Invisible Quarkonium Decays as a Sensitive Probe of Dark Matter

We examine in a model-independent manner the measurements that can be performed at B-factories with sensitivity to dark matter. If a singlet scalar, pseudo-scalar, or vector is present and mediates the Standard Model - dark matter interaction, it can mediate invisible decays of quarkonium states such as the $\Upsilon$, $J/\Psi$, and $\eta$. Such scenarios have arisen in the context of supersymmetry, extended Higgs sectors, solutions the supersymmetric $\mu$ problem, and extra U(1) gauge groups from grand unified theories and string theory. Existing B-factories running at the $\Upsilon(4S)$ can produce lower $\Upsilon$ resonances by emitting an Initial State Radiation (ISR) photon. Using a combination of ISR and radiative decays, the initial state of an invisibly decaying quarkonium resonance can be tagged, giving sensitivity to the spin and CP-nature of the particle that mediates standard model-dark matter interactions. These measurements can discover or place strong constraints on dark matter scenarios where the dark matter is approximately lighter than the $b$-quark. For the decay chains $\Upsilon(nS) \to \pi^+ \pi^- \Upsilon(1S)$ (n=2,3) we analyze the dominant backgrounds and determine that with $400 fb^{-1}$ collected at the $\Upsilon(4S)$, the B-factories can limit BR(\Upsilon(1S) \to invisible) \lsim 0.1%.Comment: 20 pages, 1 figure, accepted for publication in PR

Chile's pension reform after twenty years

The aim of this paper is to describe the 1980 Chilean pension reform and to present its main results and economic impact. It is mainly descriptive; however we have tried to emphasize the lessons that may be learned and that may be of interest to other countries in different circumstances. In particular, we focus on potential areas for regulatory improvements. In Section II, a brief description of the AFP system and its place within Chile's social security system is presented. Also, the main characteristics of the transition from the"old"to the new system are sketched, together with the main changes in regulation after 1980. Section III includes a history of pension reform in Chile along with an analysis of the circumstances which may explain why the country decided to introduce such a radical reform. In Section IV, the performance of the AFP system is summarized. In Section V, the main economic effects of pension reform are discussed. Section VI presents our view regarding future development in the regulation of the AFP system. The paper concludes with some comments on the timing of possible regulatory changes.Pensions&Retirement Systems,Banks&Banking Reform,Insurance&Risk Mitigation,Environmental Economics&Policies,Gender and Law

Species survival and scaling laws in hostile and disordered environments

In this work we study the likelihood of survival of single-species in the context of hostile and disordered environments. Population dynamics in this environment, as modeled by the Fisher equation, is characterized by negative average growth rate, except in some random spatially distributed patches that may support life. In particular, we are interested in the phase diagram of the survival probability and in the critical size problem, i.e., the minimum patch size required for surviving in the long time dynamics. We propose a measure for the critical patch size as being proportional to the participation ratio (PR) of the eigenvector corresponding to the largest eigenvalue of the linearized Fisher dynamics. We obtain the (extinction-survival) phase diagram and the probability distribution function (PDF) of the critical patch sizes for two topologies, namely, the one-dimensional system and the fractal Peano basin. We show that both topologies share the same qualitative features, but the fractal topology requires higher spatial fluctuations to guarantee species survival. We perform a finite-size scaling and we obtain the associated scaling exponents. In addition, we show that the PDF of the critical patch sizes has an universal shape for the 1D case in terms of the model parameters (diffusion, growth rate, etc.). In contrast, the diffusion coefficient has a drastic effect on the PDF of the critical patch sizes of the fractal Peano basin, and it does not obey the same scaling law of the 1D case.Comment: 20 pages, 5 Figure