2,711 research outputs found
Two-dimensional anyons and the temperature dependence of commutator anomalies
Get PDFThe temperature dependence of commutator anomalies is discussed on the
explicit example of particular (anyonic) field operators in two dimensions. The
correlation functions obtained show that effects of the non-zero temperature
might manifest themselves not only globally but also locally.Comment: 11 pages, LaTe
Formulation of the Spinor Field in the Presence of a Minimal Length Based on the Quesne-Tkachuk Algebra
Full text linkIn 2006 Quesne and Tkachuk (J. Phys. A: Math. Gen. {\bf 39}, 10909, 2006)
introduced a (D+1)-dimensional -two-parameter Lorentz-covariant
deformed algebra which leads to a nonzero minimal length. In this work, the
Lagrangian formulation of the spinor field in a (3+1)-dimensional space-time
described by Quesne-Tkachuk Lorentz-covariant deformed algebra is studied in
the case where up to first order over deformation parameter
. It is shown that the modified Dirac equation which contains higher
order derivative of the wave function describes two massive particles with
different masses. We show that physically acceptable mass states can only exist
for . Applying the condition
to an electron, the upper bound for the isotropic
minimal length becomes about . This value is near to the
reduced Compton wavelength of the electron and is not incompatible with the results obtained for
the minimal length in previous investigations.Comment: 11 pages, no figur
Measuring measurement--disturbance relationships with weak values
Full text linkUsing formal definitions for measurement precision {\epsilon} and disturbance
(measurement backaction) {\eta}, Ozawa [Phys. Rev. A 67, 042105 (2003)] has
shown that Heisenberg's claimed relation between these quantities is false in
general. Here we show that the quantities introduced by Ozawa can be determined
experimentally, using no prior knowledge of the measurement under investigation
--- both quantities correspond to the root-mean-squared difference given by a
weak-valued probability distribution. We propose a simple three-qubit
experiment which would illustrate the failure of Heisenberg's
measurement--disturbance relation, and the validity of an alternative relation
proposed by Ozawa
Electron-hole asymmetry is the key to superconductivity
Full text linkIn a solid, transport of electricity can occur via negative electrons or via
positive holes. In the normal state of superconducting materials experiments
show that transport is usually dominated by
. Instead, in the superconducting state experiments show that the
supercurrent is always carried by .
These experimental facts indicate that electron-hole asymmetry plays a
fundamental role in superconductivity, as proposed by the theory of hole
superconductivity.Comment: Presented at the New3SC-4 meeting, San Diego, Jan. 16-21 2003; to be
published in Int. J. Mod. Phys.
Determining physical properties of the cell cortex
Get PDFActin and myosin assemble into a thin layer of a highly dynamic network
underneath the membrane of eukaryotic cells. This network generates the forces
that drive cell and tissue-scale morphogenetic processes. The effective
material properties of this active network determine large-scale deformations
and other morphogenetic events. For example,the characteristic time of stress
relaxation (the Maxwell time)in the actomyosin sets the time scale of
large-scale deformation of the cortex. Similarly, the characteristic length of
stress propagation (the hydrodynamic length) sets the length scale of slow
deformations, and a large hydrodynamic length is a prerequisite for long-ranged
cortical flows. Here we introduce a method to determine physical parameters of
the actomyosin cortical layer (in vivo). For this we investigate the relaxation
dynamics of the cortex in response to laser ablation in the one-cell-stage {\it
C. elegans} embryo and in the gastrulating zebrafish embryo. These responses
can be interpreted using a coarse grained physical description of the cortex in
terms of a two dimensional thin film of an active viscoelastic gel. To
determine the Maxwell time, the hydrodynamic length and the ratio of active
stress and per-area friction, we evaluated the response to laser ablation in
two different ways: by quantifying flow and density fields as a function of
space and time, and by determining the time evolution of the shape of the
ablated region. Importantly, both methods provide best fit physical parameters
that are in close agreement with each other and that are similar to previous
estimates in the two systems. We provide an accurate and robust means for
measuring physical parameters of the actomyosin cortical layer.It can be useful
for investigations of actomyosin mechanics at the cellular-scale, but also for
providing insights in the active mechanics processes that govern tissue-scale
morphogenesis.Comment: 17 pages, 4 figure
Kinetic energy driven superconductivity, the origin of the Meissner effect, and the reductionist frontier
Full text linkIs superconductivity associated with a lowering or an increase of the kinetic
energy of the charge carriers? Conventional BCS theory predicts that the
kinetic energy of carriers increases in the transition from the normal to the
superconducting state. However, substantial experimental evidence obtained in
recent years indicates that in at least some superconductors the opposite
occurs. Motivated in part by these experiments many novel mechanisms of
superconductivity have recently been proposed where the transition to
superconductivity is associated with a lowering of the kinetic energy of the
carriers. However none of these proposed unconventional mechanisms explores the
fundamental reason for kinetic energy lowering nor its wider implications. Here
I propose that kinetic energy lowering is at the root of the Meissner effect,
the most fundamental property of superconductors. The physics can be understood
at the level of a single electron atom: kinetic energy lowering and enhanced
diamagnetic susceptibility are intimately connected. According to the theory of
hole superconductivity, superconductors expel negative charge from their
interior driven by kinetic energy lowering and in the process expel any
magnetic field lines present in their interior. Associated with this we predict
the existence of a macroscopic electric field in the interior of
superconductors and the existence of macroscopic quantum zero-point motion in
the form of a spin current in the ground state of superconductors (spin
Meissner effect). In turn, the understanding of the role of kinetic energy
lowering in superconductivity suggests a new way to understand the fundamental
origin of kinetic energy lowering in quantum mechanics quite generally
(Never) Mind your p's and q's: Von Neumann versus Jordan on the Foundations of Quantum Theory
Get PDFIn two papers entitled "On a new foundation [Neue Begr\"undung] of quantum
mechanics," Pascual Jordan (1927b,g) presented his version of what came to be
known as the Dirac-Jordan statistical transformation theory. As an alternative
that avoids the mathematical difficulties facing the approach of Jordan and
Paul A. M. Dirac (1927), John von Neumann (1927a) developed the modern Hilbert
space formalism of quantum mechanics. In this paper, we focus on Jordan and von
Neumann. Central to the formalisms of both are expressions for conditional
probabilities of finding some value for one quantity given the value of
another. Beyond that Jordan and von Neumann had very different views about the
appropriate formulation of problems in quantum mechanics. For Jordan, unable to
let go of the analogy to classical mechanics, the solution of such problems
required the identication of sets of canonically conjugate variables, i.e., p's
and q's. For von Neumann, not constrained by the analogy to classical
mechanics, it required only the identication of a maximal set of commuting
operators with simultaneous eigenstates. He had no need for p's and q's. Jordan
and von Neumann also stated the characteristic new rules for probabilities in
quantum mechanics somewhat differently. Jordan (1927b) was the first to state
those rules in full generality. Von Neumann (1927a) rephrased them and, in a
subsequent paper (von Neumann, 1927b), sought to derive them from more basic
considerations. In this paper we reconstruct the central arguments of these
1927 papers by Jordan and von Neumann and of a paper on Jordan's approach by
Hilbert, von Neumann, and Nordheim (1928). We highlight those elements in these
papers that bring out the gradual loosening of the ties between the new quantum
formalism and classical mechanics.Comment: New version. The main difference with the old version is that the
introduction has been rewritten. Sec. 1 (pp. 2-12) in the old version has
been replaced by Secs. 1.1-1.4 (pp. 2-31) in the new version. The paper has
been accepted for publication in European Physical Journal
Boson stars from a gauge condensate
Get PDFThe boson star filled with two interacting scalar fields is investigated. The
scalar fields can be considered as a gauge condensate formed by SU(3) gauge
field quantized in a non-perturbative manner. The corresponding solution is
regular everywhere, has a finite energy and can be considered as a quantum
SU(3) version of the Bartnik - McKinnon particle-like solution.Comment: errors are corrected, one reference is adde
Common Space of Spin and Spacetime
Full text linkGiven Lorentz invariance in Minkowski spacetime, we investigate a common
space of spin and spacetime. To obtain a finite spinor representation of the
non-compact homogeneous Lorentz group including Lorentz boosts, we introduce an
indefinite inner product space (IIPS) with a normalized positive probability.
In this IIPS, the common momentum and common variable of a massive fermion turn
out to be ``doubly strict plus-operators''. Due to this nice property, it is
straightforward to show an uncertainty relation between fermion mass and proper
time. Also in IIPS, the newly-defined Lagrangian operators are self-adjoint,
and the fermion field equations are derivable from the Lagrangians. Finally,
the nonlinear QED equations and Lagrangians are presented as an example.Comment: 17 pages, a reference corrected, final version published on
Foundations of Physics Letters in June of 2005, as a personal tribute to
Einstein and Dira
Gauged System Mimicking the G\"{u}rsey Model
Get PDFWe comment on the changes in the constrained model studied earlier when
constituent massless vector fields are introduced. The new model acts like a
gauge-Higgs-Yukawa system, although its origin is different.Comment: 8 pages, RevTex4; published versio
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