162 research outputs found
Oil price shocks and U.S. economic activity: an international perspective
Oil price shocks are thought to have played a prominent role in U.S. economic activity. In this paper, we employ Bayesian methods with a dynamic stochastic general equilibrium model of world economic activity to identify the various sources of oil price shocks and economic fluctuation and to assess their effects on U.S. economic activity. We find that changes in oil prices are best understood as endogenous. Oil price shocks in the 1970s and early 1980s and the 2000s reflect differing mixes of shifts in oil supply and demand, and differing sources of oil price shocks have differing effects on economic activity. We also find that U.S. output fluctuations owe mostly to domestic shocks, with productivity shocks contributing to weakness in the 1970s and 1980s and strength in the 2000s.Petroleum products - Prices ; Petroleum industry and trade ; Economic conditions - United States ; Business cycles
Oil Price Shocks and U.S. Economic Activity: An International Perspective
Oil price shocks are thought to have played a prominent role in U.S. economic activity. In this paper, we employ Bayesian methods with a dynamic stochastic general equilibrium model of world economic activity to identify the various sources of oil price shocks and economic fluctuation and to assess their effects on U.S. economic activity. We find that changes in oil prices are best understood as endogenous. Oil price shocks in the 1970s and early 1980s and the 2000s reflect differing mixes of shifts in oil supply and demand, and differing sources of oil price shocks have differing effects on economic activity. We also find that U.S. output fluctuations owe mostly to domestic shocks, with productivity shocks contributing to weakness in the 1970s and 1980s and strength in the 2000s.oil price, international business cycles, general equilibrium, Bayesian estimation
Massive Superstring Vertex Operator in D=10 Superspace
Using the pure spinor formalism for the superstring, the vertex operator for
the first massive states of the open superstring is constructed in a manifestly
super-Poincar\'e covariant manner. This vertex operator describes a massive
spin-two multiplet in terms of ten-dimensional superfields.Comment: Added reference
Huntington's Disease In a Coloured Family
A South African Coloured (of mixed descent) family with Huntington's disease in which all four members of one sibship, ranging in age from 16 to 23 years, are affected, is described. One generation back, definitely two, and possibly three, members of a sibship of six were affected with the adult form. The offspring of the one affected male all show some evidence of this condition, the age of onset being between 13 and 16 years. The offspring of the one female carrier who was definitely affected do not at this time appear to have been affected. The literature concerning juvenile Huntington's disease, especially with regard to its clinical presentation, EEG, and air encephalographic findings, is reviewed and compared with the family described. The predominance of rigidity and akinesia in the juvenile form, as opposed to chorea, which is the main adult extrapyramidal manifestation, is stressed. This is, to our knowledge, the first report of a Coloured (mixed descent) family's manifesting the clinical features of juvenile Huntington's disease
Relating the Green-Schwarz and Pure Spinor Formalisms for the Superstring
Although it is not known how to covariantly quantize the Green-Schwarz (GS)
superstring, there exists a semi-light-cone gauge choice in which the GS
superstring can be quantized in a conformally invariant manner. In this paper,
we prove that BRST quantization of the GS superstring in semi-light-cone gauge
is equivalent to BRST quantization using the pure spinor formalism for the
superstring.Comment: 16 pages, JHEP format, fixed typos and added 2 footnote
Non-renormalization conditions for four-gluon scattering in supersymmetric string and field theory
The constraints imposed by maximal supersymmetry on multi-loop contributions
to the scattering of four open superstrings in the U(N) theory are examined by
use of the pure spinor formalism. The double-trace term k^2 t_8(tr F^2)^2
(where k represents an external momentum and F the Yang--Mills field strength)
only receives contributions from L<=2 (where L is the loop number) while the
single-trace term k^2 t_8(tr F^4) receives contributions from all L. We
verified these statements up to L=5, but arguments based on supersymmetry
suggest they extend to all L. This explains why the single-trace contributions
to low energy maximally supersymmetric Yang--Mills field theory are more
divergent in the ultraviolet than the double-trace contributions. We also
comment further on the constraints on closed string amplitudes and their
implications for ultraviolet divergences in N=8 supergravity.Comment: 25 pages. 2 eps figures. Harvmac format. v2 qualifications regarding
comments on closed strings. References adde
Some Superstring Amplitude Computations with the Non-Minimal Pure Spinor Formalism
We use the non-minimal pure spinor formalism to compute in a super-Poincare
covariant manner the four-point massless one and two-loop open superstring
amplitudes, and the gauge anomaly of the six-point one-loop amplitude. All of
these amplitudes are expressed as integrals of ten-dimensional superfields in a
"pure spinor superspace" which involves five coordinates covariantly
contracted with three pure spinors. The bosonic contribution to these
amplitudes agrees with the standard results, and we demonstrate identities
which show how the and tensors naturally emerge from
integrals over pure spinor superspace.Comment: 20 pages, harvmac te
Multiloop Amplitudes and Vanishing Theorems using the Pure Spinor Formalism for the Superstring
A ten-dimensional super-Poincare covariant formalism for the superstring was
recently developed which involves a BRST operator constructed from superspace
matter variables and a pure spinor ghost variable. A super-Poincare covariant
prescription was defined for computing tree amplitudes and was shown to
coincide with the standard RNS prescription.
In this paper, picture-changing operators are used to define functional
integration over the pure spinor ghosts and to construct a suitable ghost.
A super-Poincare covariant prescription is then given for the computation of
N-point multiloop amplitudes. One can easily prove that massless N-point
multiloop amplitudes vanish for N<4, confirming the perturbative finiteness of
superstring theory. One can also prove the Type IIB S-duality conjecture that
terms in the effective action receive no perturbative contributions above
one loop.Comment: 45 pages harvmac tex, added minor clarification
Avelumab in European patients (pts) with metastatic Merkel cell carcinoma (mMCC): Experience from an ad-hoc expanded access program (EAP)
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Multiloop Superstring Amplitudes from Non-Minimal Pure Spinor Formalism
Using the non-minimal version of the pure spinor formalism, manifestly
super-Poincare covariant superstring scattering amplitudes can be computed as
in topological string theory without the need of picture-changing operators.
The only subtlety comes from regularizing the functional integral over the pure
spinor ghosts. In this paper, it is shown how to regularize this functional
integral in a BRST-invariant manner, allowing the computation of arbitrary
multiloop amplitudes. The regularization method simplifies for scattering
amplitudes which contribute to ten-dimensional F-terms, i.e. terms in the
ten-dimensional superspace action which do not involve integration over the
maximum number of 's.Comment: 23 pages harvmac, added acknowledgemen
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