542 research outputs found
Poisson Brackets of Normal-Ordered Wilson Loops
We formulate Yang-Mills theory in terms of the large-N limit, viewed as a
classical limit, of gauge-invariant dynamical variables, which are closely
related to Wilson loops, via deformation quantization. We obtain a Poisson
algebra of these dynamical variables corresponding to normal-ordered quantum
(at a finite value of ) operators. Comparing with a Poisson algebra one
of us introduced in the past for Weyl-ordered quantum operators, we find, using
ideas closly related to topological graph theory, that these two Poisson
algebras are, roughly speaking, the same. More precisely speaking, there exists
an invertible Poisson morphism between them.Comment: 34 pages, 4 eps figures, LaTeX2.09; citations adde
Superconformal field theories from IIB spectroscopy on
We report on tests of the AdS/CFT correspondence that are made possible by
complete knowledge of the Kaluza-Klein mass spectrum of type IIB supergravity
on with T^{11}=SU(2)^2/U(1). After briefly discussing
general multiplet shortening conditions in SU(2,2|1) and PSU(2,2|4), we compare
various types of short SU(2,2|1) supermultiplets on AdS_5 and different
families of boundary operators with protected dimensions. The supergravity
analysis predicts the occurrence in the SCFT at leading order in N and g_s N,
of extra towers of long multiplets whose dimensions are rational but not
protected by supersymmetry.Comment: 11 pages, To appear in the proceedings of the STRINGS '99 conference,
Potsdam (Germany), 19-25 July 199
Big Jump of Record Warm Global Mean Surface Temperature in 2014â2016 Related to Unusually Large Oceanic Heat Releases
A 0.24°C jump of record warm global mean surface temperature (GMST) over the past three consecutive recordâbreaking years (2014â2016) was highly unusual and largely a consequence of an El Niño that released unusually large amounts of ocean heat from the subsurface layer of the northwestern tropical Pacific. This heat had built up since the 1990s mainly due to greenhouseâgas (GHG) forcing and possible remote oceanic effects. Model simulations and projections suggest that the fundamental cause, and robust predictor of large recordâbreaking events of GMST in the 21st century, is GHG forcing rather than internal climate variability alone. Such events will increase in frequency, magnitude, and duration, as well as impact, in the future unless GHG forcing is reduced.Key PointsA 0.24°C jump of record warm global mean surface temperature over the past three consecutive years (2014â2016) was highly unusualIt was a result of an El Niño that released unusually large amounts of ocean heat previously accumulated in the western tropical PacificLarge recordâbreaking events of global surface temperature are projected to increase in the future unless greenhouseâgas forcing is reducedPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142431/1/grl56888_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142431/2/grl56888-sup-0001-2017GL076500-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142431/3/grl56888.pd
Symplectic connections and Fedosov's quantization on supermanifolds
A (biased and incomplete) review of the status of the theory of symplectic
connections on supermanifolds is presented. Also, some comments regarding
Fedosov's technique of quantization are made.Comment: Submitted to J. of Phys. Conf. Se
Classical and Quantum Mechanics from the universal Poisson-Rinehart algebra of a manifold
The Lie and module (Rinehart) algebraic structure of vector fields of compact
support over C infinity functions on a (connected) manifold M define a unique
universal non-commutative Poisson * algebra. For a compact manifold, a
(antihermitian) variable Z, central with respect to both the product and the
Lie product, relates commutators and Poisson brackets; in the non-compact case,
sequences of locally central variables allow for the addition of an element
with the same role.
Quotients with respect to the (positive) values taken by Z* Z define
classical Poisson algebras and quantum observable algebras, with the Planck
constant given by -iZ. Under standard regularity conditions, the corresponding
states and Hilbert space representations uniquely give rise to classical and
quantum mechanics on M.Comment: Talk given by the first author at the 40th Symposium on Mathematical
Physics, Torun, June 25-28, 200
Closedness of star products and cohomologies
We first review the introduction of star products in connection with
deformations of Poisson brackets and the various cohomologies that are related
to them. Then we concentrate on what we have called ``closed star products" and
their relations with cyclic cohomology and index theorems. Finally we shall
explain how quantum groups, especially in their recent topological form, are in
essence examples of star products.Comment: 16 page
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Cloud feedback mechanisms and their representation in global climate models
Cloud feedback â the change in top-of-atmosphere radiative flux resulting from the cloud response to warming â constitutes by far the largest source of uncertainty in the climate response to CO2 forcing simulated by global climate models (GCMs). We review the main mechanisms for cloud feedbacks, and discuss their representation in climate models and the sources of inter-model spread. Global-mean cloud feedback in GCMs results from three main effects: (1) rising free- tropospheric clouds (a positive longwave effect); (2) decreasing tropical low cloud amount (a positive shortwave effect); (3) increasing high-latitude low cloud optical depth (a negative shortwave effect). These cloud responses simulated by GCMs are qualitatively supported by theory, high-resolution modeling, and observations. Rising high clouds are consistent with the Fixed Anvil Temperature (FAT) hypothesis, whereby enhanced upper-tropospheric radiative cooling causes anvil cloud tops to remain at a nearly fixed temperature as the atmosphere warms. Tropical low cloud amount decreases are driven by a delicate balance between the effects of vertical turbulent fluxes, radiative cooling, large-scale subsidence, and lower-tropospheric stability on the boundary-layer moisture budget. High-latitude low cloud optical depth increases are dominated by phase changes in mixed- phase clouds. The causes of inter-model spread in cloud feedback are discussed, focusing particularly on the role of unresolved parameterized processes such as cloud microphysics, turbulence, and convection
BandâbyâBand Contributions to the Longwave Cloud Radiative Feedbacks
Cloud radiative feedback is central to our projection of future climate change. It can be estimated using the cloud radiative kernel (CRK) method or adjustment method. This study, for the first time, examines the contributions of each spectral band to the longwave (LW) cloud radiative feedbacks (CRFs). Simulations of three warming scenarios are analyzed, including +2 K sea surface temperature, 2 Ă CO2, and 4 Ă CO2 experiments. While the LW broadband CRFs derived from the CRK and adjustment methods agree with each other, they disagree on the relative contributions from the farâinfrared and window bands. The CRK method provides a consistent bandâbyâband decomposition of LW CRF for different warming scenarios. The simulated and observed shortâterm broadband CRFs for the 2003â2013 period are similar to the longâterm counterparts, but their bandâbyâband decompositions are different, which can be further related to the cloud fraction changes in respective simulations and observation.Plain Language SummaryWe studied how the cloud change in response to surface temperature change leads to the changes of radiation at the top of the atmosphere (referred to as cloud radiative feedback) over different frequency ranges in the longwave (referred to as spectral bands). While different methods can provide a similar estimate of broadband cloud radiative feedbacks, the decomposition to different longwave spectral bands can be different from one method to another. The cloud radiative kernel method can provide a more consistent bandâbyâband decomposition of the longwave cloud radiative feedback for different warming scenarios. The decomposition for cloud radiative feedback derived from the warming experiments is considerably different from that derived from decadalâscale observations and simulations. Such differences in spectral band decomposition can be related to the specific cloud fraction changes for different types of clouds defined with respect to cloud top pressure and cloud opacity.Key PointsThe bandâbyâband decomposition of cloud radiative feedback is studied for the first timeTwo different methods can give similar longwave broadband radiative feedbacks, but their bandâbyâband decompositions are differentSeemingly agreeable broadband cloud radiative feedbacks can have different spectral decompositions, which can be related to cloud changesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150592/1/grl59162_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150592/2/grl59162.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150592/3/grl59162-sup-0001-2019GL083466-SI.pd
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