Direct CP asymmetry in D→π−π+D\to \pi^-\pi^+ and D→K−K+D\to K^-K^+ in QCD-based approach

We present the first QCD-based calculation of hadronic matrix elements with penguin topology determining direct CP-violating asymmetries in $D^0\to \pi^-\pi^+$ and $D^0\to K^- K^+$ nonleptonic decays. The method is based on the QCD light-cone sum rules and does not rely on any model-inspired amplitude decomposition, instead leaning heavily on quark-hadron duality. We provide a Standard Model estimate of the direct CP-violating asymmetries in both pion and kaon modes and their difference and comment on further improvements of the presented computation.Comment: 19 pages, 1 figure; replaced to match published version (minor changes to text and a figure, added new references

Direct probes of flavor-changing neutral currents in e+e−e^+e^- collisions

We propose a novel method to study flavor-changing neutral currents in the $e^+e^-\to D^{*0}$ and $e^+e^-\to B_{s}^*$ transitions, tuning the energy of $e^+e^-$- collisions to the mass of the narrow vector resonance $D^{*0}$ or $B_{s}^*$. We present a thorough study of both short-distance and long-distance contributions to $e^+e^-\to D^{*0}$ in the Standard Model and investigate possible contributions of new physics in the charm sector. This process, albeit very rare, has clear advantages with respect to the $D^0 \to e^+e^-$ decay: the helicity suppression is absent, and a richer set of effective operators can be probed. Implications of the same proposal for $B_{s}^*$ are also discussed.Comment: 24 pages, 2 figure

Identifying Falsifiable Predictions of the Divisive Normalization Model of V1 Neurons

The divisive normalization model (DNM, Heeger, 1992) accounts successfully for a wide range of phenomena observed in single-cell physiological recordings from neurons in primary visual cortex (V1). The DNM has adjustable parameters to accommodate the diversity of V1 neurons, and is quite flexible. At the same time, in order to be falsifiable, the model must be rigid enough to rule out some possible data patterns. In this study, we discuss whether the DNM predicts any physiological result of the V1 neurons based on mathematical analysis and computational simulations. We identified some falsifiable predictions of the DNM. The main idea is that, while the parameters can vary flexibly across neurons, they must be fixed for a given individual neuron. This introduces constraints when this single neuron is probed with a judiciously chosen suite of stimuli. For example, the parameter governing the maintained discharge (base firing rate) is associated with three characteristic observable patterns: (A) the existence of inhibitory regions in the receptive fields of simple cells in V1, (B) the super-saturation effect in the contrast sensitivity curves, and (C) the narrowing/widening of the spatial-frequency tuning curves when the stimulus contrast decreases. Based on this fact, it is predicted that the simple cells can be categorized into two groups: one shows A, B, and widening (C) and the other one shows not-A, not-B, and narrowing (C). We will also discuss roles of other DNM parameters for emulating the V1 neurons in physiological experiments

Stability of spinning ring solitons of the cubic-quintic nonlinear Schrodinger equation

We investigate stability of (2+1)-dimensional ring solitons of the nonlinear Schrodinger equation with focusing cubic and defocusing quintic nonlinearities. Computing eigenvalues of the linearised equation, we show that rings with spin (topological charge) s=1 and s=2 are linearly stable, provided that they are very broad. The stability regions occupy, respectively, 9% and 8% of the corresponding existence regions. These results finally resolve a controversial stability issue for this class of models.Comment: 10 pages, 5 figures, accepted to Phys. Lett.

Convergence of solutions of kinetic variational inequalities in the rate-independent quasi-static limit

This paper discusses the convergence of kinetic variational inequalities to rate-independent quasi-static variational inequalities. Mathematical formulations as well as existence and uniqueness results for kinetic and rate-independent quasi-static problems are provided. Sharp a priori estimates for the kinetic problem are derived that imply that the kinetic solutions converge to the rate-independent ones, when the size of initial perturbations and the rate of application of the forces tends to 0. An application to three-dimensional elastic-plastic systems with hardening is given