Massive Gravity on a Brane

At present no theory of a massive graviton is known that is consistent with experiments at both long and short distances. The problem is that consistency with long distance experiments requires the graviton mass to be very small. Such a small graviton mass however implies an ultraviolet cutoff for the theory at length scales far larger than the millimeter scale at which gravity has already been measured. In this paper we attempt to construct a model which avoids this problem. We consider a brane world setup in warped AdS spacetime and we investigate the consequences of writing a mass term for the graviton on a the infrared brane where the local cutoff is of order a large (galactic) distance scale. The advantage of this setup is that the low cutoff for physics on the infrared brane does not significantly affect the predictivity of the theory for observers localized on the ultraviolet brane. For such observers the predictions of this theory agree with general relativity at distances smaller than the infrared scale but go over to those of a theory of massive gravity at longer distances. A careful analysis of the graviton two-point function, however, reveals the presence of a ghost in the low energy spectrum. A mode decomposition of the higher dimensional theory reveals that the ghost corresponds to the radion field. We also investigate the theory with a brane localized mass for the graviton on the ultraviolet brane, and show that the physics of this case is similar to that of a conventional four dimensional theory with a massive graviton, but with one important difference: when the infrared brane decouples and the would-be massive graviton gets heavier than the regular Kaluza--Klein modes, it becomes unstable and it has a finite width to decay off the brane into the continuum of Kaluza-Klein states.Comment: 26 pages, LaTeX. v2: extended version with an appendix added about non Fierz-Pauli mass terms. Few typos corrected. Final version appeared in PR

Quasilocalized gravity without asymptotic flatness

We present a toy model of a generic five-dimensional warped geometry in which the 4D graviton is not fully localized on the brane. Studying the tensor sector of metric perturbation around this background, we find that its contribution to the effective gravitational potential is of 4D type (1/r) at the intermediate scales and that at the large scales it becomes 1/r^{1+alpha}, 0<alpha=< 1 being a function of the parameters of the model (alpha=1 corresponds to the asymptotically flat geometry). Large-distance behavior of the potential is therefore not necessarily five-dimensional. Our analysis applies also to the case of quasilocalized massless particles other than graviton.Comment: 9 pages, 1 figure; to be published in Phys. Rev.

Human occupation and paleoenvironments in South America: expanding the notion of an “Archaic Gap”

Uma revisão das informações arqueológicas produzidas no Brasil e países vizinhos durante as últimas décadas, aliada a uma análise de estudos paleoambientais recentes, sugerem que durante o Holoceno Médio amplas áreas da América do Sul deixaram de ser ocupadas por grupos humanos. Dados independentes, como datações de esqueletos humanos, estratigrafia de abrigos rochosos e cronologia de sítios arqueológicos a céu aberto convergem para a idéia de que tais áreas foram, no mínimo, fortemente depopuladas. Dados paleoambientais sugerem que eventos de seca constituíram a principal causa por trás das tendências observadas. Nossas conclusões expandem a noção já existente de que estresses climáticos têm um papel importante na conformação de assentamentos humanos em ambientes marginais, como desertos e altitudes elevadas, mostrando que o mesmo pode ocorrer nas terras baixas tropicais e subtropicais.An overview of the archaeological data produced in the last decades for Brazil and neighbouring countries, coupled with a background of recent studies on paleoenvironments, suggests that during the mid-Holocene vast areas of South America ceased to be occupied by human groups. Independent data coming from dated human skeletons, rockshelter stratigraphy, and chronology of open-air sites converge to the idea that these areas were, at least, strongly depopulated. Paleoenvironmental data suggest that dryness events constitute the major cause behind the observed trends. Our conclusions expand the already perceived notion that climatic stresses had a major role in the shaping of human settlement patterns in marginal environments, such as deserts and high-altitude settings, showing that the same can occur in tropical and subtropical lowlands

Stability of the Higgs mass in theories with extra dimensions

We analyze the ultraviolet stability of the Higgs mass in recently proposed Kaluza-Klein models compactified on S_1/Z_2 or S_1/(Z_2\times Z_2'), both at the field theory and string theory level. Fayet-Iliopoulos terms of U(1) hypercharge are shown to be of vital importance for this discussion. Models with a single Higgs doublet seem to be generically affected by quadratic divergences.Comment: Contribution to the Proceedings of Durham IPPP meeting May 2001.(12 pages, LaTeX

Passive galaxies in the early Universe: ALMA confirmation of z~3-5 candidates in the CANDELS GOODS-South field

The selection of red, passive galaxies in the early Universe is very challenging, especially beyond z~3, and it is crucial to constrain theoretical modelling of the processes responsible for their rapid assembly and abrupt shut-down of the star formation. We present here the analysis of ALMA archival observations of 26 out of the 30 galaxies in the deep CANDELS GOODS-South field that we identified as passive at z~3-5 by means of a careful and conservative SED fitting analysis. ALMA data are used to verify the potential contamination from red, dusty but star--forming sources that could enter the sample due to similar optical--nearIR colours. With the exception of a few marginal detections at <3sigma, we could only infer upper limits, both on individual sources and on the stacks. We translated the ALMA continuum measurements into corresponding SFRs, using a variety of far-IR models. These SFRs are compared with those predicted by secondary star-forming solutions of the optical fits and with the expected position of the star formation Main Sequence. This analysis confirms the passive nature of 9 candidates with high confidence and suggests that the classification is correct for at least half of the sample in a statistical sense. For the remaining sources the analysis remain inconclusive because available ALMA data is not deep enough, although the stacking results corroborate their passive nature. Despite the uncertainties, this work provides decisive support to the existence of passive galaxies beyond z~3.Comment: Accepted for publication by MNRA

Unitarity constraints on the stabilized Randall-Sundrum scenario

Recently proposed stabilization mechanism of the Randall-Sundrum metric gives rise to a scalar radion, which couples universally to matter with a weak interaction ($\simeq 1$ TeV) scale. Demanding that gauge boson scattering as described by the effective low enerrgy theory be unitary upto a given scale leads to significant constraints on the mass of such a radion.Comment: 10 page Latex 2e file including 4 postscript figures. Accepted in Journal of Physics

More about spontaneous Lorentz-violation and infrared modification of gravity

We consider a model with Lorentz-violating vector field condensates, in which dispersion laws of all perturbations, including tensor modes, undergo non-trivial modification in the infrared. The model is free of ghosts and tachyons at high 3-momenta. At low 3-momenta there are ghosts, and at even lower 3-momenta there exist tachyons. Still, with appropriate choice of parameters, the model is phenomenologically acceptable. Beyond a certain large distance scale and even larger time scale, the gravity of a static source changes from that of General Relativity to that of van Dam--Veltman--Zakharov limit of the Fierz--Pauli theory. Yet the late time cosmological evolution is always determined by the standard Friedmann equation, modulo small correction to the ``cosmological Planck mass'', so the modification of gravity cannot by itself explain the accelerated expansion of the Universe. We argue that the latter property is generic in a wide class of models with condensates.Comment: 15 pages, 1 figure, JHEP3.cls; Added reference

Thyroid Hormones in Pregnancy in Relation to Environmental Exposure to Organochlorine Compounds and Mercury

Polychlorinated biphenyls (PCBs), chlorinated pesticides, and mercury are global environmental contaminants that can disrupt the endocrine system in animals and humans. However, there is little evidence that they can interfere with endocrine status in pregnant women and neonates at low levels of exposure. The aim of this study was to examine thyroid hormone levels during pregnancy and in cord blood in relation to blood concentrations of organochlorine compounds (OCs) and Hg in healthy women recruited during pregnancy. We found a significant negative correlation between maternal total triiodothyronine levels and three non-coplanar congeners (PCB-138, PCB-153, and PCB-180), three pesticides (p,p′-DDE, cis-nanochlor, and hexachlorobenzene), and inorganic Hg independently, without any other changes in thyroid status. No significant relationships were observed between OCs and cord serum thyroid hormones. Cord serum free thyroxin was negatively correlated with inorganic Hg. These results suggest that at even low levels of exposure, persistent environmental contaminants can interfere with thyroid status during pregnancy

Evaluation of the efficacy of anthelminthic treatments against sheep gastro-intestinal nematodes in Sardinia

Despite the rising of new methodologies for the controi of endoparasites in animais of zootechnic value, such as phytotherapy, homeopathy, and genetie selection for screening of resistant individuais (Gruner L, 2002, Acta SIPAOC, 15: 80-89; Carta A, Scala A, 2004, Parassitologia, 46: 251-255) and hypothetic vaccinations against NGI (Vercruysse J, 2004, Parassitologia, 46: 261), anthelminthie treatments stilI remains the most applied measure in the field

Wave Function of the Radion in the dS and AdS Brane Worlds

We study the linearized metric perturbation corresponding to the radion for the generalization of the five dimensional two brane setup of Randall and Sundrum to the case when the curvature of each brane is locally constant but non-zero. We find the wave fuction of the radion in a coordinate system where each brane is sitting at a fixed value of the extra coordinate. We find that the radion now has a mass$^2$, which is negative for the case of de Sitter branes but positive for anti de Sitter branes. We also determine the couplings of the radion to matter on the branes, and construct the four dimensional effective theory for the radion valid at low energies. In particular we find that in AdS space the wave function of the radion is always normalizable and hence its effects, though small, remain finite at arbitrarily large brane separations.Comment: Version which appears in Phys. Rev.