Perspectives on the Budget Surplus

This paper provides alternative measures of federal budget surpluses over 10-year and long-term horizons. Official baseline budget forecasts are based on a series of statutory requirements that may be at variance with reasonable expectation. More plausible notions of current policy toward discretionary spending, taxes and retirement trust funds imply that surpluses over the next 10 years will be substantially smaller than the baseline forecasts indicate. Properly accounting for long-term imbalances in social security and the rest of the budget implies that, under plausible definitions of current policy, the federal government faces a long-term shortfall.

Hierarchical mean-field approach to the J1J_1-J2J_2 Heisenberg model on a square lattice

We study the quantum phase diagram and excitation spectrum of the frustrated $J_1$-$J_2$ spin-1/2 Heisenberg Hamiltonian. A hierarchical mean-field approach, at the heart of which lies the idea of identifying {\it relevant} degrees of freedom, is developed. Thus, by performing educated, manifestly symmetry preserving mean-field approximations, we unveil fundamental properties of the system. We then compare various coverings of the square lattice with plaquettes, dimers and other degrees of freedom, and show that only the {\it symmetric plaquette} covering, which reproduces the original Bravais lattice, leads to the known phase diagram. The intermediate quantum paramagnetic phase is shown to be a (singlet) {\it plaquette crystal}, connected with the neighboring N\'eel phase by a continuous phase transition. We also introduce fluctuations around the hierarchical mean-field solutions, and demonstrate that in the paramagnetic phase the ground and first excited states are separated by a finite gap, which closes in the N\'eel and columnar phases. Our results suggest that the quantum phase transition between N\'eel and paramagnetic phases can be properly described within the Ginzburg-Landau-Wilson paradigm.Comment: LaTeX 2e, 14 pages, 17 figure

Nearby Doorways, Parity Doublets and Parity Mixing in Compound Nuclear States

We discuss the implications of a doorway state model for parity mixing in compound nuclear states. We argue that in order to explain the tendency of parity violating asymmetries measured in $^{233}$Th to have a common sign, doorways that contribute to parity mixing must be found in the same energy neighbourhood of the measured resonance. The mechanism of parity mixing in this case of nearby doorways is closely related to the intermediate structure observed in nuclear reactions in which compound states are excited. We note that in the region of interest ($^{233}$Th) nuclei exhibit octupole deformations which leads to the existence of nearby parity doublets. These parity doublets are then used as doorways in a model for parity mixing. The contribution of such mechanism is estimated in a simple model.Comment: 11 pages, REVTE

Response of two loci to interaction treatment

Response of two loci to interaction treatmen

Itinerant ferromagnetism in a two-dimensional atomic gas

Motivated by the first experimental evidence of ferromagnetic behavior in a three-dimensional ultracold atomic gas, we explore the possibility of itinerant ferromagnetism in a trapped two-dimensional atomic gas. Firstly, we develop a formalism that demonstrates how quantum fluctuations drive the ferromagnetic reconstruction first order, and consider the consequences of an imposed population imbalance. Secondly, we adapt this formalism to elucidate the key experimental signatures of ferromagnetism in a realistic trapped geometry.Comment: Accepted for publication in Phys. Rev.

Differences in dose-effect curves for UV-induced reverse mutations at two different loci

Differences in dose-effect curves for UV-induced reverse mutations at two different loc

Neutrino-nucleus reactions on ^{12}C and ^{16}O

Exclusive and inclusive $(\nu_\mu, \mu^-), (\nu_e, e^-)$ cross-sections and $\mu^-$-capture rates are calculated for ^{12}C and ^{16}O using the consistent random phase approximation (RPA) and pairing model. After a pairing correction is introduced to the RPA results the flux-averaged theoretical $(\nu_\mu, \mu^-), (\nu_e, e^-)$ cross-sections and $\mu^-$-capture rates in $^{12}$C are in good agreement with experiment. In particular when one takes into account the experimental error bars, the recently measured range of values for the $(\nu_\mu, \mu^-)$ cross-section is in agreement with the present theoretical results. Predictions of $(\nu_\mu, \mu^-)$ and $(\nu_e, e^-)$ cross-sections in ^{16}O are also presented.Comment: 13 pages, Revte

Distribution of Resonance Widths and Dynamics of Continuum Coupling

We analyze the statistics of resonance widths in a many-body Fermi system with open decay channels. Depending on the strength of continuum coupling, such a system reveals growing deviations from the standard chi-square (Porter-Thomas) width distribution. The deviations emerge from the process of increasing interaction of intrinsic states through common decay channels; in the limit of perfect coupling this process leads to the super-radiance phase transition. The width distribution depends also on the intrinsic dynamics (chaotic vs regular). The results presented here are important for understanding the recent experimental data concerning the width distribution for neutron resonances in nuclei.Comment: 5 pages, submitted to Phys. Rev. Let