1,286 research outputs found
Rigidity around Poisson Submanifolds
We prove a rigidity theorem in Poisson geometry around compact Poisson
submanifolds, using the Nash-Moser fast convergence method. In the case of
one-point submanifolds (fixed points), this immediately implies a stronger
version of Conn's linearization theorem, also proving that Conn's theorem is,
indeed, just a manifestation of a rigidity phenomenon; similarly, in the case
of arbitrary symplectic leaves, it gives a stronger version of the local normal
form theorem; another interesting case corresponds to spheres inside duals of
compact semisimple Lie algebras, our result can be used to fully compute the
resulting Poisson moduli space.Comment: 43 pages, v3: published versio
Photon-Photon Scattering, Pion Polarizability and Chiral Symmetry
Recent attempts to detect the pion polarizability via analysis of
measurements are examined. The connection
between calculations based on dispersion relations and on chiral perturbation
theory is established by matching the low energy chiral amplitude with that
given by a full dispersive treatment. Using the values for the polarizability
required by chiral symmetry, predicted and experimental cross sections are
shown to be in agreement.Comment: 21 pages(+10 figures available on request), LATEX, UMHEP-38
Field Dependent Specific-Heat of Rare Earth Manganites
The low temperature specific heat C(H) of several rare-earth manganites
(La_(0.7)Sr_(0.3)MnO_(3), Nd_(0.5)Sr_(0.5)MnO_(3), Pr_(0.5)Sr_(0.5)MnO_(3),
La_(0.67)Ca_(0.33)MnO$_(3), La_(0.5)Ca_(0.5)MnO_(3), La_(0.45)Ca_(0.55)MnO_(3)
and La_(0.33)Ca_(0.67)MnO_(3)) was measured as a function of magnetic field. We
observed behaviour consistent with thermodynamic expectations, i.e., C(H)
decreases with field for ferromagnetic metallic compounds by an amount which is
in quantitative agreement with spin wave theory. We also find that C(H)
increases with field in most compounds with a charge-ordered antiferromagnetic
ground state. In compounds which show evidence of a coexistence of
ferromagnetic metallic and antiferromagnetic charge-ordered states, C(H)
displays some unusual non-equilibrium effects presumably associated with the
phase-separation of the two states. We also observe a large anomalous low
temperature specific heat at the doping induced metal-insulator transition (at
x = 0.50) in La_(1-x)Ca_(x)MnO_(3).Comment: 13 pages, LATEX, 7 PDF figure
PPPC 4 DM ID: A Poor Particle Physicist Cookbook for Dark Matter Indirect Detection
We provide ingredients and recipes for computing signals of TeV-scale Dark
Matter annihilations and decays in the Galaxy and beyond. For each DM channel,
we present the energy spectra of electrons and positrons, antiprotons,
antideuterons, gamma rays, neutrinos and antineutrinos e, mu, tau at
production, computed by high-statistics simulations. We estimate the Monte
Carlo uncertainty by comparing the results yielded by the Pythia and Herwig
event generators. We then provide the propagation functions for charged
particles in the Galaxy, for several DM distribution profiles and sets of
propagation parameters. Propagation of electrons and positrons is performed
with an improved semi-analytic method that takes into account
position-dependent energy losses in the Milky Way. Using such propagation
functions, we compute the energy spectra of electrons and positrons,
antiprotons and antideuterons at the location of the Earth. We then present the
gamma ray fluxes, both from prompt emission and from Inverse Compton scattering
in the galactic halo. Finally, we provide the spectra of extragalactic gamma
rays. All results are available in numerical form and ready to be consumed.Comment: 57 pages with many figures and tables. v4: updated to include a 125
higgs boson, computation and discussion of extragalactic spectra corrected,
some other typos fixed; all these corrections and updates are reflected on
the numerical ingredients available at
http://www.marcocirelli.net/PPPC4DMID.html they correspond to Release 2.
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Secondary organic aerosol formation and composition from the photo-oxidation of methyl chavicol (estragole)
The increasing demand for palm oil for uses in biofuel
and food products is leading to rapid expansion of oil palm agriculture.
Methyl chavicol (also known as estragole and 1-allyl-4-methoxybenzene) is an
oxygenated biogenic volatile organic compound (VOC) that was recently identified
as the main floral emission from an oil palm plantation in Malaysian Borneo.
The emissions of methyl chavicol observed may impact regional atmospheric
chemistry, but little is known of its ability to form secondary organic
aerosol (SOA). The photo-oxidation of methyl chavicol was investigated at
the European Photoreactor chamber as a part of the atmospheric chemistry of
methyl chavicol (ATMECH) project. Aerosol samples were collected using a
particle into liquid sampler (PILS) and analysed offline using an extensive
range of instruments including; high-performance liquid chromatography mass
spectrometry (HPLC-ITMS), high-performance liquid chromatography quadrupole
time-of-flight mass spectrometry (HPLC-QTOFMS) and Fourier transform ion
cyclotron resonance mass spectrometry (FTICR-MS). The SOA yield was
determined as 18 and 29% for an initial VOC mixing ratio of 212 and
460 ppbv (parts per billion by volume)
respectively; using a VOC:NOx ratio of ~5:1. In
total, 59 SOA compounds were observed and the structures of 10 compounds
have been identified using high-resolution tandem mass spectrometry. The
addition of hydroxyl and/or nitro-functional groups to the aromatic
ring appears to be an important mechanistic pathway for aerosol formation.
This results in the formation of compounds with both low volatility and high
O:C ratios, where functionalisation rather than fragmentation is mainly
observed as a result of the stability of the ring. The SOA species observed
can be characterised as semi-volatile to low-volatility oxygenated organic
aerosol (SVOOA and LVOOA) components and therefore may be important in
aerosol formation and growth
Hadronic final states in deep-inelastic scattering with Sherpa
We extend the multi-purpose Monte-Carlo event generator Sherpa to include
processes in deeply inelastic lepton-nucleon scattering. Hadronic final states
in this kinematical setting are characterised by the presence of multiple
kinematical scales, which were up to now accounted for only by specific
resummations in individual kinematical regions. Using an extension of the
recently introduced method for merging truncated parton showers with
higher-order tree-level matrix elements, it is possible to obtain predictions
which are reliable in all kinematical limits. Different hadronic final states,
defined by jets or individual hadrons, in deep-inelastic scattering are
analysed and the corresponding results are compared to HERA data. The various
sources of theoretical uncertainties of the approach are discussed and
quantified. The extension to deeply inelastic processes provides the
opportunity to validate the merging of matrix elements and parton showers in
multi-scale kinematics inaccessible in other collider environments. It also
allows to use HERA data on hadronic final states in the tuning of hadronisation
models.Comment: 32 pages, 22 figure
Symposium on The New Significance of Learning:Imagination’s heartwork
Hogan has written a fine, timely book which deserves to be widely read. The main
argument is for a remembering (re-membering) of an idea of education in which it is
understood as a practice in its own right, rather than just what Hogan provocatively
and accurately terms a ‘subordinate activity’. That is, he argues persuasively for an
understanding that education has its own inherent purposes, rather than (or as well
as) extrinsic religious or political ones
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