100 research outputs found
Quantum Mechanics as a Simple Generalization of Classical Mechanics
A motivation is given for expressing classical mechanics in terms of diagonal
projection matrices and diagonal density matrices. Then quantum mechanics is
seen to be a simple generalization in which one replaces the diagonal real
matrices with suitable Hermitian matrices.Comment: 9 pages, LaTe
Spin Correlations in Pair Creation by Two-Photons and Entanglement in QED
Spin correlations of pair productions of two colliding photons
are investigated and explicit expressions for their corresponding probabilities
are derived and found to be \textit{energy} (speed) dependent, for initially
\textit{linearly} and \textit{circularly polarized} photons, different from
those obtained by simply combining the spins of the relevant particles, for
initially \textit{polarized} photons. These expressions also depend on the
angles of spin of (and/or of ), for initially {\it linearly
polarized} photons, but not for {\it circularly polarized} photons, as a
function of the energy. It is remarkable that these explicit results obtained
from quantum field theory show a clear violation of Bell's inequality of Local
Hidden Variables theories at all {\it energies} beyond that of the threshold
one for particle production, in support of quantum field theory in the
relativistic regime. We hope that our explicit expression will lead to
experiments, of the type described in the bulk of this paper, which can monitor
energy (and speed) in polarization correlation experiments.Comment: 12 pages, 4 figure
Geometric Configurations, Regular Subalgebras of E10 and M-Theory Cosmology
We re-examine previously found cosmological solutions to eleven-dimensional
supergravity in the light of the E_{10}-approach to M-theory. We focus on the
solutions with non zero electric field determined by geometric configurations
(n_m, g_3), n\leq 10. We show that these solutions are associated with rank
regular subalgebras of E_{10}, the Dynkin diagrams of which are the (line)
incidence diagrams of the geometric configurations. Our analysis provides as a
byproduct an interesting class of rank-10 Coxeter subgroups of the Weyl group
of E_{10}.Comment: 48 pages, 27 figures, 5 tables, references added, typos correcte
The Topological B-model on a Mini-Supertwistor Space and Supersymmetric Bogomolny Monopole Equations
In the recent paper hep-th/0502076, it was argued that the open topological
B-model whose target space is a complex (2|4)-dimensional mini-supertwistor
space with D3- and D1-branes added corresponds to a super Yang-Mills theory in
three dimensions. Without the D1-branes, this topological B-model is equivalent
to a dimensionally reduced holomorphic Chern-Simons theory. Identifying the
latter with a holomorphic BF-type theory, we describe a twistor correspondence
between this theory and a supersymmetric Bogomolny model on R^3. The connecting
link in this correspondence is a partially holomorphic Chern-Simons theory on a
Cauchy-Riemann supermanifold which is a real one-dimensional fibration over the
mini-supertwistor space. Along the way of proving this twistor correspondence,
we review the necessary basic geometric notions and construct action
functionals for the involved theories. Furthermore, we discuss the geometric
aspect of a recently proposed deformation of the mini-supertwistor space, which
gives rise to mass terms in the supersymmetric Bogomolny equations. Eventually,
we present solution generating techniques based on the developed twistorial
description together with some examples and comment briefly on a twistor
correspondence for super Yang-Mills theory in three dimensions.Comment: 55 pages; v2: typos fixed, published versio
From the Big Bang Theory to the Theory of a Stationary Universe
We consider chaotic inflation in the theories with the effective potentials
phi^n and e^{\alpha\phi}. In such theories inflationary domains containing
sufficiently large and homogeneous scalar field \phi permanently produce new
inflationary domains of a similar type. We show that under certain conditions
this process of the self-reproduction of the Universe can be described by a
stationary distribution of probability, which means that the fraction of the
physical volume of the Universe in a state with given properties (with given
values of fields, with a given density of matter, etc.) does not depend on
time, both at the stage of inflation and after it. This represents a strong
deviation of inflationary cosmology from the standard Big Bang paradigm. We
compare our approach with other approaches to quantum cosmology, and illustrate
some of the general conclusions mentioned above with the results of a computer
simulation of stochastic processes in the inflationary Universe.Comment: No changes to the file, but original figures are included. They
substantially help to understand this paper, as well as eternal inflation in
general, and what is now called the "multiverse" and the "string theory
landscape." High quality figures can be found at
http://www.stanford.edu/~alinde/LLMbigfigs
The role of self-gentrification in sustainable tourism: Indigenous entrepreneurship at Honghe Hani Rice Terraces World Heritage Site, China
This article examines three forms of tourism gentrification occurring within the newly inscribed (2013) Honghe Hani Rice Terraces UNESCO World Heritage Site in Yunnan, China. The indigenous Hani and Yi communities who populate this remote mountainous area, possess distinct cultural practices that have supported the rice terrace ecosystem for centuries. This article draws on interviews and non-participant observation conducted with inhabitants and newcomers to analyse the types of gentrification occurring within the site. We argue that indigenous cultural practices, and consequently rice cultivation in the area, are threatened by gentrifier-led and state-led gentrification combined with high levels of outward migration of indigenous persons. This could pose a significant threat to the sustainability of tourism at this site and may ultimately compromise the siteâs World Heritage Status. In the midst of these dangers, some indigenous people are shown to be improving their socioeconomic standing â and becoming âmiddle classâ or âgentryâ â particularly through adopting entrepreneurial strategies gleaned from their encounters with outside-gentrifiers and tourists. This article proposes the concept of âself-gentrificationâ as a way to describe individuals who seek to improve themselves and their own community, while under threat of gentrification
Spin Down of Rotating Compact Magnetized Strange Stars in General Relativity
We find that in general relativity slow down of the pulsar rotation due to
the magnetodipolar radiation is more faster for the strange star with
comparison to that for the neutron star of the same mass. Comparison with
astrophysical observations on pulsars spindown data may provide an evidence for
the strange star existence and, thus, serve as a test for distinguishing it
from the neutron star.Comment: 6 pages; Accepted for publication in Astrophysics and Space Scienc
A review of spatial causal inference methods for environmental and epidemiological applications
The scientific rigor and computational methods of causal inference have had
great impacts on many disciplines, but have only recently begun to take hold in
spatial applications. Spatial casual inference poses analytic challenges due to
complex correlation structures and interference between the treatment at one
location and the outcomes at others. In this paper, we review the current
literature on spatial causal inference and identify areas of future work. We
first discuss methods that exploit spatial structure to account for unmeasured
confounding variables. We then discuss causal analysis in the presence of
spatial interference including several common assumptions used to reduce the
complexity of the interference patterns under consideration. These methods are
extended to the spatiotemporal case where we compare and contrast the potential
outcomes framework with Granger causality, and to geostatistical analyses
involving spatial random fields of treatments and responses. The methods are
introduced in the context of observational environmental and epidemiological
studies, and are compared using both a simulation study and analysis of the
effect of ambient air pollution on COVID-19 mortality rate. Code to implement
many of the methods using the popular Bayesian software OpenBUGS is provided
Searches for lepton number violating K+ decays
The NA62 experiment at CERN reports a search for the lepton number violating decays K+âÏâe+e+ and K+âÏâÎŒ+ÎŒ+ using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of 2.2 x 10^-10 and 4.2 x 10^-11 are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively
Search for heavy neutral lepton production in K+ decays to positrons
A search for heavy neutral lepton (N) production in K+âe+N decays using the data sample collected by the NA62 experiment at CERN in 2017-2018 is reported. Upper limits of the extended neutrino mixing matrix element |Ue4|^2 are established at the level of 10^â9 over most of the accessible heavy neutral lepton mass range 144-462 MeV/c^2, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The |Ue4|^2 range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/c^2
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