Four-boson bound states from a functional renormalisation group

We use the functional renormalisation group to study the spectrum of three- and four-body states in bosonic systems around the unitary limit. Our effective action includes all energy-independent contact interactions in the four-atom sector and we introduce a running trimer field to eliminate couplings that involve the atom-atom-dimer channel. The results show qualitatively similar behaviour to those from exact approaches. The truncated action we use leads to overbinding of the two four-body states seen in those treatments. It also generates a third state, although only for a very narrow range of two-body scattering lengths.Comment: 4 pages, 2 figure

Export growth and diversification : the case of Peru

The rapid growth of exports since the early 1990s is a central feature in the extraordinary rise of Peru's economy in recent years. This study puts a lens on this export growth episode, with special attention to two issues. The first one is the role of international price levels as well as export volumes in explaining this growth. The second one is whether Peru has seen a diversification of its exports during this growth episode. The empirical analysis finds that although the increase in international mineral prices has exerted a significant impact in recent years, much of the growth of Peru's export revenues has also been related to an increase in volumes. This finding applies to traditional and non- traditional exports, although the importance of volumes is more predominant for the latter. The analysis does not reveal a trend toward greater diversification of Peru's exports since 1993. On the contrary, some of the evidence suggests that the rises in price and volumes in the mining components could be leading to greater concentration. Nonetheless, there is a clear trend toward diversification among non-traditional exports due to the significant emergence of new export products in recent years.Economic Theory&Research,Achieving Shared Growth,Agribusiness&Markets,Markets and Market Access,Tax Law

Interactive mixture of inhomogeneous dark fluids driven by dark energy: a dynamical systems analysis

We examine the evolution of an inhomogeneous mixture of non-relativistic pressureless cold dark matter (CDM), coupled to dark energy (DE) characterised by the equation of state parameter $w<-1/3$, with the interaction term proportional to the DE density. This coupled mixture is the source of a spherically symmetric Lema\^\ itre-Tolman-Bondi (LTB) metric admitting an asymptotic Friedman-Lema\^\ itre-Robertson-Walker (FLRW) background. Einstein's equations reduce to a 5-dimensional autonomous dynamical system involving quasi--local variables related to suitable averages of covariant scalars and their fluctuations. The phase space evolution around the critical points (past/future attractors and five saddles) is examined in detail. For all parameter values and both directions of energy flow (CDM to DE and DE to CDM) the phase space trajectories are compatible with a physically plausible early cosmic times behaviour near the past attractor. This result compares favourably with mixtures with the interaction driven by the CDM density in which conditions for a physically plausible past evolution are more restrictive. Numerical examples are provided describing the evolution of an initial profile that can be associated with idealised structure formation scenariosComment: 23 pages, IOP format, 8 figure

The Political Economy of Exchange Rate Policy in Colombia

This paper looks into the political economy forces that helped shape exchange rate policy in Colombia since the early 1960s. As witnessed by the remarkable longevity of the managed crawl, Colombian exchange rate policies since 1967 did not take the form of major regime changes. Policy shifts came about through variations in the rate of crawl, varying degrees of administrative restrictions on capital flows and, on occasions, ad-hoc measures to generate multiple exchange rates.

Reviving keV sterile Neutrino Dark Matter

We propose a new production mechanism for keV sterile neutrino dark matterwhich relies neither on the oscillations between sterile and active neutrinosnor on the decay of additional heavier particles. The dark matter neutrinos areinstead produced by thermal freeze-out, much like a typical WIMP. The challengeconsists in balancing a large Yukawa coupling so that the sterile neutrinosthermalize in the early universe on the one hand, and a small enough Yukawacoupling such that they are stable on cosmological scales on the other. Wesolve this problem by implementing varying Yukawa couplings. We achieve this byusing a three-sterile neutrino seesaw extension to the SM and embedding it in aFroggatt-Nielsen model with a single flavon. Because the vev of the flavonchanges during the electroweak phase transition, the effective Yukawa couplingsof the fermions have different values before and after the phase transition,thus allowing for successful dark matter genesis. Additionally, the hierarchyin the flavour structure is alleviated and the origin of the light neutrinomasses are explained by the interplay of the seesaw and Froggatt-Nielsenmechanisms.<br