Evolution of coupled fermions under the influence of an external axial-vector field

The evolution of coupled fermions interacting with external axial-vector fields is described with help of the classical field theory. We formulate the initial conditions problem for the system of two coupled fermions in (3+1)-dimensional space-time. This problem is solved using the perturbation theory. We obtain in the explicit form the expressions for the leading and next to the leading order terms in the expansion over the strength of external fields. It is shown that in the relativistic limit the intensity of the fermion field coincides with the transition probability in the two neutrinos system interacting with moving and polarized matter.Comment: RevTeX4, 8 pages, 1 eps figure; revised variant, neutral currents interactions of flavor neutrinos are included, some typos corrected, 1 reference added; accepted for publication in Eur.Phys.J.

Propagation et oscillations en théorie des champs

After a review of the problems associated with the conventional treatment of particle oscillations, an oscillation formula is derived within the framework of quantum field theory. The oscillating particle is represented by its propagator and the initial and final states by wave packets. It is obviously relativistic from the start and moreover applies both to stable (neutrinos) and unstable particles (K and B mesons, unstable neutrinos). CPLEAR and DAFNE experiments are studied as examples, with special attention directed to CP violation. The problems resulting from equal energies/momentum/velocities prescriptions are analyzed and solved. Oscillations of associated particles are found to be nonexistent. The relativistic generalization of the Wigner-Weisskopf equation is also derived

New Physics and Neutrino Oscillation

Description of neutrino oscillation in the case of Non-Standard neutrino Interaction (NSI) is briefly presented. The NSI causes the entanglement between internal degrees of freedom of neutrinos (mass, spin, flavour) and other accompanying particles in the production and detection processes. In such case neutrinos are mostly in the mixed states. Role of the density matrix in description of neutrino oscillation process is shortly explained.Comment: 3 pages. Talk given at NOW 2010: Neutrino Oscillation Workshop, Conca Specchiulla (Otranto), Lecce, Italy, 4-11 Sep 201

Mixing and oscillations of neutral particles in Quantum Field Theory

We study the mixing of neutral particles in Quantum Field Theory: neutral boson field and Majorana field are treated in the case of mixing among two generations. We derive the orthogonality of flavor and mass representations and show how to consistently calculate oscillation formulas, which agree with previous results for charged fields and exhibit corrections with respect to the usual quantum mechanical expressions.Comment: 8 pages, revised versio

Neutrino Wave Packets in Quantum Field Theory

We present a model of neutrino oscillations in the framework of quantum field theory in which the propagating neutrino and the particles participating to the production and detection processes are described by wave packets. The neutrino state is a superposition of massive neutrino wave packets determined by the production process, as naturally expected from causality. We show that the energies and momenta of the massive neutrino components relevant for neutrino oscillations are in general different from the average energies and momenta of the propagating massive neutrino wave packets, because of the effects of the detection process. Our results confirm the correctness of the standard expression for the oscillation length of extremely relativistic neutrinos and the existence of a coherence length.Comment: 25 page

Unitarity triangle test of the extra factor of two in particle oscillation phases

There are claims in the literature that in neutrino oscillations and oscillations of neutral kaons and B-mesons the oscillation phase differs from the standard one by a factor of two. We reconsider the arguments leading to this extra factor and investigate, in particular, the non-relativistic regime. We actually find that the very same arguments lead to an ambiguous phase and that the extra factor of two is a special case. We demonstrate that the unitarity triangle (UT) fit in the Standard Model with three families is a suitable means to discriminate between the standard oscillation phase and the phase with an extra factor of two. If $K_L - K_S$ and $B_{dH} - B_{dL}$ mass differences are extracted from the $K^0 - \bar K^0$ and $B_d^0 - \bar B_d^0$ data, respectively, with the extra factor of two in the oscillation phases, then the UT fit becomes significantly worse in comparison with the standard fit and the extra factor of two is disfavoured by the existing data at the level of more than 3 $\sigma$.Comment: 16 pages, 2 figure

Neutrino oscillations: Entanglement, energy-momentum conservation and QFT

We consider several subtle aspects of the theory of neutrino oscillations which have been under discussion recently. We show that the $S$-matrix formalism of quantum field theory can adequately describe neutrino oscillations if correct physics conditions are imposed. This includes space-time localization of the neutrino production and detection processes. Space-time diagrams are introduced, which characterize this localization and illustrate the coherence issues of neutrino oscillations. We discuss two approaches to calculations of the transition amplitudes, which allow different physics interpretations: (i) using configuration-space wave packets for the involved particles, which leads to approximate conservation laws for their mean energies and momenta; (ii) calculating first a plane-wave amplitude of the process, which exhibits exact energy-momentum conservation, and then convoluting it with the momentum-space wave packets of the involved particles. We show that these two approaches are equivalent. Kinematic entanglement (which is invoked to ensure exact energy-momentum conservation in neutrino oscillations) and subsequent disentanglement of the neutrinos and recoiling states are in fact irrelevant when the wave packets are considered. We demonstrate that the contribution of the recoil particle to the oscillation phase is negligible provided that the coherence conditions for neutrino production and detection are satisfied. Unlike in the previous situation, the phases of both neutrinos from $Z^0$ decay are important, leading to a realization of the Einstein-Podolsky-Rosen paradox.Comment: 30 pages, 3 eps figures; presentation improved, clarifications added. To the memory of G.T. Zatsepi

Neutrino oscillations: Quantum mechanics vs. quantum field theory

A consistent description of neutrino oscillations requires either the quantum-mechanical (QM) wave packet approach or a quantum field theoretic (QFT) treatment. We compare these two approaches to neutrino oscillations and discuss the correspondence between them. In particular, we derive expressions for the QM neutrino wave packets from QFT and relate the free parameters of the QM framework, in particular the effective momentum uncertainty of the neutrino state, to the more fundamental parameters of the QFT approach. We include in our discussion the possibilities that some of the neutrino's interaction partners are not detected, that the neutrino is produced in the decay of an unstable parent particle, and that the overlap of the wave packets of the particles involved in the neutrino production (or detection) process is not maximal. Finally, we demonstrate how the properly normalized oscillation probabilities can be obtained in the QFT framework without an ad hoc normalization procedure employed in the QM approach.Comment: LaTeX, 42 pages, 1 figure; v2: minor clarifications, matches published version; v3: Corrected the discussion of the conditions under which an oscillation probability can be sensibly defined in the QFT approach (sec. 5.2.4

Field theory approach to K0-K0bar and B0-B0bar systems

Quantum field theory provides a consistent framework to deal with unstable particles. We present here an approach based on field theory to describe the production and decay of unstable $K^0-\bar{K^0}$ and $B^0-\bar{B^0}$ mixed systems. The formalism is applied to compute the time evolution amplitudes of $K^0$ and $\bar{K^0}$ studied in DAPHNE and CPLEAR experiments. We also introduce a new set of parameters that describe CP violation in $K \to \pi\pi$ decays without recourse to isospin decomposition of the decay amplitudes.Comment: Latex, 19 page