12,776 research outputs found
A note on eigenvalues location for trace zero doubly stochastic matrices
Some results on the location of the eigenvalues of trace zero doubly stochastic matrices are provided. A result similar to that provided in [H. Perfect and L. Mirsky. Spectral properties of doublyâstochastic matrices. Monatshefte fšur Mathematik, 69(1):35â57, 1965.] for doubly stochastic matrices is given
An efficient algorithm for positive realizations
We observe that successive applications of known results from the theory of
positive systems lead to an {\it efficient general algorithm} for positive
realizations of transfer functions. We give two examples to illustrate the
algorithm, one of which complements an earlier result of \cite{large}. Finally,
we improve a lower-bound of \cite{mn2} to indicate that the algorithm is indeed
efficient in general
Spectroscopic observations of comet Kohoutek (1973f), 2
Spectroscopic observations of comet Kohoutek at the Asiago Astrophysical Observatory are described. Spectra cover six nights before perihelion and five nights after perihelion. The spectra of the coma and tail of comet Kohoutek are characterized by fairly strong, asymmetric H2O(+) emissions in the red and the near infrared spectral regions and by the appearance of the 01 forbidden lines at 6300-6364 A, already at heliocentric distance r=1.55 A.U. These peculiarities suggest that some differences in chemical abundances or in physical conditions exist between comet Kohoutek and other comets
The complex of pant decompositions of a surface
We exhibit a set of edges (moves) and 2-cells (relations) making the complex
of pant decompositions on a surface a simply connected complex. Our
construction, unlike the previous ones, keeps the arguments concerning the
structural transformations independent from those deriving from the action of
the mapping class group. The moves and the relations turn out to be supported
in subsurfaces with 3g-3+n=1,2 (where g is the genus and n is the number of
boundary components), illustrating in this way the so called Grothendieck
principle.Comment: Minor changes in the introductio
N=1 QED in 2+1 dimensions: Dualities and enhanced symmetries
We consider three-dimensional sQED with 2 flavors and minimal supersymmetry.
We discuss various models which are dual to Gross-Neveu-Yukawa theories. The
ultraviolet global symmetry is often enhanced in the infrared, for
instance to or . This is analogous to the conjectured behaviour
of non-supersymmetric QED with 2 flavors. A perturbative analysis of the
Gross-Neveu-Yukawa models in the expansion shows that the
preserving superpotential deformations of the sQED (modulo tuning mass
terms to zero) are irrelevant, so the fixed points with enhanced symmetry are
stable. We also construct an example of sQED with 4 flavors
that exhibits enhanced symmetry.Comment: 25 pages, no figure
Conformal Manifolds for the Conifold and other Toric Field Theories
In the space of couplings of the 4D N=1 gauge theory associated to D3 branes
probing Calabi-Yau singularities, there is a manifold over which superconformal
invariance is preserved. The AdS/CFT correspondence is valid precisely for this
"conformal manifold". We identify the conformal manifold for all the Y^{p,q}
toric singularities, paying special attention to the case of the conifold,
Y^{1,0}. For a general Y^{p,q} the conformal manifold is three dimensional,
while for the conifold it is five dimensional. There is always an exactly
marginal deformation, analogous to the beta-deformation of N=4 SYM, which
involves fluxes in the dual gravity description. This beta-deformation exists
for any toric Calabi-Yau singularity.Comment: 30 pages, 5 figures; V2: References added, minor change
A multi-wavelength study of the starburst galaxy NGC 7673
HST/WFPC2 images resolved NGC 7673 into a large number of star clusters.
Among these, 31 fall inside the IUE large aperture, which was used to acquire
an integrated ultraviolet spectrum of the galaxy. We have fitted Starburst99
evolutionary synthesis models to the observed colours of these clusters and
derived ages, reddenings, and masses of the clusters. Then a simple sum of the
clusters synthetic UV spectra has been compared to the observed IUE spectrum,
in order to investigate the star formation history of NGC 7673.Comment: 6 pages, 2 figures, to appear in the Proceedings of the Conference
"Starburst-from 30 Doradus to Lyman Break Galaxies
BPS Solutions in AdS/CFT
We study a class of exact supersymmetric solutions of type IIB Supergravity.
They have an SO(4) x SU(2) x U(1) isometry and preserve generically 4 of the 32
supersymmetries of the theory. Asymptotically AdS_5 x S^5 solutions in this
class are dual to 1/8 BPS chiral operators which preserve the same symmetries
in the N=4 SYM theory. We analyse the solutions to these equations in a large
radius asymptotic expansion: they carry charges with respect to two U(1) KK
gauge fields and their mass saturates the expected BPS bound. We also show how
the same formalism is suitable for the description of the AdS_5 x Y^{p,q}
geometries and a class of their excitations.Comment: 5 pages, Latex, uses w-art class (included). To appear in the
Proceedings of the RTN workshop "ForcesUniverse", Naples, October 9-13, 200
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