42,049 research outputs found
Stochastic modelling of intermittent scrape-off layer plasma fluctuations
Single-point measurements of fluctuations in the scrape-off layer of
magnetized plasmas are generally found to be dominated by large-amplitude
bursts which are associated with radial motion of blob-like structures. A
stochastic model for these fluctuations is presented, with the plasma density
given by a random sequence of bursts with a fixed wave form. Under very general
conditions, this model predicts a parabolic relation between the skewness and
kurtosis moments of the plasma fluctuations. In the case of exponentially
distributed burst amplitudes and waiting times, the probability density
function for the fluctuation amplitudes is shown to be a Gamma distribution
with the scale parameter given by the average burst amplitude and the shape
parameter given by the ratio of the burst duration and waiting times.Comment: 11 pages, 1 figur
Monodromy of the SL_2 Hitchin fibration
We calculate the monodromy action on the mod 2 cohomology for SL(2,C) Hitchin
systems and give an application of our results in terms of the moduli space of
semistable SL(2,R) Higgs bundles.Comment: 17 pages, 3 figures. v2: Version to appear in IJ
Present Bounds on New Neutral Vector Resonances from Electroweak Gauge Boson Pair Production at the LHC
Several extensions of the Standard Model predict the existence of new neutral
spin-1 resonances associated to the electroweak symmetry breaking sector. Using
the data from ATLAS (with integrated luminosity of L=1.02 fb^{-1}) and CMS
(with integrated luminosity of L=1.55 fb^{-1}) on the production of W+W- pairs
through the process pp -> l^+ l^{\prime -} \sla{E}_T, we place model
independent bounds on these new vector resonances masses, couplings and widths.
Our analyses show that the present data excludes new neutral vector resonances
with masses up to 1-2.3 TeV depending on their couplings and widths. We also
demonstrate how to extend our analysis framework to different models working a
specific example.Comment: 10 pages, 6 figure
On the geometry of moduli spaces of coherent systems on algebraic curves
Let be an algebraic curve of genus . A coherent system on consists
of a pair , where is an algebraic vector bundle over of rank
and degree and is a subspace of dimension of the space of sections
of . The stability of the coherent system depends on a parameter .
We study the geometry of the moduli space of coherent systems for different
values of when and the variation of the moduli spaces when
we vary . As a consequence, for sufficiently large , we compute
the Picard groups and the first and second homotopy groups of the moduli spaces
of coherent systems in almost all cases, describe the moduli space for the case
explicitly, and give the Poincar\'e polynomials for the case .Comment: 38 pages; v3. Appendix and new references added; v4. minor
corrections, two added references; v5. final version, one typo corrected and
one reference delete
Bounds on Scalar Leptoquarks from Z Physics
We analyse the constraints on scalar leptoquarks coming from radiative
corrections to physics. We perform a global fitting to the LEP data
including the contributions of the most general effective Lagrangian for scalar
leptoquarks, which exhibits the gauge invariance. We
show that the bounds on leptoquarks that couple to the top quark are much
stronger than the ones obtained from low energy experiments.Comment: RevTeX 3.0, 26 pages, 4 postscript figures included as uufil
Bosonic versus fermionic pairs of topological spin defects in monolayered high-T_c superconductors
The energy associated with bosonic and fermionic pairs of topological spin
defects in doped antiferromagnetic quantum spin-1/2 square lattice is estimated
within a resonating valence bond scenario, as described by a t-t'-J-like model
Hamiltonian, plus a t-perpendicular, responsible of a three-dimensional
screening of the electrostatic repulsion within the bosonic pairs. For
parameters appropriate for monolayered high-T_c superconductors, both fermionic
and bosonic pairs show x^2-y^2 symmetry. We find a critical value of doping
such that the energy of the bosonic pairs goes below twice the energy of two
fermionic pairs at their Fermi level. This finding could be related to the
onset of high-T_c superconductivity.Comment: 10 pages, 6 figures. To be published in Phys. Rev.
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