4,356 research outputs found
Fivebranes, Membranes and Non-Perturbative String Theory
Non-perturbative instanton corrections to the moduli space geometry of type
IIA string theory compactified on a Calabi-Yau space are derived and found to
contain order contributions, where is the string coupling.
The computation reduces to a weighted sum of supersymmetric extremal maps of
strings, membranes and fivebranes into the Calabi-Yau space, all three of which
enter on equal footing. It is shown that a supersymmetric 3-cycle is one for
which the pullback of the K\"ahler form vanishes and the pullback of the
holomorphic three-form is a constant multiple of the volume element. Quantum
mirror symmetry relates the sum in the IIA theory over supersymmetric,
odd-dimensional cycles in the Calabi-Yau space to a sum in the IIB theory over
supersymmetric, even-dimensional cycles in the mirror.Comment: 34 pages, phyzzx (A new section about conifold singularities in
hypermultiplet moduli spaces is added
Some tree-level string amplitudes in the NSR formalism
We calculate tree level scattering amplitudes for open strings using the NSR
formalism. We present a streamlined symmetry-based and pedagogical approach to
the computations, which we first develop by checking two-, three-, and
four-point functions involving bosons and fermions. We calculate the five-point
amplitude for massless gluons and find agreement with an earlier result by
Brandt, Machado and Medina. We then compute the five-point amplitudes involving
two and four fermions respectively, the general form of which has not been
previously obtained in the NSR formalism. The results nicely confirm
expectations from the supersymmetric effective action. Finally we use the
prescription of Kawai, Lewellen and Tye (KLT) to compute the amplitudes for the
closed string sector.Comment: 40+8 pages; v2: references added; v3: additional field theory checks
made; published version; v4: minor corrections; results unchange
Real-space renormalization group flow in quantum impurity systems: local moment formation and the Kondo screening cloud
The existence of a length-scale (with the Kondo
temperature) has long been predicted in quantum impurity systems. At low
temperatures , the standard interpretation is that a
spin- impurity is screened by a surrounding `Kondo cloud' of
spatial extent . We argue that renormalization group (RG) flow between
any two fixed points (FPs) results in a characteristic length-scale, observed
in real-space as a crossover between physical behaviour typical of each FP. In
the simplest example of the Anderson impurity model, three FPs arise; and we
show that `free orbital', `local moment' and `strong coupling' regions of space
can be identified at zero temperature. These regions are separated by two
crossover length-scales and , with the latter
diverging as the Kondo effect is destroyed on increasing temperature through
. One implication is that moment formation occurs inside the `Kondo
cloud', while the screening process itself occurs on flowing to the strong
coupling FP at distances . Generic aspects of the real-space
physics are exemplified by the two-channel Kondo model, where now
separates `local moment' and `overscreening' clouds.Comment: 6 pages; 5 figure
Impact of precipitating events on pediatric chronic pain recovery
OBJECTIVES: 1) To measure the prevalence of precipitating events in pediatric chronic pain patients and 2) to compare pain and functional disability outcomes at evaluation and 4-month follow-up by presence and type of precipitating event.
METHODS: Precipitating events (e.g., injury) were coded from the medical record for 401 youth (6-19) who presented to a tertiary care chronic pain clinic. Four-month follow-up disability and pain were collected for 187 patients. In addition to frequency of events, we examined differences in pain and disability measures by event type at evaluation and follow-up using multiple statistical analysis strategies.
RESULTS: Two-thirds of patients had a precipitating event prior to pain onset. Injury was the most common (55%), followed by chronic disease (23%), infection/illness (12.8%), and surgery (7.5%). Patients whose pain was triggered by injury reported the highest average pain levels, F(3, 340)=2.67, p<.05 and functional disability, F(3, 295)=3.54, p<.05. There were multiple cases of event groups that had significantly different baseline and follow-up psychological measures when compared to the rest of the patient population. Trajectories of pain and disability did not differ between patients with and without a precipitating event. Patients with injuries reported greater improvement in functional disability at follow-up (time x injury) F(1, 183)=4.88, p<.05 whereas patients with chronic disease reported less improvement in disability (time x chronic disease), F(1, 183)=5.49, p<.05. No other interactions were significant for disability or pain.
CONCLUSIONS: A majority of patients had experienced some form of precipitating event prior to their pain onset, and the presence of a precipitating event had varied effects on the treatment outcomes of patients at four-month follow-up. Although patients with injuries presented with greater disability and pain, they had significantly more improvement, while chronic disease patients were less likely to improve in terms of functional disability. Type of precipitating event appears to be associated with treatment response and can inform clinical prognoses
The Peculiar Periodic YSO WL 4 in ρ Ophiuchus
We present the discovery of 130.87 day periodic near-infrared flux variability for the Class II T Tauri star WL 4 (= 2MASS J16271848-2429059, ISO-Oph 128). Our data are from the 2MASS Calibration Point Source Working Database, and constitute 1580 observations in J, H and K_s of a field in ρ Ophiuchus used to calibrate the 2MASS All-Sky Survey. We identify a light curve for WL 4 with eclipse amplitudes of ~0.4 mag lasting more than one-quarter the period, and color variations in J-H and H-K_s, of ~0.1 mag. The long period cannot be explained by stellar rotation. We propose that WL 4 is a triple YSO system, with an inner binary orbital period of 130.87 days. We posulate that we are observing each component of the inner binary alternately being eclipsed by a circum-binary disk with respect to our line of sight. This system will be useful in investigating terrestrial zone YSO disk properties and dynamics at ~1 Myr
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