SLED Phenomenology: Curvature vs. Volume

We assess the question whether the SLED (Supersymmetric Large Extra Dimensions) model admits phenomenologically viable solutions with 4D maximal symmetry. We take into account a finite brane width and a scale invariance (SI) breaking dilaton-brane coupling, both of which should be included in a realistic setup. Provided that the microscopic size of the brane is not tuned much smaller than the fundamental bulk Planck length, we find that either the 4D curvature or the size of the extra dimensions is unacceptably large. Since this result is independent of the dilaton-brane couplings, it provides the biggest challenge to the SLED program. In addition, to clarify its potential with respect to the cosmological constant problem, we infer the amount of tuning on model parameters required to obtain a sufficiently small 4D curvature. A first answer was recently given in [arXiv:1508.01124], showing that 4D flat solutions are only ensured in the SI case by imposing a tuning relation, even if a brane-localized flux is included. In this companion paper, we find that the tuning can in fact be avoided for certain SI breaking brane-dilaton couplings, but only at the price of worsening the phenomenological problem. Our results are obtained by solving the full coupled Einstein-dilaton system in a completely consistent way. The brane width is implemented using a well-known ring regularization. In passing, we note that for the couplings considered here the results of [arXiv:1508.01124] (which only treated infinitely thin branes) are all consistently recovered in the thin brane limit, and how this can be reconciled with the concerns about their correctness, recently brought up in [arXiv:1509.04201].Comment: 28 pages, 4 figure

Brane Induced Gravity: From a No-Go to a No-Ghost Theorem

Numerous claims in the literature suggest that gravity induced on a higher co-dimensional surface violates unitarity in the weak coupling regime. However, it remained unclear, why a conserved source localized on this surface and giving rise to an induced gravity term at low energies would absorb and emit the associated ghost, given a consistent source-free theory. In this article it is shown that the appearance of the induced Einstein Hilbert term does not threaten the unitarity of the theory. The physics arguments behind this statement are presented in a semi-covariant language, but the detailed proof is given using Dirac's constraint analysis. It is shown that the would-be ghost highlighted in previous works is non-dynamical and therefore not associated with a state in the Hilbert space. As a result of these investigations, brane induced gravity goes without a ghost, opening an exciting window of opportunity for consistent deformations of gravity at the largest observable distances.Comment: 13 pages, v2: matches version published in Physical Review

Element distribution and noble gas isotopic abundances in lunar meteorite Allan Hills A81005

Antarctic meteorite ALLAN HILLS A81005, an anorthositic breccia, is recognized to be of lunar origin. The noble gases in this meteorite were analyzed and found to be solar-wind implanted gases, whose absolute and relative concentrations are quite similar to those in lunar regolith samples. A sample of this meteorite was obtained for the analysis of the noble gas isotopes, including Kr(81), and for the determination of the elemental abundances. In order to better determine the volume derived from the surface correlated gases, grain size fractions were prepared. The results of the instrumental measurements of the gamma radiation are listed. From the amounts of cosmic ray produced noble gases and respective production rates, the lunar surface residence times were calculated. It was concluded that the lunar surface time is about half a billion years

Natural braneworlds in six dimensions and the cosmological constant problem

The observed accelerated expansion of the universe is successfully parameterized by a cosmological constant. However, since this parameter in Einstein's equations is not protected against quantum corrections, the observed and theoretically expected value vastly differ, thus giving rise to the cosmological constant problem. In this thesis, the issue is addressed by embedding our universe--represented by a brane--in a six-dimensional bulk spacetime, where the cosmological constant plays the role of a brane tension, which then no longer needs to imply an expansion of the three apparent spatial dimensions; rather, it curves the extra space and hence stays hidden from a brane observer. In this context, the crucial question is whether this so-called degravitation mechanism may be implemented in a phenomenologically viable and 't Hooft natural way. Corresponding answers will be given in the case of four different models. The main part of this thesis has its focus on the 6D brane induced gravity model--a higher-dimensional generalization of the Dvali-Gabadadze-Porrati model--according to which a brane with sub-critical tension curves the bulk into a cone of infinite spatial extent. First, it is shown that the model is free of ghost instabilities only if the tension is not unnaturally small. This in turn opens a window of opportunity to study theoretically consistent modified cosmologies. In this context, it is shown that a homogeneous and isotropic brane acts as an antenna that emits and absorbs cylindrically symmetric Einstein-Rosen waves. We encounter two interesting types of solutions--sub-critical ones, which feature dynamical degravitation but are incompatible with observations, as well as compact super-critical ones, which still might be phenomenologically viable but certainly not technically natural. While this clearly shows that the cosmological constant problem cannot be solved in a 6D version of the model, our results point towards higher-dimensional constructions as the remaining playground for future research. Next, we introduce a new two-brane model where a thick super-critical brane curves the extra space into a cigar that closes in a microscopically thin sub-critical brane, representing our universe. In the case both branes only host a tension, we derive fully analytic solutions, which correspond to a de Sitter phase on our brane and are hence phenomenologically promising. Unfortunately, as a fine-tuning of the brane tension is required, they are not technically natural. The failure is attributed to the compactness of the extra space. To further exemplify the virtue of infinite volume extra dimensions, we devise a hybrid model where the brane is wrapped around an infinitely long cylinder of microscopic width. This construction turns out to be the minimal setup that features bulk waves as a dynamical ingredient of a modified cosmology. We find that, due to the existence of an infinitely large dimension, the system admits a degravitating solution. While being conceptually interesting, a supernova fit shows that the corresponding 4D cosmology cannot describe our universe. Finally, we turn to the model of supersymmetric large extra dimensions that had been claimed to successfully address the cosmological constant problem. Here, a Maxwell flux stabilizes the extra space that has the shape of a rugby ball. We critically review the corresponding mechanism, and find that a vanishing brane curvature--as required by the degravitation idea--is only ensured by a scale invariant brane sector, which however leads to an unavoidable parameter constraint due to a flux quantization condition. In a second step, we generalize our analysis to solutions that admit a de Sitter phase on the brane. Provided the model parameters are not tuned, we find that either the brane curvature or the volume of the extra space exceeds its phenomenological bound by many orders of magnitude. Our results significantly narrow down the search for solutions of the cosmological constant problem in the realm of extra-dimensional scenarios. In particular, models with infinite volume extra dimensions are found to offer a working mechanism, which yet requires refinement to comply with the observational bounds

Artrite e movimento

Bewegen ist ein zentrales Element für einen erfolgreichen Umgang mit einer rheumatoiden Arthritis (RA). Bewegen reduziert Schmerzen, Einschränkungen an Gelenken und Muskulatur, verbessert die Alltagsbewältigung, steigert allgemein die Gesundheit, das Wohlbefinden und die Fitness und hat damit einen grossen Einfluss auf die Lebensqualität. Gemäss neuer Forschung kann Bewegen sogar die Entzündung direkt positiv beeinflussen. Bewegen ist Medizin!Bouger est un élément essentiel pour bien gérer la polyarthrite rhumatoïde (PR). L’activité physique atténue les douleurs, améliore la motricité au niveau des muscles et des articulations, ainsi que la gestion du quotidien ou encore la santé, le bien-être et la forme en général, ce qui a donc une grande influence sur la qualité de vie. Selon les recherches récentes, le fait de bouger pourrait même avoir un effet positif directement sur l’inflammation. Bouger, c’est soigner!Il movimento è un tassello fondamentale per gestire efficacemente l’artrite reumatoide (AR). Muoversi riduce i dolori, le limitazioni articolari e muscolari, semplifica lo svolgimento delle attività quotidiane, migliora le condizioni generali di salute, il benessere e la forma fisica ed è pertanto determinante per la qualità di vita. Le più recenti ricerche mostrano che il movimento può addirittura influenzare direttamente e positivamente la flogosi. Muoversi è un toccasana