Aukosh Jagannath

A dynamic programming approach to the Parisi functional

G.Parisi predicted an important variational formula for the thermodynamic limit of the intensive free energy for a class of mean field spin glasses. In this paper, we present an elementary approach to the study of the Parisi functional using stochastic dynamic programing and semi-linear PDE. We give a derivation of important properties of the Parisi PDE avoiding the use of Ruelle Probability Cascades and Cole-Hopf transformations. As an application, we give a simple proof of the strict convexity of the Parisi functional, which was recently proved by Auffinger and Chen in [2].

Some properties of the phase diagram for mixed p-spin glasses

In this paper we study the Parisi variational problem for mixed p-spin glasses with Ising spins. Our starting point is a characterization of Parisi measures whose origin lies in the first order optimality conditions for the Parisi functional, which is known to be strictly convex. Using this characterization, we study the phase diagram in the temperature-external field plane. We begin by deriving self-consistency conditions for Parisi measures that generalize those of de Almeida and Thouless to all levels of Replica Symmetry Breaking (RSB) and all models. As a consequence, we conjecture that for all models the Replica Symmetric phase is the region determined by the natural analogue of the de Almeida–Thouless condition. We show that for all models, the complement of this region is in the RSB phase. Furthermore, we show that the conjectured phase boundary is exactly the phase boundary in the plane less a bounded set. In the case of the Sherrington–Kirkpatrick model, we extend this last result to show that this bounded set does not contain the critical point at zero external field.

Solution of the propeller conjecture in R 3

It is shown that every measurable partition {A₁,..., A_k} of R³ satisfies: ∑_i=1^k|int_{A_i} xe^-1/2|x|₂²dx|₂²≤ 9π². Let P₁,P₂,P₃ be the partition of R² into 120^o sectors centered at the origin. The bound (1) is sharp, with equality holding if A_i=P_i x R for i∈ {1,2,3} and A_i=∅ for i∈ {4,...,k}. This settles positively the 3-dimensional Propeller Conjecture of Khot and Naor (FOCS 2008). The proof of (1) reduces the problem to a finite set of numerical inequalities which are then verified with full rigor in a computer-assisted fashion. The main consequence (and motivation) of (1) is complexity-theoretic: the Unique Games hardness threshold of the Kernel Clustering problem with 4 x 4 centered and spherical hypothesis matrix equals 2π/3.

On the overlap distribution of Branching Random Walks

In this paper, we study the overlap distribution and Gibbs measure of the Branching Random Walk with Gaussian increments on a binary tree. We first prove that the Branching Random Walk is 1 step Replica Symmetry Breaking and give a precise form for its overlap distribution, verifying a prediction of Derrida and Spohn. We then prove that the Gibbs measure of this system satisfies the Ghirlanda-Guerra identities. As a consequence, the limiting Gibbs measure has Poisson-Dirichlet statistics. The main technical result is a proof that the overlap distribution for the Branching Random Walk is supported on the set

Max

\{0,1\}

\kappa

.

-cut and the inhomogeneous Potts spin glass

Abstract. We study the asymptotic behavior of the Max κ-cut on a family of sparse, inhomogeneous random graphs. In the large degree limit, the leading term is a variational problem, involving the ground state of a constrained inhomogeneous Potts spin glass. We derive a Parisi type formula for the free energy of this model, with possible constraints on the proportions, and derive the limiting ground state energy by a suitable zero temperature limit.

Random matrices and the New York City subway system

We analyze subway arrival times in the New York City subway system. We find regimes where the gaps between trains are well modeled by (unitarily invariant) random matrix statistics and Poisson statistics. The departure from random matrix statistics is captured by the value of the Coulomb potential along the subway route. This departure becomes more pronounced as trains make more stops.

Charged particle motion in electromagnetic fields varying moderately rapidly in space

Electromagnetic fields are considered which vary on the space scale of the geometric mean of the Larmor radius and the much larger scale length of variation of the magnetic field lines. It is first shown that the magnetic moment is an adiabatic invariant, even though the usual arguments for its existence fail. The motion of the guiding center is then examined. For perpendicular drifts in magnitude comparable with the particle speed, the subsequent motion is dominated by electrostatic effects. The motion of particles along the field lines occurs on a much slower time scale than the perpendicular drift time scale. When the guiding center motion is approximately periodic in time, a second adiabatic invariant exists, the magnetic flux enclosed by the almost periodic orbit. When the perpendicular drift is small compared with the particle speed, the parallel motion and the perpendicular drift occur on the same, slow timescale.