39,551 research outputs found
Adaptive Computation of the Swap-Insert Correction Distance
The Swap-Insert Correction distance from a string of length to
another string of length on the alphabet is the minimum
number of insertions, and swaps of pairs of adjacent symbols, converting
into . Contrarily to other correction distances, computing it is NP-Hard in
the size of the alphabet. We describe an algorithm computing this distance
in time within , where there are occurrences of
in , occurrences of in , and where
measures the
difficulty of the instance. The difficulty is bounded by above by various
terms, such as the length of the shortest string , and by the maximum number
of occurrences of a single character in . Those results illustrate how, in
many cases, the correction distance between two strings can be easier to
compute than in the worst case scenario.Comment: 16 pages, no figures, long version of the extended abstract accepted
to SPIRE 201
A different kind of string
In U(1) lattice gauge theory in three spacetime dimensions, the problem of
confinement can be studied analytically in a semi-classical approach, in terms
of a gas of monopoles with Coulomb-like interactions. In addition, this theory
can be mapped to a spin model via an exact duality transformation, which allows
one to perform high-precision numerical studies of the confining potential.
Taking advantage of these properties, we carried out an accurate investigation
of the effective string describing the low-energy properties of flux tubes in
this confining gauge theory. We found striking deviations from the expected
Nambu-Goto-like behavior, and, for the first time, evidence for contributions
that can be described by a term proportional to the extrinsic curvature of the
effective string worldsheet. Such term is allowed by Lorentz invariance, and
its presence in the infrared regime of the U(1) model was indeed predicted by
Polyakov several years ago. Our results show that this term scales as expected
according to Polyakov's solution, and becomes the dominant contribution to the
effective string action in the continuum limit. We also demonstrate
analytically that the corrections to the confining potential induced by the
extrinsic curvature term can be related to the partition function of the
massive perturbation of a c=1 bosonic conformal field theory. The implications
of our results for SU(N) Yang-Mills theories in three and in four spacetime
dimensions are discussed.Comment: 1+21 pages, 2 figures; v2 (1+24 pages, 2 figures): improved the
discussion in the conclusions' section, added an appendix, included new
references, updated the affiliation details for one of the authors, corrected
typos: version published in the journa
Static quark potential and effective string corrections in the (2+1)-d SU(2) Yang-Mills theory
We report on a very accurate measurement of the static quark potential in
SU(2) Yang-Mills theory in (2+1) dimensions in order to study the corrections
to the linear behaviour. We perform numerical simulations at zero and finite
temperature comparing our results with the corrections given by the effective
string picture in these two regimes. We also check for universal features
discussing our results together with those recently published for the (2+1)-d
Z(2) and SU(3) pure gauge theories.Comment: 29 pages, 6 figure
Grand-canonical simulation of two-dimensional simplicial gravity
The string susceptibility exponents of dynamically triangulated 2-dimensional
surfaces with various topologies, such as a sphere, torus and double-torus,
were calculated by the grand-canonical Monte Carlo method. These simulations
were made for surfaces coupled to -Ising spins (=0,1,2,3,5). In each
simulation the area of surface was constrained to within 1000 to 3000 of
triangles, while maintaining the detailed-balance condition. The numerical
results show excellent agreement with theoretical predictions as long as .Comment: 9 pages, Latex include 5 postscript figures, using psfig.sty and
cite.st
The confining string beyond the free-string approximation in the gauge dual of percolation
We simulate five different systems belonging to the universality class of the
gauge dual of three-dimensional random percolation to study the underlying
effective string theory at finite temperature. All the data for the finite
temperature string tension, when expressed by means of adimensional variables,
are nicely described by a unique scaling function. We calculate the first few
terms of the string tension up to order and compare to different
theoretical predictions. We obtain unambiguous evidence that the coefficients
of and terms coincide with those of the Nambu-Goto string, as
expected, while the term strongly differs and is characteristic of the
universality class of this specific gauge theory.Comment: 13 pages, 3 figure
CiNCT: Compression and retrieval for massive vehicular trajectories via relative movement labeling
In this paper, we present a compressed data structure for moving object
trajectories in a road network, which are represented as sequences of road
edges. Unlike existing compression methods for trajectories in a network, our
method supports pattern matching and decompression from an arbitrary position
while retaining a high compressibility with theoretical guarantees.
Specifically, our method is based on FM-index, a fast and compact data
structure for pattern matching. To enhance the compression, we incorporate the
sparsity of road networks into the data structure. In particular, we present
the novel concepts of relative movement labeling and PseudoRank, each
contributing to significant reductions in data size and query processing time.
Our theoretical analysis and experimental studies reveal the advantages of our
proposed method as compared to existing trajectory compression methods and
FM-index variants
The Lorentz-invariant boundary action of the confining string and its universal contribution to the inter-quark potential
We study the boundary contribution to the low energy effective action of the
open string describing the confining flux tube in gauge theories. The form of
the boundary terms is strongly constrained by the requirement of Lorentz
symmetry, which is spontaneously broken by the formation of a long confining
flux tube in the vacuum. Writing the boundary action as an expansion in the
derivatives of the Nambu-Goldstone modes describing the transverse fluctuations
of the string, we single out and put in a closed form the first few Lorentz
invariant boundary terms. We also evaluate the leading deviation from the
Nambu-Goto string produced by the boundary action on the vacuum expectation
value of the Wilson loop and we test this prediction in the 3d Ising gauge
model. Our simulation attains a level of precision which is sufficient to test
the contribution of this term.Comment: 17 pages, 5 figures, LateX 2e. V2: Final version published on JHEP.
Fixed typos in eq.s 2.2, 2.3, 3.7, 3.8, A.4. Extended explanation of the
procedures used in sec 2 to determine the possible boundary terms up to field
redefinitions and of the procedure used in sec 4 to take the continuum limit.
V3: typos corrected in eq.s (4.3) (4.5) and (4.6), acknowledgements adde
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