2,244 research outputs found
Tracking quintessence and k-essence in a general cosmological background
We derive conditions for stable tracker solutions for both quintessence and
k-essence in a general cosmological background, H^2 \propto f(\rho). We find
that tracker solutions are possible only when \eta = d ln f /d ln \rho is
constant, aside from a few special cases, which are enumerated. Expressions for
the quintessence or k-essence equation of state are derived as a function of
\eta and the equation of state of the dominant background component.Comment: 6 pages, no figure
Classification of SUSY and non-SUSY Chiral Models from Abelian Orbifolds AdS/CFT
We classify compactifications of the type IIB superstring on AdS_{5} x
S^{5}/\Gamma, where \Gamma is an abelian group of order n<= 12. Appropriate
embedding of \Gamma in the isometry of S^5 yields both SUSY and non-SUSY chiral
models that can contain the minimal SUSY standard model or the standard model.
New non-SUSY three family models with \Gamma=Z_8 are introduced, which lead to
the right Weinberg angle for TeV trinification.Comment: 12 pages, no figur
Identifying the starting point of a spreading process in complex networks
When dealing with the dissemination of epidemics, one important question that
can be asked is the location where the contamination began. In this paper, we
analyze three spreading schemes and propose and validate an effective
methodology for the identification of the source nodes. The method is based on
the calculation of the centrality of the nodes on the sampled network,
expressed here by degree, betweenness, closeness and eigenvector centrality. We
show that the source node tends to have the highest measurement values. The
potential of the methodology is illustrated with respect to three theoretical
complex network models as well as a real-world network, the email network of
the University Rovira i Virgili
Representing Structural Information of Helical Charge Distributions in Cylindrical Coordinates
Structural information in the local electric field produced by helical charge
distributions, such as dissolved DNA, is revealed in a straightforward manner
employing cylindrical coordinates. Comparison of structure factors derived in
terms of cylindrical and helical coordinates is made. A simple coordinate
transformation serves to relate the Green function in cylindrical and helical
coordinates. We also compare the electric field on the central axis of a single
helix as calculated in both systems.Comment: 11 pages in plain LaTex, no figures. Accepted for publication in PRE
March, 199
SLOCC determinant invariants of order 2^{n/2} for even n qubits
In this paper, we study SLOCC determinant invariants of order 2^{n/2} for any
even n qubits which satisfy the SLOCC determinant equations. The determinant
invariants can be constructed by a simple method and the set of all these
determinant invariants is complete with respect to permutations of qubits.
SLOCC entanglement classification can be achieved via the vanishing or not of
the determinant invariants. We exemplify the method for several even number of
qubits, with an emphasis on six qubits.Comment: J. Phys. A: Math. Theor. 45 (2012) 07530
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