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Random geometry and the Kardar–Parisi–Zhang universality class

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Random geometry and the Kardar–Parisi–Zhang universality class
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We consider a model of a quenched disordered geometry in which a random metric is defined on , which is flat on average and presents short-range correlations. We focus on the statistical properties of balls and geodesics, i.e., circles and straight lines. We show numerically that the roughness of a ball of radius R scales as , with a fluctuation exponent , while the lateral spread of the minimizing geodesic between two points at a distance L grows as , with wandering exponent value . Results on related first-passage percolation problems lead us to postulate that the statistics of balls in these random metrics belong to the Kardar–Parisi–Zhang universality class of surface kinetic roughening, with ξ and χ relating to critical exponents characterizing a corresponding interface growth process. Moreover, we check that the one-point and two-point correlators converge to the behavior expected for the Airy-2 process characterized by the Tracy–Widom (TW) probability distribution function of the largest eigenvalue of large random matrices in the Gaussian unitary ensemble (GUE). Nevertheless extreme-value statistics of ball coordinates are given by the TW distribution associated with random matrices in the Gaussian orthogonal ensemble. Furthermore, we also find TW–GUE statistics with good accuracy in arrival times.
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Transcript: English(auto-generated)
Welcome to the video abstract of our paper Random Metrics and the Kargil Barisichan Universality class. In the next few minutes, we will attempt to show you some of our results. And more importantly, we will try to whet your appetite
to read the full paper. Euclid is the first hero of our story. It is difficult to overemphasize the beauty of classical geometry, circumstances, and straight lines, mathematics with ruler and compass. But what will happen if a space itself becomes irregular?
Then the circles and the lines themselves become rough. Now we will call the lines geodesics. And we will call the circles walls of these new irregular manifold.
But since we don't want our experiments to destroy the rainforest, we will do the simulations on a computer. Here we are, computer-generated geodesics and balls. Please forgive us for the missing technical details at this stage. Let us say that this represents a randomly generated
two-dimensional manifold with only local correlators. Now we compute the balls of different radii around a certain point. A useful analogy is to imagine the manifold as a map of a certain country and the balls as a set of places where you can reach in a certain time. We wonder how the roughness of those balls
scales with the ball size. Do the balls of all sizes keep that rough look? No, they look smoother as they grow. Roughness can be seen to scale as the radius raised to the power one third. Such a simple exponent should have a simple explanation. A growth exponent of one third is not novel in kinetic roughening. Indeed, it is one of the hallmarks of the so-called
Carter-Parise-Chang universality class far from equilibrium growth. This KPZ class shows up in very different phenomena, fire propagation, biological growth, turbulence in liquid crystals. In fact, KPZ is a very special class. A huge variety of integrable models and experiments
have made research as conjecture, but it involves not only quality of scaling exponents, but also of the full fluctuation statistics. Here we can see a histogram of the radial fluctuations of the balls compared to the well-known Tracy-Wydon probability distribution function connected to the extreme eigenvalues
of random Hermitian matrices. What about minimizing geodesics? They can be traced by letting two balls grow from different points and marking their intersection. The deviation from the straight line depends with the Euclidean distance between the points as a power law with exponent two thirds.
We have also found the meaning of that exponent within the KPZ framework. Indeed, it is related to the so-called dynamic exponent, which rules the growth of the lateral correlation length. Among many other observables,
we have also evaluated the expected times of arrival at points which have a fixed Euclidean distance to the center. Indeed, the fluctuations of those times also grow as a power law of their distance to the center with power one third. They also possess Tracy-Wydon statistics. We hope to have made you want to take a look
at the full article, which contains many other interesting surprises. As a final remark, we can only say that Euclid rules even when he's drunk.