3,186 research outputs found
Five-leg photon-neutrino interactions
In a first part, we justify the feasibility of substituting a photon leg by a
neutrino current in the Euler-Heisenberg Lagrangian to obtain an effective
Lagrangian for the process and its crossed
reactions.
We establish the link between these processes and the four-photon scattering
in both the Standard Model and the effective theory. As an application, we
compute in this effective theory the processes
and and show how to use the
results as a check. We settle the question of the
disagreement between two computations in the literature concerning the reaction
. In the second part, we present results of
the direct computation of the photon-neutrino five-leg processes in the
Standard Model, discuss possible astrophysical implications of our results, and
provide simple fits to the exact expressions.Comment: 6 pages, axodraw, ltwol2e, 5 figures, contributed paper to the 29th
International Conference on High Energy Physics (Vancouver
Inelastic photon-neutrino interactions using an effective Lagrangian
We justify the feasibility of substituting a photon leg by a neutrino current
in the Euler-Heisenberg Lagrangian to obtain an effective Lagrangian for the
process and its crossed reactions. We establish
the link between these processes and the four-photon scattering in both the
Standard Model and the effective theory. As an application, we compute the
processes and
, give their polarized cross sections, and
show how to use the results as a check. We settle
the question about the disagreement between two computations in the literature
concerning the reaction .Comment: 14 pages, RevTeX, axodraw, 3 figures, comment adde
Omniscopes: Large Area Telescope Arrays with only N log N Computational Cost
We show that the class of antenna layouts for telescope arrays allowing cheap
analysis hardware (with correlator cost scaling as N log N rather than N^2 with
the number of antennas N) is encouragingly large, including not only previously
discussed rectangular grids but also arbitrary hierarchies of such grids, with
arbitrary rotations and shears at each level. We show that all correlations for
such a 2D array with an n-level hierarchy can be efficiently computed via a
Fast Fourier Transform in not 2 but 2n dimensions. This can allow major
correlator cost reductions for science applications requiring exquisite
sensitivity at widely separated angular scales, for example 21cm tomography
(where short baselines are needed to probe the cosmological signal and long
baselines are needed for point source removal), helping enable future 21cm
experiments with thousands or millions of cheap dipole-like antennas. Such
hierarchical grids combine the angular resolution advantage of traditional
array layouts with the cost advantage of a rectangular Fast Fourier Transform
Telescope. We also describe an algorithm for how a subclass of hierarchical
arrays can efficiently use rotation synthesis to produce global sky maps with
minimal noise and a well-characterized synthesized beam.Comment: Replaced to match accepted PRD version. 10 pages, 9 fig
CMB Polarization Experiments
We discuss the analysis of polarization experiments with particular emphasis
on those that measure the Stokes parameters on a ring on the sky. We discuss
the ability of these experiments to separate the and contributions to
the polarization signal. The experiment being developed at Wisconsin university
is studied in detail, it will be sensitive to both Stokes parameters and will
concentrate on large scale polarization, scanning a degree ring. We will
also consider another example, an experiment that measures one of the Stokes
parameters in a ring. We find that the small ring experiment will be able
to detect cosmological polarization for some models consistent with the current
temperature anisotropy data, for reasonable integration times. In most
cosmological models large scale polarization is too small to be detected by the
Wisconsin experiment, but because both and are measured, separate
constraints can be set on and polarization.Comment: 27 pages with 12 included figure
Structured Deformations of Continua: Theory and Applications
The scope of this contribution is to present an overview of the theory of
structured deformations of continua, together with some applications.
Structured deformations aim at being a unified theory in which elastic and
plastic behaviours, as well as fractures and defects can be described in a
single setting. Since its introduction in the scientific community of rational
mechanicists (Del Piero-Owen, ARMA 1993), the theory has been put in the
framework of variational calculus (Choksi-Fonseca, ARMA 1997), thus allowing
for solution of problems via energy minimization. Some background, three
problems and a discussion on future directions are presented.Comment: 11 pages, 1 figure, 1 diagram. Submitted to the Proceedings volume of
the conference CoMFoS1
Tagetes minuta - uma nova alternativa no controle fitoterápico de carrapatos.
Obrigatoriamente os carrapatos são parasitas hematófagos (FREIRE, 1972) da maioria dos animais vertebrados, podendo transmitir uma variedade de agentes patogênicos (ESTRADA-PENA; JONGEJAN, 1999). Depois dos mosquitos os carrapatos são considerados o primeiro grupo de artrópodes ectoparasitos a transmitirem agentes patogênicos aos seres humanos, e ocupam o primeiro lugar na transmissão de agentes causadores de doenças aos animais (JONGEJAN; UILENBERG, 2004; OGRZEWALSKA, 2009). Pertencem ao filo Arthropoda, classe Arachnida, ordem Acari e subordem Ixodida e apresentam uma ampla distribuição geográfica.bitstream/item/109847/1/DOC207.pd
As sementes da Caatinga são...: um levantamento das características das sementes da Caatinga.
O presente trabalho teve por objetivo realizar uma busca ampla sobre a expressão ?As sementes da caatinga são? e encontrar padrões característicos em estudos já realizados. A partir dos resultados da busca pode-se concluir que as sementes da Caatinga são produzidas durante todo o ano, mas a maioria é dispersada no final da estação seca. As sementes da Caatinga apresentam características morfofisiológicas de acordo com os locais onde são produzidas. Algumas sementes da Caatinga apresentam dormência tegumentar, no entanto, é raro encontrar dormência fisiológica. A maioria das sementes da Caatinga são apresentam tolerância a estresses abióticos, embora algumas espécies características deste ecossistema são sensíveis a algumas condições ambientais extremas. A comercialização das sementes da Caatinga ainda é incipiente. As sementes da Caatinga felizmente estão sendo estudadas em várias instituições do Nordeste, do Brasil e do mundo.Edição das Palestras do V Workshop de Tecnologia e Fisiologia de Sementes e Mudas, Petrolina, dez. 2014
Temperature independent band structure of WTe2 as observed from ARPES
Extremely large magnetoresistance (XMR), observed in transition metal
dichalcogendies, WTe, has attracted recently a great deal of research
interests as it shows no sign of saturation up to the magnetic field as high as
60 T, in addition to the presence of type-II Weyl fermions. Currently, there
has been a lot of discussion on the role of band structure changes on the
temperature dependent XMR in this compound. In this contribution, we study the
band structure of WTe using angle-resolved photoemission spectroscopy
(ARPES) and first-principle calculations to demonstrate that the temperature
dependent band structure has no substantial effect on the temperature dependent
XMR as our measurements do not show band structure changes on increasing the
sample temperature between 20 and 130 K. We further observe an electronlike
surface state, dispersing in such a way that it connects the top of bulk
holelike band to the bottom of bulk electronlike band. Interestingly, similar
to bulk states, the surface state is also mostly intact with the sample
temperature. Our results provide invaluable information in shaping the
mechanism of temperature dependent XMR in WTe.Comment: 7 pages, 3 figures. arXiv admin note: text overlap with
arXiv:1705.0721
The Far-Infrared Background Correlation with CMB Lensing
The intervening large--scale structure distorts cosmic microwave background
(CMB) anisotropies via gravitational lensing. The same large--scale structure,
traced by dusty star--forming galaxies, also induces anisotropies in the
far--infrared background (FIRB). We investigate the resulting inter--dependence
of the FIRB and CMB with a halo model for the FIRB. In particular, we calculate
the cross--correlation between the lensing potential and the FIRB. The lensing
potential can be quadratically estimated from CMB temperature and/or
polarization maps. We show that the cross--correlation can be measured with
high signal--to--noise with data from the Planck Surveyor. We discuss how such
a measurement can be used to understand the nature of FIRB sources and their
relation to the distribution of dark matter.Comment: 9 pages, 5 figures, submitted to Ap
Current cosmological constraints from a 10 parameter CMB analysis
We compute the constraints on a ``standard'' 10 parameter cold dark matter
(CDM) model from the most recent CMB and data and other observations, exploring
30 million discrete models and two continuous parameters. Our parameters are
the densities of CDM, baryons, neutrinos, vacuum energy and curvature, the
reionization optical depth, and the normalization and tilt for both scalar and
tensor fluctuations.
Our strongest constraints are on spatial curvature, -0.24 < Omega_k < 0.38,
and CDM density, h^2 Omega_cdm <0.3, both at 95%. Including SN 1a constraints
gives a positive cosmological constant at high significance.
We explore the robustness of our results to various assumptions. We find that
three different data subsets give qualitatively consistent constraints. Some of
the technical issues that have the largest impact are the inclusion of
calibration errors, closed models, gravity waves, reionization, nucleosynthesis
constraints and 10-dimensional likelihood interpolation.Comment: Replaced to match published ApJ version. More details added. 13 ApJ
pages. CMB movies and color figs at
http://www.hep.upenn.edu/~max/10par_frames.html or from [email protected]
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