2,514 research outputs found
Quantum Gravity - Testing Time for Theories
The extreme smallness of both the Planck length, on the one side, and the
ratio of the gravitational to the electrical forces between, say, two
electrons, on the other side has led to a widespread belief that the realm of
quantum gravity is beyond terrestrial experiments. A series of classical and
quantum arguments are put forward to dispel this view. It is concluded that
whereas the smallness of the Planck length and the ratio of gravitational to
electrical forces, does play its own essential role in nature, it does not make
quantum gravity a science where humans cannot venture to probe her secrets. In
particular attention is drawn to the latest neutron and atomic interferometry
experiments, and to gravity wave interferometers. The latter, as Giovanni
Amelino-Camelia argues [Nature 398, 216 (1999)], can be treated as probes of
space-time fuzziness down to Planck length for certain quantum-gravity models
Front Form Spinors in Weinberg-Soper Formalism and Melosh Transformations for any Spin
Using the Weinberg-Soper formalism we construct the front form
spinors. Explicit expressions for the generalised Melosh
transformations up to spin two are obtained. The formalism, without explicitly
invoking any wave equations, reproduces spin one half front-form results of
Melosh, Lepage and Brodsky, and Dziembowski.Comment: 16 Pages, RevTex. We continue to receive reprint requests for this
paper. So we now archive it her
Zero Energy of Plane-Waves for ELKOs
We consider the ELKO field in interaction through contorsion with its own
spin density, and we investigate the form of the consequent autointeractions;
to do so we take into account the high-density limit and find plane wave
solutions: such plane waves give rise to contorsional autointeractions for
which the Ricci metric curvature vanishes and therefore the energy density is
equal to zero identically. Consequences are discussed.Comment: 7 page
Special relativity with two invariant scales: Motivation, Fermions, Bosons, Locality, and Critique
We present a Master equation for description of fermions and bosons for
special relativities with two invariant scales, SR2, (c and lambda_P). We
introduce canonically-conjugate variables (chi^0, chi) to (epsilon, pi) of
Judes-Visser. Together, they bring in a formal element of linearity and
locality in an otherwise non-linear and non-local theory. Special relativities
with two invariant scales provide all corrections, say, to the standard model
of the high energy physics, in terms of one fundamental constant, lambda_P. It
is emphasized that spacetime of special relativities with two invariant scales
carries an intrinsic quantum-gravitational character. In an addenda, we also
comment on the physical importance of a phase factor that the whole literature
on the subject has missed and present a brief critique of SR2. In addition, we
remark that the most natural and physically viable SR2 shall require
momentum-space and spacetime to be non-commutative with the non-commutativity
determined by the spin content and C, P, and T properties of the examined
representation space. Therefore, in a physically successful SR2, the notion of
spacetime is expected to be deeply intertwined with specific properties of the
test particle.Comment: Int. J. Mod. Phys. D (in press). Extended version of a set of two
informal lectures given in "La Sapienza" (Rome, May 2001
Domain Size Dependence of Piezoelectric Properties of Ferroelectrics
The domain size dependence of piezoelectric properties of ferroelectrics is
investigated using a continuum Ginzburg-Landau model that incorporates the
long-range elastic and electrostatic interactions. Microstructures with desired
domain sizes are created by quenching from the paraelectric phase by biasing
the initial conditions. Three different two-dimensional microstructures with
different sizes of the domains are simulated. An electric field is
applied along the polar as well as non-polar directions and the piezoelectric
response is simulated as a function of domain size for both cases. The
simulations show that the piezoelectric coefficients are enhanced by reducing
the domain size, consistent with recent experimental results of Wada and
Tsurumi (Brit. Ceram. Trans. {\bf 103}, 93, 2004) on domain engineered
Comment: submitted to Physical Review
Neutrino oscillations with disentanglement of a neutrino from its partners
We bring attention to the fact that in order to understand existing data on
neutrino oscillations, and to design future experiments, it is imperative to
appreciate the role of quantum entanglement. Once this is accounted for, the
resulting energy-momentum conserving phenomenology requires a single new
parameter related to disentanglement of a neutrino from its partners. This
parameter may not be CP symmetric. We illustrate the new ideas, with
potentially measurable effects, in the context of a novel experiment recently
proposed by Gavrin, Gorbachev, Veretenkin, and Cleveland. The strongest impact
of our ideas is on the resolution of various anomalies in neutrino oscillations
and on neutrino propagation in astrophysical environments.Comment: 6 page
Comment on "Gravitationally Induced Neutrino-Oscillation Phases"
We critically examine the recent claim (gr-qc/9603008) of a ``new effect'' of
gravitationally induced quantum mechanical phases in neutrino oscillations. A
straightforward exercise in the Schwarzschild coordinates appropriate to a
spherically symmetric non-rotating star shows that, although there is a general
relativistic effect of the star's gravity on neutrino oscillations, it is not
of the form claimed, and is too small to be measured.Comment: Plain LaTeX, 7 pages, no figure
Relatedness Measures to Aid the Transfer of Building Blocks among Multiple Tasks
Multitask Learning is a learning paradigm that deals with multiple different
tasks in parallel and transfers knowledge among them. XOF, a Learning
Classifier System using tree-based programs to encode building blocks
(meta-features), constructs and collects features with rich discriminative
information for classification tasks in an observed list. This paper seeks to
facilitate the automation of feature transferring in between tasks by utilising
the observed list. We hypothesise that the best discriminative features of a
classification task carry its characteristics. Therefore, the relatedness
between any two tasks can be estimated by comparing their most appropriate
patterns. We propose a multiple-XOF system, called mXOF, that can dynamically
adapt feature transfer among XOFs. This system utilises the observed list to
estimate the task relatedness. This method enables the automation of
transferring features. In terms of knowledge discovery, the resemblance
estimation provides insightful relations among multiple data. We experimented
mXOF on various scenarios, e.g. representative Hierarchical Boolean problems,
classification of distinct classes in the UCI Zoo dataset, and unrelated tasks,
to validate its abilities of automatic knowledge-transfer and estimating task
relatedness. Results show that mXOF can estimate the relatedness reasonably
between multiple tasks to aid the learning performance with the dynamic feature
transferring.Comment: accepted by The Genetic and Evolutionary Computation Conference
(GECCO 2020
Phantom energy from graded algebras
We construct a model of phantom energy using the graded Lie algebra SU(2/1).
The negative kinetic energy of the phantom field emerges naturally from the
graded Lie algebra, resulting in an equation of state with w<-1. The model also
contains ordinary scalar fields and anti-commuting (Grassmann) vector fields
which can be taken as two component dark matter. A potential term is generated
for both the phantom fields and the ordinary scalar fields via a postulated
condensate of the Grassmann vector fields. Since the phantom energy and dark
matter arise from the same Lagrangian the phantom energy and dark matter of
this model are coupled via the Grassman vector fields. In the model presented
here phantom energy and dark matter come from a gauge principle rather than
being introduced in an ad hoc manner.Comment: 8 pages no figures; references added and discussion on condensate of
vector grassman fields added. To be published MPL
Elastic Deformation of Polycrystals
We propose a framework to model elastic properties of polycrystals by
coupling crystal orientational degrees of freedom with elastic strains. Our
model encodes crystal symmetries and takes into account explicitly the strain
compatibility induced long-range interaction between grains. The coupling of
crystal orientation and elastic interactions allows for the rotation of
individual grains by an external load. We apply the model to simulate uniaxial
tensile loading of a 2D polycrystal within linear elasticity and a system with
elastic anharmonicities that describe structural phase transformations. We
investigate the constitutive response of the polycrystal and compare it to that
of single crystals with crystallographic orientations that form the
polycrystal.Comment: 4 pages, 4 ps figure
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