29,091 research outputs found
Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators
We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general
On p-Robust Saturation for hp-AFEM
We consider the standard adaptive finite element loop SOLVE, ESTIMATE, MARK,
REFINE, with ESTIMATE being implemented using the -robust equilibrated flux
estimator, and MARK being D\"orfler marking. As a refinement strategy we employ
-refinement. We investigate the question by which amount the local
polynomial degree on any marked patch has to be increase in order to achieve a
-independent error reduction. The resulting adaptive method can be turned
into an instance optimal -adaptive method by the addition of a coarsening
routine
Combining Experimental and Cosmological Constraints on Heavy Neutrinos
We study experimental and cosmological constraints on the extension of the
Standard Model by three right handed neutrinos with masses between those of the
pion and W boson. We combine for the first time direct, indirect and
cosmological constraints in this mass range. This includes experimental
constraints from neutrino oscillation data, neutrinoless double decay,
electroweak precision data, lepton universality, searches for rare lepton
decays, tests of CKM unitarity and past direct searches at colliders or fixed
target experiments. On the cosmological side, big bang nucleosynthesis has the
most pronounced impact. Our results can be used to evaluate the discovery
potential of searches for heavy neutrinos at LHCb, BELLE II, SHiP, ATLAS, CMS
or a future lepton collider.Comment: 64 pages, 22 figures. Matches published versio
The chaotic effects in a nonlinear QCD evolution equation
The corrections of gluon fusion to the DGLAP and BFKL equations are discussed
in a united partonic framework. The resulting nonlinear evolution equations are
the well-known GLR-MQ-ZRS equation and a new evolution equation. Using the
available saturation models as input, we find that the new evolution equation
has the chaos solution with positive Lyaponov exponents in the perturbative
range. We predict a new kind of shadowing caused by chaos, which blocks the QCD
evolution in a critical small range. The blocking effect in the evolution
equation may explain the Abelian gluon assumption and even influence our
expectations to the projected Large Hadron Electron Collider (LHeC), Very Large
Hadron Collider (VLHC) and the upgrade (CppC) in a circular collider
(SppC).Comment: 58 pages, 23 figures,. Final version to appear in NP
Adaptive boundary element methods with convergence rates
This paper presents adaptive boundary element methods for positive, negative,
as well as zero order operator equations, together with proofs that they
converge at certain rates. The convergence rates are quasi-optimal in a certain
sense under mild assumptions that are analogous to what is typically assumed in
the theory of adaptive finite element methods. In particular, no
saturation-type assumption is used. The main ingredients of the proof that
constitute new findings are some results on a posteriori error estimates for
boundary element methods, and an inverse-type inequality involving boundary
integral operators on locally refined finite element spaces.Comment: 48 pages. A journal version. The previous version (v3) is a bit
lengthie
A saturation property for the spectral-Galerkin approximation of a Dirichlet problem in a square
Both practice and analysis of adaptive -FEMs and -FEMs raise the
question what increment in the current polynomial degree guarantees a
-independent reduction of the Galerkin error. We answer this question for
the -FEM in the simplified context of homogeneous Dirichlet problems for the
Poisson equation in the two dimensional unit square with polynomial data of
degree . We show that an increment proportional to yields a -robust
error reduction and provide computational evidence that a constant increment
does not
Possible scenario for MaVaN's as the only neutrino flavor conversion mechanism in the Sun
Mass Varying neutrino mechanisms were proposed to link the neutrino mass
scale with dark energy, addressing the coincidence problem. In some scenarios
this mass can present a dependence on the baryonic density felt by neutrinos,
creating an effective neutrino mass that depends both on the neutrino and
baryonic densities. In this article we investigate the possibility that a
neutrino effective mass is the only flavour conversion mechanism acting in
neutrino oscillation experiments. We present a parameterization on the
environmental effects on neutrino mass that produces the right flavour
conversion probabilities for solar and terrestrial neutrinos experiments.Comment: 12 pages, 4 figure
Gravitational waves from single neutron stars: an advanced detector era survey
With the doors beginning to swing open on the new gravitational wave
astronomy, this review provides an up-to-date survey of the most important
physical mechanisms that could lead to emission of potentially detectable
gravitational radiation from isolated and accreting neutron stars. In
particular we discuss the gravitational wave-driven instability and
asteroseismology formalism of the f- and r-modes, the different ways that a
neutron star could form and sustain a non-axisymmetric quadrupolar "mountain"
deformation, the excitation of oscillations during magnetar flares and the
possible gravitational wave signature of pulsar glitches. We focus on progress
made in the recent years in each topic, make a fresh assessment of the
gravitational wave detectability of each mechanism and, finally, highlight key
problems and desiderata for future work.Comment: 39 pages, 12 figures, 2 tables. Chapter of the book "Physics and
Astrophysics of Neutron Stars", NewCompStar COST Action 1304. Minor
corrections to match published versio
Implications of an r-mode in XTE J1751-305: Mass, radius and spin evolution
Recently Strohmayer and Mahmoodifar presented evidence for a coherent
oscillation in the X-ray light curve of the accreting millisecond pulsar XTE
J1751-305, using data taken by RXTE during the 2002 outburst of this source.
They noted that a possible explanation includes the excitation of a non-radial
oscillation mode of the neutron star, either in the form of a g-mode or an
r-mode. The r-mode interpretation has connections with proposed spin-evolution
scenarios for systems such as XTE J1751-305. Here we examine in detail this
interesting possible interpretation. Using the ratio of the observed
oscillation frequency to the star's spin frequency, we derive an approximate
neutron star mass-radius relation which yields reasonable values for the mass
over the range of expected stellar radius (as constrained by observations of
radius-expansion burst sources). However, we argue that the large mode
amplitude suggested by the Strohmayer and Mahmoodifar analysis would inevitably
lead to a large spin-down of the star, inconsistent with its observed spin
evolution, regardless of whether the r-mode itself is in a stable or unstable
regime. We therefore conclude that the r-mode interpretation of the observed
oscillation is not consistent with our current understanding of neutron star
dynamics and must be considered unlikely. Finally we note that, subject to the
availability of a sufficiently accurate timing model, a direct
gravitational-wave search may be able to confirm or reject an r-mode
interpretation unambiguously, should such an event, with a similar inferred
mode amplitude, recur during the Advanced detector era.Comment: 8 pages, 3 figures; submitted to MNRA
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