9,968 research outputs found
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 countryâs policies and institutions may increase Chileâs 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
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 . 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
-primitiveness, which is shown to be equivalent to the one already in the
literature.Comment: Latex, 24 pages. Submitted to Commun. Math. Phy
Parasitized mates increase infection risk for partners
Peer reviewedPublisher PD
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
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 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 âsocial bufferingâ. 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
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