Matter around Kerr black holes in scalar-tensor theories: scalarization and superradiant instability

In electrovacuum stationary, asymptotically flat black holes in scalar-tensor theories of gravity are described by the Kerr-Newman family of solutions, just as in general relativity. We show that there exist two mechanisms which can render Kerr black holes unstable when matter is present in the vicinity of the black hole, as this induces an effective mass for the scalar. The first mechanism is a tachyonic instability that appears when the effective mass squared is negative, triggering the development of scalar hair --- a black hole version of "spontaneous scalarization". The second instability is associated with superradiance and is present when the effective mass squared is positive and when the black hole spin exceeds a certain threshold. The second mechanism is also responsible for a resonant effect in the superradiant scattering of scalar waves, with amplification factors as large as 10^5 or more.Comment: 11 pages, 3 figures. v2: published versio

Black holes with surrounding matter in scalar-tensor theories

We uncover two mechanisms that can render Kerr black holes unstable in scalar-tensor gravity, both associated to the presence of matter in the vicinity of the black hole and the fact that this introduces an effective mass for the scalar. Our results highlight the importance of understanding the structure of spacetime in realistic, astrophysical black holes in scalar-tensor theories.Comment: 5 pages. Published version. arXiv admin note: substantial text overlap with arXiv:1305.693

Cosmic reionization history and dark matter scenarios

Summary plot is Fig. 8: constraints on escape fraction and UV limiting magnitude for cold and non-cold dark matter. This version matches the published oneInternational audienceWe perform an analysis of the cosmic reionization in the standard cold dark matter (CDM) paradigm and in alternative dark matter scenarios. Building upon the work of Corasaniti et al. (2017), we predict the reionization history for CDM, for warm dark matter (WDM), late-forming dark matter (LFDM) and ultra-light axion dark matter (ADM) models which reproduce state-of-art measurements of the galaxy luminosity function at very high-redshifts $6\le z\le 10$. To this purpose we adopt a reionization model parametrized in terms of the limiting UV-magnitude of galaxies contributing to the reionization $M_{\rm lim}$ and the average effective escape fraction of UV photons reaching the intergalactic medium $\tilde{f}$. For each DM model we compute the redshift evolution of the Thomson scattering optical depth $\tau_e(z)$ and the comoving ionization fraction $Q_{\rm HII}(z)$. We find the different DM models to have similar reionization histories. Differences with respect to the CDM case increase at fainter limiting UV-magnitudes and are degenerate with the effect of varying the reionization model parameters. Using Planck's determination of the integrated optical depth in combination with measurements of the neutral hydrogen fraction at different redshifts, we infer constraints on $\tilde{f}$ and $M_{\rm lim}$. The results are largely independent of the assumed DM scenario, in particular for $M_{\rm lim}\gtrsim -13$ we obtain that the effective escape fraction lies in the range $0.07\lesssim \tilde{f}\lesssim 0.15$ at $2\sigma$

Particle ejection during mergers of dark matter halos

Dark matter halos are built from accretion and merging. During merging some of the dark matter particles may be ejected with velocities higher than the escape velocity. We use both N-body simulations and single-particle smooth-field simulations to demonstrate that rapid changes to the mean field potential are responsible for such ejection, and in particular that dynamical friction plays no significant role in it. Studying a range of minor mergers, we find that typically between 5-15% of the particles from the smaller of the two merging structures are ejected. We also find that the ejected particles originate essentially from the small halo, and more specifically are particles in the small halo which pass later through the region in which the merging occurs.Comment: 18 pages, 12 figures. Accepted for publication in JCA

Nomenclatural synopsis of cirsium sect. Eriolepis (asteraceae) in Italy

The names of the Italian taxa in Cirsium sect. Eriolepis are discussed. The accepted names are: Cirsium echinatum, C. eriophorum subsp. eriophorum, C. eriophorum subsp. spathulatum, C. ferox, C. italicum, C. lacaitae, C. lobelii, C. morisianum, C. scabrum, C. tenoreanum, C. vallis-demonii subsp. vallis-demonii, C. vallis-demonii subsp. calabrum comb. nov., and C. vulgare (= C. crinitum, C. sylvaticum). Four accepted names are typified by specimens preserved at FI (one lectotype), G (one lectotype and one neotype), P (one lectotype), and by illustrations (two lectotypes). Several other heterotypic synonyms of taxa described from Italy are discussed and six of them are typified. A new combination and status are proposed: C. vallis-demonii subsp. calabrum, based on C. eriophorum var. vallisdemonii f. calabrum

Prognostic factors facilitating multiple food allergies and atopiv march occurrence in children with Non-IgE mediated gastrointestinal Food Allergy: results of two years follow up of the NIGEFA project

Objectives and Study: Non-IgE mediated gastrointestinal food allergies (non-IgE-GIFA) are an increasing problem in pediatric gastroenterology clinical practice. These conditions include food protein-induced: enterocolitis syndrome (FPIES), enteropathy (FPE), allergic proctocolitis (FPIAP), and motility disorders (FPIMD). The NIGEFA project is focused on the investigation of main clinical features, prognostic factors (presence atopic dermatitis (AD), multiple food allergies, diagnostic delay, and familial history of allergy), and natural history (atopic march (AM) prevalence and timing of immune tolerance acquisition). Methods: Prospective observational study evaluating children with non-IgE-GIFA diagnosed according to standard criteria observed at a tertiary center for pediatric gastroenterology and allergy (both sexes, aged <36 m, follow up 12 m after diagnosis). Main anamnestic, demographic, and clinical data were collected from all enrolled patients. Immune tolerance acquisition was evaluated by the result of oral food challenge. Results: A total of 100 patients were enrolled: 58% male, mean age at diagnosis (SD) 8.5(8.8) m. Non-IgE-GIFA conditions were: FPE (44%), FPIES (11%), FPIAP (18%), FPIMD (27%). Mean diagnostic delay was 5.3 (7.4) m. Multiple non-IgE-GIFA were observed in 47% at baseline. Familial history of allergy was observed in 64% of subjects. Presence of AD before the onset of non-IgE-GIFA was observed in 40% of subjects. The overall rate of immune tolerance acquisition at 12 m was 27%, with a higher rate in FPIAP (44%) compared with FPIMD (29.6%), FPE (22.7%) and FPIES (9.1%) subjects (p<0.05). The rate of immune tolerance acquisition at 12 m was significantly lower in children with familial history of allergy (-48%, estimated risk ratio (RR)0.52 (95% CI 0.28 to 0.99, p<0.05)) and in those with multiple non-IgE-GIFA (-61%, RR at 12 m 0.39 (95% CI 0.18 to 0.85, p<0.05)). At 12 m follow up, the rate of subjects presenting AM was 24% with no difference among the 4 disease groups. The occurrence of AM was significantly higher in subjects with multiple (38%) vs. mono non-IgE-GIFA (11%) (p<.001) at baseline, with an estimated RR of 3.38 (95% CI 1.47 to 7.81, p<0.01) at 12 m. Moreover, for every 1-month of diagnostic delay there was an increase of 1.04 RR(95% CI 1.01 to 1.07) of AM occurrence at 12 m. No associations with other potential predictors (sex, familial allergy risk, AD before the onset of GIFA, type of non-IgE-GIFA) were found. Conclusions: These data shed lights on prognostic factors and natural history of non-IgE-GIFA suggesting the importance of early diagnosis in preventing the occurrence of AM occurrence in these patients. Contac