Probability Of Pair Production Research Articles

Effect of a critical magnetic field on the control of scalar neutral boson pair production in the context of Lorentz-symmetry violation

This study investigates the production of neutral scalar boson pairs in static electromagnetic fields resulting from Lorentz-symmetry violation (LSV), with a focus on the parity-even sector of the CPT-even photon sector in the Standard Model Extension (SME). Utilizing a cross-configuration involving inhomogeneous static electric fields and homogeneous static magnetic fields, the analysis of the probability of bosons pair production identifies three different regimes determined by a critical magnetic field. Below the critical value, creation is exponentially suppressed; at the critical value, the number density of created bosons remains constant, and above the critical field, there is exponential amplification. This behavior prompts an additional investigation using von Neumann entanglement entropy to analyze fluctuations in the bosonic vacuum.

Bi-local fields interacting with a constant electric field and related problems including the Schwinger effect

The bi-local fields are the quantum fields of two-particle systems, the bi-local systems, bounded by relativistic potentials. Since those form constrained dynamical systems, it is limited to introduce the interactions of the bi-local fields with other fields. In this paper, the interaction between the bi-local fields and a constant electric field E is studied with consideration for the consistency of constraints. Then, we evaluate the Schwinger effect for the bi-local systems, which gives the pair production probability of the bound states as a function of the charges of respective particles and the coupling constant in the binding potential. Through this analysis, we also discuss the possibility for the dissociation of bi-local systems due to the electric field.

Worldline instantons for nonlinear Breit-Wheeler pair production and Compton scattering

Worldline instantons have previously been used to study the probability of Schwinger pair production (both the exponential and preexponential parts) and photon-stimulated pair production (the exponential part). Previous studies obtained the pair-production probability on the probability level by using unitarity, i.e., the imaginary part of the effective action for Schwinger pair production or the imaginary part of the polarization tensor for photon-stimulated pair production. The corresponding instantons are closed loops in the complex plane. Here, we show how to use instantons on the amplitude level, which means open instanton lines with start and end points representing fermions at asymptotic times. The amplitude is amputated with the Lehmann-Symanzik-Zimmermann reduction formula using, in general, field-dependent asymptotic states. We show how to use this formalism for photon-stimulated/Breit-Wheeler pair production and nonlinear Compton scattering.

Particle-antiparticle pair production from vacuum and the imaginary proper time method

Using the imaginary proper time method, based on the Fock method of solving the relativistic wave equations, the process of fermionic and scalar pairs production from a vacuum by a constant uniform electric field is considered. The relative (conditional) probability of the one pair production, which does not depend on the possible production of other pairs, was obtained with exponential accuracy, and the absolute probability of pair production, which takes into account the particle statistics, was obtained with pre-exponential accuracy.

Keldysh field theory of a driven dissipative Mott insulator: Nonequilibrium response and phase transitions

Understanding strongly correlated systems driven out of equilibrium is a challenging task necessitating the simultaneous treatment of quantum mechanics,dynamical constraints and strong interactions. A Mott insulator subjected to a uniform and static electric field is prototypical, raising key questions such as the fate of Bloch oscillations with increasing correlation strength, the approach to a steady state DC transport regime and the role of dissipation in it, and electric field driven phase transitions. We develop here an effective large-N Keldysh field theory for studying nonequilibrium transport in a regular one-dimensional dissipative Mott insulator system subjected to a uniform electric field. Upon abruptly turning on the electric field (a quench), a transient oscillatory current response reminiscent of Bloch oscillations is found. In the regime of small tunneling conductance the amplitude of these oscillations, over a large time window, decreases as an inverse square power-law in time, ultimately going over to an exponential decay beyond a large characteristic time that increases with N. Such a relaxation to a steady state DC response is absent in the dissipation free Hubbard chain at half filling. The steady state current at small fields is governed by large distance cotunneling, a process absent in the equilibrium counterpart. The low-field DC current has a Landau-Zener-Schwinger form but qualitatively differs from the expression for pair-production probability for the dissipation free counterpart. The breakdown of perturbation theory in the Mott phase possibly signals a nonequilibrium phase transition to a metallic phase. Our study sheds light on the approach of a driven, dissipative strongly correlated system to a nonequilibrium steady state and also provides a general analytic microscopic framework for understanding other nonequilibrium phenomena in these systems.

Perturbative methods for assisted nonperturbative pair production

In the dynamically assisted Schwinger mechanism, the pair production probability is significantly enhanced by including a weak, rapidly varying field in addition to a strong, slowly varying field. In a previous paper we showed that several features of dynamical assistance can be understood by a perturbative treatment of the weak field. Here we show how to calculate the prefactors of the higher-orders terms, which is important because the dominant contribution can come from higher orders. We give a new and independent derivation of the momentum spectrum using the worldline formalism, and extend our WKB approach to calculate the amplitude to higher orders. We show that these methods are also applicable to doubly assisted pair production.

Ground state instability in nonrelativistic QFT and Euler\u2013Heisenberg Lagrangian via holography

We study the ground state instability of a strongly coupled QFT with the z=2 Schrödinger symmetry in a constant electric field using probe branes holography. The system is N_f{mathcal {N}}=2 hypermultiplet fermions at zero charge density in the supergravity Schrödinger background. We show that the instability occurs due to Schwinger-like effect and an insulator state will undergo a transition to a conductor state. We calculate the decay rate of instability and pair production probability by using the gauge / gravity duality. At zero temperature for massive fermions, we suggest that the instability occurs if the critical electric field is larger than the confining force between fermions, which is proportional to an effective mass. We demonstrate that, at zero temperature, the Schrödinger background simulates the role of a crystal lattice for massive particles. We also show that at finite ’t Hooft coupling for particles with a mass higher than frac{sqrt{lambda }}{pi beta }, in this background, instability does not occur, no matter how large the external electric field is, meaning that we have a perfect insulator. Moreover, we derive Euler–Heisenberg effective Lagrangian for the non-relativistic strongly correlated quantum theory from probe branes holography in Schrödinger spacetime.

Pair Production Induced by Ultrashort and Ultraintense Laser Pulses in Plasmas

The probability of Schwinger pair production is calculated, which is induced by an ultraintense and ultrashort laser pulse propagating in a plasma. The dependence of the probability on the amplitude of the laser pulse and the frequency of plasmas is analyzed. Particularly, the effect of the pulse duration on the probability is discussed, by introducing a pulse-shape function to describe the temporal shape of the laser pulse. The results show that a laser with shorter pulse is more efficient in pair production. The probability of pair production increases when the order of the duration is comparable to the period of a laser.

Fermion production by a dependent of time electric field in de Sitter universe

Fermion production in external electric field on de Sitter expanding universe is analyzed. The amplitude and probability of pair production are computed. We obtain from our calculations that the modulus of the momentum is no longer conserved. The rate of pair production in an electric field is found to be important in the early universe when the expansion factor was large comparatively with the particle mass. A computation of the total probability is presented in a particular case and the result proves to be nonvanishing only in strong gravitational fields.

Critical Schwinger pair production. II. Universality in the deeply critical regime

We study electron-positron pair production by spatially inhomogeneous electric fields. Depending on the localization of the field, a critical point (critical surface) exists in the space of field configurations where the pair production probability vanishes. Near criticality, pair production exhibits universal properties similar to those of continuous phase transitions. We extend results previously obtained in the semiclassical (weak-field) critical regime to the deeply critical regime for arbitrary peak field strength. In this regime, we find an enhanced universality, featuring a unique critical exponent $\ensuremath{\beta}=3$ for all sufficiently localized fields. For a large class of field profiles, we also compute the nonuniversal amplitudes.

Asymptotic expansion of pair production probability in a time-dependent electric field

We study particle creation in a single pulse of an electric field in scalar quantum electrodynamics. We investigate the parameter condition for the case where the dynamical pair creation and Schwinger mechanism respectively dominate. Then, an asymptotic expansion for the particle distribution in terms of the time interval of the applied electric field is derived. We compare our result with particle creation in a constant electric field with a finite-time interval. These results coincide in an extremely strong field, however they differ in general field strength. We interpret the reason of this difference as a nonperturbative effect of high-frequency photons in external electric fields. Moreover, we find that the next-to-leading-order term in our asymptotic expansion coincides with the derivative expansion of the effective action.

Semiclassical description of soliton-antisoliton pair production in particle collisions

We develop a consistent semiclassical method to calculate the probability of topological soliton-antisoliton pair production in collisions of elementary particles. In our method one adds an auxiliary external field pulling the soliton and antisoliton in the opposite directions. This transforms the original scattering process into a Schwinger pair creation of the solitons induced by the particle collision. One describes the Schwinger process semiclassically and recovers the original scattering probability in the limit of vanishing external field. We illustrate the method in (1+1)-dimensional scalar field model where the suppression exponents of soliton-antisoliton production in the multiparticle and two-particle collisions are computed numerically.

Nonperturbative pair production in interpolating fields

We compare the effects of timelike, lightlike and spacelike one-dimensional inhomogeneities on the probability of nonperturbative pair production in strong fields. Using interpolating coordinates we give a unifying picture in which the effect of the inhomogeneity is encoded in branch cuts and poles circulated by complex worldline instantons. For spacelike inhomogeneities the length of the cut is related to the existence of critical points, while for lightlike inhomogeneities the cut contracts to a pole and the instantons become contractable to points, leading to simplifications particular to the lightlike case. We calculate the effective action in fields with up to three nonzero components, and investigate its behaviour under changes in field dependence.

Pair production from residues of complex worldline instantons

We study nonperturbative pair production in electric fields with lightlike inhomogeneities, using complex worldline instantons. We show that the instanton contribution to the pair production probability is a complex contour integral over the instanton itself, and that pair production in the considered fields can be recast in terms of Cauchy's residue theorem. The instantons contribute residues from the poles they circulate (i.e. give local contributions), and the invariance of complex integrals under contour deformation manifests in the instanton contributions as invariance under a set of generalised, complex, reparameterisations.

Characterization of novel water-equivalent PRESAGE® dosimeters for megavoltage and kilovoltage x-ray beam dosimetry

In this paper we introduce three novel PRESAGE® dosimeters referred to as metal optimized dosimeters (MODs) 1, 2 and 3, and determine their sensitivity, as well as their water equivalency. All three formulations contained very small concentrations (0.01 wt%) of metal compounds. The radiological properties were key factors that were considered when designing and formulating the new dosimeters. The dosimeters were prepared in spectrophotometric cuvettes, irradiated with a 6 MV X-ray beam, and the change in optical density of each dosimeter was measured using a spectrophotometer. Results show that all three MOD formulations exhibit radiological properties closer to water than the recently introduced PRESAGE® dosimeter formulation referred to as formulation A, with mass densities of the novel formulations varying by only 3.9% from that of water, as compared to 5.3% for the commercial formulation. Whereas the novel formulations have almost identical Zeff values to that of water (Zeff = 7.42), the Zeff for the commercial formulation was 3.7% higher than that of water. Comparison of mass energy coefficients for all MOD formulations showed a maximum variation of approximately 0.6 times closer to water especially MOD 3 whereas commercial formulation was 1.23 times larger than water at approximately 40 keV. The same effect was observed for mass attenuation coefficients comparison. MOD 3 was also more sensitive to radiation than MOD 1 and 2 as a result of the inclusion of bromine-based halocarbons in the formulation. All novel MOD formulations were comparable to commercial formulation in terms of probability of Compton scatter and pair production compared to water. However, the probability of photoelectric absorption in the three novel MOD formulations varied significantly less (1.3 times greater) from that of water as compared to the commercial formulation (1.8 times greater). Given that all three novel MOD formulations displayed improved radiological properties over any of the currently available PRESAGE® dosimeter formulations makes them ideal candidates for tissue mimics in dosimetry of clinical megavoltage and kilovoltage x-ray beams.

Spontaneous parametric downconversion in waveguides: what's loss got to do with it?

We derive frequency correlation and exit probability expressions for photons generated via spontaneous parametric downconversion (SPDC) in nonlinear waveguides that exhibit linear scattering loss. Such loss is included within a general Hamiltonian formalism by connecting waveguide modes to reservoir modes with a phenomenological coupling Hamiltonian, the parameters of which are later related to the usual loss coefficients. In the limit of a low probability of SPDC pair production, the presence of loss requires that we write the usual lossless generated pair state as a reduced density operator, and we find that this density operator is naturally composed of two photon, one photon, and zero photon contributions. The biphoton probability density, or joint spectral intensity (JSI), associated with the two-photon contribution is determined not only by a phase matching term, but also by a loss matching term. The relative sizes of the loss coefficients within this term lead to three qualitatively different regimes of SPDC JSIs. If either the pump or generated photon loss is much higher than the other, the side lobes of the phase matching squared sinc function are washed out. On the other hand, if pump and generated photon loss are appropriately balanced, the lossy JSI is identical to the lossless JSI. Finally, if the generated photon loss is frequency dependent, the shape of the JSI can be altered more severely, potentially leading to generated photons that are less frequency correlated though also produced less efficiently when compared to photons generated in low-loss waveguides.

Pair production of Dirac particles in a $$d+1$$ d + 1 -dimensional noncommutative space–time

This work addresses the computation of the probability of fermionic particle pair production in \((d+1)\)-dimensional noncommutative Moyal space. Using Seiberg–Witten maps, which establish relations between noncommutative and commutative field variables, up to the first order in the noncommutative parameter \(\theta \), we derive the probability density of vacuum–vacuum pair production of Dirac particles. The cases of constant electromagnetic, alternating time-dependent, and space-dependent electric fields are considered and discussed.

Localisation in worldline pair production and lightfront zero-modes

The nonperturbative probability of pair production in electric fields depending on lightfront time is given exactly by the locally constant approximation. We explain this by showing that the worldline path integral defining the effective action contains a constraint, which localises contributing paths on hypersurfaces of constant lightfront time. These paths are lightfront zero-modes and there can be no pair production without them; the effective action vanishes if they are projected out.

Nonlinear Breit-Wheeler process in the collision of a photon with two plane waves

The nonlinear Breit-Wheeler process of electron-positron pair production off a probe photon colliding with a low-frequency and a high-frequency electromagnetic wave that propagate in the same direction is analyzed. We calculate the pair-production probability and the spectra of the created pair in the nonlinear Breit-Wheeler processes of pair production off a probe photon colliding with two plane waves or one of these two plane waves. The differences of these two cases are discussed. We evidently show, in the two-wave case, the possibility of Breit-Wheeler pair production with simultaneous photon emission into the low-frequency wave and the high multiphoton phenomena: (i) Breit-Wheeler pair production by absorption of the probe photon and a large number of photons from the low-frequency wave, in addition to the absorption of one photon from the high-frequency wave; (ii) Breit-Wheeler pair production by absorption of the probe photon and one photon from the high-frequency wave with simultaneous emission of a large number of photons into the low-frequency wave. The phenomenon of photon emission into the wave cannot happen in the one-wave case. Compared with the one-wave case, the contributions from high multiphoton processes are largely enhanced in the two-wave case. The results presented in this article show a possible way to access the observations of the phenomenon of photon emission into the wave and high multiphoton phenomenon in Breit-Wheeler pair production even with the laser-beam intensity of order ${10}^{18}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$.

Semiclassical analysis of pair creation in de Sitter space

We study a massive scalar field theory in de Sitter space. Using worldline instanton approach, we calculate probability of pair production in weak-field limit. In addition to exponential factor we derive pre-exponential factor. Within this approach the vanishing probability for odd-dimensional de Sitter space gets a clear geometrical interpretation. We find leading contribution to imaginary part of two point correlator in $\phi^3$-theory.