1,176 research outputs found
Classical skyrmions in SU(N)/SO(N) cosets
We construct the skyrmion solutions appearing in the coset spaces SU(N)/SO(N)
for N > 2 and compute their classical mass. For N = 3, the third homotopy group
pi_3(SU(3)/SO(3)) = Z_4 implies the existence of two distinct solutions: the
skyrmion of winding number two has spherical symmetry and is found to be the
lightest non-trivial field configuration; the skyrmion and antiskyrmion of
winding number plus and minus one are slightly heavier and of toroidal shape.
For N >= 4, there is only one skyrmion since the third homotopy group is Z_2.
It is found to have spherical symmetry and is significantly lighter than the N
= 3 solutions.Comment: 14 pages, 3 figures; v2: discussion improve
Spatial, Temporal and Spectral Properties of X-ray Emission from the Magnetar SGR~0501+4516
SGR~0501+4516 was discovered with the Swift satellite on 2008 August 22,
after it emitted a series of very energetic bursts. Since then, the source was
extensively monitored with Swift, the Rossi X-ray Timing Explorer (RXTE) and
observed with Chandra and XMM-Newton, providing a wealth of information about
its outburst behavior and burst induced changes of its persistent X-ray
emission. Here we report the most accurate location of SGR~0501+4516 (with an
accuracy of 0.11'') derived with Chandra. Using the combined RXTE, Swift/X-ray
Telescope, Chandra and XMM-Newton observations we construct a phase connected
timing solution with the longest time baseline (~240 days) to date for the
source. We find that the pulse profile of the source is energy dependent and
exhibits remarkable variations associated with the SGR~0501+4516 bursting
activity. We also find significant spectral evolution (hardening) of the source
persistent emission associated with bursts. Finally, we discuss the
consequences of the SGR~0501+4516 proximity to the supernova remnant, SNR
G160.9+2.6 (HB9).Comment: Accepted for publication in the Ap
Chandra Smells a RRAT: X-ray Detection of a Rotating Radio Transient
"Rotating RAdio Transients" (RRATs) are a newly discovered astronomical
phenomenon, characterised by occasional brief radio bursts, with average
intervals between bursts ranging from minutes to hours. The burst spacings
allow identification of periodicities, which fall in the range 0.4 to 7
seconds. The RRATs thus seem to be rotating neutron stars, albeit with
properties very different from the rest of the population. We here present the
serendipitous detection with the Chandra X-ray Observatory of a bright
point-like X-ray source coincident with one of the RRATs. We discuss the
temporal and spectral properties of this X-ray emission, consider counterparts
in other wavebands, and interpret these results in the context of possible
explanations for the RRAT population.Comment: 5 pages, 2 b/w figures, 1 color figure. To appear in the proceedings
of "Isolated Neutron Stars", Astrophysics & Space Science, in pres
Anomalous X-ray pulsars and soft gamma-ray repeaters - the connection with supernova remnants
Many of the properties of anomalous X-ray pulsars (AXPs) and soft gamma-ray
repeaters (SGRs) are still a matter of much debate, as is the connection (if
any) between these two groups of sources. In cases where we can identify the
supernova remnant (SNR) associated with an AXP or SGR, the extra information
thus obtained can provide important constraints as to the nature of these
exotic objects. In this paper, I explain the criteria by which an association
between a SNR and an AXP/SGR should be judged, review the set of associations
which result, and discuss the implications provided by these associations for
the ages, environments and evolutionary pathways of the AXPs and SGRs. There
are several convincing associations between AXPs and SNRs, demonstrating that
AXPs are young neutron stars with moderate space velocities. The lack of
associations between SGRs and SNRs implies that the SGRs either represent an
older population of neutron stars than do the AXPs, or originate from more
massive progenitors.Comment: 10 pages, 3 embedded EPS figures, 3 JPG figures, uses cospar.sty.
Invited review to appear in "High Energy Studies of Supernova Remnants and
Neutron Stars" (COSPAR 2002), Advances in Space Research, in press. PS
version with all figures embedded available at
http://cfa-www.harvard.edu/~bgaensler/preprints/0212086.p
Dangerous Skyrmions in Little Higgs Models
Skyrmions are present in many models of electroweak symmetry breaking where
the Higgs is a pseudo-Goldstone boson of some strongly interacting sector. They
are stable, composite objects whose mass lies in the range 10-100 TeV and can
be naturally abundant in the universe due to their small annihilation
cross-section. They represent therefore good dark matter candidates. We show
however in this work that the lightest skyrmion states are electrically charged
in most of the popular little Higgs models, and hence should have been directly
or indirectly observed in nature already. The charge of the skyrmion under the
electroweak gauge group is computed in a model-independent way and is related
to the presence of anomalies in the underlying theory via the
Wess-Zumino-Witten term.Comment: 31 pages, 4 figures; v2: minor changes, one reference added, version
to appear in JHEP; v3: erratum added, conclusions unchange
Isolation of a Novel Swine Influenza Virus from Oklahoma in 2011 Which Is Distantly Related to Human Influenza C Viruses
Of the Orthomyxoviridae family of viruses, only influenza A viruses are thought to exist as multiple subtypes and has nonhuman maintenance hosts. In April 2011, nasal swabs were collected for virus isolation from pigs exhibiting influenza-like illness. Subsequent electron microscopic, biochemical, and genetic studies identified an orthomyxovirus with seven RNA segments exhibiting approximately 50% overall amino acid identity to human influenza C virus. Based on its genetic organizational similarities to influenza C viruses this virus has been provisionally designated C/Oklahoma/1334/2011 (C/OK). Phylogenetic analysis of the predicted viral proteins found that the divergence between C/OK and human influenza C viruses was similar to that observed between influenza A and B viruses. No cross reactivity was observed between C/OK and human influenza C viruses using hemagglutination inhibition (HI) assays. Additionally, screening of pig and human serum samples found that 9.5% and 1.3%, respectively, of individuals had measurable HI antibody titers to C/OK virus. C/OK virus was able to infect both ferrets and pigs and transmit to naive animals by direct contact. Cell culture studies showed that C/ OK virus displayed a broader cellular tropism than a human influenza C virus. The observed difference in cellular tropism was further supported by structural analysis showing that hemagglutinin esterase (HE) proteins between two viruses have conserved enzymatic but divergent receptor-binding sites. These results suggest that C/OK virus represents a new subtype of influenza C viruses that currently circulates in pigs that has not been recognized previously. The presence of multiple subtypes of co-circulating influenza C viruses raises the possibility of reassortment and antigenic shift as mechanisms of influenza C virus evolution
Estética e Imperio. El sentido de belleza femenina en la construcción del archipiélago imperial estadounidense
This article examines the “sense of beauty” in the United States imperial archipelago, composed of the island territories of Cuba, Hawai`i, Philippines, and Puerto Rico, all acquired in 1898. The theoretical connection among these two elements –aesthetics and empire– is provided by a revision of the concepts “economy of colonial desire” and “complex of visuality.” This paper analyzes the most advanced visual technology of the late nineteenth century: the mass- produced, printed photograph. In particular, it focuses upon the representations of feminine beauty as found the illustrated “new-possessions” books which described recent island acquisitions of the United States. The connections between aesthetics and the forms of governance in each territory will also be elucidated.Este artĂculo examina el “sentido de belleza” en el archipiĂ©lago imperial estadounidense, compuesto de los territorios isleños de Cuba, Hawai`i, Filipinas y Puerto Rico, todos adquiridos en 1898. La conexiĂłn teĂłrica entre estos dos elementos –estĂ©tica e imperio– se establece mediante una revisiĂłn de los conceptos de “economĂa de deseo colonial” y el “complejo de visualidad”. Este artĂculo analiza la tecnologĂa visual más avanzada del siglo diecinueve tardĂo: la fotografĂa impresa. En particular, se enfoca en las representaciones de belleza femenina en los libros ilustrados de las “nuevas posesiones” los cuales describĂan las adquisiciones recientes de los Estados Unidos. TambiĂ©n, se dilucidarán las conexiones entre estĂ©tica y las formas de gobernanza en cada territorio
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