330,611 research outputs found
String Fragmentation with a Time-Dependent Tension
Motivated by recent theoretical arguments that expanding strings can be
regarded as having a temperature that is inversely proportional to the proper
time, tau, we investigate the consequences of adding a term proportional to
1/tau to the string tension in the Lund string-hadronization model. The lattice
value for the tension, kappa0 ~ 0.18 GeV^2 ~ 0.9 GeV/fm, is then interpreted as
the late-time/equilibrium limit. A generic prediction of this type of model is
that early string breaks should be associated with higher strangeness (and
baryon) fractions and higher fragmentation values. It should be possible
to use archival ee data sets to provide model-independent constraints on this
type of scenario, and we propose a few simple key measurements to do so.Comment: v2: included predictions for strange baryon
Comments on Yang-Mills thermodynamics, the Hagedorn spectrum and the gluon gas
We discuss the dependence of pure Yang-Mills equation of state on the choice
of gauge algebra. In the confined phase, we generalize to an arbitrary simple
gauge algebra Meyer's proposal of modelling the Yang-Mills matter by an ideal
glueball gas in which the high-lying glueball spectrum is approximated by a
Hagedorn spectrum of closed-bosonic-string type. Such a formalism is undefined
above the Hagedorn temperature, corresponding to the phase transition toward a
deconfined state of matter in which gluons are the relevant degrees of freedom.
Under the assumption that the adjoint string tension and the typical energy
scale of the running coupling are gauge-algebra independent, we discuss about
how the behavior of thermodynamical quantities such as the trace anomaly should
depend on the gauge algebra in both the confined and deconfined phase. The
obtained results compare favourably with recent and accurate lattice data in
the case and support the idea that the more the gauge
algebra has generators, the more the phase transition is of first-order type.Comment: Discussion extended in v2 ; to appear in Phys Lett
Mutable strings in Java: design, implementation and lightweight text-search algorithms
AbstractThe Java string classes, String and StringBuffer, lie at the extremes of a spectrum (immutable, reference based, and mutable, content based). Analogously, available text-search methods on string classes are implemented either as trivial, brute-force double loops, or as very sophisticated and resource-consuming regular-expression search methods. Motivated by our experience in data-intensive text applications, we propose a new string class, MutableString, which tries to get the right balance between extremes in both cases. Mutable strings can be in one of two states, compact and loose, in which they behave more like String and StringBuffer, respectively. Moreover, they support a wide range of sophisticated text-search algorithms with a very low resource usage and set-up time, using a new, very simple randomised data structure (a generalisation of Bloom filters) that stores an approximation from above of a lattice-valued function. Computing the function value requires a constant number of steps, and the error probability can be balanced with space usage. As a result, we obtain practical implementations of Boyer–Moore type algorithms that can be used with very large alphabets, such as Unicode collation elements. The techniques we develop are very general and amenable to a wide range of applications
Two-dimensional shape recognition using sparse distributed memory
Researchers propose a method for recognizing two-dimensional shapes (hand-drawn characters, for example) with an associative memory. The method consists of two stages: first, the image is preprocessed to extract tangents to the contour of the shape; second, the set of tangents is converted to a long bit string for recognition with sparse distributed memory (SDM). SDM provides a simple, massively parallel architecture for an associative memory. Long bit vectors (256 to 1000 bits, for example) serve as both data and addresses to the memory, and patterns are grouped or classified according to similarity in Hamming distance. At the moment, tangents are extracted in a simple manner by progressively blurring the image and then using a Canny-type edge detector (Canny, 1986) to find edges at each stage of blurring. This results in a grid of tangents. While the technique used for obtaining the tangents is at present rather ad hoc, researchers plan to adopt an existing framework for extracting edge orientation information over a variety of resolutions, such as suggested by Watson (1987, 1983), Marr and Hildreth (1980), or Canny (1986)
K\"{a}hler moduli inflation and WMAP7
Inflationary potentials are investigated for specific models in type IIB
string theory via flux compactification. As concrete models, we investigate
several cases where the internal spaces are weighted projective spaces. The
models we consider have two, three, or four K\"{a}hler moduli. The K\"{a}hler
moduli play a role of inflaton fields and we consider the cases where only one
of the moduli behaves as the inflaton field. For the cases with more than two
moduli, we choose the diagonal basis for the expression of the Calabi-Yau
volume, which can be written down as a function of four-cycle. With the
combination of multiple moduli, we can express the multi-dimensional problem as
an effective one-dimensional problem. In the large volume scenario, the
potentials of these three models turn out to be of the same type. By taking the
specific limit of the relation between the moduli and the volume, the
potentials are reduced to simpler ones which induce inflation. As a toy model
we first consider the simple potential. We calculate the slow roll parameters
, and for each inflationary potential. Then, we check
whether the potentials give reasonable spectral indices and their running
's by comparing with the recently released seven-year WMAP data. For
both models, we see reasonable spectral indices for the number of e-folding
. Conversely, by inserting the observed seven-year WMAP data, we see
that the potential of the toy model gives requisite number of e-folds while the
potential of the K\"{a}hler moduli gives much smaller number of e-folding.
Finally, we see that two models do not produce reasonable values of the running
of the spectral index.Comment: 22 pages, 6 figure
Qubits from extra dimensions
We link the recently discovered black hole-qubit correspondence to the
structure of extra dimensions. In particular we show that for toroidal
compactifications of type IIB string theory simple qubit systems arise
naturally from the geometrical data of the tori parametrized by the moduli. We
also generalize the recently suggested idea of the attractor mechanism as a
distillation procedure of GHZ-like entangled states on the event horizon, to
moduli stabilization for flux attractors in F-theory compactifications on
elliptically fibered Calabi-Yau four-folds. Finally using a simple example we
show that the natural arena for qubits to show up is an embedded one within the
realm of fermionic entanglement of quantum systems with indistinguishable
constituents.Comment: 32 pages Late
- …