1,377 research outputs found

    On the Catalysis of the Electroweak Vacuum Decay by Black Holes at High Temperature

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    We study the effect of primordial black holes on the classical rate of nucleation of AdS regions within the standard electroweak vacuum at high temperature. We find that the energy barrier for transitions to the new vacuum, which determines the exponential suppression of the nucleation rate, can be reduced significantly, or even eliminated completely, in the black-hole background if the Standard Model Higgs is coupled to gravity through the renormalizable term ξRh2\xi {\cal R} h^2.Comment: LaTeX file, 15 pages, 5 figure

    Wide-field LOFAR-LBA power-spectra analyses: Impact of calibration, polarization leakage and ionosphere

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    Contamination due to foregrounds (Galactic and Extra-galactic), calibration errors and ionospheric effects pose major challenges in detection of the cosmic 21 cm signal in various Epoch of Reionization (EoR) experiments. We present the results of a pilot study of a field centered on 3C196 using LOFAR Low Band (56-70 MHz) observations, where we quantify various wide field and calibration effects such as gain errors, polarized foregrounds, and ionospheric effects. We observe a `pitchfork' structure in the 2D power spectrum of the polarized intensity in delay-baseline space, which leaks into the modes beyond the instrumental horizon (EoR/CD window). We show that this structure largely arises due to strong instrumental polarization leakage (∼30%\sim30\%) towards {Cas\,A} (∼21\sim21 kJy at 81 MHz, brightest source in northern sky), which is far away from primary field of view. We measure an extremely small ionospheric diffractive scale (rdiff≈430r_{\text{diff}} \approx 430 m at 60 MHz) towards {Cas\,A} resembling pure Kolmogorov turbulence compared to rdiff∼3−20r_{\text{diff}} \sim3 - 20 km towards zenith at 150 MHz for typical ionospheric conditions. This is one of the smallest diffractive scales ever measured at these frequencies. Our work provides insights in understanding the nature of aforementioned effects and mitigating them in future Cosmic Dawn observations (e.g. with SKA-low and HERA) in the same frequency window.Comment: 20 pages, 11 figures, accepted for publication in MNRA

    Prospects for detecting the 21cm forest from the diffuse intergalactic medium with LOFAR

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    We discuss the feasibility of the detection of the 21cm forest in the diffuse IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been derived using simulations of reionization which include detailed radiative transfer of ionizing photons. We find that the spectra from reionization models with similar total comoving hydrogen ionizing emissivity but different frequency distribution look remarkably similar. Thus, unless the reionization histories are very different from each other (e.g. a predominance of UV vs. x-ray heating) we do not expect to distinguish them by means of observations of the 21cm forest. Because the presence of a strong x-ray background would make the detection of 21cm line absorption impossible, the lack of absorption could be used as a probe of the presence/intensity of the x-ray background and the thermal history of the universe. Along a random line of sight LOFAR could detect a global suppression of the spectrum from z>12, when the IGM is still mostly neutral and cold, in contrast with the more well-defined, albeit broad, absorption features visible at lower redshift. Sharp, strong absorption features associated with rare, high density pockets of gas could be detected also at z~7 along preferential lines of sight.Comment: 12 pages, 13 figures. MNRAS, in pres

    Recovering the H II region size statistics from 21-cm tomography

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    We introduce a novel technique, called ‘granulometry’, to characterize and recover the mean size and the size distribution of H II regions from 21-cm tomography. The technique is easy to implement, but places the previously not very well-defined concept of morphology on a firm mathematical foundation. The size distribution of the cold spots in 21-cm tomography can be used as a direct tracer of the underlying probability distribution of H II region sizes. We explore the capability of the method using large-scale reionization simulations and mock observational data cubes while considering capabilities of Square Kilometre Array 1 (SKA1) low and a future extension to SKA2. We show that the technique allows the recovery of the H II region size distribution with a moderate signal-to-noise ratio from wide-field imaging (SNR 3), for which the statistical uncertainty is sample variance dominated. We address the observational requirements on the angular resolution, the field of view, and the thermal noise limit for a successful measurement. To achieve a full scientific return from 21-cm tomography and to exploit a synergy with 21-cm power spectra, we suggest an observing strategy using wide- field imaging (several tens of square degrees) by an interferometric mosaicking/multibeam observation with additional intermediate baselines (∼2−4 km) in an SKA phase 2

    Bioaugmentation of sewage sludge with Trametes versicolor in solid-phase biopiles produces degradation of pharmaceuticals and affects microbial communities

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    The use of sludge (biosolids) in land application may contribute to the spread of organic micropollutants as wastewater treatments do not completely remove these compounds. Therefore, the development of alternative strategies for sludge treatment is a matter of recent concern. The elimination of pharmaceuticals at pre-existent concentrations from sewage sludge was assessed, for the first time, in nonsterile biopiles by means of fungal bioaugmentation with Trametes versicolor (BTV-systems) and compared with the effect of autochthonous microbiota (NB-systems). The competition between the autochthonous fungal/bacterial communities and T. versicolor was studied using denaturing gradient gel electrophoresis (DGGE) and the cloning/ sequencing approach. An inhibitory effect exerted by T. versicolor over bacterial populations was suggested. However, after 21 days, T. versicolor was no longer the main taxon in the fungal communities. The elimination profiles revealed an enhanced removal of atorvastatin-diclofenac-hydrochlorothiazide (during the whole treatment) and ranitidine-fenofibrate (at short periods) in the BTV biopiles in respect to NB biopiles, coincident with the presence of the fungus. For ibuprofen-clarithromycin-furosemide, the elimination profiles were similar irrespective of the system, and with carbamazepine no significant degradation was obtained. The results suggest that a fungal treatment with T. versicolor could be a promising process for the remediation of some pharmaceuticals in complex matrices such as biosolids.Portuguese-Spanish action E51/1

    Foregrounds for observations of the cosmological 21 cm line: I. First Westerbork measurements of Galactic emission at 150 MHz in a low latitude field

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    We present the first results from a series of observations conducted with the Westerbork telescope in the 140--160 MHz range with a 2 arcmin resolution aimed at characterizing the properties of the foregrounds for epoch of reionization experiments. For the first time we have detected fluctuations in the Galactic diffuse emission on scales greater than 13 arcmin at 150 MHz, in the low Galactic latitude area known as Fan region. Those fluctuations have an rmsrms of 14 K. The total intensity power spectrum shows a power--law behaviour down to ℓ∼900\ell \sim 900 with slope βℓI=−2.2±0.3\beta^I_\ell = -2.2 \pm 0.3. The detection of diffuse emission at smaller angular scales is limited by residual point sources. We measured an rmsrms confusion noise of ∼\sim3 mJy beam−1^{-1}. Diffuse polarized emission was also detected for the first time at this frequency. The polarized signal shows complex structure both spatially and along the line of sight. The polarization power spectrum shows a power--law behaviour down to ℓ∼2700\ell \sim 2700 with slope βℓP=−1.65±0.15\beta^P_\ell = -1.65 \pm 0.15. The rmsrms of polarization fluctuations is 7.2 K on 4 arcmin scales. By extrapolating the measured spectrum of total intensity emission, we find a contamination on the cosmological signal of δT=ℓ(ℓ+1)CℓI/2π∼5.7\delta T= \sqrt{\ell (\ell+1) C^I_\ell / 2\pi} \sim 5.7 K on 5 arcmin scales and a corresponding rmsrms value of ∼\sim18.3 K at the same angular scale. The level of the polarization power spectrum is δT∼3.3\delta T \sim 3.3 K on 5 arcmin scales. Given its exceptionally bright polarized signal, the Fan region is likely to represent an upper limit on the sky brightness at moderate and high Galactic latitude.Comment: Minor corrections made to match the final version printed on A&A. A version with high resolution figures is available at http://www.astro.rug.nl/~bernardi/FAN/fan.pd

    Euclid preparation -XIX. Impact of magnification on photometric galaxy clustering

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    Aims. We investigate the importance of lensing magnification for estimates of galaxy clustering and its cross-correlation with shear for the photometric sample of Euclid. Using updated specifications, we study the impact of lensing magnification on the constraints and the shift in the estimation of the best fitting cosmological parameters that we expect if this effect is neglected. Methods. We follow the prescriptions of the official Euclid Fisher matrix forecast for the photometric galaxy clustering analysis and the combination of photometric clustering and cosmic shear. The slope of the luminosity function (local count slope), which regulates the amplitude of the lensing magnification, and the galaxy bias have been estimated from the Euclid Flagship simulation. Results. We find that magnification significantly affects both the best-fit estimation of cosmological parameters and the constraints in the galaxy clustering analysis of the photometric sample. In particular, including magnification in the analysis reduces the 1σ errors on Ωm, 0, w0, wa at the level of 20–35%, depending on how well we will be able to independently measure the local count slope. In addition, we find that neglecting magnification in the clustering analysis leads to shifts of up to 1.6σ in the best-fit parameters. In the joint analysis of galaxy clustering, cosmic shear, and galaxy–galaxy lensing, magnification does not improve precision, but it leads to an up to 6σ bias if neglected. Therefore, for all models considered in this work, magnification has to be included in the analysis of galaxy clustering and its cross-correlation with the shear signal (3 × 2pt analysis) for an accurate parameter estimation. Key words: large-scale structure of Universe / cosmological parameters / cosmology: theor
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