722 research outputs found
On D-branes in the Nappi-Witten and GMM gauged WZW models
We construct D-branes in the Nappi-Witten (NW) and
Guadagnini-Martellini-Mintchev (GMM) gauged WZW models. For the NW and GMM models we present
the explicit equations describing the D-brane hypersurfaces in their target
spaces. In the latter case we show that the D-branes are classified according
to the Cardy theorem. We also present the semiclassical mass computation and
find its agreement with the CFT predictions.Comment: 16 pages, harvma
On canonical quantization of the gauged WZW model with permutation branes
In this paper we perform canonical quantization of the product of the gauged
WZW models on a strip with boundary conditions specified by permutation branes.
We show that the phase space of the -fold product of the gauged WZW model
on a strip with boundary conditions given by permutation branes is
symplectomorphic to the phase space of the double Chern-Simons theory on a
sphere with holes times the time-line with and gauge fields both
coupled to two Wilson lines. For the special case of the topological coset
we arrive at the conclusion that the phase space of the -fold product
of the topological coset on a strip with boundary conditions given by
permutation branes is symplectomorphic to the phase space of Chern-Simons
theory on a Riemann surface of the genus times the time-line with four
Wilson lines.Comment: 18 page
Market and regional segmentation and risk premia in the first era of financial globalization
We study market segmentation effects using data on U.S. railroads that list their bonds in New York and London between 1873 and 1913. This sample provides a unique setting for such analysis because of the precision offered by bond yields in cost of capital estimation, the geography-specific nature of railroad assets, and ongoing substantial technological change. We document a significant
reduction in market segmentation over time. Whilst New York bond yields exceeded those in London in the 1870s, this premium disappeared by the early 1900s. However, the segmentation premium persisted in the more remote regions of the United States.Chambers acknowledges financial support from his Keynes Fellowship, the Newton Centre for Endowment Asset Management and the Cambridge Endowment for Research in Finance, Sarkissian acknowledges financial support from the Social Sciences & Humanities Research Council of Canada, and Schill acknowledges financial support from the Darden School Foundation
Peculiar Spin Frequency and Radio Profile Evolution of PSR J11196127 Following Magnetar-like X-ray Bursts
We present the spin frequency and profile evolution of the radio pulsar
J11196127 following magnetar-like X-ray bursts from the system in 2016 July.
Using data from the Parkes radio telescope, we observe a smooth and fast
spin-down process subsequent to the X-ray bursts resulting in a net change in
the pulsar rotational frequency of \,Hz.
During the transition, a net spin-down rate increase of
\,Hz\,s is observed, followed by a
return of to its original value. In addition, the radio pulsations
disappeared after the X-ray bursts and reappeared about two weeks later with
the flux density at 1.4\,GHz increased by a factor of five. The flux density
then decreased and undershot the normal flux density followed by a slow
recovery back to normal. The pulsar's integrated profile underwent dramatic and
short-term changes in total intensity, polarization and position angle. Despite
the complex evolution, we observe correlations between the spin-down rate,
pulse profile shape and radio flux density. Strong single pulses have been
detected after the X-ray bursts with their energy distributions evolving with
time. The peculiar but smooth spin frequency evolution of PSR~J11196127
accompanied by systematic pulse profile and flux density changes are most
likely to be a result of either reconfiguration of the surface magnetic fields
or particle winds triggered by the X-ray bursts. The recovery of spin-down rate
and pulse profile to normal provides us the best case to study the connection
between high magnetic-field pulsars and magnetars.Comment: Accepted for publication in MNRAS on 2018 July 2
DBI analysis of generalised permutation branes
We investigate D-branes on the product GxG of two group manifolds described
as Wess-Zumino-Novikov-Witten models. When the levels of the two groups
coincide, it is well known that there exist permutation D-branes which are
twisted by the automorphism exchanging the two factors. When the levels are
different, the D-brane charge group demands that there should be
generalisations of these permutation D-branes, and a geometric construction for
them was proposed in hep-th/0509153. We give further evidence for this proposal
by showing that the generalised permutation D-branes satisfy the
Dirac-Born-Infeld equations of motion for arbitrary compact, simply connected
and simple Lie groups G.Comment: 19 pages, computation in section 3.5.1 corrected, conclusions
unchange
Spin-down evolution and radio disappearance of the magnetar PSR J16224950
We report on 2.4 yr of radio timing measurements of the magnetar PSR
J16224950 using the Parkes telescope, between 2011 November and 2014 March.
During this period the torque on the neutron star (inferred from the rotational
frequency derivative) varied greatly, though much less erratically than in the
2 yr following its discovery in 2009. During the last year of our measurements
the frequency derivative decreased in magnitude monotonically by 20\%, to a
value of s, a factor of 8 smaller than when
discovered. The flux density continued to vary greatly during our monitoring
through 2014 March, reaching a relatively steady low level after late 2012. The
pulse profile varied secularly on a similar timescale as the flux density and
torque. A relatively rapid transition in all three properties is evident in
early 2013. After PSR J16224950 was detected in all of our 87 observations
up to 2014 March, we did not detect the magnetar in our resumed monitoring
starting in 2015 January and have not detected it in any of the 30 observations
done through 2016 September.Comment: 8 pages, 5 figures, submitted to Ap
Radio disappearance of the magnetar XTE J1810-197 and continued X-ray timing
We report on timing, flux density, and polarimetric observations of the
transient magnetar and 5.54 s radio pulsar XTE J1810-197 using the GBT, Nancay,
and Parkes radio telescopes beginning in early 2006, until its sudden
disappearance as a radio source in late 2008. Repeated observations through
2016 have not detected radio pulsations again. The torque on the neutron star,
as inferred from its rotation frequency derivative f-dot, decreased in an
unsteady manner by a factor of 3 in the first year of radio monitoring. In
contrast, during its final year as a detectable radio source, the torque
decreased steadily by only 9%. The period-averaged flux density, after
decreasing by a factor of 20 during the first 10 months of radio monitoring,
remained steady in the next 22 months, at an average of 0.7+/-0.3 mJy at 1.4
GHz, while still showing day-to-day fluctuations by factors of a few. There is
evidence that during this last phase of radio activity the magnetar had a steep
radio spectrum, in contrast to earlier behavior. There was no secular decrease
that presaged its radio demise. During this time the pulse profile continued to
display large variations, and polarimetry indicates that the magnetic geometry
remained consistent with that of earlier times. We supplement these results
with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the
first 4 years, XTE J1810-197 experienced non-monotonic excursions in f-dot by
at least a factor of 8. But since 2007, its f-dot has remained relatively
stable near its minimum observed value. The only apparent event in the X-ray
record that is possibly contemporaneous with the radio shut-down is a decrease
of ~20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However,
the permanence of the high-amplitude, thermal X-ray pulse, even after the radio
demise, implies continuing magnetar activity.Comment: ApJ, accepted, 12 pages, 9 figure
Negotiating the Personal and Professional: Ethnomusicologists and Uncomfortable Truths
The panel, “Negotiating the Personal and Professional: Ethnomusicologists and Uncomfortable Truths,” presented at the Forty-third ICTM World Conference in Astana, Kazakhstan, grew out of informal conversations common among ethnomusicologists. As practitioners in our discipline, we are involved in complex webs of experience, relationships, and representations focused around music, broadly defined. Our work is inherently social and, when in the field, we develop close relationships with our teachers and consultants as we become comfortable in our sites of research. We are grateful for priceless access to communities and individuals. The intensity and combination of certain relationships and circumstances, however, can lead to conflicting expectations, unanticipated misunderstanding, and situations of personal and professional conflict
Five New Millisecond Pulsars From a Radio Survey of 14 Unidentified Fermi-LAT Gamma-ray Sources
We have discovered five millisecond pulsars (MSPs) in a survey of 14
unidentified Fermi-LAT sources in the southern sky using the Parkes radio
telescope. PSRs J0101-6422, J1514-4946, and J1902-5105 reside in binaries,
while PSRs J1658-5324 and J1747-4036 are isolated. Using an ephemeris derived
from timing observations of PSR J0101-6422 (P =2.57 ms, DM=12 pc cm-3), we have
detected {\gamma}-ray pulsations and measured its proper motion. Its
{\gamma}-ray spectrum (a power law of {\Gamma} = 0.9 with a cutoff at 1.6 GeV)
and efficiency are typical of other MSPs, but its radio and {\gamma}-ray light
curves challenge simple geometric models of emission. The high success rate of
this survey-enabled by selecting {\gamma}-ray sources based on their detailed
spectral characteristics-and other similarly successful searches indicate that
a substantial fraction of the local population of MSPs may soon be known.Comment: 6 pages, 3 figures, 2 tables, accepted by ApJ
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