1,932 research outputs found
Cosmological constant and Euclidean space from nonperturbative quantum torsion
Heisenberg's nonperturbative quantization technique is applied to the
nonpertrubative quantization of gravity. An infinite set of equations for all
Green's functions is obtained. An approximation is considered where: (a) the
metric remains as a classical field; (b) the affine connection can be
decomposed into classical and quantum parts; (c) the classical part of the
affine connection are the Christoffel symbols; (d) the quantum part is the
torsion. Using a scalar and vector fields approximation it is shown that
nonperturbative quantum effects gives rise to a cosmological constant and an
Euclidean solution.Comment: title is changed. arXiv admin note: text overlap with arXiv:1201.106
Photon decay in a CPT-violating extension of quantum electrodynamics
We consider the process of photon decay in quantum electrodynamics with a
CPT-violating Chern-Simons-like term added to the action. For a simplified
model with only the quadratic Maxwell and Chern-Simons-like terms and the
quartic Euler-Heisenberg term, we obtain a nonvanishing probability for the
decay of a particular photon state into three others.Comment: LaTeX with elsart.cls, 16 pages; v4: published versio
Collective polarization exchanges in collisions of photon clouds
The one-loop "vacuum" Heisenberg-Euler coupling of four electromagnetic
fields can lead to interesting collective effects in the collision of two
photon clouds, on a time scale orders of magnitude faster than one estimates
from the cross-section and density. We estimate the characteristic time for
macroscopic transformation of positive to negative helicity in clouds that are
initially totally polarized and for depolarization of a polarized beam
traversing an unpolarized cloud.Comment: Recapitulates much that is in hep-ph/0402127, with new results in the
last section, and the first section drastically reduced in view of the
previous work of Kotkin and Serbo. Typo corrected in eq. 1
Determining physical properties of the cell cortex
Actin 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
Gauged System Mimicking the G\"{u}rsey Model
We 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
A Model with Interacting Composites
We show that we can construct a model in 3+1 dimensions where only composite
scalars take place in physical processes as incoming and outgoing particles,
whereas constituent spinors only act as intermediary particles. Hence while the
spinor-spinor scattering goes to zero, the scattering of composites gives
nontrivial results.Comment: 9 Page
Information-disturbance tradeoff in estimating a maximally entangled state
We derive the amount of information retrieved by a quantum measurement in
estimating an unknown maximally entangled state, along with the pertaining
disturbance on the state itself. The optimal tradeoff between information and
disturbance is obtained, and a corresponding optimal measurement is provided.Comment: 4 pages. Accepted for publication on Physical Review Letter
Symmetry-preserving Loop Regularization and Renormalization of QFTs
A new symmetry-preserving loop regularization method proposed in \cite{ylw}
is further investigated. It is found that its prescription can be understood by
introducing a regulating distribution function to the proper-time formalism of
irreducible loop integrals. The method simulates in many interesting features
to the momentum cutoff, Pauli-Villars and dimensional regularization. The loop
regularization method is also simple and general for the practical calculations
to higher loop graphs and can be applied to both underlying and effective
quantum field theories including gauge, chiral, supersymmetric and
gravitational ones as the new method does not modify either the lagrangian
formalism or the space-time dimension of original theory. The appearance of
characteristic energy scale and sliding energy scale offers a
systematic way for studying the renormalization-group evolution of gauge
theories in the spirit of Wilson-Kadanoff and for exploring important effects
of higher dimensional interaction terms in the infrared regime.Comment: 13 pages, Revtex, extended modified version, more references adde
Extra-Dimensions effects on the fermion-induced quantum energy in the presence of a constant magnetic field
We consider a U(1) gauge field theory with fermion fields (or with scalar
fields) that live in a space with extra compact dimensions, and we
compute the fermion-induced quantum energy in the presence of a constant
magnetic field, which is directed towards the x_3 axis. Our motivation is to
study the effect of extra dimensions on the asymptotic behavior of the quantum
energy in the strong field limit (eB>>M^{2}), where M=1/R. We see that the weak
logarithmic growth of the quantum energy for four dimensions, is modified by a
rapid power growth in the case of the extra dimensions.Comment: 18 pages, 4 figures, 2 tables, several correction
Fractal Characterizations of MAX Statistical Distribution in Genetic Association Studies
Two non-integer parameters are defined for MAX statistics, which are maxima
of simpler test statistics. The first parameter, , is the
fractional number of tests, representing the equivalent numbers of independent
tests in MAX. If the tests are dependent, . The second
parameter is the fractional degrees of freedom of the chi-square
distribution that fits the MAX null distribution. These two
parameters, and , can be independently defined, and can be
non-integer even if is an integer. We illustrate these two parameters
using the example of MAX2 and MAX3 statistics in genetic case-control studies.
We speculate that is related to the amount of ambiguity of the model
inferred by the test. In the case-control genetic association, tests with low
(e.g. ) are able to provide definitive information about the disease
model, as versus tests with high (e.g. ) that are completely uncertain
about the disease model. Similar to Heisenberg's uncertain principle, the
ability to infer disease model and the ability to detect significant
association may not be simultaneously optimized, and seems to measure the
level of their balance
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