arXiv subjects

Rafael C. Nunes

Publications and source records attributed to Rafael C. Nunes.

At least 91 records · Page 5Linked to original sources

arXiv2020

Rastall gravity extension of the standard $Λ$CDM model: theoretical features and observational constraints

We present a detailed investigation of the Rastall gravity extension of the standard $Λ$CDM model. We review the model for two simultaneous modifications of different nature in the Friedmann equation due to the Rastall gravity: the new contributions of the material (actual) sources (considered as effective source) and the altered evolution of the material sources. We discuss the role/behavior of these modifications with regard to some low redshift tensions, including the so-called $H_0$ tension, prevailing within the standard $Λ$CDM. We constrain the model at the level of linear perturbations, and obtain the first constraints through a robust and accurate analysis using the latest full Planck CMB data, with and without including BAO data. We find that the Rastall parameter $ε$ (null for general relativity) is consistent with zero at 68\% CL (with a tendency towards positive values, $-0.0001 < ε< 0.0007$ (CMB+BAO) at 68\% CL), which in turn implies no significant statistical evidence for deviation from general relativity, and also a precision of $\mathcal{O}(10^{-4})$ for the coefficient $-1/2$ of the term $g_{μν}R$ in the Einstein field equations of general relativity (guaranteeing the local energy-momentum conservation). We explore the consequences led by the Rastall gravity on the cosmological parameters in the light of the observational analyses. It turns out that the effective source dynamically screens the usual vacuum energy at high redshifts, but this mechanism barely works due to the opposition by the altered evolution of CDM. Consequently, two simultaneous modifications of different nature in the Friedmann equation act against each other, and do not help to considerably relax the so-called low redshift tensions. Our results may offer a guide for the research community that studies the Rastall gravity in various aspects of gravitation and cosmology.

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arXiv2020

BAO signatures in the 2-point angular correlations and the Hubble tension

An observational tension on estimates of the Hubble parameter, $H_0$, using early and late Universe information, is being of intense discussion in the literature. Additionally, it is of great importance to measure $H_0$ independently of CMB data and local distance ladder method. In this sense, we analyze 15 measurements of the transversal BAO scale, $θ_{\rm BAO}$, obtained in a weakly model-dependent approach, in combination with other data sets obtained in a model-independent way, namely, Big Bang Nucleosynthesis (BBN) information, 6 gravitationally lensed quasars with measured time delays by the H0LiCOW team, and measures of cosmic chronometers (CC). We find $H_0 = 74.88_{-2.1}^{+1.9}$ km s${}^{-1}$ Mpc${}^{-1}$ and $H_0 = 72.06_{-1.3}^{+1.2}$ km s${}^{-1}$ Mpc${}^{-1}$ from $θ_{BAO}$+BBN+H0LiCOW and $θ_{BAO}$+BBN+CC, respectively, in fully accordance with local measurements. Moreover, we estimate the sound horizon at drag epoch, $r_{\rm d}$, independent of CMB data, and find $r_{\rm d}=144.1_{-5.5}^{+5.3}$ Mpc (from $θ_{BAO}$+BBN+H0LiCOW) and $r_{\rm d} =150.4_{-3.3}^{+2.7}$ Mpc (from $θ_{BAO}$+BBN+CC). In a second round of analysis, we test how the presence of a possible spatial curvature, $Ω_k$, can influence the main results. We compare our constraints on $H_0$ and $r_{\rm d}$ with other reported values. Our results show that it is possible to use a robust compilation of transversal BAO data, $θ_{BAO}$, jointly with other model-independent measurements, in such a way that the tension on the Hubble parameter can be alleviated.

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arXiv2020

Cosmology Intertwined III: $f σ_8$ and $S_8$

The standard $Λ$ Cold Dark Matter cosmological model provides a wonderful fit to current cosmological data, but a few tensions and anomalies became statistically significant with the latest data analyses. While these anomalies could be due to the presence of systematic errors in the experiments, they could also indicate the need for new physics beyond the standard model. In this Letter of Interest we focus on the tension of the Planck data with weak lensing measurements and redshift surveys, about the value of the matter energy density $Ω_m$, and the amplitude or rate of the growth of structure ($σ_8,fσ_8$). We list a few interesting models for solving this tension, and we discuss the importance of trying to fit with a single model a full array of data and not just one parameter at a time.

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arXiv2020

Cosmology Intertwined II: The Hubble Constant Tension

The current cosmological probes have provided a fantastic confirmation of the standard $Λ$ Cold Dark Matter cosmological model, that has been constrained with unprecedented accuracy. However, with the increase of the experimental sensitivity a few statistically significant tensions between different independent cosmological datasets emerged. While these tensions can be in portion the result of systematic errors, the persistence after several years of accurate analysis strongly hints at cracks in the standard cosmological scenario and the need for new physics. In this Letter of Interest we will focus on the $4.4σ$ tension between the Planck estimate of the Hubble constant $H_0$ and the SH0ES collaboration measurements. After showing the $H_0$ evaluations made from different teams using different methods and geometric calibrations, we will list a few interesting new physics models that could solve this tension and discuss how the next decade experiments will be crucial.

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arXiv2020

Cosmology Intertwined I: Perspectives for the Next Decade

The standard $Λ$ Cold Dark Matter cosmological model provides an amazing description of a wide range of astrophysical and astronomical data. However, there are a few big open questions, that make the standard model look like a first-order approximation to a more realistic scenario that still needs to be fully understood. In this Letter of Interest we will list a few important goals that need to be addressed in the next decade, also taking into account the current discordances present between the different cosmological probes, as the Hubble constant $H_0$ value, the $σ_8 - S_8$ tension, and the anomalies present in the Planck results. Finally, we will give an overview of upgraded experiments and next-generation space-missions and facilities on Earth, that will be of crucial importance to address all these questions.

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arXiv2020

Cosmology Intertwined IV: The Age of the Universe and its Curvature

A precise measurement of the curvature of the Universe is of primeval importance for cosmology since it could not only confirm the paradigm of primordial inflation but also help in discriminating between different early Universe scenarios. The recent observations, while broadly consistent with a spatially flat standard $Λ$ Cold Dark Matter ($Λ$CDM) model, are showing tensions that still allow (and, in some cases, even suggest) a few percent deviations from a flat universe. In particular, the Planck Cosmic Microwave Background power spectra, assuming the nominal likelihood, prefer a closed universe at more than 99\% confidence level. While new physics could be in action, this anomaly may be the result of an unresolved systematic error or just a statistical fluctuation. However, since a positive curvature allows a larger age of the Universe, an accurate determination of the age of the oldest objects provides a smoking gun in confirming or falsifying the current flat $Λ$CDM model.

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arXiv2020

Cosmological parameter analyses using transversal BAO data

We investigate observational constraints on cosmological parameters combining 15 measurements of the transversal BAO scale (obtained free of any fiducial cosmology) with Planck-CMB data to explore the parametric space of some cosmological models. We investigate how much Planck + transversal BAO data can constraint the minimum $Λ$CDM model, and extensions, including neutrinos mass scale $M_ν$, and the possibility for a dynamical dark energy (DE) scenario. Assuming the $Λ$CDM cosmology, we find $H_0 = 69.23 \pm 0.50$ km s${}^{-1}$ Mpc${}^{-1}$, $M_ν < 0.11$ eV and $r_{\rm drag} = 147.59 \pm 0.26$ Mpc (the sound horizon at drag epoch) from Planck + transversal BAO data. When assuming a dynamical DE cosmology, we find that the inclusion of the BAO data can indeed break the degeneracy of the DE free parameters, improving the constraints on the full parameter space significantly. We note that the model is compatible with local measurements of $H_0$ and there is no tension on $H_0$ estimates in this dynamical DE context. Also, we discuss constraints and consequences from a joint analysis with the local $H_0$ measurement from SH0ES. Finally, we perform a model-independent analysis for the deceleration parameter, $q(z)$, using only information from transversal BAO data.

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arXiv2020

Searching for modified gravity in the astrophysical gravitational wave background: Application to ground-based interferometers

We investigate how the propagation of an astrophysical gravitational wave background (AGWB) is modified over cosmological volumes when considering theories beyond general relativity of the type Horndeski gravity. We first deduce an amplitude correction on the AGWB induced for the presence of a possible running in the Planck mass. Then, we apply the spectral noise density from some ground-based interferometers, namely, the Advanced LIGO (aLIGO), Einstein Telescope (ET) and Cosmic Explore (CE), to evaluate the signal-to-noise ratio (SNR) as a function of the amplitude of the running of the Planck mass for two different scenarios. We find that for observation time period $\gtrsim$ 5 yrs and $\gtrsim$ 1 yr, we can have a significant signal of the AGWB in the band [1-100] Hz from the ET and CE sensitivity, respectively. Using Fisher information, we find some forecast bounds, and we deduce $\lesssim$ 27\% and $\lesssim$ 18\% correction at 1$σ$ confidence level on the amplitude of the running of the Planck mass from ET and CE, respectively. It is clear that a detection of a AGWB in future can open a new window to probe the nature of gravity with good accuracy.

gr-qc↗

arXiv2020

Effects of the Hubble Parameter on the Cosmic Growth of the First Quasars

Supermassive black holes (SMBHs) play a crucial role in the evolution of galaxies and are currently detected up to $z\sim 7.5$. Theories describing black hole (BH) growth are challenged by how rapidly seeds with initial mass $M_{\bullet} \lesssim 10^5 \, \mathrm{M_{\odot}}$, formed at $z \sim 20-30$, grew to $M_{\bullet} \sim 10^9 \, \mathrm{M_{\odot}}$ by $z\sim 7$. Here we study the effects of the value of the Hubble parameter, $H_0$, on models describing the early growth of BHs. First, we note that the predicted mass of a quasar at $z=6$ changes by $> 300$% if the underlying Hubble parameter used in the model varies from $H_0 = 65$ to $H_0 = 74$ km s$^{-1}$Mpc$^{-1}$, a range encompassing current estimates. Employing an MCMC approach based on priors from $z \gtrsim 6.5$ quasars and on $H_0$, we study the interconnection between $H_0$ and the parameters describing BH growth: seed mass $M_i$ and Eddington ratio $f_{\rm Edd}$. Assuming an Eddington ratio of $f_{\rm Edd} = 0.7$, in agreement with previous estimates, we find $H_0 = 73.6^{+1.2}_{-3.3}$ km s$^{-1}$Mpc$^{-1}$. In a second analysis, allowing all the parameters to vary freely, we find $\log(M_{i}/\mathrm{M_{\odot}}) > 4.5$ (at 95% CL), $H_0 = 74^{+1.5}_{-1.4}$ km s$^{-1}$Mpc$^{-1}$ and $f_{\rm Edd}=0.77^{+0.035}_{-0.026}$ at 68% CL. Our results on the typical Eddington ratio are in agreement with previous estimates. Current values of the Hubble parameter strongly favour heavy seed formation scenarios, with $M_i \gtrsim 10^4 \, \mathrm{M_{\odot}}$. In our model, with the priors on BH masses of quasars used, light seed formation scenarios are rejected at $\sim 3σ$.

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arXiv2020

Measurements of $H_0$ in modified gravity theories: The role of lensed quasars in the late-time Universe

In this work, we obtain measurements of the Hubble constant in the context of modified gravity theories. We set up our theoretical framework by considering viable cosmological $f(R)$ and $f(T)$ models, and we analyzed them through the use of geometrical data sets obtained in a model-independent way, namely, gravitationally lensed quasars with measured time delays, standard clocks from cosmic chronometers, and standard candles from the Pantheon Supernovae Ia sample. We find $H_0=(72.4\pm 1.4)$ km s$^{-1}$ Mpc$^{-1}$ and $H_0=(71.5\pm 1.3)$ km s$^{-1}$ Mpc$^{-1}$ for the $f(R)$ and $f(T)$ models, respectively. Our results represent 1.9\% and 1.8\% measurements of the Hubble constant, which are fully consistent with the local estimate of $H_0$ by the Hubble Space Telescope. We do not find significant departures from general relativity, as our study shows that the characteristic parameters of the extensions of gravity beyond general relativity are compatible with the $Λ$CDM cosmology. Moreover, within the standard cosmological framework, our full joint analysis suggests that it is possible to measure the dark energy equation of state parameter at 1.2\% accuracy, although we find no statistical evidence for deviations from the cosmological constant case.

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arXiv2020

All-inclusive interacting dark sector cosmologies

In this paper we explore possible extensions of Interacting Dark Energy cosmologies, where Dark Energy and Dark Matter interact non-gravitationally with one another. In particular, we focus on the neutrino sector, analyzing the effect of both neutrino masses and the effective number of neutrino species. We consider the Planck 2018 legacy release data combined with several other cosmological probes, finding no evidence for new physics in the dark radiation sector. The current neutrino constraints from cosmology should be therefore regarded as robust, as they are not strongly dependent on the dark sector physics, once all the available observations are combined. Namely, we find a total neutrino mass $M_ν<0.15$ eV and a number of effective relativistic degrees of freedom of $N_{\rm eff}=3.03^{+0.33}_{-0.33}$, both at 95\% CL, which are close to those obtained within the $Λ$CDM cosmology, $M_ν<0.12$ eV and $N_{\rm eff}=3.00^{+0.36}_{-0.35}$ for the same data combination.

astro-ph.CO↗

arXiv2020

Dark calling Dark: Interaction in the dark sector in presence of neutrino properties after Planck CMB final release

We investigate a well known scenario of interaction in the dark sector where the vacuum energy is interacting with cold dark matter throughout the cosmic evolution in light of the cosmic microwave background (CMB) data from final Planck 2018 release. In addition to this minimal scenario, we generalize the model baseline by including the properties of neutrinos, such as the neutrino mass scale ($M_ν$) and the effective number of neutrino species ($N_{\rm eff}$) as free parameters, in order to verify the possible effects that such parameters might generate on the coupling parameter, and vice versa. As already known, we again confirm that in light of the Planck 2018 data, such dark coupling can successfully solve the $H_0$ tension (with and without the presence of neutrinos). Concerning the properties of neutrinos, we find that $M_ν$ may be wider than expected within the $Λ$CDM model and $N_{\rm eff}$ is fully compatible with three neutrino species (similar to $Λ$CDM prevision). The parameters characterizing the properties of neutrinos do not correlate with the coupling parameter of the interaction model. When considering the joint analysis of CMB from Planck 2018 and an estimate of $H_0$ from Hubble Space Telescope 2019 data, {\it we find an evidence for a non-null value of the coupling parameter at more than 3$σ$ confidence-level.} We also discuss the possible effects on the interacting scenario due to the inclusion of baryon acoustic oscillations data with Planck 2018. Our main results updating the dark sectors' interaction and neutrino properties in the model baseline, represent a new perspective in this direction. Clearly, a possible new physics in light of some dark interaction between dark energy and dark matter can serve as an alternative to $Λ$CDM scenario to explain the observable Universe, mainly in light of the current tension on $H_0$.

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arXiv2020

Forecasts on the speed of gravitational waves at high $z$

The observation of GW170817 binary neutron star (BNS) merger event has imposed strong bounds on the speed of gravitational waves (GWs) locally, inferring that the speed of GWs propagation is equal to the speed of light. Current GW detectors in operation will not be able to observe BNS merger to long cosmological distance, where possible cosmological corrections on the cosmic expansion history are expected to play an important role, specially for investigating possible deviations from general relativity. Future GW detectors designer projects will be able to detect many coalescences of BNS at high $z$, such as the third generation of the ground GW detector called Einstein Telescope (ET) and the space-based detector deci-hertz interferometer gravitational wave observatory (DECIGO). In this paper, we relax the condition $c_T/c = 1$ to investigate modified GW propagation where the speed of GWs propagation is not necessarily equal to the speed of light. Also, we consider the possibility for the running of the Planck mass corrections on modified GW propagation. We parametrize both corrections in terms of an effective GW luminosity distance and we perform a forecast analysis using standard siren events from BNS mergers, within the sensitivity predicted for the ET and DECIGO. We find at high $z$ very strong forecast bounds on the running of the Planck mass, namely $\mathcal{O}(10^{-1})$ and $\mathcal{O}(10^{-2})$ from ET and DECIGO, respectively. Possible anomalies on GW propagation are bound to $|c_T/c - 1| \leq 10^{-2} \,\,\, (10^{-2})$ from ET (DECIGO), respectively. We finally discuss the consequences of our results on modified gravity phenomenology.

gr-qc↗

arXiv2019

Testing the warmness of dark matter

Dark matter (DM) as a pressureless perfect fluid provides a good fit of the standard $Λ$CDM model to the astrophysical and cosmological data. In this paper, we investigate two extended properties of DM: a possible time dependence of the equation of state of DM via Chevallier-Polarski-Linder parametrization, $w_{\rm dm} = w_{\rm dm 0} + w_{\rm dm 1}(1-a)$, and the constant non-null sound speed $\hat{c}^2_{\rm s,dm}$. We analyze these DM properties on top of the base $Λ$CDM model by using the data from Planck cosmic microwave background (CMB) temperature and polarization anisotropy, baryonic acoustic oscillations (BAO) and the local value of the Hubble constant from the Hubble Space Telescope (HST). We find new and robust constraints on the extended free parameters of DM. The most tight constraints are imposed by CMB + BAO data where the three parameters $w_{\rm dm0}$, $w_{\rm dm1}$ and $\hat{c}^2_{\rm s,dm}$ are respectively constrained to be less than $1.43\times 10^{-3}$, $1.44\times 10^{-3}$ and $1.79\times 10^{-6}$ at 95\% CL. All the extended parameters of DM show consistency with zero at 95\% CL, indicating no evidence beyond the CDM paradigm. We notice that the extended properties of DM significantly affect several parameters of the base $Λ$CDM model. In particular, in all the analyses performed here, we find significantly larger mean values of $H_0$ and lower mean values of $σ_8$ in comparison to the base $Λ$CDM model. Thus, the well-known $H_0$ and $σ_8$ tensions might be reconciled in the presence of extended DM parameters within the $Λ$CDM framework. Also, we estimate the warmness of DM particles as well as its mass scale and find a lower bound: $\sim$ 500 eV from our analyses.

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arXiv2019

Forecast constraints on $f(T)$ gravity with gravitational waves from compact binary coalescences

The direct detection of gravitational waves (GWs) opened a new chapter in the modern cosmology to probe possible deviations from the general relativity (GR) theory. In the present work, we investigate for the first time the modified GW form propagation from the inspiraling of compact binary systems within the context of $f(T)$ gravity in order to obtain new forecasts/constraints on the free parameter of the theory. First, we show that the modified waveform differs from the GR waveform essentially due to induced corrections on the GWs amplitude. Then, we discuss the forecasts on the $f(T)$ gravity assuming simulated sources of GWs as black hole binaries, neutron star binaries and black hole - neutron star binary systems, which emit GWs in the frequency band of the Advanced LIGO (aLIGO) interferometer and of the third generation Einstein Telescope (ET). We show that GWs sources detected within the aLIGO sensitivity can return estimates of the same order of magnitude of the current cosmological observations. On the other hand, detection within the ET sensitivity can improve by up to 2 orders of magnitude the current bound on the $f(T)$ gravity. Therefore, the statistical accuracy that can be achieved by future ground based GW observations, mainly with the ET detector (and planed detectors with a similar sensitivity), can allow strong bounds on the free parameter of the theory, and can be decisive to test the theory of gravitation.

gr-qc↗

arXiv2019

Probing observational bounds on scalar-tensor theories from standard sirens

Standard sirens are the gravitational wave (GW) analog of the astronomical standard candles, and can provide powerful information about the dynamics of the Universe. In this work, we simulate a catalog with 1000 standard siren events from binary neutron star mergers, within the sensitivity predicted for the third generation of the ground GW detector called Einstein telescope. After correctly modifying the propagation of GWs as input to generate the catalog, we apply our mock data set on scalar-tensor theories where the speed of GW propagation is equal to the speed of light. As a first application, we find new observational bounds on the running of the Planck mass, when considering appropriate values within the stability condition of the theory, and we discuss some consequences on the amplitude of the running of the Planck mass. In the second part, we combine our simulated standard sirens catalog with other geometric cosmological tests (Supernovae Ia and cosmic chronometers measurements) to constrain the Hu-Sawicki $f(R)$ gravity model. We thus find new and non-null deviations from the standard $Λ$CDM model, showing that in the future the $f(R)$ gravity can be tested up to 95\% confidence level. The results obtained here show that the statistical accuracy achievable by future ground based GW observations, mainly with the ET detector (and planed detectors with a similar sensitivity), can provide strong observational bounds on modified gravity theories.

gr-qc↗

arXiv2019

Listening to the sound of dark sector interactions with gravitational wave standard sirens

We consider two stable Interacting Dark Matter -- Dark Energy models and confront them against current Cosmic Microwave Background data from the \textit{Planck} satellite. We then generate luminosity distance measurements from ${\cal O}(10^3)$ mock Gravitational Wave events matching the expected sensitivity of the proposed Einstein Telescope. We use these to forecast how the addition of Gravitational Wave standard sirens data can improve current limits on the Dark Matter -- Dark Energy coupling strength ($ξ$). We find that the addition of Gravitational Waves data can reduce the current uncertainty by a factor of $5$. Moreover, if the underlying cosmological model truly features Dark Matter -- Dark Energy interactions with a value of $ξ$ within the currently allowed $1σ$ upper limit, the addition of Gravitational Wave data would help disentangle such an interaction from the standard case of no interaction at a significance of more than $3σ$.

astro-ph.CO↗

arXiv2019

Dark sector interaction: a remedy of the tensions between CMB and LSS data

The well-known tensions on the cosmological parameters $H_0$ and $σ_8$ within the $Λ$CDM cosmology shown by the Planck-CMB and LSS data are possibly due to the systematics in the data or our ignorance of some new physics beyond the $Λ$CDM model. In this letter, we focus on the second possibility, and investigate a minimal extension of the $Λ$CDM model by allowing a coupling between its dark sector components (dark energy and dark matter). We analyze this scenario with Planck-CMB, KiDS and HST data, and find that the $H_0$ and $σ_8$ tensions disappear at 68\% CL. In the joint analyzes with Planck, HST and KiDS data, we find non-zero coupling in the dark sector up to 99\% CL. Thus, we find a strong statistical support from the observational data for an interaction in the dark sector of the Universe while solving the $H_0$ and $σ_8$ tensions simultaneously.

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