Inflationary dynamics of kinetically-coupled gauge fields

We investigate the inflationary dynamics of two kinetically-coupled massless $U(1)$ gauge fields with time-varying kinetic-term coefficients. Ensuring that the system does not have strongly coupled regimes shrinks the parameter space. Also, we further restrict ourselves to systems that can be quantized using the standard creation, annihilation operator algebra. This second constraint limits us to scenarios where the system can be diagonalized into the sum of two decoupled, massless, vector fields with a varying kinetic-term coefficient. Such a system might be interesting for magnetogenesis because of how the strong coupling problem generalizes. We explore this idea by assuming that one of the gauge fields is the Standard Model $U(1)$ field and that the other dark gauge field has no particles charged under its gauge group. We consider whether it would be possible to transfer a magnetic field from the dark sector, generated perhaps before the coupling was turned on, to the visible sector. We also investigate whether the simple existence of the mixing provides more opportunities to generate magnetic fields. We find that neither possibility works efficiently, consistent with the well-known difficulties in inflationary magnetogenesis.Comment: 17 pages, 0 figures. Matches JCAP versio

Traversable Wormholes and Time Machines in non-minimally coupled curvature-matter f(R)f(R) theories

We obtain traversable wormhole and time machine solutions of the field equations of an alternative of gravity with non-minimally curvature-matter coupling. Our solutions exhibit a non-trivial redshift function and allow for matter that satisfy the dominant energy condition.Comment: Revtex4, 7 pages. Version to match the one to appear in Physical Review

Culturing Bursaphelenchus cocophilus in vitro and in vivo.

Red ring disease (RRD) is of particular importance in many African oil palms- and coconut-producing regions in Central and South America and the Caribbean. Its causal agent, the nematode Bursaphelenchus cocophilus (Cobb) Baujard, causes extensive damage to tissues in the plant trunk that typically leads to plant death within months. Nearly 100 years after its first report RRD remains understudied largely because the nematode cannot be cultured in vivo or in vitro, what hinders sustained research efforts on basic and applied aspects of the pathosystem. To overcome this problem we attempted in vivo culturing in coconut seedlings, paying attention to aspects that had been overlooked in previous trials. We also attempted in vitro culturing on several fungi endophytic to healthy and RRD-affected coconut trees. In the two in vivo assays performed we were able to recover hundreds of nematodes from the seedlings up to 60 days after inoculation, but the nematodes seemed unable to sustain parasitism in most seedlings. No nematode was recovered from the endophytic fungal cultures in neither of the two assays performed. Hence B. cocophilus continues to stand as the only obligatory plant-parasitic species of the speciose genus Bursaphelenchus and a somewhat intractable plant-parasitic nematode to study on

Central Government Transfers and Regional Convergence in Portugal

Over the last decades, the Portuguese economy exhibited an outstanding growth performance. This period of fast economic growth allowed the country to consistently reduce its income gap with respect to the EU average. In spite of this, regions in Portugal exhibited large differences between each other in terms of GDP per capita. Yet, the Portuguese government did make attempts at regional intervention by means of some policy instruments, namely public transfers to local (and regional) government. How successful these policies have been in terms of achieving their goal is still an open question, especially as far as Portuguese Central Government transfers are concerned. The main purpose of the paper is to evaluate if the system of Central Government transfers has affected the intra-regional Portuguese convergence. We haven’t found unquestionable evidence that these policies have been effective at stimulating convergence among Portuguese regions and at improving the overall economies of the poorer regions. Keywords: Regional convergence, Central Government transfers, Regional policy JEL Classification: H71; O18; R58