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Christopher Shirley

Publications and source records attributed to Christopher Shirley.

6 recordsLinked to original sources
arXiv2022

Cherenkov radiation with massive bosons and quantum friction

This work is devoted to several translation-invariant models in non-relativistic quantum field theory (QFT), describing a non-relativistic quantum particle interacting with a quantized relativistic field of bosons. In this setting, we aim at the rigorous study of Cherenkov radiation or friction effects at small disorder, which amounts to the metastability of the embedded mass shell of the free non-relativistic particle when the coupling to the quantized field is turned on. Although this problem is naturally approached by means of Mourre's celebrated commutator method, important regularity issues are known to be inherent to QFT models and restrict the application of this method. In this perspective, we introduce a novel non-standard construction procedure for Mourre conjugate operators, which differs from second quantization and allows to circumvent regularity issues. To show its versatility, we apply this construction to the Nelson model with massive bosons, to Fr\"ohlich's polaron model, and to a quantum friction model with massless bosons introduced by Bruneau and De Bi\`evre: for each of these examples, we improve on previous results.

math-ph↗
arXiv2022

Approximate normal forms via Floquet-Bloch theory: Nehorosev stability for linear waves in quasiperiodic media

We study the long-time behavior of the Schr{ö}dinger flow in a heterogeneous potential $λ$V with small intensity 0<$λ$$\ll$1 (or alternatively at high frequencies). The main new ingredient, which we introduce in the general setting of a stationary ergodic potential, is an approximate stationary Floquet--Bloch theory that is used to put the perturbed Schr{ö}dinger operator into approximate normal form. We apply this approach to quasiperiodic potentials and establish a Nehoro{\v s}ev-type stability result. In particular, this ensures asymptotic ballistic transport up to a stretched exponential timescale exp($λ$--1/s) for some s>0. More precisely, the approximate normal form leads to an accurate long-time description of the Schr{ö}dinger flow as an effective unitary correction of the free flow. The approach is robust and generically applies to linear waves. For classical waves, for instance, this allows to extend diffractive geometric optics to quasiperiodically perturbed media.

math.AP↗
arXiv2020

A new spectral analysis of stationary random Schr\"odinger operators

Motivated by the long-time transport properties of quantum waves in weakly disordered media, the present work puts random Schr\"odinger operators into a new spectral perspective. Based on a stationary random version of a Floquet type fibration, we reduce the description of the quantum dynamics to a fibered family of abstract spectral perturbation problems on the underlying probability space. We state a natural resonance conjecture for these fibered operators: in contrast with periodic and quasiperiodic settings, this would entail that Bloch waves do not exist as extended states, but rather as resonant modes, and this would justify the expected exponential decay of time correlations. Although this resonance conjecture remains open, we develop new tools for spectral analysis on the probability space, and in particular we show how ideas from Malliavin calculus lead to rigorous Mourre type results: we obtain an approximate dynamical resonance result and the first spectral proof of the decay of time correlations on the kinetic timescale. This spectral approach suggests a whole new way of circumventing perturbative expansions and renormalization techniques.

math-ph↗
arXiv2015

Decorrelation estimates for some continuous and discrete random Schr{ö}dinger operators in dimension one, without covering condition

The purpose of the present work is to establish decorrelation estimates at distinct energies for some random Schr{ö}dinger operator in dimension one. In particular, we establish the result for some random operators on the continuum with alloy-type potential without covering condition assumption. These results are used to give a description of the spectral statistics.

math-ph↗
arXiv2013

Decorrelation estimates for random discrete Schrödinger operators in dimension one and applications to spectral statistics

The purpose of the present work is to establish decorrelation estimates for some random discrete Schrodinger operator in dimension one. We prove that the Minami estimates are consequences of the Wegner estimates and Localization. We also prove decorrelation estimates at distinct energies for the random hopping model and Schrodinger operators with alloy-type potentials. These results are used to give a description of the spectral statistics.

math-ph↗