Hyperfine Populations Prior to Muon Capture

It is shown that the 1S level hyperfine populations prior to muon capture will be statistical when either target or beam are unpolarised independent of the atomic level at which the hyperfine interaction becomes appreciable. This assertion holds in the absence of magnetic transitions during the cascade and is true because of minimal polarisation after atomic capture and selective feeding during the cascade.Comment: (revtex, 6 preprint pages, no figures

Final state interaction effects in mu-capture induced two-body decay of 3He

The mu-capture process on 3He leading to a neutron, a deuteron and a mu-neutrino in the final state is studied. Three-nucleon Faddeev wave functions for the initial 3He bound and the final neutron-deuteron scattering states are calculated using the BonnB and Paris nucleon-nucleon potentials. The nuclear weak current operator is restricted to impulse approximation. Large effects on the decay rates of the final state interaction are found. The comparison to recent experimental data shows that the inclusion of final state interactions drastically improves the description of the data.Comment: 14 pages, 6 eps figure

The Axial-Vector Current in Nuclear Many-Body Physics

Weak-interaction currents are studied in a recently proposed effective field theory of the nuclear many-body problem. The Lorentz-invariant effective field theory contains nucleons, pions, isoscalar scalar ($\sigma$) and vector ($\omega$) fields, and isovector vector ($\rho$) fields. The theory exhibits a nonlinear realization of $SU(2)_L \times SU(2)_R$ chiral symmetry and has three desirable features: it uses the same degrees of freedom to describe the axial-vector current and the strong-interaction dynamics, it satisfies the symmetries of the underlying theory of quantum chromodynamics, and its parameters can be calibrated using strong-interaction phenomena, like hadron scattering or the empirical properties of finite nuclei. Moreover, it has recently been verified that for normal nuclear systems, it is possible to systematically expand the effective lagrangian in powers of the meson fields (and their derivatives) and to reliably truncate the expansion after the first few orders. Here it is shown that the expressions for the axial-vector current, evaluated through the first few orders in the field expansion, satisfy both PCAC and the Goldberger--Treiman relation, and it is verified that the corresponding vector and axial-vector charges satisfy the familiar chiral charge algebra. Explicit results are derived for the Lorentz-covariant, axial-vector, two-nucleon amplitudes, from which axial-vector meson-exchange currents can be deduced.Comment: 32 pages, REVTeX 4.0 with 12pt.rtx, aps.rtx, revsymb.sty, revtex4.cls, plus 14 figures; two sentences added in Summary; two references adde

Theoretical Study of the ^3He(mu^-,nu_mu)^3H Capture

The ^3He(mu^-,nu_mu)^3H weak capture is studied using correlated-hyperspherical-harmonics wave functions, obtained from realistic Hamiltonians consisting of the Argonne $v_{14}$ or Argonne $v_{18}$ two-nucleon, and Tucson-Melbourne or Urbana-IX three-nucleon interactions. The nuclear weak charge and current operators have vector and axial-vector components that include one- and two-body contributions. The strength of the leading two-body operator in the axial-vector current is adjusted to reproduce the Gamow-Teller matrix element in tritium $\beta$-decay. The calculated total capture rate is in excellent agreement with the most recent experimental determination $1496\pm 4$ sec$^{-1}$, when the PCAC value is adopted for the induced pseudo-scalar coupling constant $g_{PS}$. The predictions for the capture rate and angular correlation parameters $A_v$, $A_t$, and $A_\Delta$ are found to be only very weakly dependent on the model input Hamiltonian. The variation of these observables with $g_{PS}$ and the theoretical uncertainties deriving from the model-dependent procedure used to constrain the axial current are investigated.Comment: 16 pages, 1 figure, submitted to PR

Induced pseudoscalar coupling of the proton weak interaction

The induced pseudoscalar coupling $g_p$ is the least well known of the weak coupling constants of the proton's charged--current interaction. Its size is dictated by chiral symmetry arguments, and its measurement represents an important test of quantum chromodynamics at low energies. During the past decade a large body of new data relevant to the coupling $g_p$ has been accumulated. This data includes measurements of radiative and non radiative muon capture on targets ranging from hydrogen and few--nucleon systems to complex nuclei. Herein the authors review the theoretical underpinnings of $g_p$, the experimental studies of $g_p$, and the procedures and uncertainties in extracting the coupling from data. Current puzzles are highlighted and future opportunities are discussed.Comment: 58 pages, Latex, Revtex4, prepared for Reviews of Modern Physic

Governments, decentralisation, and the risk of electoral defeat

<p>In the last three decades several countries around the world have transferred authority from their national to their regional governments. However, not all their regions have been empowered to the same degree and important differences can be observed between and within countries. Why do some regions obtain more power than others? Current literature argues that variation in the redistribution of power and resources between regions is introduced by demand. Yet these explanations are conditional on the presence of strong regionalist parties or territorial cleavages. This article proposes instead a theory that links the government’s risk of future electoral defeat with heterogeneous decentralisation, and tests its effects using data from 15 European countries and 141 regions. The results provide evidence that parties in government protect themselves against the risk of electoral defeat by selectively targeting decentralisation towards regions in which they are politically strong. The findings challenge previous research that overestimates the importance of regionalist parties while overlooking differences between regions.</p

The Collective Action Problem: Within-Group Cooperation and Between-Group Competition in a Repeated Rent-Seeking Game

This paper analyzes the ability of group members to cooperate in rent-seeking activities in a context of between-group competition. For this purpose, we develop an infinitely repeated rent-seeking game between two groups of different size. We first investigate Nash reversion strategies to support cooperative behavior in a given group before analyzing double-edge trigger strategies which have the property that cheating on the cooperative agreement in a given group is followed by non-cooperation in this group and cooperation in the rival group. The main conclusion is that the set of parameters for which cooperation can be sustained within the larger group as a subgame perfect outcome is as large as that for which cooperation can be sustained in the smaller group. Hence, in contrast with Olson’s (1965) celebrated thesis but in accordance with many informal and formal observations, the larger group is as effective as the smaller group in furthering its interest

An evolutionary approach to international political economy: the case of corporate tax avoidance

Corporate tax avoidance is both widespread and diverse in its practical mechanics. The scope of the phenomenon often leads economists to conclude that in the jungle of economic competition, tax planning (or optimisation) is among the necessary tools to ensure the survival of the fittest. This theory is increasingly associated with a Darwinian theory of economic evolution. In this paper, I develop a contrasting framework of the evolutionary political economy of corporate tax avoidance. Analysing core concepts of Old Institutionalist Economics (OIE), I examine the core drivers of corporate tax avoidance in a globalised system of states. The major contrast, I find, is between that of the corporate and legal personality and the institutional environment in which it operates. Historically, each corporate entity has been considered a separate legal person, yet a series of ‘mutations’ of incorporations laws created a widening gap between theory and reality, and these, in turn, give rise to tax arbitrage. Narrowing this gap, however, impinges on another venerable historical institution, the institution of sovereignty and sovereign inequality