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Villanueva-Domingo, P., & Villaescusa-Navarro, F. (2021). Removing Astrophysics in 21 cm Maps with Neural Networks. Astrophys. J., 907(1), 44–14pp.
Abstract: Measuring temperature fluctuations in the 21 cm signal from the epoch of reionization and the cosmic dawn is one of the most promising ways to study the universe at high redshifts. Unfortunately, the 21 cm signal is affected by both cosmology and astrophysics processes in a nontrivial manner. We run a suite of 1000 numerical simulations with different values of the main astrophysical parameters. From these simulations we produce tens of thousands of 21 cm maps at redshifts 10 <= z <= 20. We train a convolutional neural network to remove the effects of astrophysics from the 21 cm maps and output maps of the underlying matter field. We show that our model is able to generate 2D matter fields not only that resemble the true ones visually but whose statistical properties agree with the true ones within a few percent down to scales 2 Mpc(-1). We demonstrate that our neural network retains astrophysical information that can be used to constrain the value of the astrophysical parameters. Finally, we use saliency maps to try to understand which features of the 21 cm maps the network is using in order to determine the value of the astrophysical parameters.
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Villanueva-Domingo, P., Gnedin, N. Y., & Mena, O. (2018). Warm Dark Matter and Cosmic Reionization. Astrophys. J., 852(2), 139–7pp.
Abstract: 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 luminosity 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.
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de Salas, P. F., Gariazzo, S., Martinez-Mirave, P., Pastor, S., & Tortola, M. (2021). Cosmological radiation density with non-standard neutrino-electron interactions. Phys. Lett. B, 820, 136508–9pp.
Abstract: Neutrino non-standard interactions (NSI) with electrons are known to alter the picture of neutrino de coupling from the cosmic plasma. NSI modify both flavour oscillations through matter effects, and the annihilation and scattering between neutrinos and electrons and positrons in the thermal plasma. In view of the forthcoming cosmological observations, we perform a precision study of the impact of non universal and flavour-changing NSI on the effective number of neutrinos, Neff. We present the variation of Neff arising from the different NSI parameters and discuss the existing degeneracies among them, from cosmology alone and in relation to the current bounds from terrestrial experiments. Even though cosmology is generally less sensitive to NSI than these experiments, we find that future cosmological data would provide competitive and complementary constraints for some of the couplings and their combinations.
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de Putter, R., Mena, O., Giusarma, E., Ho, S., Cuesta, A., Seo, H. J., et al. (2012). New Neutrino Mass Bounds from SDSS-III Data Release 8 Photometric Luminous Galaxies. Astrophys. J., 761(1), 12–12pp.
Abstract: We present neutrino mass bounds using 900,000 luminous galaxies with photometric redshifts measured from Sloan Digital Sky Survey III Data Release 8. The galaxies have photometric redshifts between z = 0.45 and z = 0.65 and cover 10,000 deg(2), thus probing a volume of 3 h(-3) Gpc(3) and enabling tight constraints to be derived on the amount of dark matter in the form of massive neutrinos. A new bound on the sum of neutrino masses Sigma m nu < 0.27 eV, at the 95% confidence level (CL), is obtained after combining our sample of galaxies, which we call “CMASS,” with Wilkinson Microwave Anisotropy Probe (WMAP) seven-year cosmic microwave background data and the most recent measurement of the Hubble parameter from the Hubble Space Telescope (HST). This constraint is obtained with a conservative multipole range of 30 < l < 200 in order to minimize nonlinearities, and a free bias parameter in each of the four redshift bins. We study the impact of assuming this linear galaxy bias model using mock catalogs and find that this model causes a small (similar to 1 sigma-1.5 sigma) bias in Omega(DM)h(2). For this reason, we also quote neutrino bounds based on a conservative galaxy bias model containing additional, shot-noise-like free parameters. In this conservative case, the bounds are significantly weakened, e. g., Sigma m(nu) < 0.38 eV (95% CL) for WMAP+HST+CMASS (l(max) = 200). We also study the dependence of the neutrino bound on the multipole range (l(max) = 150 versus l(max) = 200) and on which combination of data sets is included as a prior. The addition of supernova and/or baryon acoustic oscillation data does not significantly improve the neutrino mass bound once the HST prior is included. A companion paper describes the construction of the angular power spectra in detail and derives constraints on a general cosmological model, including the dark energy equation of state w and the spatial curvature Omega(K), while a second companion paper presents a measurement of the scale of baryon acoustic oscillations from the same data set. All three works are based on the catalog by Ross et al.
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Seo, H. J. et al, & de Putter, R. (2012). Acoustic scale from the angular power spectra of SDSS-III DR8 photometric luminous galaxies. Astrophys. J., 761(1), 13–16pp.
Abstract: We measure the acoustic scale from the angular power spectra of the Sloan Digital Sky Survey III (SDSS-III) Data Release 8 imaging catalog that includes 872, 921 galaxies over similar to 10,000 deg(2) between 0.45 < z < 0.65. The extensive spectroscopic training set of the Baryon Oscillation Spectroscopic Survey luminous galaxies allows precise estimates of the true redshift distributions of galaxies in our imaging catalog. Utilizing the redshift distribution information, we build templates and fit to the power spectra of the data, which are measured in our companion paper, to derive the location of Baryon acoustic oscillations (BAOs) while marginalizing over many free parameters to exclude nearly all of the non-BAO signal. We derive the ratio of the angular diameter distance to the sound horizon scale D-A(z)/r(s) = 9.212(-0.404)(+0.416) at z = 0.54, and therefore D-A(z) = 1411 +/- 65 Mpc at z = 0.54; the result is fairly independent of assumptions on the underlying cosmology. Our measurement of angular diameter distance D-A(z) is 1.4 sigma higher than what is expected for the concordance Lambda CDM, in accordance to the trend of other spectroscopic BAO measurements for z greater than or similar to 0.35. We report constraints on cosmological parameters from our measurement in combination with the WMAP7 data and the previous spectroscopic BAO measurements of SDSS and WiggleZ. We refer to our companion papers (Ho et al.; de Putter et al.) for investigations on information of the full power spectrum.
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Olmo, G. J., & Rubiera-Garcia, D. (2015). Brane-world and loop cosmology from a gravity-matter coupling perspective. Phys. Lett. B, 740, 73–79.
Abstract: We show that the effective brane-world and the loop quantum cosmology background expansion histories can be reproduced from a modified gravity perspective in terms of an f (R) gravity action plus a g(R) term non-minimally coupled with the matter Lagrangian. The reconstruction algorithm that we provide depends on a free function of the matter density that must be specified in each case and allows to obtain analytical solutions always. In the simplest cases, the function f (R) is quadratic in the Ricci scalar, R, whereas g(R) is linear. Our approach is compared with recent results in the literature. We show that working in the Palatini formalism there is no need to impose any constraint that keeps the equations second order, which is a key requirement for the successful implementation of the reconstruction algorithm.
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Beltran Jimenez, J., Heisenberg, L., Olmo, G. J., & Rubiera-Garcia, D. (2018). Born-Infeld inspired modifications of gravity. Phys. Rep., 727, 1–129.
Abstract: General Relativity has shown an outstanding observational success in the scales where it has been directly tested. However, modifications have been intensively explored in the regimes where it seems either incomplete or signals its own limit of validity. In particular, the breakdown of unitarity near the Planck scale strongly suggests that General Relativity needs to be modified at high energies and quantum gravity effects are expected to be important. This is related to the existence of spacetime singularities when the solutions of General Relativity are extrapolated to regimes where curvatures are large. In this sense, Born-Infeld inspired modifications of gravity have shown an extraordinary ability to regularise the gravitational dynamics, leading to non-singular cosmologies and regular black hole spacetimes in a very robust manner and without resorting to quantum gravity effects. This has boosted the interest in these theories in applications to stellar structure, compact objects, inflationary scenarios, cosmological singularities, and black hole and wormhole physics, among others. We review the motivations, various formulations, and main results achieved within these theories, including their observational viability, and provide an overview of current open problems and future research opportunities.
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Sanchis-Lozano, M. A., Melia, F., Lopez-Corredoira, M., & Sanchis-Gual, N. (2022). Missing large-angle correlations versus even-odd point-parity imbalance in the cosmic microwave background. Astron. Astrophys., 660, A121–10pp.
Abstract: Context. The existence of a maximum correlation angle (theta(max) & 60 greater than or similar to degrees) in the two-point angular temperature correlations of cosmic microwave background (CMB) radiation, measured by WMAP and Planck, stands in sharp contrast to the prediction of standard inflationary cosmology, in which the correlations should extend across the full sky (i.e., 180 degrees). The introduction of a hard lower cuto ff (k(min)) in the primordial power spectrum, however, leads naturally to the existence of theta(max). Among other cosmological anomalies detected in these data, an apparent dominance of odd-over-even parity multipoles has been seen in the angular power spectrum of the CMB. This feature, however, may simply be due to observational contamination in certain regions of the sky. Aims. In attempting to provide a more detailed assessment of whether this odd-over-even asymmetry is intrinsic to the CMB, we therefore proceed in this paper, first, to examine whether this odd-even parity imbalance also manifests itself in the angular correlation function and, second, to examine in detail the interplay between the presence of theta(max) and this observed anomaly. Methods. We employed several parity statistics and recalculated the angular correlation function for di fferent values of the cuto ff kmin in order to optimize the fit to the di fferent Planck 2018 data. Results. We find a phenomenological connection between these features in the data, concluding that both must be considered together in order to optimize the theoretical fit to the Planck 2018 data. Conclusions. This outcome is independent of whether the parity imbalance is intrinsic to the CMB, but if it is, the odd-over-even asymmetry would clearly point to the emergence of new physics.
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Schiavone, T., Montani, G., & Bombacigno, F. (2023). f(R) gravity in the Jordan frame as a paradigm for the Hubble tension. Mon. Not. Roy. Astron. Soc., 522(1), L72–L77.
Abstract: We analyse the f(R) gravity in the so-called Jordan frame, as implemented to the isotropic Universe dynamics. The goal of the present study is to show that according to recent data analyses of the supernovae Ia Pantheon sample, it is possible to account for an effective redshift dependence of the Hubble constant. This is achieved via the dynamics of a non-minimally coupled scalar field, as it emerges in the f(R) gravity. We face the question both from an analytical and purely numerical point of view, following the same technical paradigm. We arrive to establish that the expected decay of the Hubble constant with the redshift z is ensured by a form of the scalar field potential, which remains essentially constant for z less than or similar to 0.3, independently if this request is made a priori, as in the analytical approach, or obtained a posteriori, when the numerical procedure is addressed. Thus, we demonstrate that an f(R) dark energy model is able to account for an apparent variation of the Hubble constant due to the rescaling of the Einstein constant by the f(R) scalar mode.
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Giare, W., Renzi, F., Mena, O., Di Valentino, E., & Melchiorri, A. (2023). Is the Harrison-Zel'dovich spectrum coming back? ACT preference for n(s) similar to 1 and its discordance with Planck. Mon. Not. Roy. Astron. Soc., 521(2), 2911–2918.
Abstract: The Data Release 4 of the Atacama Cosmology Telescope (ACT) shows an agreement with an Harrison-Zel'dovich primordial spectrum (n(s) = 1.009 +/- 0.015), introducing a tension with a significance of 99.3 per cent Confidence Level (CL) with the results from the Planck satellite. The discrepancy on the value of the scalar spectral index is neither alleviated with the addition of large scale structure information nor with the low multipole polarization data. We discuss possible avenues to alleviate the tension relying on either neglecting polarization measurements from ACT or in extending different sectors of the theory.
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