21,968 research outputs found
Variational calculations for K-few-nucleon systems
Deeply bound KNN, KNNN and KNNNN states are discussed. The effective force
exerted by the K meson on the nucleons is calculated with static nucleons. Next
the binding energies are obtained by solving the Schrodinger equation or by
variational calculations.
The dominant attraction comes from the S-wave Lambda(1405) and an additional
contribution is due to Sigma(1385). The latter state is formed at the nuclear
peripheries and absorbs a sizable piece of the binding energy. It also
generates new branches of quasi-bound states. The lowest binding energies based
on a phenomenological KN input fall into the 40-80 MeV range for KNN, 90-150
MeV for KNNN and 120-220 MeV for K-alpha systems. The uncertainties are due to
unknown KN interactions in the distant subthreshold energy region.Comment: 19 pages, 1 figur
Are There Topological Black Hole Solitons in String Theory?
We point out that the celebrated Hawking effect of quantum instability of
black holes seems to be related to a nonperturbative effect in string theory.
Studying quantum dynamics of strings in the gravitational background of black
holes we find classical instability due to emission of massless string
excitations. The topology of a black hole seems to play a fundamental role in
developing the string theory classical instability due to the effect of sigma
model instantons. We argue that string theory allows for a qualitative
description of black holes with very small masses and it predicts topological
solitons with quantized spectrum of masses. These solitons would not decay into
string massless excitations but could be pair created and may annihilate also.
Semiclassical mass quantization of topological solitons in string theory is
based on the argument showing existence of nontrivial zeros of beta function of
the renormalization group.Comment: 12 pages, TeX, requires phyzzx.tex, published in Gen. Rel. Grav. 19
(1987) 1173; comment added on December 18, 199
Island-arc Ankaramites: Primitive Melts from Fluxed Refractory Lherzolitic Mantle
The distinctive island-arc ankaramites exemplified by the active Vanuatu arc may be produced by melting of refractory lherzolite under conditions in which melting is fluxed by H2O + CO2. Parental picritic ankaramite magmas with maximum CaO/Al2O3 to ≥1·5 are produced by melt segregation from residual chromite-bearing harzburgite at 1·5 GPa, ∼1320-1350°C. A pre-condition for derivation of such high CaO/Al2O3 melts from orthopyroxene-bearing sources/residues is that pyroxenes have low Al2O3 (70. Bulk compositions have CaO/Al2O3 ≥ 1·3, i.e. much higher than chondritic values. The effects of both (CO3)2− and (OH)− dissolved in the silicate melt combine with the refractory wedge composition to produce ankaramitic picrite magmas that segregate from residual harzburgite at pressures of spinel stability. Other primitive arc and back-arc magmas such as boninites (low Ca and high Ca) share the primitive signatures of island-arc ankaramites (liquidus olivine Mg number ≥90, spinels with Cr number >70). Consideration of the relative proportions of Na2O, CaO and Al2O3 in these primitive arc magmas leads to the inference of a common factor of refractory mantle fluxed by differing agents. H2O-rich fluid alone carries these refractory major element characteristics into the primitive melts (high-CaO boninites, tholeiitic picrites). Fluxing with dolomitic carbonatite melt, which may develop from C-O-H-fluids within the mantle wedge, generates high CaO/Al2O3 sources and thus facilitates the formation of picritic ankaramites. Alternatively, melting may be fluxed by hydrous dacitic to rhyodacitic melt derived from the subducted slab (garnet amphibolite or eclogite melting). In this case, higher Na2O/CaO, lower CaO/Al2O3 and higher SiO2 contents characterize the low-CaO boninite
Explicit determination of a 727-dimensional root space of the hyperbolic Lie algebra
The 727-dimensional root space associated with the level-2 root \bLambda_1
of the hyperbolic Kac--Moody algebra is determined using a recently
developed string theoretic approach to hyperbolic algebras. The explicit form
of the basis reveals a complicated structure with transversal as well as
longitudinal string states present.Comment: 12 pages, LaTeX 2
Ultra-calcic Magmas Generated from Ca-depleted Mantle: an Experimental Study on the Origin of Ankaramites
Ultra-calcic ankaramitic magmas or melt inclusions are ubiquitous in arc, ocean-island and mid-ocean ridge settings. They are primitive in character (XMg > 0·65) and have high CaO contents (>14 wt %) and CaO/Al2O3 (>1·1). Experiments on an ankaramite from Epi, Vanuatu arc, demonstrate that its liquidus surface has only clinopyroxene at pressures of 15 and 20 kbar, with XCO2 in the volatile component from 0 to 0·86. The parental Epi ankaramite is thus not an unfractionated magma. However, forcing the ankaramite experimentally into saturation with olivine, orthopyroxene and spinel results in more magnesian, ultra-calcic melts with CaO/Al2O3 of 1·21-1·58. The experimental melts are not extremely Ca-rich but high in CaO/Al2O3 and in MgO (up to 18.5 wt %), and would evolve to high-CaO melts through olivine fractionation. Fractionation models show that the Epi parent magma can be derived from such ultra-calcic experimental melts through mainly olivine fractionation. We show that the experimental ultra-calcic melts could form through low-degree melting of somewhat refractory mantle. The latter would have been depleted by previous melt extraction, which increases the CaO/Al2O3 in the residue as long as some clinopyroxene remains residual. This finding corrects the common assumption that ultra-calcic magmas must come from a Ca-rich pyroxenite-type source. The temperatures necessary for the generation of ultra-calcic magmas are ≥1330°C, and their presence would suggest melting regimes that are at the upper temperature end of previous interpretations made on the basis of picritic magma
Mapping target signatures via partial unmixing of AVIRIS data
A complete spectral unmixing of a complicated AVIRIS scene may not always be possible or even desired. High quality data of spectrally complex areas are very high dimensional and are consequently difficult to fully unravel. Partial unmixing provides a method of solving only that fraction of the data inversion problem that directly relates to the specific goals of the investigation. Many applications of imaging spectrometry can be cast in the form of the following question: 'Are my target signatures present in the scene, and if so, how much of each target material is present in each pixel?' This is a partial unmixing problem. The number of unmixing endmembers is one greater than the number of spectrally defined target materials. The one additional endmember can be thought of as the composite of all the other scene materials, or 'everything else'. Several workers have proposed partial unmixing schemes for imaging spectrometry data, but each has significant limitations for operational application. The low probability detection methods described by Farrand and Harsanyi and the foreground-background method of Smith et al are both examples of such partial unmixing strategies. The new method presented here builds on these innovative analysis concepts, combining their different positive attributes while attempting to circumvent their limitations. This new method partially unmixes AVIRIS data, mapping apparent target abundances, in the presence of an arbitrary and unknown spectrally mixed background. It permits the target materials to be present in abundances that drive significant portions of the scene covariance. Furthermore it does not require a priori knowledge of the background material spectral signatures. The challenge is to find the proper projection of the data that hides the background variance while simultaneously maximizing the variance amongst the targets
Towards Loop Quantum Supergravity (LQSG) II. p-Form Sector
In our companion paper, we focussed on the quantisation of the
Rarita-Schwinger sector of Supergravity theories in various dimensions by using
an extension of Loop Quantum Gravity to all spacetime dimensions. In this
paper, we extend this analysis by considering the quantisation of additional
bosonic fields necessary to obtain a complete SUSY multiplet next to graviton
and gravitino in various dimensions. As a generic example, we study concretely
the quantisation of the 3-index photon of 11d SUGRA, but our methods easily
extend to more general p-form fields. Due to the presence of a Chern-Simons
term for the 3-index photon, which is due to local SUSY, the theory is
self-interacting and its quantisation far from straightforward. Nevertheless,
we show that a reduced phase space quantisation with respect to the 3-index
photon Gauss constraint is possible. Specifically, the Weyl algebra of
observables, which deviates from the usual CCR Weyl algebras by an interesting
twist contribution proportional to the level of the Chern-Simons theory, admits
a background independent state of the Narnhofer-Thirring type.Comment: 12 pages. v2: Journal version. Minor clarifications and correction
Electronic properties of disclinated flexible membrane beyond the inextensional limit: Application to graphene
Gauge-theory approach to describe Dirac fermions on a disclinated flexible
membrane beyond the inextensional limit is formulated. The elastic membrane is
considered as an embedding of 2D surface into R^3. The disclination is
incorporated through an SO(2) gauge vortex located at the origin, which results
in a metric with a conical singularity. A smoothing of the conical singularity
is accounted for by replacing a disclinated rigid plane membrane with a
hyperboloid of near-zero curvature pierced at the tip by the SO(2) vortex. The
embedding parameters are chosen to match the solution to the von Karman
equations. A homogeneous part of that solution is shown to stabilize the
theory. The modification of the Landau states and density of electronic states
of the graphene membrane due to elasticity is discussed.Comment: 15 pages, Journal of Physics:Condensed Matter in pres
Subcritical Superstrings
We introduce the Liouville mode into the Green-Schwarz superstring. Like
massive supersymmetry without central charges, there is no kappa symmetry.
However, the second-class constraints (and corresponding Wess-Zumino term)
remain, and can be solved by (twisted) chiral superspace in dimensions D=4 and
6. The matter conformal anomaly is c = 4-D < 1. It thus can be canceled for
physical dimensions by the usual Liouville methods, unlike the bosonic string
(for which the consistency condition is c = D <= 1).Comment: 9 pg., compressed postscript file (.ps.Z), other formats (.dvi, .ps,
.ps.Z, 8-bit .tex) available at
http://insti.physics.sunysb.edu/~siegel/preprints/ or at
ftp://max.physics.sunysb.edu/preprints/siege
Heterotic/type I duality, D-instantons and an N=2 AdS/CFT correspondence
D-instanton effects are studied for the IIB orientifold T^2/I\Omega(-1)^{F_L}
of Sen using type I/heterotic duality. An exact one loop threshold calculation
of t_8 \tr F^4 and t_8(\tr F^2)^2 terms for the heterotic string on T^2 with
Wilson lines breaking SO(32) to SO(8)^4 is related to D-instanton induced terms
in the worldvolume of D7 branes in the orientifold. Introducing D3 branes and
using the AdS/CFT correspondence in this case, these terms are used to
calculate Yang-Mills instanton contributions to four point functions of the
large N_c limit of N=2 USp(2N_c) SYM with four fundamental and one
antisymmetric tensor hypermultiplets.Comment: 25 pages, harvmac(b), one figure, v2: minor changes, version to
appear in PR
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