24,071 research outputs found
Saturation and Confinement: Analyticity, Unitarity and AdS/CFT Correspondence
In expansion, analyticity and crossing lead to crossing even and odd
() vacuum exchanges at high-energy, the {\em Pomeron} and the {\em
Odderon}. We discuss how, using {\em String/Gauge duality}, these can be
identified with a reggeized {\em Graviton} and the anti-symmetric {\em
Kalb-Ramond fields} in background. With confinement, these Regge
singularities interpolate with glueball states. We also discuss unitarization
based on eikonal sum in .Comment: more references added. presented at ISMD 2008, 15-20 Sept. 200
Magnetic monopole loop for the Yang-Mills instanton
We investigate 't Hooft-Mandelstam monopoles in QCD in the presence of a
single classical instanton configuration. The solution to the Maximal Abelian
projection is found to be a circular monopole trajectory with radius
centered on the instanton. At zero loop radius, there is a marginally stable
(or flat) direction for loop formation to . We argue that loops
will form, in the semi-classical limit, due to small perturbations such as the
dipole interaction between instanton anti-instanton pairs. As the instanton gas
becomes a liquid, the percolation of the monopole loops may therefore provide a
semi-classical precursor to the confinement mechanism.Comment: 19 pages, ReVTeX, 5 Encaptulated Postscript figure
On the Eikonal Approximation in AdS Space
We explore the eikonal approximation to graviton exchange in AdS_5 space, as
relevant to scattering in gauge theories. We restrict ourselves to the regime
where conformal invariance of the dual gauge theory holds, and to large 't
Hooft coupling where the computation involves pure gravity. We give a heuristic
argument, a direct loop computation, and a shock wave derivation. The scalar
propagator in AdS_3 plays a key role, indicating that even at strong coupling,
two-dimensional conformal invariance controls high-energy four-dimensional
gauge-theory scattering.Comment: 22 pages, 2 figures; published version: updated references and
several clarifying remarks adde
The Impact of Feedback in Massive Star Formation. II. Lower Star Formation Efficiency at Lower Metallicity
We conduct a theoretical study of the formation of massive stars over a wide
range of metallicities from 1e-5 to 1Zsun and evaluate the star formation
efficiencies (SFEs) from prestellar cloud cores taking into account multiple
feedback processes. Unlike for simple spherical accretion, in the case of disk
accretion feedback processes do not set upper limits on stellar masses. At
solar metallicity, launching of magneto-centrifugally-driven outflows is the
dominant feedback process to set SFEs, while radiation pressure, which has been
regarded to be pivotal, has only minor contribution even in the formation of
over-100Msun stars. Photoevaporation becomes significant in over-20Msun star
formation at low metallicities of <1e-2Zsun, where dust absorption of ionizing
photons is inefficient. We conclude that if initial prestellar core properties
are similar, then massive stars are rarer in extremely metal-poor environments
of 1e-5 - 1e-3Zsun. Our results give new insight into the high-mass end of the
initial mass function and its potential variation with galactic and
cosmological environments.Comment: 13 pages, 9 figures, accepted for publication in The Astrophysical
Journa
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