160 research outputs found
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 and mass
differences are extracted from the and
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 .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 -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 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 and mixed
systems. The formalism is applied to compute the time evolution amplitudes of
and studied in DAPHNE and CPLEAR experiments. We also
introduce a new set of parameters that describe CP violation in
decays without recourse to isospin decomposition of the decay amplitudes.Comment: Latex, 19 page
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