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Jeremie Unterberger

Publications and source records attributed to Jeremie Unterberger.

26 records · Page 2Linked to original sources
arXiv2009

A classification of periodic time-dependent generalized harmonic oscillators using a Hamiltonian action of the Schrödinger-Virasoro group

In the wake of a preceding article \cite{RogUnt06} introducing the Schrödinger-Virasoro group, we study its affine action on a space of $(1+1)$-dimensional Schrödinger operators with time- and space-dependent potential $V$ periodic in time. We focus on the subspace corresponding to potentials that are at most quadratic in the space coordinate, which is in some sense the natural quantization of the space of Hill (Sturm-Liouville) operators on the one-dimensional torus. The orbits in this subspace have finite codimension, and their classification by studying the stabilizers can be obtained by extending Kirillov's results on the orbits of the space of Hill operators under the Virasoro group. We then explain the connection to the theory of Ermakov-Lewis invariants for time-dependent harmonic oscillators. These exact adiabatic invariants behave covariantly under the action of the Schrödinger-Virasoro group, which allows a natural classification of the orbits in terms of a monodromy operator on $L^2(\R)$ which is closely related to the monodromy matrix for the corresponding Hill operator.

math-ph↗
arXiv2008

A central limit theorem for the rescaled Lévy area of two-dimensional fractional Brownian motion with Hurst index $H<1/4$

Let $B=(B^{(1)},B^{(2)})$ be a two-dimensional fractional Brownian motion with Hurst index $α\in (0,1/4)$. Using an analytic approximation $B(η)$ of $B$ introduced in \cite{Unt08}, we prove that the rescaled Lévy area process $(s,t)\to η^{\half(1-4α)}\int_s^t dB_{t_1}^{(1)}(η) \int_s^{t_1} dB_{t_2}^{(2)}(η)$ converges in law to $W_t-W_s$ where $W$ is a Brownian motion independent from $B$. The method relies on a very general scheme of analysis of singularities of analytic functions, applied to the moments of finite-dimensional distributions of the Lévy area.

math.PR↗
arXiv2007

On vertex algebra representations of the Schrödinger-Virasoro Lie algebra

The Schrödinger-Virasoro Lie algebra \mathfrak{sv} is an extension of the Virasoro Lie algebra by a nilpotent Lie algebra formed with a bosonic current of weight 3/2 and a bosonic current of weight 1. It is also a natural infinite-dimensional extension of the Schrödinger Lie algebra, which -leaving aside the invariance under time-translation - has been proved to be a symmetry algebra for many statistical physics models undergoing a dynamics with dynamical exponent z=2; it should consequently play a role akin to that of the Virasoro Lie algebra in two-dimensional equilibrium statistical physics. We define in this article general Schrödinger-Virasoro primary fields by analogy with conformal field theory, characterized by a 'spin' index and a (non-relativistic) mass, and construct vertex algebra representations of \mathfrak{sv} out of a charged symplectic boson and a free boson. We also compute two- and three-point functions of still conjectural massive fields that are defined by analytic continuation with respect to a formal parameter.

cond-mat.stat-mech↗
arXiv2006

The Schrödinger-Virasoro Lie group and algebra: from geometry to representation theory

This article is concerned with an extensive study of an infinite-dimensional Lie algebra $\mathfrak{sv}$, introduced in the context of non-equilibrium statistical physics, containing as subalgebras both the Lie algebra of invariance of the free Schrödinger equation and the central charge-free Virasoro algebra $Vect(S^1)$. We call $\mathfrak{sv}$ the Schrödinger-Virasoro algebra. We choose to present $\mathfrak{sv}$ from a Newtonian geometry point of view first, and then in connection with conformal and Poisson geometry. We turn afterwards to its representation theory: realizations as Lie symmetries of field equations, coadjoint representation, coinduced representations in connection with Cartan's prolongation method (yielding analogues of the tensor density modules for $Vect(S^1)$), and finally Verma modules with a Kac determinant formula. We also present a detailed cohomological study, providing in particular a classification of deformations and central extensions; there appears a non-local cocycle.

math-ph↗
arXiv2005

Supersymmetric extensions of Schrödinger-invariance

The set of dynamic symmetries of the scalar free Schrödinger equation in d space dimensions gives a realization of the Schrödinger algebra that may be extended into a representation of the conformal algebra in d+2 dimensions, which yields the set of dynamic symmetries of the same equation where the mass is not viewed as a constant, but as an additional coordinate. An analogous construction also holds for the spin-1/2 Lévy-Leblond equation. A N=2 supersymmetric extension of these equations leads, respectively, to a `super-Schrödinger' model and to the (3|2)-supersymmetric model. Their dynamic supersymmetries form the Lie superalgebras osp(2|2) *_s sh(2|2) and osp(2|4), respectively. The Schrödinger algebra and its supersymmetric counterparts are found to be the largest finite-dimensional Lie subalgebras of a family of infinite-dimensional Lie superalgebras that are systematically constructed in a Poisson algebra setting, including the Schrödinger-Neveu-Schwarz algebra sns^(N) with N supercharges. Covariant two-point functions of quasiprimary superfields are calculated for several subalgebras of osp(2|4). If one includes both N=2 supercharges and time-inversions, then the sum of the scaling dimensions is restricted to a finite set of possible values.

math-ph↗
arXiv2003

Local scale invariance and its applications to strongly anisotropic critical phenomena

The generalization of dynamical scaling to local scale invariance is reviewed. Starting from a recapitulation of the phenomenology of ageing phenomena, the generalization of dynamical scaling to local scale transformation for any given dynamical exponent $z$ is described and the two distinct types of local scale invariance are presented. The special case $z=2$ and the associated Ward identity of Schrödinger invariance is treated. Local scale invariance predicts the form of the two-point functions. Existing confirmations of these predictions for (I) the Lifshitz points in spin systems with competing interactions such as the ANNNI model and (II) non-equilibrium ageing phenomena as occur in the kinetic Ising model with Glauber dynamics are described.

cond-mat.stat-mech↗
arXiv2003

Schr"odinger invariance and space-time symmetries

The free Schrödinger equation with mass M can be turned into a non-massive Klein-Gordon equation via Fourier transformation with respect to M. The kinematic symmetry algebra sch_d of the free d-dimensional Schrödinger equation with M fixed appears therefore naturally as a parabolic subalgebra of the complexified conformal algebra conf_d+2 in d+2 dimensions. The explicit classification of the parabolic subalgebras of conf_3 yields physically interesting dynamic symmetry algebras. This allows us to propose a new dynamic symmetry group relevant for the description of ageing far from thermal equilibrium, with a dynamical exponent z=2. The Ward identities resulting from the invariance under conf_d+2 and its parabolic subalgebras are derived and the corresponding free-field energy-momentum tensor is constructed. We also derive the scaling form and the causality conditions for the two- and three-point functions and their relationship with response functions in the context of Martin-Siggia-Rose theory.

hep-th↗