arXiv subjects

Olga Mena

Publications and source records attributed to Olga Mena.

At least 91 records · Page 5Linked to original sources

arXiv2019

Constraining the primordial black hole abundance with 21cm cosmology

The discoveries of a number of binary black hole mergers by LIGO and VIRGO has reinvigorated the interest that primordial black holes (PBHs) of tens of solar masses could contribute non-negligibly to the dark matter energy density. Should even a small population of PBHs with masses $\gtrsim \mathcal{O}(M_\odot)$ exist, they could profoundly impact the properties of the intergalactic medium and provide insight into novel processes at work in the early Universe. We demonstrate here that observations of the 21cm transition in neutral hydrogen during the epochs of reionization and cosmic dawn will likely provide one of the most stringent tests of solar mass PBHs. In the context of 21cm cosmology, PBHs give rise to three distinct observable effects: ${\textit{(i)}}$ the modification to the primordial power spectrum (and thus also the halo mass function) induced by Poisson noise, ${\textit{(ii)}}$ a uniform heating and ionization of the intergalactic medium via X-rays produced during accretion, and ${\textit{(iii)}}$ a local modification to the temperature and density of the ambient medium surrounding isolated PBHs. Using a four-parameter astrophysical model, we show that experiments like SKA and HERA could potentially improve upon existing constraints derived using observations of the cosmic microwave background by more than one order of magnitude.

astro-ph.CO↗

arXiv2019

Comprehensive Study of Neutrino-Dark Matter Mixed Damping

Mixed damping is a physical effect that occurs when a heavy species is coupled to a relativistic fluid which is itself free streaming. As a cross-case between collisional damping and free-streaming, it is crucial in the context of neutrino-dark matter interactions. In this work, we establish the parameter space relevant for mixed damping, and we derive an analytical approximation for the evolution of dark matter perturbations in the mixed damping regime to illustrate the physical processes responsible for the suppression of cosmological perturbations. Although extended Boltzmann codes implementing neutrino-dark matter scattering terms automatically include mixed damping, this effect has not been systematically studied. In order to obtain reliable numerical results, it is mandatory to reconsider several aspects of neutrino-dark matter interactions, such as the initial conditions, the ultra-relativistic fluid approximation and high order multiple moments in the neutrino distribution. Such a precise treatment ensures the correct assessment of the relevance of mixed damping in neutrino-dark matter interactions.

astro-ph.CO↗

arXiv2018

Dark Matter microphysics and 21 cm observations

Dark matter interactions with massless or very light Standard Model particles, as photons or neutrinos, may lead to a suppression of the matter power spectrum at small scales and of the number of low mass haloes. Bounds on the dark matter scattering cross section with light degrees of freedom in such interacting dark matter (IDM) scenarios have been obtained from e.g. early time cosmic microwave background physics and large scale structure observations. Here we scrutinize dark matter microphysics in light of the claimed 21 cm EDGES 78 MHz absorption signal. IDM is expected to delay the 21 cm absorption features due to collisional damping effects. We identify the astrophysical conditions under which the existing constraints on the dark matter scattering cross section could be largely improved due to the IDM imprint on the 21 cm signal, providing also an explicit comparison to the WDM scenario.

astro-ph.CO↗

arXiv2018

Constraints on the sum of the neutrino masses in dynamical dark energy models with $w(z) \geq -1$ are tighter than those obtained in $Λ$CDM

We explore cosmological constraints on the sum of the three active neutrino masses $M_ν$ in the context of dynamical dark energy (DDE) models with equation of state (EoS) parametrized as a function of redshift $z$ by $w(z)=w_0+w_a\,z/(1+z)$, and satisfying $w(z)\geq-1$ for all $z$. We perform a Bayesian analysis and show that, within these models, the bounds on $M_ν$ \textit{do not degrade} with respect to those obtained in the $Λ$CDM case; in fact the bounds are slightly tighter, despite the enlarged parameter space. We explain our results based on the observation that, for fixed choices of $w_0\,,w_a$ such that $w(z)\geq-1$ (but not $w=-1$ for all $z$), the upper limit on $M_ν$ is tighter than the $Λ$CDM limit because of the well-known degeneracy between $w$ and $M_ν$. The Bayesian analysis we have carried out then integrates over the possible values of $w_0$-$w_a$ such that $w(z)\geq-1$, all of which correspond to tighter limits on $M_ν$ than the $Λ$CDM limit. We find a 95\% confidence level (C.L.) upper bound of $M_ν<0.13\,\mathrm{eV}$. This bound can be compared with $M_ν<0.16\,\mathrm{eV}$ at 95\%~C.L., obtained within the $Λ$CDM model, and $M_ν<0.41\,\mathrm{eV}$ at 95\%~C.L., obtained in a DDE model with arbitrary EoS (which allows values of $w < -1$). Contrary to the results derived for DDE models with arbitrary EoS, we find that a dark energy component with $w(z)\geq-1$ is unable to alleviate the tension between high-redshift observables and direct measurements of the Hubble constant $H_0$. Finally, in light of the results of this analysis, we also discuss the implications for DDE models of a possible determination of the neutrino mass hierarchy by laboratory searches. (abstract abridged)

astro-ph.CO↗

arXiv2018

A fresh look into the interacting dark matter scenario

The elastic scattering between dark matter particles and radiation represents an attractive possibility to solve a number of discrepancies between observations and standard cold dark matter predictions, as the induced collisional damping would imply a suppression of small-scale structures. We consider this scenario and confront it with measurements of the ionization history of the Universe at several redshifts and with recent estimates of the counts of Milky Way satellite galaxies. We derive a conservative upper bound on the dark matter-photon elastic scattering cross section of $σ_{γ\rm{DM}} < 8 \times 10^{-10} \, σ_T \, \left(m_{\rm DM}/{\rm GeV}\right)$ at $95\%$~CL, about one order of magnitude tighter than previous {constraints from satellite number counts}. Due to the strong degeneracies with astrophysical parameters, the bound on the dark matter-photon scattering cross section derived here is driven by the estimate of the number of Milky Way satellite galaxies. Finally, we also argue that future 21~cm probes could help in disentangling among possible non-cold dark matter candidates, such as interacting and warm dark matter scenarios. Let us emphasize that bounds of similar magnitude to the ones obtained here could be also derived for models with dark matter-neutrino interactions and would be as constraining as the tightest limits on such scenarios.

astro-ph.CO↗

arXiv2018

EDGES result versus CMB and low-redshift constraints on ionization histories

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-$α$ emission from star-forming galaxies, for a variety of possible reionization models within the standard $Λ$CDM framework (that is, a Universe with a cosmological constant and cold dark matter). When, conservatively, we only try to accommodate the location of the absorption dip, we identify a region in the parameter space of the astrophysical parameters that successfully explains all of the aforementioned observations. However, one of the most abnormal features of the EDGES measurement is the absorption amplitude, which is roughly a factor of two larger than the maximum allowed value in the $Λ$CDM framework. We point out that the simple considered astrophysical models that produce the largest absorption amplitudes are unable to explain the depth of the dip and of reproducing the observed shape of the absorption profile.

astro-ph.CO↗

arXiv2018

Warm dark matter and the ionization history of the Universe

In warm dark matter scenarios structure formation is suppressed on small scales with respect to the cold dark matter case, reducing the number of low-mass halos and the fraction of ionized gas at high redshifts and thus, delaying reionization. This has an impact on the ionization history of the Universe and measurements of the optical depth to reionization, of the evolution of the global fraction of ionized gas and of the thermal history of the intergalactic medium, can be used to set constraints on the mass of the dark matter particle. However, the suppression of the fraction of ionized medium in these scenarios can be partly compensated by varying other parameters, as the ionization efficiency or the minimum mass for which halos can host star-forming galaxies. Here we use different data sets regarding the ionization and thermal histories of the Universe and, taking into account the degeneracies from several astrophysical parameters, we obtain a lower bound on the mass of thermal warm dark matter candidates of $m_X > 1.3$ keV, or $m_s > 5.5$ keV for the case of sterile neutrinos non-resonantly produced in the early Universe, both at 90\% confidence level.

astro-ph.CO↗

arXiv2018

Reconciling tensor and scalar observables in G-inflation

The simple $m^2ϕ^2$ potential as an inflationary model is coming under increasing tension with limits on the tensor-to-scalar ratio $r$ and measurements of the scalar spectral index $n_s$. Cubic Galileon interactions in the context of the Horndeski action can potentially reconcile the observables. However, we show that this cannot be achieved with only a constant Galileon mass scale because the interactions turn off too slowly, leading also to gradient instabilities after inflation ends. Allowing for a more rapid transition can reconcile the observables but moderately breaks the slow-roll approximation leading to a relatively large and negative running of the tilt $α_s$ that can be of order $n_s-1$. We show that the observables on CMB and large scale structure scales can be predicted accurately using the optimized slow-roll approach instead of the traditional slow-roll expansion. Upper limits on $|α_s|$ place a lower bound of $r\gtrsim 0.005$ and conversely a given $r$ places a lower bound on $|α_s|$, both of which are potentially observable with next generation CMB and large scale structure surveys.

astro-ph.CO↗

arXiv2018

Was there an early reionization component in our universe?

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 our universe and that only one marginal class of models, based on a particular realization of reionization, may point to that. In addition, the frequentist Akaike Information Criterion (AIC) provides strong evidence against alternative reionization histories, favoring the most simple reionization scenario, which describes reionization by means of only one (constant) reionization optical depth $τ$.

astro-ph.CO↗

arXiv2017

Exploring dark matter microphysics with galaxy surveys

We use present cosmological observations and forecasts of future experiments to illustrate the power of large-scale structure (LSS) surveys in probing dark matter (DM) microphysics and unveiling potential deviations from the standard $Λ$CDM scenario. To quantify this statement, we focus on an extension of $Λ$CDM with DM-neutrino scattering, which leaves a distinctive imprint on the angular and matter power spectra. After finding that future CMB experiments (such as COrE+) will not significantly improve the constraints set by the Planck satellite, we show that the next generation of galaxy clustering surveys (such as DESI) could play a leading role in constraining alternative cosmologies and even have the potential to make a discovery. Typically we find that DESI would be an order of magnitude more sensitive to DM interactions than Planck, thus probing effects that until now have only been accessible via $N$-body simulations.

astro-ph.CO↗

arXiv2017

Unveiling $ν$ secrets with cosmological data: neutrino masses and mass hierarchy

Using some of the latest cosmological datasets publicly available, we derive the strongest bounds in the literature on the sum of the three active neutrino masses, $M_ν$, within the assumption of a background flat $Λ$CDM cosmology. In the most conservative scheme, combining Planck cosmic microwave background (CMB) temperature anisotropies and baryon acoustic oscillations (BAO) data, as well as the up-to-date constraint on the optical depth to reionization ($τ$), the tightest $95\%$ confidence level (C.L.) upper bound we find is $M_ν<0.151$~eV. The addition of Planck high-$\ell$ polarization data, which however might still be contaminated by systematics, further tightens the bound to $M_ν<0.118$~eV. A proper model comparison treatment shows that the two aforementioned combinations disfavor the IH at $\sim 64\%$~C.L. and $\sim 71\%$~C.L. respectively. In addition, we compare the constraining power of measurements of the full-shape galaxy power spectrum versus the BAO signature, from the BOSS survey. Even though the latest BOSS full shape measurements cover a larger volume and benefit from smaller error bars compared to previous similar measurements, the analysis method commonly adopted results in their constraining power still being less powerful than that of the extracted BAO signal. Our work uses only cosmological data; imposing the constraint $M_ν>0.06\,{\rm eV}$ from oscillations data would raise the quoted upper bounds by ${\cal O}(0.1σ)$ and would not affect our conclusions.

astro-ph.CO↗

arXiv2017

A novel approach to quantifying the sensitivity of current and future cosmological datasets to the neutrino mass ordering through Bayesian hierarchical modeling

We present a novel approach to derive constraints on neutrino masses from cosmological data, while taking into account our ignorance of the neutrino mass ordering. We derive constraints from a combination of current and future cosmological datasets on the total neutrino mass $M_ν$ and on the mass fractions carried by each of the mass eigenstates, after marginalizing over the (unknown) neutrino mass ordering, either normal (NH) or inverted (IH). The bounds take therefore into account the uncertainty related to our ignorance of the mass hierarchy. This novel approach is carried out in the framework of Bayesian analysis of a typical hierarchical problem. In this context, the choice of the neutrino mass ordering is modeled via the discrete hyperparameter $h_{type}$. The preference for either the NH or the IH scenarios is then encoded in the posterior distribution of $h_{type}$ itself. Current CMB measurements assign equal odds to the two hierarchies, and are thus unable to distinguish between them. However, after the addition of BAO measurements, a weak preference for NH appears, with odds of 4:3 from Planck temperature and large-scale polarization in combination with BAO (3:2 if small-scale polarization is also included). Forecasts suggest that the combination of upcoming CMB (COrE) and BAO surveys (DESI) may determine the neutrino mass hierarchy at a high statistical significance if the mass is very close to the minimal value allowed by oscillations, as for NH and $M_ν=0.06$ eV there is a 9:1 preference of NH vs IH. On the contrary, if $M_ν$ is of the order of 0.1 eV or larger, even future cosmological observations will be inconclusive. The unbiased limit on $M_ν$ we obtain with this innovative statistical strategy is crucial for ongoing and planned neutrinoless double beta decay searches.

astro-ph.CO↗

arXiv2017

Warm Dark Matter and Cosmic Reionization

In models with dark matter made of particles with keV masses, such as a sterile neutrino, small-scale density perturbations are suppressed, delaying the period at which the lowest mass galaxies are formed and therefore shifting the reionization processes to later epochs. In this study, focusing on Warm Dark Matter (WDM) with masses close to its present lower bound, i.e. around the $3$ keV region, we derive constraints from galaxy luminosy functions, the ionization history and the Gunn-Peterson effect. We show that even if star formation efficiency in the simulations is adjusted to match the observed UV galaxy luminosity functions in both CDM and WDM models, the full distribution of Gunn-Peterson optical depth retains the strong signature of delayed reionization in the WDM model. However, until the star formation and stellar feedback model used in modern galaxy formation simulations is constrained better, any conclusions on the nature of dark matter derived from reionization observables remain model-dependent.

astro-ph.CO↗

arXiv2017

Cold dark matter plus not-so-clumpy dark relics

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 matter. To this end, we employ the latest Planck Cosmic Microwave Background data, the recent BOSS DR11 and other Baryon Acoustic Oscillation measurements, and also constraints on the number of Milky Way satellites, the latter of which provides a measure of the suppression of the matter power spectrum at the smallest scales due to the free-streaming of the non-cold dark matter component. We present the results on the fraction $f_{\rm ncdm}$ of non-cold dark matter with respect to the total dark matter for different ranges of the non-cold dark matter masses. We find that the 2$σ$ limits for non-cold dark matter particles with masses in the range 1--10 keV are $f_{\rm ncdm}\leq0.29$ (0.23) for fermions (bosons), and for masses in the 10--100 keV range they are $f_{\rm ncdm}\leq0.43$ (0.45), respectively.

astro-ph.CO↗

arXiv2017

Can interacting dark energy solve the $H_0$ tension?

The answer is Yes! We indeed find that interacting dark energy can alleviate the current tension on the value of the Hubble constant $H_0$ between the Cosmic Microwave Background anisotropies constraints obtained from the Planck satellite and the recent direct measurements reported by Riess et al. 2016. The combination of these two datasets points towards an evidence for a non-zero dark matter-dark energy coupling $ξ$ at more than two standard deviations, with $ξ=-0.26_{-0.12}^{+0.16}$ at $95\%$ CL. However the $H_0$ tension is better solved when the equation of state of the interacting dark energy component is allowed to freely vary, with a phantom-like equation of state $w=-1.184\pm0.064$ (at $68 \%$ CL), ruling out the pure cosmological constant case, $w=-1$, again at more than two standard deviations. When Planck data are combined with external datasets, as BAO, JLA Supernovae Ia luminosity distances, cosmic shear or lensing data, we find good consistency with the cosmological constant scenario and no compelling evidence for a dark matter-dark energy coupling.

astro-ph.CO↗

arXiv2016

Analysis of the 4-year IceCube high-energy starting events

After four years of data taking, the IceCube neutrino telescope has detected 54 high-energy starting events (HESE, or contained-vertex events) with deposited energies above 20TeV. They represent the first ever detection of high-energy extraterrestrial neutrinos and therefore, the first step in neutrino astronomy. In order to study the energy, flavor and isotropy of the astrophysical neutrino flux arriving at Earth, we perform different analyses of two different deposited energy intervals, [10 TeV $-$ 10 PeV] and [60 TeV $-$ 10 PeV]. We first consider an isotropic unbroken power-law spectrum and constrain its shape, normalization and flavor composition. Our results are in agreement with the preliminary IceCube results, although we obtain a slightly softer spectrum. We also find that current data are not sensitive to a possible neutrino-antineutrino asymmetry in the astrophysical flux. Then, we show that although a two-component power-law model leads to a slightly better fit, it does not represent a significant improvement with respect to a single power-law flux. Finally, we analyze the possible existence of a North-South asymmetry, hinted at by the combination of the HESE sample with the through-going muon data. If only using HESE data, the scarce statistics from the northern hemisphere does not allow us to reach any conclusive answer, which indicates that the HESE sample alone is not driving the potential North-South asymmetry.

astro-ph.HE↗

arXiv2016

Impact of neutrino properties on the estimation of inflationary parameters from current and future observations

We study the impact of assumptions about neutrino properties on the estimation of inflationary parameters from cosmological data, with a specific focus on the allowed contours in the $n_s/r$ plane. We study the following neutrino properties: (i) the total neutrino mass $ M_ν=\sum_i m_i$; (ii) the number of relativistic degrees of freedom $N_{eff}$; and (iii) the neutrino hierarchy: whereas previous literature assumed 3 degenerate neutrino masses or two massless neutrino species (that do not match neutrino oscillation data), we study the cases of normal and inverted hierarchy. Our basic result is that these three neutrino properties induce $< 1 σ$ shift of the probability contours in the $n_s/r$ plane with both current or upcoming data. We find that the choice of neutrino hierarchy has a negligible impact. However, the minimal cutoff on the total neutrino mass $M_{ν,{min}}=0 $ that accompanies previous works using the degenerate hierarchy does introduce biases in the $n_s/r$ plane and should be replaced by $M_{ν,min}= 0.059$ eV as required by oscillation data. Using current CMB data from Planck and Bicep/Keck, marginalizing over $ M_ν$ and over $r$ can lead to a shift in the mean value of $n_s$ of $\sim0.3σ$ towards lower values. However, once BAO measurements are included, the standard contours in the $n_s/r$ plane are basically reproduced. Larger shifts of the contours in the $n_s/r$ plane (up to 0.8$σ$) arise for nonstandard values of $N_{eff}$. We also provide forecasts for the future CMB experiments COrE and Stage-IV and show that the incomplete knowledge of neutrino properties, taken into account by a marginalization over $M_ν$, could induce a shift of $\sim0.4σ$ towards lower values in the determination of $n_s$ (or a $\sim 0.8σ$ shift if one marginalizes over $N_{eff}$). Comparison to specific inflationary models is shown.

astro-ph.CO↗

arXiv2016

Non-standard interactions with high-energy atmospheric neutrinos at IceCube

Non-standard interactions in the propagation of neutrinos in matter can lead to significant deviations from expectations within the standard neutrino oscillation framework and atmospheric neutrino detectors have been considered to set constraints. However, most previous works have focused on relatively low-energy atmospheric neutrino data. Here, we consider the one-year high-energy through-going muon data in IceCube, which has been already used to search for light sterile neutrinos, to constrain new interactions in the $μτ$-sector. In our analysis we include several systematic uncertainties on both, the atmospheric neutrino flux and on the detector properties, which are accounted for via nuisance parameters. After considering different primary cosmic-ray spectra and hadronic interaction models, we obtain the most stringent bound on the off-diagonal $\varepsilon_{μτ}$ parameter to date, with the 90\% credible interval given by $-6.0 \times 10^{-3} < \varepsilon_{μτ} < 5.4 \times 10^{-3}$. In addition, we also estimate the expected sensitivity after 10~years of collected data in IceCube and study the precision at which non-standard parameters could be determined for the case of $\varepsilon_{μτ}$ near its current bound.

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