1,794 research outputs found
Invariant solutions to the Strominger system and the heterotic equations of motion
We construct many new invariant solutions to the Strominger system with
respect to a 2-parameter family of metric connections
in the anomaly cancellation equation. The ansatz
is a natural extension of the canonical 1-parameter
family of Hermitian connections found by Gauduchon, as one recovers the Chern
connection for , and the Bismut
connection for . In particular,
explicit invariant solutions to the Strominger system with respect to the Chern
connection, with non-flat instanton and positive are obtained.
Furthermore, we give invariant solutions to the heterotic equations of motion
with respect to the Bismut connection. Our solutions live on three different
compact non-K\"ahler homogeneous spaces, obtained as the quotient by a lattice
of maximal rank of a nilpotent Lie group, the semisimple group
SL(2,) and a solvable Lie group. To our knowledge, these are the
only known invariant solutions to the heterotic equations of motion, and we
conjecture that there is no other such homogeneous space admitting an invariant
solution to the heterotic equations of motion with respect to a connection in
the ansatz .Comment: 27 pages, 3 figure
The ascending central series of nilpotent Lie algebras with complex structure
We obtain several restrictions on the terms of the ascending central series
of a nilpotent Lie algebra under the presence of a complex
structure . In particular, we find a bound for the dimension of the center
of when it does not contain any non-trivial -invariant ideal.
Thanks to these results, we provide a structural theorem describing the
ascending central series of 8-dimensional nilpotent Lie algebras
admitting this particular type of complex structures . Since our method is
constructive, it allows us to describe the complex structure equations that
parametrize all such pairs .Comment: 28 pages, 1 figure. To appear in Trans. Amer. Math. So
Symplectically harmonic cohomology of nilmanifolds
This paper can be considered as an extension to our paper [On symplectically
harmonic forms on six-dimensional nilmanifolds, Comment. Math. Helv. 76 (2001),
n 1, 89-109]. Also, it contains a brief survey of recent results on
symplectically harmonic cohomology.Comment: 18 page
A young stellar environment for the superluminous supernova PTF12dam
The progenitors of super luminous supernovae (SLSNe) are still a mystery.
Hydrogen-poor SLSN hosts are often highly star-forming dwarf galaxies and the
majority belongs to the class of extreme emission line galaxies hosting young
and highly star-forming stellar populations. Here we present a resolved
long-slit study of the host of the hydrogen-poor SLSN PTF12dam probing the kpc
environment of the SN site to determine the age of the progenitor. The galaxy
is a "tadpole" with uniform properties and the SN occurred in a star-forming
region in the head of the tadpole. The galaxy experienced a recent star-burst
superimposed on an underlying old stellar population. We measure a very young
stellar population at the SN site with an age of ~3 Myr and a metallicity of
12+log(O/H)=8.0 at the SN site but do not observe any WR features. The
progenitor of PTF12dam must have been a massive star of at least 60 M_solar and
one of the first stars exploding as a SN in this extremely young starburst.Comment: submitted to MNRAS letters. 5 pages, 3 figures, supplementary
material: 2 figures, 2 table
CDS wide slit time-series of EUV coronal bright points
Wide slit (90" x 240" ) movies of four Extreme Ultraviolet coronal bright points (BPs) obtained with the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SoHO) have been inspected. The wavelet analysis of the He I 584.34 Ă
, O V 629.73 Ă
and Mg VII/IX 368 Ă
time-series confirms the oscillating nature of the BPs, with periods ranging between 600 and 1100 s. In one case we detect periods as short as 236 s. We suggest that these oscillations are the same as those seen in the chromospheric network and that a fraction of the network bright points are most likely the cool footpoints of the loops comprising coronal bright points. These oscillations are interpreted in terms of global acoustic modes of the closed magnetic structures associated with BPs
The Temperature Dependence of Solar Active Region Outflows
Spectroscopic observations with the EUV Imaging Spectrometer (EIS) on Hinode
have revealed large areas of high speed outflows at the periphery of many solar
active regions. These outflows are of interest because they may connect to the
heliosphere and contribute to the solar wind. In this Letter we use slit
rasters from EIS in combination with narrow band slot imaging to study the
temperature dependence of an active region outflow and show that it is more
complicated than previously thought. Outflows are observed primarily in
emission lines from Fe XI - Fe XV. Observations at lower temperatures (Si VII),
in contrast, show bright fan-like structures that are dominated by downflows.
The morphology of the outflows is also different than that of the fans. This
suggests that the fan loops, which often show apparent outflows in imaging
data, are contained on closed field lines and are not directly related to the
active region outflows.Comment: Movies are available online at:
http://tcrb.nrl.navy.mil/~hwarren/temp/papers/flow_temperatures/ To be
submitted to ApJ
Is Small Perfect? Size Limit to Defect Formation in Pyramidal Pt Nanocontacts
We report high resolution transmission electron microscopy and ab initio
calculation results for the defect formation in Pt nanocontacts (NCs). Our
results show that there is a size limit to the existence of twins (extended
structural defects). Defects are always present but blocked away from the tip
axes. The twins may act as scattering plane, influencing contact electron
transmission for Pt NC at room temperature and Ag/Au NC at low temperature.Comment: 4 pages, 3 figure
On the real homotopy type of generalized complex nilmanifolds
We prove that for any n = 4, there are infinitely many real homotopy types of 2n-dimensional nilmanifolds admitting generalized complex structures of every type k, for 0 = k = n
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