378 research outputs found
Analyticity of the Scattering Amplitude, Causality and High-Energy Bounds in Quantum Field Theory on Noncommutative Space-Time
In the framework of quantum field theory (QFT) on noncommutative (NC)
space-time with the symmetry group , we prove that the
Jost-Lehmann-Dyson representation, based on the causality condition taken in
connection with this symmetry, leads to the mere impossibility of drawing any
conclusion on the analyticity of the -scattering amplitude in
, being the scattering angle. Discussions on the possible
ways of obtaining high-energy bounds analogous to the Froissart-Martin bound on
the total cross-section are also presented.Comment: 25 page
"Minus c" Symmetry in Classical and Quantum Theories
It is shown that the transformations of the charge conjugation in classical
electrodynamics and in quantum theory can be interpreted as the consequences of
the symmetry of Maxwell and Dirac equations with respect to the inversion of
the speed of light: c to -c; t to t; (x,y,z) to (x,y,z), where c is the speed
of light; t is the time; x, y, z are the spatial variables.
The elements of physical interpretation are given.Comment: 12 pages, LaTeX, Poster at the Fifth International Conference on
Squeezed States and Uncertainty Relations, May 27-31, 1997, Balatonfured,
Hungar
On the Relationship between Resolution Enhancement and Multiphoton Absorption Rate in Quantum Lithography
The proposal of quantum lithography [Boto et al., Phys. Rev. Lett. 85, 2733
(2000)] is studied via a rigorous formalism. It is shown that, contrary to Boto
et al.'s heuristic claim, the multiphoton absorption rate of a ``NOON'' quantum
state is actually lower than that of a classical state with otherwise identical
parameters. The proof-of-concept experiment of quantum lithography [D'Angelo et
al., Phys. Rev. Lett. 87, 013602 (2001)] is also analyzed in terms of the
proposed formalism, and the experiment is shown to have a reduced multiphoton
absorption rate in order to emulate quantum lithography accurately. Finally,
quantum lithography by the use of a jointly Gaussian quantum state of light is
investigated, in order to illustrate the trade-off between resolution
enhancement and multiphoton absorption rate.Comment: 14 pages, 7 figures, submitted, v2: rewritten in response to
referees' comments, v3: rewritten and extended, v4: accepted by Physical
Review
Taylor-Lagrange renormalization scheme, Pauli-Villars subtraction, and light-front dynamics
We show how the recently proposed Taylor-Lagrange renormalization scheme can
lead to extensions of singular distributions which are reminiscent of the
Pauli-Villars subtraction. However, at variance with the Pauli-Villars
regularization scheme, no infinite mass limit is performed in this scheme. As
an illustration of this mechanism, we consider the calculation of the
self-energy in second order perturbation theory in the Yukawa model, within the
covariant formulation of light-front dynamics. We show in particular how
rotational invariance is preserved in this scheme.Comment: 9 pages, 1 figure To be published in Physical Review
Relativistic Lee Model on Riemannian Manifolds
We study the relativistic Lee model on static Riemannian manifolds. The model
is constructed nonperturbatively through its resolvent, which is based on the
so-called principal operator and the heat kernel techniques. It is shown that
making the principal operator well-defined dictates how to renormalize the
parameters of the model. The renormalization of the parameters are the same in
the light front coordinates as in the instant form. Moreover, the
renormalization of the model on Riemannian manifolds agrees with the flat case.
The asymptotic behavior of the renormalized principal operator in the large
number of bosons limit implies that the ground state energy is positive. In 2+1
dimensions, the model requires only a mass renormalization. We obtain rigorous
bounds on the ground state energy for the n-particle sector of 2+1 dimensional
model.Comment: 23 pages, added a new section, corrected typos and slightly different
titl
I. The Isotopic Foldy-Wouthuysen Representation and Chiral Symmetry
The paper introduces the isotopic Foldy-Wouthuysen representation. This
representation was used to derive equations for massive interacting fermion
fields. When the interaction Hamiltonian commutes with the matrix, these
equations possess chiral invariance irrespective of whether fermions have mass
or are massless. The isotopic Foldy-Wouthuysen representation preserves the
vector and axial currents irrespective of the fermion mass value. In the Dirac
representation, the axial current is preserved only for massless fermions. In
the isotopic Foldy-Wouthuysen representation, the ground state of fermions
(vacuum) turns out to be degenerate, and therefore there is the possibility of
spontaneously breaking parity (P - symmetry). This study considers the example
of constructing a chirally symmetric quantum electrodynamics framework in the
isotopic Foldy-Wouthuysen representation. A number of physical processes are
calculated in the lowest orders of the perturbation theory. Final results of
the calculations agree with the results of the standard quantum
electrodynamics.Comment: 37 pages, 9 figure
Trajectories and Particle Creation and Annihilation in Quantum Field Theory
We develop a theory based on Bohmian mechanics in which particle world lines
can begin and end. Such a theory provides a realist description of creation and
annihilation events and thus a further step towards a "beable-based"
formulation of quantum field theory, as opposed to the usual "observable-based"
formulation which is plagued by the conceptual difficulties--like the
measurement problem--of quantum mechanics.Comment: 11 pages LaTeX, no figures; v2: references added and update
Identical Particles and Permutation Group
Second quantization is revisited and creation and annihilation operators
areshown to be related, on the same footing both to the algebra h(1), and to
the superalgebra osp(1|2) that are shown to be both compatible with Bose and
Fermi statistics.
The two algebras are completely equivalent in the one-mode sector but,
because of grading of osp(1|2), differ in the many-particle case.
The same scheme is straightforwardly extended to the quantum case h_q(1) and
osp_q(1|2).Comment: 8 pages, standard TEX, DFF 205/5/94 Firenz
Forward scattering amplitudes and the thermal operator representation
We develop systematically to all orders the forward scattering description
for retarded amplitudes in field theories at zero temperature. Subsequently,
through the application of the thermal operator, we establish the forward
scattering description at finite temperature. We argue that, beyond providing a
graphical relation between the zero temperature and the finite temperature
amplitudes, this method is calculationally quite useful. As an example, we
derive the important features of the one loop retarded gluon self-energy in the
hard thermal loop approximation from the corresponding properties of the zero
temperature amplitude.Comment: 16 pages, 6 figure
Current conservation, screening and the magnetic moment of the resonance. -- 1. Formulation without quark degrees of freedom
The pion-nucleon bremsstrahlung is
studied in a new form of current conservation. According to this condition, the
internal and external particle radiation parts of the radiation
amplitude have opposite signs, i.e., they contain terms which must cancel each
other.
Therefore, one has a screening of the internal and external particle
radiation in the bremsstrahlung. In particular, it is shown that the
double exchange diagram with the vertex
cancel against the appropriate longitudinal part of the external particle
radiation diagrams. Consequently, a model independent relation between the
magnetic dipole moments of the and resonances and the
anomalous magnetic moment of the proton is obtained, where
is expressed by as and in agreement
with the values extracted from the fit for the experimental cross section of
the reaction.Comment: 37 pages, 2 figures and 1 tabl
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