45,044 research outputs found
Returning magnetic flux in sunspot penumbrae
We study the presence of reversed polarity magnetic flux in sunspot penumbra.
We applied a new regularized method to deconvolve spectropolarimetric data
observed with the spectropolarimeter SP onboard Hinode. The new regularization
is based on a principal component decomposition of the Stokes profiles. The
resulting Stokes profiles were inverted to infer the magnetic field vector
using SIR. We find, for the first time, reversed polarity fields at the border
of many bright penumbral filaments in the whole penumbra.Comment: 5 pages, 5 figures, accepted for publication in A&A Letter
Electroweak non-resonant corrections to top pair production close to threshold
The production of W+ W- b bbar from e+ e- collisions at energies close to the
t tbar threshold is dominated by the resonant process with a nearly on-shell t
tbar intermediate state. The W b pairs in the final state can also be reached
through the decay of off-shell tops or through background processes containing
no or only single top quarks. This non-resonant production starts to contribute
at NLO to the W+ W- b bbar total cross section in the non-relativistic
power-counting v ~ alpha_s ~ sqrt(alpha_EW). The NLO non-resonant corrections
presented in this talk represent the non-trivial NLO electroweak corrections to
the e+ e- -> W+ W- b bbar cross section in the top anti-top resonance region.
In contrast to the QCD corrections which have been calculated (almost) up to
NNNLO, the parametrically larger NLO electroweak contributions have not been
completely known so far, but are mandatory for the required accuracy at a
future linear collider. We consider the total cross section of the e+ e- -> W+
W- b bbar process and additionally implement cuts on the invariant masses of
the W+ b and W- bbar pairs.Comment: Talk presented at the 35th International Conference of High Energy
Physics - ICHEP2010, July 22-28, 2010, Paris France. 4 pages, 2 figure
Nonautonomous Hamiltonian Systems and Morales-Ramis Theory I. The Case
In this paper we present an approach towards the comprehensive analysis of
the non-integrability of differential equations in the form
which is analogous to Hamiltonian systems with 1+1/2 degree of freedom. In
particular, we analyze the non-integrability of some important families of
differential equations such as Painlev\'e II, Sitnikov and Hill-Schr\"odinger
equation.
We emphasize in Painlev\'e II, showing its non-integrability through three
different Hamiltonian systems, and also in Sitnikov in which two different
version including numerical results are shown. The main tool to study the
non-integrability of these kind of Hamiltonian systems is Morales-Ramis theory.
This paper is a very slight improvement of the talk with the almost-same title
delivered by the author in SIAM Conference on Applications of Dynamical Systems
2007.Comment: 15 pages without figures (19 pages and 6 figures in the published
version
Stationary configurations of two extreme black holes obtainable from the Kinnersley-Chitre solution
Stationary axisymmetric systems of two extreme Kerr sources separated by a
massless strut, which arise as subfamilies of the well-known Kinnersley-Chitre
solution, are studied. We present explicit analytical formulas for the
individual masses and angular momenta of the constituents and establish the
range of the parameters for which such systems can be regarded as describing
black holes. The mass-angular momentum relations and the interaction force in
the black-hole configurations are also analyzed. Furthermore, we construct a
charging generalization of the Kinnersley-Chitre metric and, as applications of
the general formulas obtained, discuss two special cases describing a pair of
identical co- and counterrotating extreme Kerr-Newman black holes kept apart by
a conical singularity. From our analysis it follows in particular that the
equality relating the mass, angular momentum per unit mass and
electric charge of a single Kerr-Newman extreme black hole is no longer
verified by the analogous extreme black-hole constituents in binary
configurations.Comment: final version revised according to referee's suggestion
Implications of the Measured Image Size for the Radio Afterglow of GRB 030329
We use data on the image size of the radio afterglow of GRB 030329 (Taylor et
al. 2004) to constrain the physical parameters of this explosion. Together with
the observed broad band spectrum, this data over-constrains the physical
parameters, thus enabling to test different GRB jet models for consistency. We
consider two extreme models for the lateral spreading of the jet: model 1 with
relativistic expansion in the local rest frame, and model 2 with little lateral
expansion as long as the jet is highly relativistic. We find that both models
are consistent with the data for a uniform external medium, while for a stellar
wind environment model 1 is consistent with the data but model 2 is disfavored
by the data. Our derivations can be used to place tighter constraints on the
dynamics and structure of GRB jets in future afterglows, following a denser
monitoring campaign for the temporal evolution of their image size.Comment: 12 pages, 6 figues; submitted to Ap
- …