6,339 research outputs found
Rotational Behaviors and Magnetic Field Evolution of Radio Pulsars
The observed long-term spin-down evolution of isolated radio pulsars cannot
be explained by the standard magnetic dipole radiation with a constant braking
torque. However how and why the torque varies still remains controversial,
which is an outstanding problem in our understanding of neutron stars. We have
constructed a phenomenological model of the evolution of surface magnetic
fields of pulsars, which contains a long-term decay modulated by short-term
oscillations; a pulsar's spin is thus modified by its magnetic field evolution.
The predictions of this model agree with the precisely measured spin evolutions
of several individual pulsars; the derived parameters suggest that the Hall
drift and Hall waves in the NS crusts are probably responsible for the
long-term change and short-term quasi-periodical oscillations, respectively.
Many statistical properties of the timing noise of pulsars can be well
re-produced with this model, including correlations and the distributions of
the observed braking indices of the pulsars, which span over a range of more
than 100 millions. We have also presented a phenomenological model for the
recovery processes of classical and slow glitches, which can successfully model
the observed slow and classical glitch events without biases.Comment: 6 pages, 9 figures, submitted to conference proceedings of SMFNS2013
(Strong electromagnetic field and neutron stars 2013
Tensor Hierarchy and Generalized Cartan Calculus in SL(3)SL(2) Exceptional Field Theory
We construct exceptional field theory for the duality group
SL(3)SL(2). The theory is defined on a space with 8 `external'
coordinates and 6 `internal' coordinates in the fundamental
representation, leading to a 14-dimensional generalized spacetime. The bosonic
theory is uniquely determined by gauge invariance under generalized external
and internal diffeomorphisms. The latter invariance can be made manifest by
introducing higher form gauge fields and a so-called tensor hierarchy, which we
systematically develop to much higher degree than in previous studies. To this
end we introduce a novel Cartan-like tensor calculus based on a covariant
nil-potent differential, generalizing the exterior derivative of conventional
differential geometry. The theory encodes the full or type IIB
supergravity, respectively.Comment: 49 page
A Monte Carlo exploration of threefold base geometries for 4d F-theory vacua
We use Monte Carlo methods to explore the set of toric threefold bases that
support elliptic Calabi-Yau fourfolds for F-theory compactifications to four
dimensions, and study the distribution of geometrically non-Higgsable gauge
groups, matter, and quiver structure. We estimate the number of distinct
threefold bases in the connected set studied to be . The
distribution of bases peaks around . All bases encountered
after "thermalization" have some geometric non-Higgsable structure. We find
that the number of non-Higgsable gauge group factors grows roughly linearly in
of the threefold base. Typical bases have isolated gauge
factors as well as several larger connected clusters of gauge factors with
jointly charged matter. Approximately 76% of the bases sampled contain
connected two-factor gauge group products of the form SU(3)SU(2), which
may act as the non-Abelian part of the standard model gauge group.
SU(3)SU(2) is the third most common connected two-factor product group,
following SU(2)SU(2) and SU(2), which arise more frequently.Comment: 38 pages, 22 figure
Non-toric bases for elliptic Calabi-Yau threefolds and 6D F-theory vacua
We develop a combinatorial approach to the construction of general smooth
compact base surfaces that support elliptic Calabi-Yau threefolds. This extends
previous analyses that have relied on toric or semi-toric structure. The
resulting algorithm is used to construct all classes of such base surfaces
with and all base surfaces over which there is an
elliptically fibered Calabi-Yau threefold with Hodge number . These two sets can be used todescribe all 6D F-theory models that
have fewer than seven tensor multiplets or more than 150 neutral scalar fields
respectively in their maximally Higgsed phase. Technical challenges to
constructing the complete list of base surfaces for all Hodge numbers are
discussed.Comment: 51 pages, 10 figure
- …