3,910 research outputs found
A Lorentz-Violating Alternative to Higgs Mechanism?
We consider a four-dimensional field-theory model with two massless fermions,
coupled to an Abelian vector field without flavour mixing, and to another
Abelian vector field with flavour mixing. Both Abelian vectors have a
Lorentz-violating kinetic term, introducing a Lorentz-violation mass scale ,
from which fermions and the flavour-mixing vector get their dynamical masses,
whereas the vector coupled without flavour mixing remains massless. When the
two coupling constants have similar values in order of magnitude, a mass
hierarchy pattern emerges, in which one fermion is very light compared to the
other, whilst the vector mass is larger than the mass of the heavy fermion. The
work presented here may be considered as a Lorentz-symmetry-Violating
alternative to the Higgs mechanism, in the sense that no scalar particle
(fundamental or composite) is necessary for the generation of the vector-meson
mass. However, the model is not realistic given that, as a result of Lorentz
Violation, the maximal (light-cone) speed seen by the fermions is smaller than
that of the massless gauge boson (which equals the speed of light in vacuo) by
an amount which is unacceptably large to be compatible with the current tests
of Lorentz Invariance, unless the gauge couplings assume unnaturally small
values. Possible ways out of this phenomenological drawback are briefly
discussed, postponing a detailed construction of more realistic models for
future work.Comment: 16 pages revtex, three eps figures incorporate
Sequential measurement of conjugate variables as an alternative quantum state tomography
It is shown how it is possible to reconstruct the initial state of a
one-dimensional system by measuring sequentially two conjugate variables. The
procedure relies on the quasi-characteristic function, the Fourier-transform of
the Wigner quasi-probability. The proper characteristic function obtained by
Fourier-transforming the experimentally accessible joint probability of
observing "position" then "momentum" (or vice versa) can be expressed as a
product of the quasi-characteristic function of the two detectors and that,
unknown, of the quantum system. This allows state reconstruction through the
sequence: data collection, Fourier-transform, algebraic operation, inverse
Fourier-transform. The strength of the measurement should be intermediate for
the procedure to work.Comment: v2, 5 pages, no figures, substantial improvements in the
presentation, thanks to an anonymous referee. v3, close to published versio
Comparative evaluation of agricultural publications and other farming news media
Call number: LD2668 .T4 1958 P3
Vacuum polarization induced by a uniformly accelerated charge
We consider a point charge fixed in the Rindler coordinates which describe a
uniformly accelerated frame. We determine an integral expression of the induced
charge density due to the vacuum polarization at the first order in the fine
structure constant. In the case where the acceleration is weak, we give
explicitly the induced electrostatic potential.Comment: 13 pages, latex, no figures, to appear in Int. J. Theor. Phys
Double-valuedness of the electron wave function and rotational zero-point motion of electrons in rings
I propose that the phase of an electron's wave function changes by when
the electron goes around a loop maintaining phase coherence. Equivalently, that
the minimum orbital angular momentum of an electron in a ring is
rather than zero as generally assumed, hence that the electron in a ring has
azimuthal zero point motion. This proposal provides a physical explanation for
the origin of electronic `quantum pressure', it implies that a spin current
exists in the ground state of aromatic ring molecules, and it suggests an
explanation for the ubiquitousness of persistent currents observed in
mesoscopic rings
Casimir repulsion in moving media
Casimir-Lifshitz interaction emerging from relative movement of layers in
stratified dielectric media (e.g., non-uniformly moving fluids) is considered.
It is shown that such movement may result in a repulsive Casimir-Lifshitz force
exerted on the layers, with the simplest possible structure consisting of three
adjacent layers of the same dielectric medium, where the middle one is
stationary and the other two are sliding along a direction parallel to the
interfaces of the layers.Comment: 22 pages, 10 figure
Interference in Bohmian Mechanics with Complex Action
In recent years, intensive effort has gone into developing numerical tools
for exact quantum mechanical calculations that are based on Bohmian mechanics.
As part of this effort we have recently developed as alternative formulation of
Bohmian mechanics in which the quantum action, S, is taken to be complex [JCP
{125}, 231103 (2006)]. In the alternative formulation there is a significant
reduction in the magnitude of the quantum force as compared with the
conventional Bohmian formulation, at the price of propagating complex
trajectories. In this paper we show that Bohmian mechanics with complex action
is able to overcome the main computational limitation of conventional Bohmian
methods -- the propagation of wavefunctions once nodes set in. In the vicinity
of nodes, the quantum force in conventional Bohmian formulations exhibits rapid
oscillations that pose severe difficulties for existing numerical schemes. We
show that within complex Bohmian mechanics, multiple complex initial conditions
can lead to the same real final position, allowing for the description of nodes
as a sum of the contribution from two or more crossing trajectories. The idea
is illustrated on the reflection amplitude from a one-dimensional Eckart
barrier. We believe that trajectory crossing, although in contradiction to the
conventional Bohmian trajectory interpretation, provides an important new tool
for dealing with the nodal problem in Bohmian methods
Self-induced decoherence approach: Strong limitations on its validity in a simple spin bath model and on its general physical relevance
The "self-induced decoherence" (SID) approach suggests that (1) the
expectation value of any observable becomes diagonal in the eigenstates of the
total Hamiltonian for systems endowed with a continuous energy spectrum, and
(2), that this process can be interpreted as decoherence. We evaluate the first
claim in the context of a simple spin bath model. We find that even for large
environments, corresponding to an approximately continuous energy spectrum,
diagonalization of the expectation value of random observables does in general
not occur. We explain this result and conjecture that SID is likely to fail
also in other systems composed of discrete subsystems. Regarding the second
claim, we emphasize that SID does not describe a physically meaningful
decoherence process for individual measurements, but only involves destructive
interference that occurs collectively within an ensemble of presupposed
"values" of measurements. This leads us to question the relevance of SID for
treating observed decoherence effects.Comment: 11 pages, 4 figures. Final published versio
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