Extra symmetries in the effective theory of heavy quarks

Extra symmetries are shown to exist in the effective theory of heavy quarks when both quarks and anti-quarks with the same velocity are included. These symmetries mix the quark with the anti-quark sector and they resemble axial-type of symmetries. Together with the known flavor and spin symmetries they form a $u(4)$ algebra when a single flavor is considered. It is shown that the full $U(4)$ set of symmetries breaks spontaneously down to $U(2) \otimes U(2)$. The Goldstone modes corresponding to the spontaneously broken currents are identified. Finally, the precise connection of this theory with the fundamental QCD is derived and it is investigated under some approximations. Some physical processes where these extra symmetries may be relevant are pointed out.Comment: 26 pages (two figures available upon request), tex file, UB-ECM-PF-93/

Low energy scattering parameters from the solutions of the non-relativistic Yukawa model on a 3-dimensional lattice

The numerical solutions of the non-relativistic Yukawa model on a 3-dimensional size lattice with periodic boundary conditions are obtained. The possibility to extract the corresponding -- infinite space -- low energy parameters and bound state binding energies from eigensates computed at finite lattice size is discussed

On a Speculated Relation Between Chv\'atal-Sankoff Constants of Several Sequences

It is well known that, when normalized by n, the expected length of a longest common subsequence of d sequences of length n over an alphabet of size sigma converges to a constant gamma_{sigma,d}. We disprove a speculation by Steele regarding a possible relation between gamma_{2,d} and gamma_{2,2}. In order to do that we also obtain new lower bounds for gamma_{sigma,d}, when both sigma and d are small integers.Comment: 13 pages. To appear in Combinatorics, Probability and Computin

SPECIES I: Spectroscopic Parameters and atmosphEric ChemIstriEs of Stars

The detection and subsequent characterisation of exoplanets are intimately linked to the characteristics of their host star. Therefore, it is necessary to study the star in detail in order to understand the formation history and characteristics of their companion(s). Our aims were to develop a community tool that allows the automated calculation of stellar parameters for a large number of stars, using high resolution echelle spectra and minimal photometric magnitudes, and introduce the first results in this work. We measured the equivalent widths of several iron lines and used them to solve the radiative transfer equation assuming local thermodynamic equilibrium to obtain the atmospheric parameters ($T_{\text{eff}}$, [Fe/H], logg and $\xi_t$). We used these values to derive the abundance of 11 chemical elements in the stellar photosphere (Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Ni, Cu and Zn). Rotation and macroturbulent velocity were obtained using temperature calibrators and synthetic line profiles to match the observed spectra of five absorption lines. Finally, by interpolating in a grid of MIST isochrones, we derived the mass, radius and age using a Bayesian approach. SPECIES obtains bulk parameters that are in good agreement with measured values from different existing catalogues, including when different methods are used to derive them. We find excellent agreement with previous works that used similar methodologies. We find discrepancies in the chemical abundances for some elements with respect to other works, which could be produced by differences in $T_{\text{eff}}$, or in the line list or the atomic line data used to derive them. We also obtained analytic relations to describe the correlations between different parameters, and we implemented new methods to better handle these correlations, which provides a better description of the uncertainties associated with the measurements.Comment: 28 pages, 26 figures, resubmitted to A&

Variations on the adiabatic invariance: the Lorentz pendulum

We analyze a very simple variant of the Lorentz pendulum, in which the length is varied exponentially, instead of uniformly, as it is assumed in the standard case. We establish quantitative criteria for the condition of adiabatic changes in both pendula and put in evidence their substantially different physical behavior with regard to adiabatic invariance.Comment: To appear in American Journal of Physic

Social Security Disability Insurance, Medicare And Work: A Review of the SSDI and Medicare Rules Related to Work Activity. Guidelines for Proactively Using the SSDI and Medicare Work Incentives to Help Individuals with Disabilities Maximize Independence Through Work

This policy-to-practice brief will focus on issues related to benefits and work for the SSDI beneficiary. After first explaining what SSDI is and the differences between SSDI and SSI, we will explain two historical work disincentives: the substantial gainful activity (SGA) rule and the continuing disability review (CDR). We will then explore a number of work incentives or special rules that seek to encourage work by either allowing benefits to continue for limited periods while working (trial work period (TWP), extended period of eligibility (EPE)), or allow individuals to quickly return to benefits status when a work effort stops or wage levels dip below the SGA level (expedited reinstatement). We will also explain special rules for either ignoring some short-term employment efforts (unsuccessful work attempts) or reducing countable monthly wages to be measured against the SGA amount for the year in question (impairment related work expenses, subsidies, paid time off)