Signature change events: A challenge for quantum gravity?

Within the framework of either Euclidian (functional-integral) quantum gravity or canonical general relativity the signature of the manifold is a priori unconstrained. Furthermore, recent developments in the emergent spacetime programme have led to a physically feasible implementation of signature change events. This suggests that it is time to revisit the sometimes controversial topic of signature change in general relativity. Specifically, we shall focus on the behaviour of a quantum field subjected to a manifold containing regions of different signature. We emphasise that, regardless of the underlying classical theory, there are severe problems associated with any quantum field theory residing on a signature-changing background. (Such as the production of what is naively an infinite number of particles, with an infinite energy density.) From the viewpoint of quantum gravity phenomenology, we discuss possible consequences of an effective Lorentz symmetry breaking scale. To more fully understand the physics of quantum fields exposed to finite regions of Euclidean-signature (Riemannian) geometry, we show its similarities with the quantum barrier penetration problem, and the super-Hubble horizon modes encountered in cosmology. Finally we raise the question as to whether signature change transitions could be fully understood and dynamically generated within (modified) classical general relativity, or whether they require the knowledge of a full theory of quantum gravity.Comment: 33 pages. 4 figures; V2: 3 references added, no physics changes; V3: now 24 pages - significantly shortened - argument simplified and more focused - no physics changes - this version accepted for publication in Classical and Quantum Gravit

Preliminary data on the distribution of species and forms of the Anopheles gambiae complex (Diptera: Culicidae) at sites of Angola.

Parassitologia, 46 (Suppl.1): 85

Distribution and chromosomal characterization of the anopheles gambiae complex in Angola

Mosquitoes of the Anopheles gambiae complex (N = 1,336) were sampled (2001-2005) across Angola to identify taxa, study inversion polymorphisms, and detect the circumsporozoite protein of Plasmodium falciparum. Anopheles gambiae s.s. was found in all sites; it was characterized as M-form in localities of the tropical dry and semi-desertic belts, whereas the S-form was predominant in comparatively more humid and less anthropized sites. Both forms were characterized by low degrees of chromosomal polymorphism based solely on the 2La inversion, a pattern usually associated with An. gambiae populations from forested, humid, and derived savanna areas. Unexpectedly, this pattern was also observed in M-form populations collected in dry/pre-desertic areas, where this form largely predominates over An. arabiensis, which was also detected in central/inland sites. Anopheles melas was found in northern coastal sites. Three of 534 An. gambiae s.s. were positive for P. falciparum CS-protein, whereas none of the 1.05 An. melas were positive