Polytropic spheres in Palatini f(R) gravity

We examine static spherically symmetric polytropic spheres in Palatini f(R) gravity and show that no regular solutions to the field equations exist for physically relevant cases such as a monatomic isentropic gas or a degenerate electron gas, thus casting doubt on the validity of Palatini f(R) gravity as an alternative to General Relativity.Comment: Talk given by EB at the 30th Spanish Relativity Meeting, 10 - 14 September 2007, Tenerife (Spain). Based on arXiv:gr-qc/0703132 and arXiv:0712.1141 [gr-qc

A no-go theorem for polytropic spheres in Palatini f(R) gravity

Non-vacuum static spherically-symmetric solutions in Palatini f(R) gravity are examined. It is shown that for generic choices of f(R), there are commonly-used equations of state for which no satisfactory physical solution of the field equations can be found within this framework, apart from in the special case of General Relativity, casting doubt on whether Palatini f(R) gravity can be considered as giving viable alternatives to General Relativity.Comment: 7 pages, 1 figure. Version accepted for publication as a Fast Track Communication in CQ

Two phase galaxy formation: The Evolutionary Properties of Galaxies

We use our model for the formation and evolution of galaxies within a two-phase galaxy formation scenario, showing that the high-redshift domain typically supports the growth of spheroidal systems, whereas at low redshifts the predominant baryonic growth mechanism is quiescent and may therefore support the growth of a disc structure. Under this framework we investigate the evolving galaxy population by comparing key observations at both low and high-redshifts, finding generally good agreement. By analysing the evolutionary properties of this model, we are able to recreate several features of the evolving galaxy population with redshift, naturally reproducing number counts of massive star-forming galaxies at high redshifts, along with the galaxy scaling relations, star formation rate density and evolution of the stellar mass function. Building upon these encouraging agreements, we make model predictions that can be tested by future observations. In particular, we present the expected evolution to z=2 of the super-massive black hole mass function, and we show that the gas fraction in galaxies should decrease with increasing redshift in a mass, with more and more evolution going to higher and higher masses. Also, the characteristic transition mass from disc to bulge dominated system should decrease with increasing redshift.Comment: 15 pages, 11 figures. Version polished for publication in MNRA

Post-Newtonian expansion for Gauss-Bonnet Gravity

The Parametrized Post-Newtonian expansion of gravitational theories with a scalar field coupled to the Gauss-Bonnet invariant is performed and confrontation of such theories with Solar system experiments is discussed.Comment: 4 pages; typos corrected, published versio

Non-singular Universes a la Palatini

It has recently been shown that f(R) theories formulated in the Palatini variational formalism are able to avoid the big bang singularity yielding instead a bouncing solution. The mechanism responsible for this behavior is similar to that observed in the effective dynamics of loop quantum cosmology and an f(R) theory exactly reproducing that dynamics has been found. I will show here that considering more general actions, with quadratic contributions of the Ricci tensor, results in a much richer phenomenology that yields bouncing solutions even in anisotropic (Bianchi I) scenarios. Some implications of these results are discussed.Comment: 4 pages, no figures. Contribution to the Spanish Relativity Meeting (ERE2010), 6-10 Sept. Granada, Spai

Posterior Jaw Rehabilitation Using Partial Prostheses Supported by Implants 4.0 X 4.0 Mm or Longer: Three-year Post- Loading Results of a Multicentre Randomised Controlled Trial

PURPOSE. To evaluate whether 4.0 x 4.0-mm dental implants could be viable alternatives to implants of length at least 8.5 mm when placed in posterior jaws with adequate bone volumes. MATERIALS AND METHODS. One hundred and fifty patients with posterior (premolar and molar areas) jaws having at least 12.5 mm bone height above the mandibular canal or 11.5 mm below the maxillary sinus, as applicable, were randomised according to a paral-lel-group design and received one to three 4.0 mm-long implants or one to three implants which were at least 8.5 mm-long at three treatment centres. All implants had a diameter of 4.0 mm. Implants were loaded with permanent screw-retained prostheses after 4 months. Patients were followed-up until 3-year post-loading, and outcome measures considered were prosthesis and implant failure, any complications, and changes in pe-ri-implant marginal bone levels. RESULTS. Seventy-five patients were randomly allocated to each group. Drop-outs at 3-year post-loading assessment were five patients from the long implant group and three from the short implant group. Up to 3 years post-loadings, three patients lost one 4.0 mm-long implant each, in comparison to two patients who lost one long implant each (difference in proportion =-0.013; 95% CI:-0.079 to 0.054; P = 1). All failures occurred before loading; failed implants were replaced, delaying delivery of two prostheses in each group by several months (difference in proportion = 0; 95% CI:-0.061 to 0.062; P = 1). Five short-implant patients experienced six complications versus the three complications seen in three long implant patients (difference in proportion =-0.026; 95% CI:-0.103 to 0.053; P = 0.719). There were no statistically significant differences between groups in prosthesis failures, implant failures or complications. Patients with short implants lost on average 0.55 mm of peri-implant bone, and patients with longer implants lost 0.61 mm. There were no statistically significant differences between short and long implants in bone level changes up to 3 years (mean difference = 0.05 mm; 95% CI:-0.05 to 0.16; P = 0.221). CONCLUSIONS. Outcomes 3 years after loading were similar with 4.0 x 4.0 mm-long implants and 8.5 x 4.0 mm or longer implants in posterior jaws, in the presence of adequate bone volumes. However, 5 to 10-year post-loading data will be necessary before reliable recommendations can be made. CONFLICT OF INTEREST STATEMENT. Global D (Brignais, France) partially supported this trial and donated the implants and prosthetic components. OsteoBiol (Tecnoss, Giaveno, Italy) donated the biomaterials used for bone augmentation. However, the data property belonged to the authors and neither Global D nor OsteoBiol interfered in any way with the conduct of the trial or the publication of the results

Can gravitational-wave memory help constrain binary black-hole parameters? A LISA case study

Besides the transient effect, the passage of a gravitational wave also causes a persistent displacement in the relative position of an interferometer’s test masses through the nonlinear memory effect. This effect is generated by the gravitational backreaction of the waves themselves, and encodes additional information about the source. In this work, we explore the implications of using this information for the parameter estimation of massive binary black holes with LISA. Based on a Fisher analysis for nonprecessing black hole binaries, our results show that the memory can help to reduce the degeneracy between the luminosity distance and the inclination for binaries observed only for a short time (∼few hours) before merger. To assess how many such short signals will be detected, we utilized state-of-the-art predictions for the population of massive black hole binaries and models for the gaps expected in the LISA data. We forecast from tens to few hundreds of binaries with observable memory, but only ∼Oð0.1Þ events in 4 years for which the memory helps to reduce the degeneracy between distance and inclination. Based on this, we conclude that the new information from the nonlinear memory, while promising for testing general relativity in the strong field regime, has probably a limited impact on further constraining the uncertainty on massive black hole binary parameters with LISA

A no-go theorem for slowly rotating black holes in Horava-Lifshitz gravity

We consider slowly rotating, stationary, axisymmetric black holes in the infrared limit of Horava-Lifshitz gravity. We show that such solutions do not exist, provided that they are regular everywhere apart from the central singularity. This has profound implications for the viability of the theory, considering the astrophysical evidence for the existence of black holes with non-zero spin. NOTE ADDED: A subtlety in the dynamical equivalence between Horava-Lifshitz gravity and Einstein-aether theory has been missed and this has seriously affected the conclusions of this paper. Please see arXiv:1212.1334 for a full discussionComment: 5 pages, 1 figure. Very minor changes to text (results unchanged) to match version accepted for publication in Phys. Rev. Let

Ultra-high-energy cosmic rays and neutrinos from tidal disruptions by massive black holes

Tidal disruptions are extremely powerful phenomena that have been designated as candidate sources of ultra-high-energy cosmic rays. The disruption of a star by a black hole can naturally provide protons and heavier nuclei, which can be injected and accelerated to ultra-high energies within a jet. Inside the jet, accelerated nuclei are likely to interact with a dense photon field, leading to a significant production of neutrinos and secondary particles. We model numerically the propagation and interactions of high-energy nuclei in jetted tidal disruption events in order to evaluate consistently their signatures in cosmic rays and neutrinos. We propose a simple model of the light curve of tidal disruption events, consisting of two stages: a high state with bright luminosity and short duration and a medium state, less bright and longer lasting. These two states have different impacts on the production of cosmic rays and neutrinos. In order to calculate the diffuse fluxes of cosmic rays and neutrinos, we model the luminosity function and redshift evolution of jetted tidal disruption events. We find that we can fit the latest ultra-high-energy cosmic-ray spectrum and composition results of the Auger experiment for a range of reasonable parameters. The diffuse neutrino flux associated with this scenario is found to be subdominant, but nearby events can be detected by IceCube or next-generation detectors such as IceCube-Gen2

Enucleation of a multilocular odontogenic keratocyst using sagittal osteotomy: A case report

Odontogenic keratocysts are significant cysts of the jaw that are characterized by aggressive behavior and a high tendency to recur. The treatments of choice may be radical or conservative, and in the literature a debate is still open about the gold standard in the treatment of OKCs.This report describes a wide multilocular OKC extended in the right mandibular ramus and illustrates atypical behavior of a cystic lobe after marsupialization, not found to our knowledge in the previous literature. Moreover, an orthognathic procedure, consisting of sagittal osteotomy was chosen for the excision of the cyst to preserve as much bone as possible and the integrity of the inferior alveolar nerve