526 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
The demographics of fund turnover
This article documents various demographic factors which influence mutual fund turnover including managerial experience, location, education, and gender. On average, funds in financial centers trade more but this excess turnover declines with experience. While most extra trading is concentrated among less experienced managers in financial centers, they do not outperform inexperienced managers located in smaller towns. Furthermore, managers in financial centers increase trading after good performance. This result is particularly strong for inexperienced, more educated male fund managers investing in growth stocks and located in New York. Our results provide strong evidence that demographic factors influence fund manager trading behavior.Labor market; Mutual funds; Overconfident trading; Performance evaluation
Spurious Regressions in Financial Economics?
Even though stock returns are not highly autocorrelated, there is a spurious regression bias in predictive regressions for stock returns related to the classic studies of Yule (1926) and Granger and Newbold (1974). Data mining for predictor variables interacts with spurious regression bias. The two effects reinforce each other, because more highly persistent series are more likely to be found significant in the search for predictor variables. Our simulations suggest that many of the regressions in the literature, based on individual predictor variables, may be spurious
Asset Pricing Models with Conditional Betas and Alphas: The Effects of Data Snooping and Spurious Regression
This paper studies the estimation of asset pricing model regressions with conditional alphas and betas, focusing on the joint effects of data snooping and spurious regression. We find that the regressions are reasonably well specified for conditional betas, even in settings where simple predictive regressions are severely biased. However, there are biases in estimates of the conditional alphas. When time-varying alphas are suppressed and only time-varying betas are considered, the betas become baised. Previous studies overstate the significance of time-varying alphas.
One year of monitoring the Vela pulsar using a Phased Array Feed
We have observed the Vela pulsar for one year using a Phased Array Feed (PAF)
receiver on the 12-metre antenna of the Parkes Test-Bed Facility. These
observations have allowed us to investigate the stability of the PAF
beam-weights over time, to demonstrate that pulsars can be timed over long
periods using PAF technology and to detect and study the most recent glitch
event that occurred on 12 December 2016. The beam-weights are shown to be
stable to 1% on time scales on the order of three weeks. We discuss the
implications of this for monitoring pulsars using PAFs on single dish
telescopes.Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in PAS
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
Timing of Millisecond Pulsars in NGC 6752: Evidence for a High Mass-to-Light Ratio in the Cluster Core
Using pulse timing observations we have obtained precise parameters,
including positions with about 20 mas accuracy, of five millisecond pulsars in
NGC 6752. Three of them, located relatively close to the cluster center, have
line-of-sight accelerations larger than the maximum value predicted by the
central mass density derived from optical observation, providing dynamical
evidence for a central mass-to-light ratio >~ 10, much higher than for any
other globular cluster. It is likely that the other two millisecond pulsars
have been ejected out of the core to their present locations at 1.4 and 3.3
half-mass radii, respectively, suggesting unusual non-thermal dynamics in the
cluster core.Comment: Accepted by ApJ Letter. 5 pages, 2 figures, 1 tabl
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