Final Particle States Research Articles

Description of processes passing at finite space-time intervals in the framework of quantum field theory

We consider a novel quantum field-theoretical approach to the description of processes passing at finite space-time intervals based on the Feynman diagram technique in the coordinate representation. The most know phenomena of this type are neutrino and neutral kaon oscillations. The experimental setting of these processes demands that the rules of passing to the momentum representation in the Feynman diagram technique be adjusted in accordance with it, which leads to a modification of the Feynman propagator in the momentum representation. The approach does not make use of wave packets: both initial and final particle states are described by plane waves, which simplifies the calculations considerably. We demonstrate the validity of the formalism by applying it to describing the decay of an unstable particle and neutrino oscillations. It is shown that the considered approach correctly reproduces the known results.

Coherence length of neutrino oscillations in a quantum field-theoretical approach

We consider a novel quantum field-theoretical approach to the description of processes passing at finite space-time intervals based on the Feynman diagram technique in the coordinate representation. The most known processes of this type are neutrino and neutral kaon oscillations. The experimental setting of these processes requires one to adjust the rules of passing to the momentum representation in the Feynman diagram technique in accordance with it, which leads to a modification of the Feynman propagator in the momentum representation. The approach does not make use of wave packets, both initial and final particle states are described by plane waves, which simplifies the calculations considerably. We consider neutrino oscillation processes, where the neutrinos are produced in three-particle weak decays of nuclei and detected in the charged-current interaction with nuclei or in the charged- and neutral-current interactions with electrons. Particular examples are considered and it is shown that the momentum spread of the produced neutrinos and the energy dependence of the differential cross section of the detection process result in the suppression of neutrino oscillation, which is characterized by a coherence length specific for a pair of production and detection processes. This coherence length turns out to be much less than the coherence length in the standard quantum-mechanical approach defined by the quantum uncertainty of neutrino momentum.

Description of processes passing at finite space and time intervals in the framework of QFT

We consider a new approach to the description in the framework of QFT of processes passing at finite space and time intervals. The formalism is based on the Feynman diagram technique in the coordinate representation, in which the rules of passing to the momentum representation are modified in accordance with the experimental setup of neutrino oscillation experiments. In effect, only the propagators of particles in the momentum representation are modified, while all the other standard Feynman rules in the momentum representation remain the same. Since the initial and final particle states are described by plane waves, the approach does not need the use of wave packets, which greatly simplifies the calculations of amplitudes. Taking as examples the processes of displaced pion decay, neutral kaon and neutrino oscillations we show that the approach under consideration correctly reproduces the known standard results.

Quantum field-theoretical descriprion of neutrino oscillations in T2K experiment

We consider neutrino oscillations in the T2K experiment using a new quantum field-theoretical approach to the description of processes passing at finite space-time intervals. It is based on the Feynman diagram technique in the coordinate representation, supplemented by modified rules of passing to the momentum representation. Effectively this leads to the Feynman propagators in the momentum representation being modified, while the rest of the Feynman rules remain unchanged. The approach does not make use ofwave packets, the initial and final particle states are described by plane waves, which essentially simplifies the calculations. The oscillation fading out due to momentum distribution of the initial particles is taken into account. The obtained results reproduce the predictions of the standard description and confirm that the far detector position corresponds to the first minimum for muon production probability and the first maximum for electron production probability.

Quantum black holes with charge, color and spin at the LHC

In low-scale gravity scenarios, quantum black holes could be produced at the Large Hadron Collider (LHC) provided the Planck scale is not higher than a few TeV. Based on fundamental principles and a few basic assumptions, we have constructed a model for quantum black hole production and decay in proton–proton collisions. By performing a particle-level simulation at LHC energies, we have estimated cross sections and branching fractions for final-state particle topologies that would uniquely identify quantum black holes in LHC detectors. If the Planck scale is about a TeV, even with the most pessimistic assumptions, the rates for quantum black hole production are estimated to be above backgrounds, and some of the final-particle states are not found in standard model processes. Our results could form the starting point for a detailed investigation of quantum black holes by the LHC experiments.

Auger recombination in strained quantum wells

A nonthreshold mechanism for Auger recombination of nonequilibrium carriers in quantum wells with strained layers is investigated theoretically. It is shown that the dependence of the Auger recombination rate on the magnitude of the strain and the height of the heterobarriers for electrons and holes can be analyzed only by calculating the overlap integrals between initial and final particle states microscopically. In quantum wells with strained layers the presence of strain affects qualitatively and quantitatively the electron-hole overlap integral. The dependence of the Auger recombination rate on the quantum well parameters, the magnitude of the stress, and temperature are analyzed for heterostructures based on InGaAsP/InP and InGaAlAs/InP.

Scattering of superstrings by cosmic strings

We exactly solve the superstring scattering by a straight cosmic string. That is, we exactly quantize the Neveu-Schwarz-Ramond and the Green-Schwarz superstrings propagating in a conical space of deficit angle 8π Gμ, μ being the cosmic-string tension. As for the purely bosonic string, if the superstring touches the cosmic string, the scattering is inelastic, since the internal superstring modes become excited and mixing of particle- and antiparticle-modes takes place, leading to different initial and final particle states. If there is no collision, the superstring only suffers a deflection of ±4 πGμ and the oscillator modes only suffer a polarization change. All the transformations between the ingoing and outgoing states are explicitly computed in closed form. The mass formula and number operators are analyzed. We also generalize all these results to the case when the cosmic string is spinning; the new features, in this case, appear for the time string-coordinate; the propagation of fermionic coordinates is not affected by the cosmic-string spin.