Abstract:
We consider decaying oscillatory perturbations of periodic Schr\"odinger
operators on the half line. More precisely, the perturbations we study
satisfy a generalized bounded variation condition at infinity and an $L^p$
decay condition. We show that the absolutely continuous spectrum is
preserved, and give bounds on the Hausdorff dimension of the singular part
of the resulting perturbed measure. Under additional assumptions, we
instead show that the singular part embedded in the essential spectrum is
contained in an explicit countable set. Finally, we demonstrate that this
explicit countable set is optimal. That is, for every point in this set
there is an open and dense class of periodic Schr\"odinger operators for
which an appropriate perturbation will result in the spectrum having an
embedded eigenvalue at that point.
The classical Lieb-Robinson bounds provide control over the speed of
propagation in quantum spin systems. In analogy to relativistic systems,
they establish a ``light cone'' $x \leq vt$ outside of which commutators
of initially localized observables are exponentially small. We consider an
XY spin chain in a quasiperiodic magnetic field and prove a new anomalous
Lieb-Robinson bound which features the modified light cone $x \leq
vt^\alpha$ for some $0<\alpha<1$. In fact, we can characterize $\alpha$
exactly as the upper transport exponent of a one-body Schr\"odinger
operator. This may be interpreted as a rigorous proof of anomalous quantum
many-body transport. Joint work with David Damanik, Milivoje Lukic and
William Yessen.
Mathematical computational biology (MCB) has proven fruitful for all three fields:
mathematics, computation, and biology. One approach to the intersection begins
with symbolic representations of models, so that high-level abstractions and
advantageous problem transformations can be applied computationally before
good numerical methods are called in to do the heavy work of simulation and optimization.
This is the potential advantage of “declarative” modeling. It opens up further connections
between applied mathematics, artificial intelligence (including current trends in hybrid
logical/statistical inference), and foundational mathematics including logic and type theory.
I will illustrate the possibilities with recent work in complex, multiscale computational
biology including signal transduction in synapses and gene regulation/signaling networks
in developmental biology, by means of stochastic model reduction, enriched graphical
models expressed using computer algebra, and declarative modeling languages for
multiscale heterogeneous dynamics.
In this talk I will describe a cohomological formula for a higher
index pairing between invariant elliptic differential operators and
differentiable group cohomology classes. This index theorem generalizes the
Connes-Moscovici L^2-index theorem and its variants. This is joint work with
Markus Pflaum and Hessel Posthuma.
A classical result of Khinchin says that for almost all real numbers α, the geometric mean of the first n digits ai(α) in the continued fraction expansion of α converges to a number K ≈ 2.6854520 . . . (Khinchin’s constant) as n → ∞. On the other hand, for almost all α, the arithmetic mean of the first n continued fraction digits ai(α) approaches infinity as n → ∞. There is a sequence of refinements of the AM-GM inequality, known as Maclaurin’s inequalities, relating the 1/kthpowers of the kth elementary symmetric means of n numbers for 1 ≤ k ≤ n. On the left end (when k = n) we have the geometric mean, and on the right end (k = 1) we have the arithmetic mean. We analyze what happens to the means of continued fraction digits of a typical real number in the limit as one moves f (n) steps away from either extreme. We also study the limiting behavior of such means for quadratic irrational α.
(Joint work with Francesco Cellarosi, Doug Hensley and Steven J. Miller)
For discrete Schrödinger operators with potential given by a trigonometric polynomial of cosines (called generalized Harper's model), we use the complexified Lyapunov exponent to prove a criterion for subcritical energies in the spectrum and a criterion for supercritical energies. This work was done through the Caltech SURF program, with mentor Christoph Marx.
We’ll introduce a common model framework for valuing and measuring risk for
options on pools of mortgages. In some market conditions this model does
not accurately match option market prices. Different ways of dealing with
this issue lead to different risk measurements. We’ll consider a “model
free” way of looking at risk through a local vol calculation, and use this
for comparison. As background we’ll introduce agency Mortgage Backed
Securities and some of their associated risk management issues.
At UCI he got a solid training in logic, then in algebraic geometry,
before finally getting his PHD in mathematical physics, in 2001, that
earned a department's Kovalevsky outstanding PhD thesis award. In the
postdoctoral period his interests switched to financial math. Now he is
the head of risk and quantitative opportunities for Catalina Asset
Management, the investment arm for the non-life insurance consolidator
Catalina Holdings. Before Catalina Michael was a Director in Quantitative
Risk Control at UBS Investment Bank. He has also had positions in the
financial industry at MSCI, PIMCO and Rimrock Capital Management, and he
has had faculty positions at Idaho State University and UC Santa Barbara.
Prior to the UCI PhD he got a BA in mathematics at the University of
Chicago.