Convexity of the effective action from functional flows

We show that convexity of the effective action follows from its functional flow equation. Our analysis is based on a new, spectral representation. The results are relevant for the study of physical instabilities. We also derive constraints for convexity-preserving regulators within general truncation schemes including proper-time flows, and bounds for infrared anomalous dimensions of propagators.Comment: 4 pages, 3 figure

Productivity and Economic Growth: the Case of Chile

After a decade and a half of economic growth above 7% per year, the Chilean economy has been growing at rates below 3% during the last five years. In this article we suggest that in order to produce a new surge in economic growth, Chile needs a productivity shock arising from economic policy initiatives aimed at improving economic efficiency and institutions. Although Chile has a good record in both, it is still possible to have an upgrade. We run a cross section regression in which the dependent variable is total factor productivity. We conclude that modest changes in the country’s policies and institutions may increase Chile’s rate of growth in 1.5 percent points.

Normal Coordinates and Primitive Elements in the Hopf Algebra of Renormalization

We introduce normal coordinates on the infinite dimensional group $G$ introduced by Connes and Kreimer in their analysis of the Hopf algebra of rooted trees. We study the primitive elements of the algebra and show that they are generated by a simple application of the inverse Poincar\'e lemma, given a closed left invariant 1-form on $G$. For the special case of the ladder primitives, we find a second description that relates them to the Hopf algebra of functionals on power series with the usual product. Either approach shows that the ladder primitives are given by the Schur polynomials. The relevance of the lower central series of the dual Lie algebra in the process of renormalization is also discussed, leading to a natural concept of $k$-primitiveness, which is shown to be equivalent to the one already in the literature.Comment: Latex, 24 pages. Submitted to Commun. Math. Phy

Effect of the nearby levels on the resonance fluorescence spectrum of the atom-field interaction

We study the resonance fluorescence in the Jaynes-Cummings model when nearby levels are taking into account. We show that the Stark shift produced by such levels generates a displacement of the peaks of the resonance fluorescence due to an induced effective detuning and also induces an asymmetry. Specific results are presented assuming a coherent and a thermal fields

Parasitized mates increase infection risk for partners

Peer reviewedPublisher PD

Real sector of the nonminimally coupled scalar field to self-dual gravity

A scalar field nonminimally coupled to gravity is studied in the canonical framework, using self-dual variables. The corresponding constraints are first class and polynomial. To identify the real sector of the theory, reality conditions are implemented as second class constraints, leading to three real configurational degrees of freedom per space point. Nevertheless, this realization makes non-polynomial some of the constraints. The original complex symplectic structure reduces to the expected real one, by using the appropriate Dirac brackets. For the sake of preserving the simplicity of the constraints, an alternative method preventing the use of Dirac brackets, is discussed. It consists of converting all second class constraints into first class by adding extra variables. This strategy is implemented for the pure gravity case.Comment: Latex file, 22 pages, no figure

The Kepler problem and non commutativity

We investigate the Kepler problem using a symplectic structure consistent with the commutation rules of the noncommutative quantum mechanics. We show that a noncommutative parameter of the order of $10^{-58} \text m^2$ gives observable corrections to the movement of the solar system. In this way, modifications in the physics of smaller scales implies modifications at large scales, something similar to the UV/IR mixing.Comment: 10 page

Social buffering of brain cell proliferation and behavioral responses to tail injury in weakly electric fish, Apteronotus leptorhynchus

Social interactions can mitigate the damaging effects of threatening stimuli, a phenomenon termed ‘social buffering’. In two different forms of social buffering, social interactions reduce stress-induced decreases in brain cell proliferation and enhance recovery from somatic injury. However, the positive effects of social interactions on the brain cell proliferation response to somatic injury have not been extensively examined. Here, I investigated the social buffering of the brain cell proliferation response to tail injury in an electric fish, Apteronotus leptorhynchus. I ask three major questions: 1) Does social interaction mitigate the decrease in brain cell proliferation caused by simulated predatory tail injury?; 2) Does the timing of social interaction relative to injury alter this social buffering response?; and 3) Does tail injury modify affiliation with a non-injured social partner? I mimicked predatory injury through experimental tail amputation, exposed fish to paired interactions that varied in timing, duration, and recovery period, and measured cell proliferation (PCNA+ cell density) in the forebrain and midbrain. I also measured social affiliation based on the position of fish in retreat sites located near or distant to a stimulus fish. Social interaction either before or after tail amputation mitigated the negative effects of tail injury on brain cell proliferation. This buffering effect was specific to the forebrain and occurred after short-term (1 d) or long-term (7 d) recovery periods following tail amputation. However, social interaction both before (4 d) and after (7 d) tail amputation produced an even greater buffering effect in localized regions of the forebrain and midbrain. Similarly, fish exposed to social interaction both before and after tail amputation sought close affiliation with non-injured stimulus fish, but this effect did not occur in fish exposed to social interaction only after injury. Thus, despite the social buffering response on brain cell proliferation, it remains unclear whether fish modify their affiliation behavior in response to tail injury