29,444 research outputs found
Constructing Gravitational Dimensions
It would be extremely useful to know whether a particular low energy
effective theory might have come from a compactification of a higher
dimensional space. Here, this problem is approached from the ground up by
considering theories with multiple interacting massive gravitons. It is
actually very difficult to construct discrete gravitational dimensions which
have a local continuum limit. In fact, any model with only nearest neighbor
interactions is doomed. If we could find a non-linear extension for the
Fierz-Pauli Lagrangian for a graviton of mass mg which does not break down
until the scale Lambda_2=(mg Mpl)^(1/2), this could be used to construct a
large class of models whose continuum limit is local in the extra dimension.
But this is shown to be impossible: a theory with a single graviton must break
down by Lambda_3 = (mg^2 Mpl)^(1/3). Next, we look at how the discretization
prescribed by the truncation of the KK tower of an honest extra diemsinon
rasies the scale of strong coupling. It dictates an intricate set of
interactions among various fields which conspire to soften the strongest
scattering amplitudes and allow for a local continuum limit. A number of
canditate symmetries associated with locality in the discretized dimension are
also discussed.Comment: 21 pages, 6 diagrams, 1 figur
A new estimate on Evans' Weak KAM approach
We consider a recent formulation of weak KAM theory proposed by Evans. As
well as for classical integrability, for one dimensional mechanical Hamiltonian
systems all the computations can be explicitly done. This allows us on the one
hand to illustrate the geometric content of the theory, on the other hand to
prove new lower bounds which extend also to the generic n degrees of freedom
case
Discrete Gravitational Dimensions
We study the physics of a single discrete gravitational extra dimension using
the effective field theory for massive gravitons. We first consider a minimal
discretization with 4D gravitons on the sites and nearest neighbor hopping
terms. At the linear level, 5D continuum physics is recovered correctly, but at
the non-linear level the theory becomes highly non-local in the discrete
dimension. There is a peculiar UV/IR connection, where the scale of strong
interactions at high energies is related to the radius of the dimension. These
new effects formally vanish in the limit of zero lattice spacing, but do not do
so quickly enough to reproduce the continuum physics consistently in an
effective field theory up to the 5D Planck scale. Nevertheless, this model does
make sense as an effective theory up to energies parametrically higher than the
compactification scale. In order to have a discrete theory that appears local
in the continuum limit, the lattice action must have interactions between
distant sites. We speculate on the relevance of these observations to the
construction of finite discrete theories of gravity in four dimensions.Comment: 5 pages, 4 diagrams. Important typos in some equations corrected;
conclusion s unchange
Recommended from our members
Complement protein levels in plasma astrocyte-derived exosomes are abnormal in conversion from mild cognitive impairment to Alzheimer's disease dementia.
IntroductionLevels of complement proteins (CPs) in plasma astrocyte-derived exosomes (ADEs) that are abnormal in Alzheimer's disease (AD) have not been assessed in mild cognitive impairment (MCI).MethodsParticipants (n = 20 per group) had either MCI converting to dementia within 3 years (MCIC), MCI remaining stable over 3 years (MCIS), Alzheimer's disease, or were controls. CPs of ADEs isolated from plasmas by anti-human glutamine aspartate transporter antibody absorption were quantified by ELISAs.ResultsADE levels of C1q and C4b of the classical pathway, factor D and fragment Bb of the alternative pathway, and C5b, C3b, and C5b-C9 of both pathways were significantly higher in patients with MCIC than those with MCIS. ADE levels of inhibitory CPs decay-accelerating factor, CD46, CD59, and type 1 complement receptor were significantly lower in patients with MCIC than those with MCIS.DiscussionADE CPs are components of neurotoxic neuroinflammation that may be predictive biomarkers of MCI conversion to Alzheimer's disease
Temporal behavior of two-wave-mixing in photorefractive InP:Fe versus temperature
The temporal response of two-wave-mixing in photorefractive InP:Fe under a dc
electric field at different temperatures has been studied. In particular, the
temperature dependence of the characteristic time constant has been studied
both theoretically and experimentally, showing a strongly decreasing time
constant with increasing temperature
Whats The Rush? IFRS, The SEC, And The Pressure On Accounting Instructors To Teach Still More Financial Reporting Rules
This paper addresses the problems facing accounting instructors in the U.S. as they struggle with pressure to incorporate IFRS into an already crowded financial accounting curriculum. To help instructors better understand the advantages and disadvantages of financial reporting under IFRS, we provide a critical analysis of arguments that have been made for and against IFRS adoption. This analysis should aid instructors in their design of lectures and assignments related to IFRS. We also show that adoption still faces serious obstacles, including the use of U.S. GAAP in contracts and regulations, the prohibition against the use of LIFO, and the Sarbanes-Oxley requirements for funding of a financial reporting standard-setter. We then provide support for an approach for incorporating IFRS in the financial accounting curriculum that places greater emphasis on teaching concepts than on teaching more rules. We conclude by presenting a model for a concepts course that would be taken by students as they begin the accounting major in their junior year
Ducks on the torus: existence and uniqueness
We show that there exist generic slow-fast systems with only one
(time-scaling) parameter on the two-torus, which have canard cycles for
arbitrary small values of this parameter. This is in drastic contrast with the
planar case, where canards usually occur in two-parametric families. Here we
treat systems with a convex slow curve. In this case there is a set of
parameter values accumulating to zero for which the system has exactly one
attracting and one repelling canard cycle. The basin of the attracting cycle is
almost the whole torus.Comment: To appear in Journal of Dynamical and Control Systems, presumably
Vol. 16 (2010), No. 2; The final publication is available at
www.springerlink.co
Random field Ising systems on a general hierarchical lattice: Rigorous inequalities
Random Ising systems on a general hierarchical lattice with both, random
fields and random bonds, are considered. Rigorous inequalities between
eigenvalues of the Jacobian renormalization matrix at the pure fixed point are
obtained. These inequalities lead to upper bounds on the crossover exponents
.Comment: LaTeX, 13 pages, figs. 1a,1b,2. To be published in PR
In-flight calibration of the Herschel-SPIRE instrument
SPIRE, the Spectral and Photometric Imaging REceiver, is the Herschel Space Observatory's submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 μm, and an imaging Fourier-transform spectrometer (FTS) covering 194–671 μm (447-1550 GHz). In this paper we describe the initial approach taken to the absolute calibration of the SPIRE instrument using a combination of the emission from the Herschel telescope itself and the modelled continuum emission from solar system objects and other astronomical targets. We present the photometric, spectroscopic and spatial accuracy that is obtainable in data processed through the “standard” pipelines. The overall photometric accuracy at this stage of the mission is estimated as 15% for the photometer and between 15 and 50% for the spectrometer. However, there remain issues with the photometric accuracy of the spectra of low flux sources in the longest wavelength part of the SPIRE spectrometer band. The spectrometer wavelength accuracy is determined to be better than 1/10th of the line FWHM. The astrometric accuracy in SPIRE maps is found to be 2 arcsec when the latest calibration data are used. The photometric calibration of the SPIRE instrument is currently determined by a combination of uncertainties in the model spectra of the astronomical standards and the data processing methods employed for map and spectrum calibration. Improvements in processing techniques and a better understanding of the instrument performance will lead to the final calibration accuracy of SPIRE being determined only by uncertainties in the models of astronomical standards
Web ontology representation and reasoning via fragments of set theory
In this paper we use results from Computable Set Theory as a means to
represent and reason about description logics and rule languages for the
semantic web.
Specifically, we introduce the description logic \mathcal{DL}\langle
4LQS^R\rangle(\D)--admitting features such as min/max cardinality constructs
on the left-hand/right-hand side of inclusion axioms, role chain axioms, and
datatypes--which turns out to be quite expressive if compared with
\mathcal{SROIQ}(\D), the description logic underpinning the Web Ontology
Language OWL. Then we show that the consistency problem for
\mathcal{DL}\langle 4LQS^R\rangle(\D)-knowledge bases is decidable by
reducing it, through a suitable translation process, to the satisfiability
problem of the stratified fragment of set theory, involving variables
of four sorts and a restricted form of quantification. We prove also that,
under suitable not very restrictive constraints, the consistency problem for
\mathcal{DL}\langle 4LQS^R\rangle(\D)-knowledge bases is
\textbf{NP}-complete. Finally, we provide a -translation of rules
belonging to the Semantic Web Rule Language (SWRL)
- …