398 research outputs found
A Genetic Algorithm based Approach for Topological Optimization of Interconnection Networks
AbstractThe paper addresses the two terminal reliability while designing the interconnection networks. Thus a topological optimization problem is defined as the existence of at least a reliable path between a pair of nodes satisfying the predefined cost of the network. A new method based on Genetic Algorithm is proposed to solve the above said problem. In the proposed method the chromosome as well as the genes are efficiently encoded so that the cross over provides the optimal solution with better convergence rate. The reliability of some benchmark interconnection networks are evaluated by the proposed method. The population size and the computational time of the said networks as reported in this paper ensures that the proposed method converges to it's optimal solution in very few cpu secondss, while maximizing the value of the reliability of the said network to a greater extent
Comments on the four-dimensional effective theory for warped compactification
We derive four-dimensional effective theories for warped compactification of
the ten-dimensional IIB supergravity and the eleven-dimensional Horava-Witten
model. We show that these effective theories allow a much wider class of
solutions than the original higher-dimensional theories. In particular, the
effective theories have cosmological solutions in which the size of the
internal space decreases with the cosmic expansion in the Einstein frame. This
type of compactifying solutions are not allowed in the original
higher-dimensional theories. This result indicates that the effective
four-dimensional theories should be used with caution, if one regards the
higher-dimensional theories more fundamental.Comment: 21 pages, no figure. Minor errors are correcte
Counting fermionic zero modes on M5 with fluxes
We study the Dirac equation on an M5 brane wrapped on a divisor in a
Calabi--Yau fourfold in the presence of background flux. We reduce the
computation of the normal bundle U(1) anomaly to counting the solutions of a
finite--dimensional linear system on cohomology. This system depends on the
choice of flux. In an example, we find that the presence of flux changes the
anomaly and allows instanton corrections to the superpotential which would
otherwise be absent.Comment: 14 pages. v2: reference added, typos corrected, few change
Critical points of the Black-Hole potential for homogeneous special geometries
We extend the analysis of N=2 extremal Black-Hole attractor equations to the
case of special geometries based on homogeneous coset spaces. For non-BPS
critical points (with non vanishing central charge) the (Bekenstein-Hawking)
entropy formula is the same as for symmetric spaces, namely four times the
square of the central charge evaluated at the critical point. For non
homogeneous geometries the deviation from this formula is given in terms of
geometrical data of special geometry in presence of a background symplectic
charge vector.Comment: 17 pages, LaTeX fil
Non-Abelian Einstein-Born-Infeld Black Holes
We construct regular and black hole solutions in SU(2) Einstein-Born-Infeld
theory. These solutions have many features in common with the corresponding
SU(2) Einstein-Yang-Mills solutions. In particular, sequences of neutral
non-abelian solutions tend to magnetically charged limiting solutions, related
to embedded abelian solutions. Thermodynamic properties of the black hole
solutions are addressed.Comment: LaTeX, 14 pages, 6 postscript figures; typos corrected in reference
Flow Equations for Non-BPS Extremal Black Holes
We exploit some common features of black hole and domain wall solutions of
(super)gravity theories coupled to scalar fields and construct a class of
stable extremal black holes that are non-BPS, but still can be described by
first-order differential equations. These are driven by a "superpotential'',
which replaces the central charge Z in the usual black hole potential. We
provide a general procedure for finding this class and deriving the associated
"superpotential''. We also identify some other cases which do not belong to
this class, but show a similar behaviour.Comment: LaTeX, 21 pages, 2 figures. v2: reference added, JHEP versio
Electron neutrino mass scale in spectrum of Dirac equation with the 5-form flux term on the AdS(5)xS(5) background
Dimensional reduction from 10 to 5 dimensions of the IIB supergravity Dirac
equation written down on the AdS(5)xS(5) (+ self-dual 5-form) background
provides the unambiguous values of bulk masses of Fermions in the effective 5D
Randall Sundrum theory. The use of "untwisted" and "twisted" (hep-th/0012378)
boundary conditions at the UV and IR ends of the warped space-time results in
two towers of spectrum of Dirac equation: the ordinary one which is linear in
spectral number and the "twisted" one exponentially decreasing with growth of
spectral number. Taking into account of the Fermion-5-form interaction
(hep-th/9811106) gives the electron neutrino mass scale in the "twisted"
spectrum of Dirac equation. Profiles in extra space of the eigenfunctions of
left and right "neutrinos" drastically differ which may result in the extremely
small coupling of light right neutrino with ordinary matter thus joining it to
plethora of candidates for Dark Matter.Comment: 11 page
New Attractors and Area Codes
In this note we give multiple examples of the recently proposed New
Attractors describing supersymmetric flux vacua and non-supersymmetric extremal
black holes in IIB string theory. Examples of non-supersymmetric extremal black
hole attractors arise on a hypersurface in . For flux vacua
on the orientifold of the same hypersurface existence of multiple basins of
attraction is established. It is explained that certain fluxes may give rise to
multiple supersymmetric flux vacua in a finite region on moduli space, say at
the Landau-Ginzburg point and close to conifold point. This suggests the
existence of multiple basins for flux vacua and domain walls in the landscape
for a fixed flux and at interior points in moduli space.Comment: 16 pages, harvmac. v2: acknowledgement update
Moduli Instability in Warped Compactifications of the Type IIB Supergravity
We show that the conifold and deformed-conifold warped compactifications of
the ten-dimensional type IIB supergravity, including the Klebanov-Strassler
solution, are dynamically unstable in the moduli sector representing the scale
of a Calabi-Yau space, although it can be practically stable for a quite long
time in a region with a large warp factor. This instability is associated with
complete supersymmetry breaking except for a special case and produces
significant time-dependence in the structure of the four-dimensional base
spacetime as well as of the internal space.Comment: 24 pages, no figure. Typos corrected, and some arguments in section 5
are adde
An index for the Dirac operator on D3 branes with background fluxes
We study the problem of instanton generated superpotentials in Calabi-Yau
orientifold compactifications directly in type IIB string theory. To this end,
we derive the Dirac equation on a Euclidean D3 brane in the presence of
background fluxes. We propose an index which governs whether the generation of
a superpotential in the effective 4d theory by D3 brane instantons is possible.
Applying the formalism to various classes of examples, including the K3 x
T^2/Z_2 orientifold, in the absence and presence of fluxes, we show that our
results are consistent with conclusions attainable via duality from an M-theory
analysis.Comment: Fermion coupling to five-form restored, conclusions of the paper
unchange
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