0000000000826344
AUTHOR
Stefano Gariazzo
showing 11 related works from this author
Towards a precision calculation of the effective number of neutrinos đť–_đť–ľđť–żđť–ż in the Standard Model. Part II. Neutrino decoupling in the presence of…
2021
Abstract We present in this work a new calculation of the standard-model benchmark value for the effective number of neutrinos, Neff SM, that quantifies the cosmological neutrino-to-photon energy densities. The calculation takes into account neutrino flavour oscillations, finite-temperature effects in the quantum electrodynamics plasma to O(e3), where e is the elementary electric charge, and a full evaluation of the neutrino-neutrino collision integral. We provide furthermore a detailed assessment of the uncertainties in the benchmark Neff SM value, through testing the value's dependence on (i) optional approximate modelling of the weak collision integrals, (ii) measurement errors in the ph…
EDGES result versus CMB and low-redshift constraints on ionization histories
2018
We examine the results from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES), which has recently claimed the detection of a strong absorption in the 21 cm hyperfine transition line of neutral hydrogen, at redshifts demarcating the early stages of star formation. More concretely, we study the compatibility of the shape of the EDGES absorption profile, centered at a redshift of $z \sim 17.2$, with measurements of the reionization optical depth, the Gunn-Peterson optical depth, and Lyman-$\alpha$ emission from star-forming galaxies, for a variety of possible reionization models within the standard $\Lambda$CDM framework (that is, a Universe with a cosmological consta…
Dark Radiation and Inflationary Freedom after Planck 2015
2016
The simplest inflationary models predict a primordial power spectrum (PPS) of the curvature fluctuations that can be described by a power-law function that is nearly scale-invariant. It has been shown, however, that the low-multipole spectrum of the CMB anisotropies may hint the presence of some features in the shape of the scalar PPS, which could deviate from its canonical power-law form. We study the possible degeneracies of this non-standard PPS with the neutrino anisotropies, the neutrino masses, the effective number of relativistic species and a sterile neutrino or a thermal axion mass. The limits on these additional parameters are less constraining in a model with a non-standard PPS w…
Cold dark matter plus not-so-clumpy dark relics
2017
Various particle physics models suggest that, besides the (nearly) cold dark matter that accounts for current observations, additional but sub-dominant dark relics might exist. These could be warm, hot, or even contribute as dark radiation. We present here a comprehensive study of two-component dark matter scenarios, where the first component is assumed to be cold, and the second is a non-cold thermal relic. Considering the cases where the non-cold dark matter species could be either a fermion or a boson, we derive consistent upper limits on the non-cold dark relic energy density for a very large range of velocity dispersions, covering the entire range from dark radiation to cold dark matte…
Was there an early reionization component in our universe?
2017
A deep understanding of the Epoch of Reionization is still missing in our knowledge of the universe. While future probes will allow us to test the precise evolution of the free electron fraction from redshifts between $z\simeq 6$ and $z\simeq 20$, at present one could ask what kind of reionization processes are allowed by present Cosmic Microwave Background temperature and polarization measurements. An early contribution to reionization could imply a departure from the standard picture where star formation determines the reionization onset. BBy considering a broad class of possible reionization parameterizations, we find that current data do not require an early reionization component in ou…
Robustness of cosmological axion mass limits
2015
We present cosmological bounds on the thermal axion mass in an extended cosmological scenario in which the primordial power spectrum of scalar perturbations differs from the usual power-law shape predicted by the simplest inflationary models. The power spectrum is instead modeled by means of a "piecewise cubic Hermite interpolating polynomial" (PCHIP). When using Cosmic Microwave Background measurements combined with other cosmological data sets, the thermal axion mass constraints are degraded only slightly. The addition of the measurements of $\sigma_8$ and $\Omega_m$ from the 2013 Planck cluster catalogue on galaxy number counts relaxes the bounds on the thermal axion mass, mildly favouri…
Soundness of Dark Energy properties
2020
Type Ia Supernovae (SNeIa) used as standardizable candles have been instrumental in the discovery of cosmic acceleration, usually attributed to some form of dark energy (DE). Recent studies have raised the issue of whether intrinsic SNeIa luminosities might evolve with redshift. While the evidence for cosmic acceleration is robust to this possible systematic, the question remains of how much the latter can affect the inferred properties of the DE component responsible for cosmic acceleration. This is the question we address in this work. We use SNeIa distance moduli measurements from the Pantheon and JLA samples. We consider models where the DE equation of state is a free parameter, either …
Bounds on light sterile neutrino mass and mixing from cosmology and laboratory searches
2020
We provide a consistent framework to set limits on properties of light sterile neutrinos coupled to all three active neutrinos using a combination of the latest cosmological data and terrestrial measurements from oscillations, $\beta$-decay and neutrinoless double-$\beta$ decay ($0\nu\beta\beta$) experiments. We directly constrain the full $3+1$ active-sterile mixing matrix elements $|U_{\alpha4}|^2$, with $\alpha \in ( e,\mu ,\tau )$, and the mass-squared splitting $\Delta m^2_{41} \equiv m_4^2-m_1^2$. We find that results for a $3+1$ case differ from previously studied $1+1$ scenarios where the sterile is only coupled to one of the neutrinos, which is largely explained by parameter space …
Primordial power spectrum features in phenomenological descriptions of inflation
2016
We extend an alternative, phenomenological approach to inflation by means of an equation of state and a sound speed, both of them functions of the number of $e$-folds and four phenomenological parameters. This approach captures a number of possible inflationary models, including those with non-canonical kinetic terms or scale-dependent non-gaussianities. We perform Markov Chain Monte Carlo analyses using the latest cosmological publicly available measurements, which include Cosmic Microwave Background (CMB) data from the Planck satellite. Within this parametrization, we discard scale invariance with a significance of about $10\sigma$, and the running of the spectral index is constrained as …
Running of featureful primordial power spectra
2017
Current measurements of the temperature and polarization anisotropy power spectra of the Cosmic Microwave Background (CMB) seem to indicate that the naive expectation for the slow-roll hierarchy within the most simple inflationary paradigm may not be respected in nature. We show that a primordial power spectra with localized features could in principle give rise to the observed slow-roll anarchy when fitted to a featureless power spectrum. Future CMB missions have the key to disentangle among the two possible paradigms and firmly establish the slow-roll mechanism as the responsible one for the inflationary period in the early universe. From a model comparison perspective, and assuming that …
Primordial power spectrum features and f(NL) constraints
2015
The simplest models of inflation predict small non-gaussianities and a featureless power spectrum. However, there exist a large number of well-motivated theoretical scenarios in which large non-gaussianties could be generated. In general, in these scenarios the primordial power spectrum will deviate from its standard power law shape. We study, in a model-independent manner, the constraints from future large scale structure surveys on the local non-gaussianity parameter $f_{\rm NL}$ when the standard power law assumption for the primordial power spectrum is relaxed. If the analyses are restricted to the large scale-dependent bias induced in the linear matter power spectrum by non-gaussianite…