145 research outputs found
Waves on Noncommutative Spacetimes
Waves on ``commutative'' spacetimes like R^d are elements of the commutative
algebra C^0(R^d) of functions on R^d. When C^0(R^d) is deformed to a
noncommutative algebra {\cal A}_\theta (R^d) with deformation parameter \theta
({\cal A}_0 (R^d) = C^0(R^d)), waves being its elements, are no longer
complex-valued functions on R^d. Rules for their interpretation, such as
measurement of their intensity, and energy, thus need to be stated. We address
this task here. We then apply the rules to interference and diffraction for d
\leq 4 and with time-space noncommutativity. Novel phenomena are encountered.
Thus when the time of observation T is so brief that T \leq 2 \theta w, where w
is the frequency of incident waves, no interference can be observed. For larger
times, the interference pattern is deformed and depends on \frac{\theta w}{T}.
It approaches the commutative pattern only when \frac{\theta w}{T} goes to 0.
As an application, we discuss interference of star light due to cosmic strings.Comment: 19 pages, 5 figures, LaTeX, added references, corrected typo
Interacting Quantum Topologies and the Quantum Hall Effect
The algebra of observables of planar electrons subject to a constant
background magnetic field B is given by A_theta(R^2) x A_theta(R^2) the product
of two mutually commuting Moyal algebras. It describes the free Hamiltonian and
the guiding centre coordinates. We argue that A_theta(R^2) itself furnishes a
representation space for the actions of these two Moyal algebras, and suggest
physical arguments for this choice of the representation space. We give the
proper setup to couple the matter fields based on A_theta(R^2) to
electromagnetic fields which are described by the abelian commutative gauge
group G_c(U(1)), i.e. gauge fields based on A_0(R^2). This enables us to give a
manifestly gauge covariant formulation of integer quantum Hall effect (IQHE).
Thus, we can view IQHE as an elementary example of interacting quantum
topologies, where matter and gauge fields based on algebras A_theta^prime with
different theta^prime appear. Two-particle wave functions in this approach are
based on A_theta(R^2) x A_theta(R^2). We find that the full symmetry group in
IQHE, which is the semi-direct product SO(2) \ltimes G_c(U(1)) acts on this
tensor product using the twisted coproduct Delta_theta. Consequently, as we
show, many particle sectors of each Landau level have twisted statistics. As an
example, we find the twisted two particle Laughlin wave functions.Comment: 10 pages, LaTeX, Corrected typos, Published versio
Spontaneous Breaking of Lorentz Symmetry and Vertex Operators for Vortices
We first review the spontaneous Lorentz symmetry breaking in the presence of
massless gauge fields and infraparticles. This result was obtained long time
ago in the context of rigorious quantum field theory by Frohlich et. al. and
reformulated by Balachandran and Vaidya using the notion of superselection
sectors and direction-dependent test functions at spatial infinity for the
non-local observables. Inspired by these developments and under the assumption
that the spectrum of the electric charge is quantized, (in units of a
fundamental charge e) we construct a family of vertex operators which create
winding number k, electrically charged Abelian vortices from the vacuum (zero
winding number sector) and/or shift the winding number by k units. In
particular, we find that for rotating vortices the vertex operator at level k
shifts the angular momentum of the vortex by k \frac{{\tilde q}}{q}, where
\tilde q is the electric charge of the quantum state of the vortex and q is the
charge of the vortex scalar field under the U(1) gauge field. We also show
that, for charged-particle-vortex composites angular momentum eigenvalues shift
by k \frac{{\tilde q}}{q}, {\tilde q} being the electric charge of the
charged-particle-vortex composite. This leads to the result that for
\frac{{\tilde q}}{q} half-odd integral and for odd k our vertex operators flip
the statistics of charged-particle-vortex composites from bosons to fermions
and vice versa. For fractional values of \frac{{\tilde q}}{q}, application of
vertex operator on charged-particle-vortex composite leads in general to
composites with anyonic statistics.Comment: Published version, 15+1 pages, 1 figur
Spontaneous Lorentz Violation: The Case of Infrared QED
It is by now clear that infrared sector of QED has an intriguingly complex
structure. Based on earlier pioneering works on this subject, two of us
recently proposed a simple modification of QED by constructing a generalization
of the charge group of QED to the "Sky" group incorporating the known
spontaneous Lorentz violation due to infrared photons, but still compatible in
particular with locality. There it was shown that the "Sky" group is generated
by the algebra of angle dependent charges and a study of its superselection
sectors has revealed a manifest description of spontaneous breaking of Lorentz
symmetry. We further elaborate this approach here and investigate in some
detail the properties of charged particles dressed by the infrared photons. We
find that Lorentz violation due to soft photons may be manifestly codified in
an angle dependent fermion mass modifying therefore the fermion dispersion
relations. The fact that the masses of the charged particles are not Lorentz
invariant affects their spin content too.Time dilation formulae for decays
should also get corrections. We speculate that these effects could be measured
possibly in muon decay experiments.Comment: 18+1 pages, revised version, expanded discussion in section 5
Quantum Hall Effect on the Grassmannians
Quantum Hall Effects (QHEs) on the complex Grassmann manifolds
are formulated. We set up the Landau problem in
and solve it using group theoretical techniques
and provide the energy spectrum and the eigenstates in terms of the
Wigner -functions for charged particles on
under the influence of abelian and non-abelian
background magnetic monopoles or a combination of these thereof. In particular,
for the simplest case of we explicitly write down
the background gauge field as well as the single and many-particle
eigenstates by introducing the Pl\"{u}cker coordinates and show by calculating
the two-point correlation function that the Lowest Landau Level (LLL) at
filling factor forms an incompressible fluid. Our results are in
agreement with the previous results in the literature for QHE on and generalize them to all in a suitable
manner. Finally, we heuristically identify a relation between the Hall
effect on and the Hall effect on the odd sphere
, which is yet to be investigated in detail, by appealing to the already
known analogous relations between the Hall effects on and
and those on the spheres and , respectively.Comment: 34 pages, revtex 4-1, Minor Correction
Morphological variation of carotid artery bifurcation level in digital angiography
Knowing of the level of carotid artery bifurcation (CB) is important for vascular surgery in the neck, radical neck dissections, carotid sinus baroreceptor stimulation, catheterisations, and aneurysms. The aim of this study was to determine the CB level in relation with the cervical vertebral levels, compare them on the right and the left sides, and investigate the relation of CB level with the length of neck. In this study, 100 conventional carotid angiographies were performed. The CB level was determined in relation with 10 different levels which were the levels of the cervical vertebrae and intervertebral disks, and the relation of CB level with the length of neck was investigated. The right and left CB levels of the patients were also determined, and compared. The highest level of CB was at the level of C2 vertebra, and the lowest level of CB was at the level of C6–C7 intervertebral disk in both male and female. When all patients were taken into consideration, CB level was most frequently seen at the level of C4–C5 (29%) on the right side, and at the level of C4 (26%) on the left side. The CB levels were not symmetrical in 10 female and 23 male. Knowing of the anatomical variations of CB level is important in surgical procedures. The anatomical differences must be taken into consideration since the neighbouring structures of CB change in case of variations. We believe that the results of this study will shed light to planning of all interventional methods concerning common carotid artery and its branches as well as surgery in the neck, and will help to minimise the complications
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