35 research outputs found
Disjoint optimizers and the directed landscape
We study maximal length collections of disjoint paths, or `disjoint
optimizers', in the directed landscape. We show that disjoint optimizers always
exist, and that their lengths can be used to construct an extended directed
landscape. The extended directed landscape can be built from an independent
collection of extended Airy sheets, which we define from the Airy line
ensemble. We show that the extended directed landscape and disjoint optimizers
are scaling limits of the corresponding objects in Brownian last passage
percolation (LPP). As two consequences of this work, we show that one direction
of the Robinson-Schensted-Knuth bijection passes to the KPZ limit, and we find
a criterion for geodesic disjointness in the directed landscape that uses only
a single Airy line ensemble.
The proofs rely on a new notion of multi-point LPP across the Airy line
ensemble, combinatorial properties of multi-point LPP, and probabilistic
resampling ideas
Fractal geometry of the space-time difference profile in the directed landscape via construction of geodesic local times
The Directed Landscape, a random directed metric on the plane (where the
first and the second coordinates are termed spatial and temporal respectively),
was constructed in the breakthrough work of Dauvergne, Ortmann, and Vir\'ag,
and has since been shown to be the scaling limit of various integrable models
of Last Passage percolation, a central member of the Kardar-Parisi-Zhang
universality class. It exhibits several scale invariance properties making it a
natural source of rich fractal behavior. Such a study was initiated in
Basu-Ganguly-Hammond, where the difference profile i.e., the difference of
passage times from two fixed points (say ), was considered. Owing to
geodesic geometry, it turns out that this difference process is almost surely
locally constant. The set of non-constancy is connected to disjointness of
geodesics and inherits remarkable fractal properties. In particular, it has
been established that when only the spatial coordinate is varied, the set of
non-constancy of the difference profile has Hausdorff dimension , and
bears a rather strong resemblance to the zero set of Brownian motion. The
arguments crucially rely on a monotonicity property, which is absent when the
temporal structure of the process is probed, necessitating the development of
new methods.
In this paper, we put forth several new ideas, and show that the set of
non-constancy of the 2D difference profile and the 1D temporal process (when
the spatial coordinate is fixed and the temporal coordinate is varied) have
Hausdorff dimensions and respectively. A particularly crucial
ingredient in our analysis is the novel construction of a local time process
for the geodesic akin to Brownian local time, supported on the "zero set" of
the geodesic. Further, we show that the latter has Hausdorff dimension in
contrast to the zero set of Brownian motion which has dimension Comment: 89 pages, 23 figure
Pearcey universality at cusps of polygonal lozenge tiling
We study uniformly random lozenge tilings of general simply connected
polygons. Under a technical assumption that is presumably generic with respect
to polygon shapes, we show that the local statistics around a cusp point of the
arctic curve converge to the Pearcey process. This verifies the widely
predicted universality of edge statistics in the cusp case. Together with the
smooth and tangent cases proved in Aggarwal-Huang and Aggarwal-Gorin, these are
believed to be the three types of edge statistics that can arise in a generic
polygon. Our proof is via a local coupling of the random tiling with
non-intersecting Bernoulli random walks (NBRW). To leverage this coupling, we
establish an optimal concentration estimate for the tiling height function
around the cusp. As another step and also a result of potential independent
interest, we show that the local statistics of NBRW around a cusp converge to
the Pearcey process when the initial configuration consists of two parts with
proper density growth, via careful asymptotic analysis of the determinantal
formula.Comment: 59 pages, 9 figure
Brownian bridge limit of path measures in the upper tail of KPZ models
For models in the KPZ universality class, such as the zero temperature model
of planar last passage-percolation (LPP) and the positive temperature model of
directed polymers, its upper tail behavior has been a topic of recent interest,
with particular focus on the associated path measures (i.e., geodesics or
polymers). For Exponential LPP, diffusive fluctuation had been established in
Basu-Ganguly. In the directed landscape, the continuum limit of LPP, the
limiting Gaussianity at one point, as well as of related finite-dimensional
distributions of the KPZ fixed point, were established, using exact formulas in
Liu and Wang-Liu. It was further conjectured in these works that the limit of
the corresponding geodesic should be a Brownian bridge. We prove it in both
zero and positive temperatures; for the latter, neither the one-point limit nor
the scale of fluctuations was previously known. Instead of relying on formulas
(which are still missing in the positive temperature literature), our arguments
are geometric and probabilistic, using the results on the shape of the weight
and free energy profiles under the upper tail from Ganguly-Hegde as a starting
point. Another key ingredient involves novel coalescence estimates, developed
using the recently discovered shift-invariance Borodin-Gorin-Wheeler in these
models. Finally, our proof also yields insight into the structure of the
polymer measure under the upper tail conditioning, establishing a quenched
localization exponent around a random backbone.Comment: 76 pages, 6 figure
Infinite order phase transition in the slow bond TASEP
In the slow bond problem the rate of a single edge in the Totally Asymmetric
Simple Exclusion Process (TASEP) is reduced from 1 to for some
small . Janowsky and Lebowitz posed the well-known question of
whether such very small perturbations could affect the macroscopic current.
Different groups of physicists, using a range of heuristics and numerical
simulations reached opposing conclusions on whether the critical value of
is 0. This was ultimately resolved rigorously in
Basu-Sidoravicius-Sly which established that .
Here we study the effect of the current as tends to 0 and in
doing so explain why it was so challenging to predict on the basis of numerical
simulations. In particular we show that the current has an infinite order phase
transition at 0, with the effect of the perturbation tending to 0 faster than
any polynomial. Our proof focuses on the Last Passage Percolation formulation
of TASEP where a slow bond corresponds to reinforcing the diagonal. We give a
multiscale analysis to show that when is small the effect of
reinforcement remains small compared to the difference between optimal and near
optimal geodesics. Since geodesics can be perturbed on many different scales,
we inductively bound the tails of the effect of reinforcement by controlling
the number of near optimal geodesics and giving new tail estimates for the
local time of (near) geodesics along the diagonal.Comment: 33 pages, 4 figures. Revised according to referee reports. Comm. Pure
Appl. Math. to appea
Istraživanje simultane lokalizacije, kalibracije i kartiranja umreženim robotskim sustavima
In a network robot system, a robot and a sensor network are integrated smoothly to develop their advantages and benefit from each other. Robot localization, sensor network calibration and environment mapping are three coupled issues to be solved once network robot system is introduced into a service environment. In this article, the problem of simultaneous localization, calibration and mapping is raised in order to improve their precision. The coupled relations among localization, calibration and mapping are denoted as a joint conditional distribution and then decomposed into three separate analytic terms according to Bayesian and Markov properties. The framework of Rao-Blackwellized particle filtering is used to solve the three analytic terms, in which extended particle filter is used for localization and unscented Kalman filter is used for both calibration and mapping. Simulations have been performed to demonstrate the validity and efficiency of the proposed solutions.U umreženom robotskom sustavu, robot i senzorska mreža su međusobno integrirani i povezani na način da i jedan i drugi iskoriste svoje prednosti, te da imaju koristi jedan od drugoga. Kako bi umreženi robotski sustav mogao djelovati u radnom okruženju potrebno je riješiti tri međusobno povezana problema: lokalizaciju, kalibraciju senzorske mreže i kartiranje prostora. U ovom radu razmatraju se problemi istodobne lokalizacije, kalibracije i kartiranja te se razmatraju mogućnosti poboljšanja njihove preciznosti. Povezanost lokalizacije, kartiranja i kalibracije predstavljena je pomoću zajedničke uvjetne razdiobe i zatim rastavljena u tri razdvojena analitička izraza korištenjem Bayesovih i Markovljevih svojstava. Za rješavanje svih triju analitičkih izraza koristi se Rao-Blackwell čestično filtriranje, pri čemu se prošireni čestični filtar koristi kod lokalizacije a nederivirajući Kalmanov filtar za kalibraciju i kartiranje. Ispravnost i efikasnost predloženog pristupa pokazana je kroz provedene simulacije