The formation and abundance of primordial black holes (PBHs) arising from the curvature perturbation ζ is studied. The non-linear relation between ζ and the density contrast δ means that, even when ζ ...has an exactly Gaussian distribution, significant non-Gaussianities affecting PBH formation must be considered. Numerical simulations are used to investigate the critical value and the mass of PBHs which form, and peaks theory is used to calculate the mass fraction of the universe collapsing to form PBHs at the time of formation. A formalism to calculate the total present day PBH abundance and mass function is also derived. It is found that the abundance of PBHs is very sensitive to the non-linear effects, and that the power spectrum ζ must be a factor of (2) larger to produce the same number of PBHs as if using the linear relation between ζ and δ (where the exact value depends on the critical value for a region to collapse and form a PBH). This also means that the derived constraints on the small-scale power spectrum from constraints on the abundance of PBHs are weaker by the same factor.
We conduct a thorough Bayesian analysis of the possibility that the black hole merger events seen in gravitational waves are primordial black hole (PBH) mergers. Using the latest merger rate models ...for PBH binaries drawn from a log-normal mass function, we compute posterior parameter constraints and Bayesian evidences using data from the first two observing runs of LIGO-Virgo. We account for theoretical uncertainty due to possible disruption of the binary by surrounding PBHs, which can suppress the merger rate significantly. We also consider simple astrophysically motivated models and find that these are favored decisively over the PBH scenario, quantified by the Bayesian evidence ratio. Paying careful attention to the influence of the parameter priors and the quality of the model fits, we show that the evidence ratios can be understood by comparing the predicted chirp mass distribution to that of the data. We identify the posterior predictive distribution of chirp mass as a vital tool for discriminating between models. A model in which all mergers are PBH binaries is strongly disfavored compared with astrophysical models, in part due to the overprediction of heavy systems having Mchirp ≳ 40 M⊙ and positive skewness over the range of observed masses which does not match the observations. We find that the fit is not significantly improved by adding a maximum mass cutoff or a bimodal mass function or imposing that PBH binaries form at late times. We argue that a successful PBH model must either modify the log-normal shape of the initial mass function significantly or abandon the hypothesis that all observed merging binaries are primordial. We develop and apply techniques for analyzing PBH models with gravitational wave data, which will be necessary for robust statistical inference as the gravitational wave source sample size increases.
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We propose an expression for a local planetesimal formation rate proportional to the instantaneous radial pebble flux. The result-a radial planetesimal distribution-can be used as an initial ...condition to study the formation of planetary embryos. We follow the idea that one needs particle traps to locally enhance the dust-to-gas ratios sufficiently, such that particle gas interactions can no longer prevent planetesimal formation on small scales. The locations of these traps can emerge everywhere in the disk. Their occurrence and lifetime is subject to ongoing research; thus, here they are implemented via free parameters. This enables us to study the influence of the disk properties on the formation of planetesimals, predicting their time-dependent formation rates and the location of primary pebble accretion. We show that large -values of 0.01 (strong turbulence) prevent the formation of planetesimals in the inner part of the disk, arguing for lower values of around 0.001 (moderate turbulence), at which planetesimals form quickly at all places where they are needed for proto-planets. Planetesimals form as soon as dust has grown to pebbles (mm to dm) and the pebble flux reaches a critical value, which is after a few thousand years at 2-3 au and after a few hundred thousand years at 20-30 au. Planetesimal formation lasts until the pebble supply has decreased below a critical value. The final spatial planetesimal distribution is steeper compared to the initial dust and gas distribution, which helps explain the discrepancy between the minimum mass solar nebula and viscous accretion disks.
We derive analytic bounds on the shape of the primordial power spectrum in the context of single-field inflation. In particular, the steepest possible growth has a spectral index of ns−1=4 once ...transients have died down. Its primary implication is that any constraint on the power spectrum at a particular scale can be extrapolated to an upper bound over an extended range of scales. This is important for models which generate relics due to an enhanced amplitude of the primordial scalar perturbations, such as primordial black holes. In order to generate them, the power spectrum needs to grow many orders of magnitude larger than its observed value on CMB scales—typically achieved through a phase of ultra slow-roll inflation—and is thus subject to additional constraints at small scales. We plot all relevant constraints including CMB spectral distortions and gravitational waves sourced by scalar perturbations at second order. We show how this limits the allowed mass of PBHs, especially for the large masses of interest following recent detections by LIGO and prospects for constraining them further with future observations. We show that any transition from approximately constant ε slow-roll inflation to a phase where the power spectrum rapidly rises necessarily implies an intervening dip in power. We also show how to reconstruct a potential that can reproduce an arbitrary time-varying ε, offering a complementary perspective on how ultra slow-roll can be achieved.
A
bstract
The implementation of a new final-state parton-shower algorithm in the P
ythia
event generator is described. The shower algorithm, dubbed A
pollo
, combines central aspects of the V
incia
...antenna shower with the global transverse-recoil scheme of the A
laric
framework in order to achieve formal consistency with next-to-leading logarithmic (NLL) resummation. The shower algorithm is constructed in such a way that it facilitates a straightforward combination with fixed-order calculations. As an explicit proof of concept, a general scheme for matrix-element corrections (MECs) and two separate multiplicative next-to-leading order (NLO) matching schemes are outlined. It is argued that both matching schemes retain the logarithmic accuracy of the shower. The improved modelling of radiation is examined by contrasting the new algorithm with existing leading-logarithmic parton showers in P
ythia
.
Visual kinetic analysis Nielsen, Christian D-T; Burés, Jordi
Chemical science,
01/2019, Volume:
10, Issue:
2
Journal Article
Peer reviewed
Open access
Visual kinetic analyses extract meaningful mechanistic information from experimental data using the naked-eye comparison of appropriately modified progress reaction profiles. Basic kinetic ...information is obtained easily and quickly from just a few experiments. Therefore, these methods are valuable tools for all chemists working in process chemistry, synthesis or catalysis with an interest in mechanistic studies. This minireview describes the visual kinetic analyses developed in the last fifteen years and provides answers to the most common queries of new users. Furthermore, a video tutorial is attached detailing the implementation of both VTNA and RPKA.
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IJS, KILJ, NUK, UL, UM, UPUK
If the primordial curvature perturbation followed a Gaussian distribution, primordial black holes (PBHs) will be Poisson distributed with no additional clustering. We consider local non-Gaussianity ...and its impact on the initial PBH clustering and mass function due to mode coupling between long and short wavelength modes. We show that even a small amount of non-Gaussianity results in a significant enhancement on the PBH initial clustering and subsequent merger rate and that the PBH mass function shifts to higher mass PBHs. However, as the clustering becomes strong, the local number density of PBHs becomes large, leading to a large theoretical uncertainty in the merger rate.
Electroglottography – An Update Herbst, Christian T.
Journal of voice,
July 2020, 2020-Jul, 2020-07-00, 20200701, Volume:
34, Issue:
4
Journal Article
Peer reviewed
Electroglottography (EGG) is a low-cost, noninvasive technology for measuring changes of relative vocal fold contact area during laryngeal voice production. EGG was introduced about 60 years ago and ...has gone through a “golden era” of increased scientific attention in the late 1980s and early 90s. During that period, four eminent review papers were written. Here, an update to these reviews is given, recapitulating some earlier landmark contributions and documenting noteworthy developments during the past 25 years.
After presenting an algorithmic bibliographic analysis, some methodological aspects pertaining to measurement technology, qualitative and quantitative analysis, and respective interpretation are discussed. In particular, the interpretation of landmarks in the (first derivative of the) EGG waveform is critically examined. It is argued that because of inferior-superior and anterior-posterior phase differences of vocal fold vibration, vocal fold (de)contacting does not occur instantaneously, but over an interval of time. For this reason, instants of vocal fold closing and opening cannot be resolved exactly from the EGG signal. Consequently, any quantitative analysis parameter relying on the determination of (de)contacting events (such as the EGG contact quotient) should be interpreted with care.
Finally, recent developments are reviewed for the various fields of application of EGG, including basic voice science and voice production physiology, speech signal processing and classification, clinical practice including swallowing, phonetics, hearing sciences, psychology, singing, trumpet playing, and mammalian and avian bioacoustics. Overall, EGG has over the past six decades developed into a mature technology with a wide range of applications. However, due to current limitations, the full potential of the methodology has as yet not been fully exploited. Future development may occur on three levels: (a) rigorous validation of existent measurement approaches; (b) introduction and rigorous validation of novel quantitative and interpretative approaches; and (c) advancement of the measurement technology itself.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We reinspect the calculation for the mass fraction of primordial black holes (PBHs) which are formed from primordial perturbations, finding that performing the calculation using the comoving ...curvature perturbation Rc in the standard way vastly overestimates the number of PBHs, by many orders of magnitude. This is because PBHs form shortly after horizon entry, meaning modes significantly larger than the PBH are unobservable and should not affect whether a PBH forms or not - this important effect is not taken into account by smoothing the distribution in the standard fashion. We discuss alternative methods and argue that the density contrast, Delta , should be used instead as super-horizon modes are damped by a factor k super(2). We make a comparison between using a Press-Schechter approach and peaks theory, finding that the two are in close agreement in the region of interest. We also investigate the effect of varying the spectral index, and the running of the spectral index, on the abundance of primordial black holes.
Photons can carry angular momentum, not only due to their spin, but also due to their spatial structure. This extra twist has been used, for example, to drive circular motion of microscopic particles ...in optical tweezers as well as to create vortices in quantum gases. Here we excite an atomic transition with a vortex laser beam and demonstrate the transfer of optical orbital angular momentum to the valence electron of a single trapped ion. We observe strongly modified selection rules showing that an atom can absorb two quanta of angular momentum from a single photon: one from the spin and another from the spatial structure of the beam. Furthermore, we show that parasitic ac-Stark shifts from off-resonant transitions are suppressed in the dark centre of vortex beams. These results show how light's spatial structure can determine the characteristics of light-matter interaction and pave the way for its application and observation in other systems.
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