113 research outputs found
Optimal Control of Quantum Dynamics : A New Theoretical Approach
A New theoretical formalism for the optimal quantum control has been
presented. The approach stems from the consideration of describing the
time-dependent quantum system in terms of the real physical observables, viz.,
the probability density rho(x,t) and the quantum current j(x,t) which is well
documented in the Bohm's hydrodynamical formulation of quantum mechanics. The
approach has been applied for manipulating the vibrational motion of HBr in its
ground electronic state under an external electric field.Comment: 4 figure
A note on "symmetric" vielbeins in bimetric, massive, perturbative and non perturbative gravities
We consider a manifold endowed with two different vielbeins
and corresponding to two different metrics and
. Such a situation arises generically in bimetric or massive
gravity (including the recently discussed version of de Rham, Gabadadze and
Tolley), as well as in perturbative quantum gravity where one vielbein
parametrizes the background space-time and the other the dynamical degrees of
freedom. We determine the conditions under which the relation can be
imposed (or the "Deser-van Nieuwenhuizen" gauge chosen). We clarify and correct
various statements which have been made about this issue.Comment: 20 pages. Section 7, prop. 6 and 7. added. Some results made more
precis
Two Theorems on Flat Space-Time Gravitational Theories
The first theorem states that all flat space-time gravitational theories must
have a Lagrangian with a first term that is an homogeneous (degree-I) function
of the 4-velocity , plus a functional of . The second
theorem states that all gravitational theories that satisfy the strong
equivalence principle have a Lagrangian with a first term
plus an irrelevant term. In both cases the theories must issue from a unique
variational principle. Therefore, under this condition it is impossible to find
a flat space-time theory that satisfies the strong equivalence principle.Comment: 11 page
Reality, measurement and locality in Quantum Field Theory
It is currently believed that the local causality of Quantum Field Theory
(QFT) is destroyed by the measurement process. This belief is also based on the
Einstein-Podolsky-Rosen (EPR) paradox and on the so-called Bell's theorem, that
are thought to prove the existence of a mysterious, instantaneous action
between distant measurements. However, I have shown recently that the EPR
argument is removed, in an interpretation-independent way, by taking into
account the fact that the Standard Model of Particle Physics prevents the
production of entangled states with a definite number of particles. This result
is used here to argue in favor of a statistical interpretation of QFT and to
show that it allows for a full reconciliation with locality and causality.
Within such an interpretation, as Ballentine and Jarret pointed out long ago,
Bell's theorem does not demonstrate any nonlocality.Comment: 15 pages. Published versio
Negative Energy Density States for the Dirac Field in Flat Spacetime
Negative energy densities in the Dirac field produced by state vectors that
are the superposition of two single particle electron states are examined. I
show that for such states the energy density of the field is not bounded from
below and that the quantum inequalities derived for scalar fields are
satisfied. I also show that it is not possible to produce negative energy
densities in a scalar field using state vectors that are arbitrary
superpositions of single particle states.Comment: 11 pages, LaTe
Spin-Statistics Theorem in Path Integral Formulation
We present a coherent proof of the spin-statistics theorem in path integral
formulation. The local path integral measure and Lorentz invariant local
Lagrangian, when combined with Green's functions defined in terms of time
ordered products, ensure causality regardless of statistics. The Feynman's
prescription ensures the positive energy condition regardless of
statistics, and the abnormal spin-statistics relation for both of spin-0 scalar
particles and spin-1/2 Dirac particles is excluded if one imposes the positive
norm condition in conjunction with Schwinger's action principle. The minus
commutation relation between one Bose and one Fermi field arises naturally in
path integral. The Feynman's prescription also ensures a smooth
continuation to Euclidean theory, for which the use of the Weyl anomaly is
illustrated to exclude the abnormal statistics for the scalar and Dirac
particles not only in 4-dimensional theory but also in 2-dimensional theory.Comment: 19 pages. Some minor changes in the presentation and a correction of
a misprint. Int. J. Mod. Phys. A (in press
Massive Spin 3/2 Electrodynamics
We study the general non-minimally coupled charged massive spin 3/2 model
both for its low energy phenomenological properties and for its unitarity,
causality and degrees of freedom behaviour. When the model is viewed as an
effective theory, its parameters (after ensuring the correct excitation count)
are related to physical characteristics, such as the magnetic moment g factor,
by means of low energy theorems. We also provide the corresponding higher spin
generalisation. Separately, we consider both low and high energy unitarity, as
well as the causality aspects of our models. None (including truncated N=2
supergravity) is free of the minimal model's acausality.Comment: 23 pages, 1 figure, LaTeX and axodraw.sty, novel Majorana-type term
included; results unaltere
Polarization Correlations of 1S0 Proton Pairs as Tests of Bell and Wigner Inequalities
In an experiment designed to overcome the loophole of observer dependent
reality and satisfying the counterfactuality condition, we measured
polarization correlations of 1S0 proton pairs produced in 12C(d,2He) and
1H(d,He) reactions in one setting. The results of these measurements are used
to test the Bell and Wigner inequalties against the predictions of quantum
mechanics.Comment: 8 pages, 4 figure
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