhanced ionization of molecular physics. This phenomenon could be used to increase the number of pairs produced at low field strength, allowing the study of the Dirac vacuum.

Strangeness production within parton–hadron–string dynamics (PHSD)

Parton-hadron–string dynamics (PHSD) transport approach consistently simulates the full evolution of a relativistic heavy ion collision from the initial hard scatterings and string formation through the dynamical deconfinement phase transition to quark gluon plasma (QGP) to the hadronization and to the subsequent interactions in the hadronic phase. The transport theoretical description of quarks and gluons is based on a dynamical quasiparticle model for partons matched to reproduce lattice QCD results in thermodynamic equilibrium. The transition from partonic to hadronic degrees of freedom is described by covariant transition rates for the fusion of quark–antiquark pairs or three quarks (antiquarks). Studying Pb+Pb reactions from 40 to 158 A GeV, we find that at most 40% of the collision energy is stored in the dynamics of the partons. This implies a large fraction of non-partonic, i.e. hadronic or string-like matter, which can be viewed as a hadronic corona; thus, neither hadronic nor purely partonic models can be employed to extract physical conclusions in comparing model results with data. On the other hand, comparing the PHSD results to those of the hadron-string dynamics (HSD) approach without the phase transition to QGP, we observe that the existence of the partonic phase has a sizeable influence on the transverse mass distribution of final kaons due to the repulsive partonic mean fields. Furthermore, we find a significant effect of the QGP on the production of multi-strange antibaryons due to a slightly enhanced pair production in the partonic phase from massive time-like gluon decay and to a more abundant formation of strange antibaryons in the hadronization process.

Anomalous 4-jet events at LEP: a signal of low scale technicolour?

We suggest that the anomalous 4-jet events recently reported by ALEPH may be the first indication of low scale technicolour. According to our interpretation about half of the events are due to resonantly enhanced pair production of charged technipions, of mass around 55 GeV, each decaying into a pair of jets, the other half being due to standard processes. The resonant enhancement is due to a nearby technirho resonance in the mass range 150–200 GeV, leading to hugely enhanced signals at the forthcoming LEP run at s = 160 GeV since the CM energy would be closer to the peak of the resonance.