Lyman-α Data Research Articles

Weighing massive neutrinos with Lyman-α observations

The presence of massive neutrinos has still not been revealedby the cosmological data. We considera novel method based on the two-point line-of-sight correlation function ofhigh-resolution Lyman-α data to achieve this end in the paper.We adopt semi-analytic models of Lyman-αclouds for the study. We employ Fisher matrix technique to show thatit is possible to achieve a scenario in whichthe covariance of the two-point function nearly vanishes for both the spectroscopic noise and the signal.We analyze this near `zero noise' outcome in detail to argue it might be possible to detect neutrinosof mass range m ν ≃ 0.05–0.1 eV with signal-to-noise of unity witha single QSO line of sight. We show that this estimate can be improved to SNR ≃ 3–6 with data along multiple line of sightswithin the redshift range z ≃ 2–2.5.Such data sets already exist in the literature.We further carry outprincipal component analysis of the Fisher matrix to study the degeneraciesof the neutrino mass with otherparameters. We show that Planck priors lift the degeneracies betweenthe neutrino mass and other cosmological parameters.However, the prospects of the detection of neutrino mass are driven by the poorly-determined parameters characterizing the ionization and thermal state of Lyman-α clouds. We have also mentioned the possible limitations andobservational challenges posed in measuring the neutrino mass using our method.

Constraining ultra slow roll inflation using cosmological datasets

In recent years, the detection of gravitational waves by LIGO and PTA collaborationshave raised the intriguing possibility of excess matter power at small scales. Such anincrease can be achieved by ultra slow roll (USR) phase during inflationary epoch.We constrain excess power over small scales within the framework of such models usingcosmological datasets, particularly of CMB anisotropies and Lyman-α.We parameterize the USR phase in terms of thee-fold at the onset of USR (counted from the end of inflation) N̅1 andthe duration of USR phase Δ N.The former dictates the scale of enhancement in the primordial power spectrum, while the latter determines the amplitude of such anenhancement.From a joint dataset of CMB and galaxy surveys, we obtainN̅1 ≲ 45 with no bound on Δ N. This in turn implies thatthe scales over which the power spectrum can deviate significantly from thenearly scale invariant behavior of a typical slow-roll model isk ≳1 Mpc-1.On the other hand, the Lyman-α data is sensitive to baryonic powerspectrum along the line of sight. We consider a semi-analytic theoretical methodand high spectral-resolution Lyman-α data to constrain the model.The Lyman-α data limits both the USR parameters:N̅1 ≲ 41 and Δ N ≲ 0.4.This constrains the amplitude of the power spectrum enhancement to be less thana factor of hundred over scales 1 ≲ k/ Mpc-1≲ 100,thereby considerably improving the constraint on power over these scales ascompared to the bounds arrived at from CMB spectral distortion.

Cosmological constraints from the eBOSS Lyman-α forest using the PRIYA simulations

We present new cosmological parameter constraints from the eBOSS Lyman-α forest survey. We use a new theoretical model and likelihood based on the PRIYA simulation suite. PRIYA is the first suite to resolve the Lyman-α forest in a (120 Mpc/h)3 volume, using a multi-fidelity emulation technique. We use PRIYA to predict Lyman-α forest observables with ≲ 1% interpolation error over an 11 dimensional (9 simulated, 2 in post-processing) parameter space. We identify an internal tension within the flux power spectrum data. Once the discrepant data is removed, we find the primeval scalar spectral index measured at a pivot scale of k 0 = 0.78 Mpc-1 to be nP = 1.009+0.027 -0.018 at 68% confidence. This measurement from the Lyman-α forest flux power spectrum alone is in reasonable agreement with Planck, and in tension with earlier eBOSS analyses. The amplitude of matter fluctuations is σ 8 = 0.733+0.026 -0.029 at 68% confidence, in agreement with Dark Energy Survey weak lensing measurements and other small-scale structure probes and in tension with CMB measurements from Planck and ACT. The effective optical depth to Lyman-α photons from our pipeline is in good agreement with earlier high resolution measurements. We find a linear power at z = 3 and k = 0.009 s/km of Δ2 L = 0.302+0.024 -0.027 with a slope n eff = -2.264+0.026 -0.018. Our flux power spectrum only chains prefer a low level of heating during helium reionization. When we add IGM temperature data we find nP = 0.983 ± 0.020 and σ 8 = 0.703+0.023 -0.027. Our chains prefer an early and long helium reionization event, as suggested by measurements from the helium Lyman-α forest. In the near future we will use our pipeline to infer cosmological parameters from the DESI Lyman-α data.

Decaying Dark Matter and Lyman-α forest constraints

Decaying Cold Dark Matter (DCDM) is a model that is currently under investigation regarding primarily the S 8 tension between cosmic microwave background (CMB) and certain large-scale structure measurements. The decay into one massive and one (or more) massless daughter particle(s) leads to a suppression of the power spectrum in the late universe that depends on the relative mass splitting ϵ = (1 - m 2/M 2)/2 between the mother and massive daughter particle as well as the lifetime τ. In this work we investigate the impact of the BOSS DR14 one-dimensional Lyman-α forest flux power spectrum on the DCDM model using a conservative effective model approach to account for astrophysical uncertainties. Since the suppression of the power spectrum due to decay builds up at low redshift, we find that regions in parameter space that address the S 8 tension can be well compatible with the Lyman-α forest. Nevertheless, for values of the degeneracy parameter ϵ ∼ 0.1-0.5%, for which the power suppression occurs within the scales probed by BOSS Lyman-α data, we find improved constraints compared to previous CMB and galaxy clustering analyses, obtaining τ ≳ 18 Gyrs for small mass splitting. Furthermore, our analysis of the BOSS Lyman-α flux power spectrum allows for values τ ∼ 102 Gyrs, ϵ ∼ 1%, that have been found to be preferred by a combination of Planck and galaxy clustering data with a KiDS prior on S 8, and we even find a hint for a marginal preference within this regime.

Model selection with baryonic acoustic oscillations in the Lyman-α forest

The recent release of the final, complete survey of Lyman-α baryonic acoustic oscillation measurements provides the most significant and accurate data base for studying cosmic geometry at an effective redshift , which is inaccessible to other sources. In this paper, we use these data to select among four distinct cosmologies: Planck ΛCDM, the universe, the Milne universe and the Einstein-de Sitter universe. Given the breadth and depth of the Lyman-α study, this BAO measurement alone provides a strong model comparison, complementary to previous studies that combined Lyman-α data with measurements at lower redshifts. Though both approaches are useful, the latter tends to dilute the disparity between model predictions and the observations. We therefore examine how the models compare to each other strictly based on the BAO scale measured in the Lyman-α forest and background quasars. We find that the Milne universe and the Einstein-de Sitter universe are strongly ruled out by these data. There is also strong evidence disfavoring the standard model. The Lyman-α measurements are completely consistent with the cosmic geometry predicted by . As such, evidence continues to grow that the zero active mass condition from general relativity ought to be an essential ingredient in ΛCDM.

One likelihood to bind them all: Lyman-α constraints on non-standard dark matter

Recent cosmological tensions have rekindled the search for models beyond ΛCDM that cause a suppression of the matter power spectrum. Due to the small scales accessible to Lyman-α data they are an excellent additional tool to probe such models. In this work we extend a recently-developed approach for using Lyman-α data to constrain the power spectrum suppression caused by almost any mixture of cold and non-standard dark matter. We highlight the steps involved in the development of a corresponding likelihood that will be publicly released upon publication of this work. We study three examples of models suppressing the power spectrum, namely feebly interacting dark matter, dark matter interacting with baryons, and mixed cold+warm dark matter. The latter two can be well constrained from Lyman-α data, and we derive novel conclusions on the cosmologically allowed parameter spaces, including finding a mild preference for non-zero interactions between dark matter and baryons. The consistency of the constraints obtained on these models highlight the robustness and flexibility of the likelihood developed here.

Dark matter self-interactions in the matter power spectrum

We study the imprints of secluded dark sectors with a mass gap and self-interactions on the matter power spectrum. When Dark Matter (DM) is sufficiently light, in the ballpark of a few KeV, and self-interacting we find qualitative difference with respect to ΛCDM and also to free streaming DM. In order to emphasize the role of interactions for the evolution of the primordial perturbations we discuss various regimes: ranging from the ideal case of a tightly coupled perfect fluid to the free case of Warm Dark Matter, including the realistic case of small but non-vanishing self-interactions. We compute the matter power spectrum in all these regimes with the aid of Boltzmann solvers. Light dark sectors with self-interactions are efficiently constrained by Lyman-α data and we find that the presence of self-interactions relaxes the bound on the DM mass. As a concrete realization we study models with dark QCD-like sectors, where DM is made of light dark-pions.

Using the redshift evolution of the Lyman-α effective opacity as a probe of dark matter models

Lyman-α forest data are known to be a good probe of the small scale matter power. In this paper, we explore the redshift evolution of the observable effective optical depth τeff (z) from the Lyman-α data as a discriminator between dark matter models that differ from the ΛCDM model on small scales. We consider the thermal warm dark matter (WDM) and the ultra-light axion (ULA) models for the following set of parameters: the mass of ULA, ma ≃ 10-24–5 × 10-22 eV and WDM mass, m_ wdm = 0.1 – 4.6 keV. We simulate the line-of-sight HI density and velocity fields using semi-analytic methods. The simulated effective optical depth for the alternative dark matter models diverges from the ΛCDM model for z ≳ 3, which provides a meaningful probe of the matter power at small scales. Using likelihood analysis, we compare the simulated data with the high-resolution Lyman-α forest data in the redshift range 2 < z < 4.2. The analysis yields the following 1σ bounds on dark matter masses: m_ wdm > 0.7 keV and m_ a > 2 × 10-23 eV. To further test the efficacy of our proposed method, we simulate synthetic data sets compatible with the ΛCDM model in the redshift range 2 ≤ z ≤ 6.5 and compare with theory. The 1σ bounds obtained are significantly tighter: m_ wdm > 1.5 keV and m_ a > 7 × 10-23 eV. Although our method provides an alternative way of constraining dark matter models, we note that these bounds are weaker than those obtained by high-resolution hydrodynamical simulations.

The cosmological evolution of self-interacting dark matter

We study the evolution of cosmological perturbations in dark-matter models with elastic and velocity-independent self interactions. Such interactions are imprinted in the matter-power spectrum as dark acoustic oscillations, which can be experimentally explored to determine the strength of the self scatterings. Models with self interactions have similarities to warm dark matter, as they lead to suppression of power on small scales when the dark-matter velocity dispersion is sizable. Nonetheless, both the physical origin and the extent of the suppression differ for self-interacting dark matter from conventional warm dark matter, with a dark sound horizon controlling the reduction of power in the former case, and a free-streaming length in the latter.We thoroughly analyze these differences by performing computations of the linear power spectrum using a newly developed Boltzmann code. We find that while current Lyman-α data disfavor conventional warm dark matter with a mass less than 5.3 keV, when self interactions are included at their maximal value consistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4 keV. Finally, we make use of our analysis to set novel bounds on light scalar singlet dark matter.

Neutrino mass bounds from confronting an effective model with BOSS Lyman-α data

We present an effective model for the one-dimensional Lyman-α flux power spectrum far above the baryonic Jeans scale. The main new ingredient is constituted by a set of two parameters that encode the impact of small, highly non-linear scales on the one-dimensional power spectrum on large scales, where it is measured by BOSS. We show that, by marginalizing over the model parameters that capture the impact of the intergalactic medium, the flux power spectrum from both simulations and observations can be described with high precision. The model displays a degeneracy between the neutrino masses and the (unknown, in our formalism) normalization of the flux power spectrum. This degeneracy can be lifted by calibrating one of the model parameters with simulation data, and using input from Planck CMB data. We demonstrate that this approach can be used to extract bounds on the sum of neutrino masses with comparably low numerical effort, while allowing for a conservative treatment of uncertainties from the dynamics of the intergalactic medium. An explorative analysis yields an upper bound of 0.16eV at 95% C.L. when applied to BOSS data at 3 ≤ z ≤ 4.2. We also forecast that if the systematic and statistical errors will be reduced by a factor two the upper bound will become 0.1eV at 95% C.L, and 0.056eV when assuming a 1% error.

Non-cold dark matter from primordial black hole evaporation

Dark matter coupled solely gravitationally can be produced through the decay of primordial black holes in the early universe. If the dark matter is lighter than the initial black hole temperature, it could be warm enough to be subject to structure formation constraints. In this paper we perform a more precise determination of these constraints. We first evaluate the dark matter phase-space distribution, without relying on the instantaneous decay approximation. We then interface this phase-space distribution with the Boltzmann code to extract the corresponding matter power spectrum, which we find to match closely those of warm dark matter models, albeit with a different dark matter mass. This mapping allows us to extract constraints from Lyman-α data without the need to perform hydrodynamical simulations. We robustly rule out the possibility, consistent with previous analytic estimates, of primordial black holes having come to dominate the energy density of the universe and simultaneously given rise to all the DM through their decay. Consequences and implications for dark radiation and leptogenesis are also briefly discussed.

Hints, neutrino bounds, and WDM constraints from SDSS DR14 Lyman-α and Planck full-survey data

The Lyman-α forest 1D flux power spectrum is a powerful probe of several cosmological parameters. Assuming a ΛCDM cosmology including massive neutrinos, we find that the latest SDSS DR14 BOSS and eBOSS Lyman-α forest data is in very good agreement with current weak lensing constraints on (Ωm, σ8) and has the same small level of tension with Planck. We did not identify a systematic effect in the data analysis that could explain this small tension, but we show that it can be reduced in extended cosmological models where the spectral index is not the same on the very different times and scales probed by CMB and Lyman-α data. A particular case is that of a ΛCDM model including a running of the spectral index on top of massive neutrinos. With combined Lyman-α and Planck data, we find a slight (3σ) preference for negative running, αs= −0.010 ± 0.004 (68%CL). Neutrino mass bounds are found to be robust against different assumptions. In the ΛCDM model with running, we find ∑ mν <0.11 eV at the 95% confidence level for combined Lyman-α and Planck (temperature and polarisation) data, or ∑ mν < 0.09 eV when adding CMB lensing and BAO data. We further provide strong and nearly model-independent bounds on the mass of thermal warm dark matter. For a conservative configuration consisting of SDSS data restricted to z<4.5 combined with XQ-100 Lyman-α data, we find mX > 5.3 keV (95%CL).

Constraining Dark Matter-Dark Radiation interactions with CMB, BAO, and Lyman-α

Several interesting Dark Matter (DM) models invoke a dark sector leading to two types of relic particles, possibly interacting with each other: non-relativistic DM, and relativistic Dark Radiation (DR) . These models have interesting consequences for cosmological observables, and could in principle solve problems like the small-scale cold DM crisis, Hubble tension, and/or low σ8 value. Their cosmological behaviour is captured by the ETHOS parametrisation, which includes a DR-DM scattering rate scaling like a power-law of the temperature, Tn. Scenarios with n=0, 2, or 4 can easily be realised in concrete dark sector set-ups. Here we update constraints on these three scenarios using recent CMB, BAO, and high-resolution Lyman-α data. We introduce a new Lyman-α likelihood that is applicable to a wide range of cosmological models with a suppression of the matter power spectrum on small scales. For n=2 and 4, we find that Lyman-α data strengthen the CMB+BAO bounds on the DM-DR interaction rate by many orders of magnitude. However, models offering a possible solution to the missing satellite problem are still compatible with our new bounds. For n=0, high-resolution Lyman-α data bring no stronger constraints on the interaction rate than CMB+BAO data, except for extremely small values of the DR density. Using CMB+BAO data and a theory-motivated prior on the minimal density of DR, we find that the n=0 model can reduce the Hubble tension from 4.1σ to 2.7σ, while simultaneously accommodating smaller values of the σ8 and S8 parameters hinted by cosmic shear data.

Lyman-α forest constraints on interacting dark sectors

The Lyman-α forest is a valuable probe of dark matter models featuring a scale-dependent suppression of the power spectrum as compared to ΛCDM . In this work, we present a new estimator of the Lyman-α flux power spectrum that does not rely on hydrodynamical simulations. Our framework is characterized by nuisance parameters that encapsulate the complex physics of the intergalactic medium and sensitivity to highly non-linear small-scale modes. After validating the approach based on high-resolution hydrodynamical simulations for ΛCDM, we derive conservative constraints on interacting dark matter models from BOSS Lyman-α data on large scales, k<0.02 (km/s)−1, with the relevant nuisance parameters left free in the model fit. The estimator yields lower bounds on the mass of cannibal dark matter, where freeze-out occurs through 3 → 2 annihilation, in the MeV range. Furthermore, we find that models of dark matter interacting with dark radiation, which have been argued to address the H0 and σ8 tensions, are compatible with BOSS Lyman-α data.

How late can the dark matter form in our universe?

We put constraints on the epoch of dark matter formation for a class of non-WIMP (Weakly Interacting Massive Particle) dark matter candidates. These models allow a fraction of Cold Dark Matter (CDM) to be formed between the epoch of Big Bang Nucleosynthesis (BBN) and the matter radiation equality. We show that for such models the matter power spectra might get strong suppression even on scales that could be probed by linear perturbation theory at low redshifts. Unlike the case of Warm Dark Matter (WDM), where the mass of the dark matter particle controls the suppression scale, in Late Forming Dark Matter (LFDM) scenario, it is the redshift of the dark matter formation which determines the form of the matter power spectra. We use the Sloan Digital Sky Survey (SDSS) galaxy clustering data and the linear matter power spectrum reconstructed from the Lyman-α data to find the latest epoch of the dark matter formation in our universe. If all the observed dark matter is late forming, we find lower bounds on the redshift of dark matter formation zf > 1.08 × 105 at 99.73 % C.L from the SDSS data and zf > 9 × 105, at the same C.L, from the Lyman-α data. If only a fraction of the dark matter is late forming then we find tentative evidence of the presence of LFDM from the Lyman-α data. Upcoming data from SDSS-III/BOSS (Baryon Oscillation Spectroscopic Survey) will allow us to explore this issue in more detail.

TESTING FOR FEATURES IN THE PRIMORDIAL POWER SPECTRUM

Well-known causality arguments show that events occurring during or at the end of inflation, associated with reheating or preheating, could contribute a blue component to the spectrum of primordial curvature perturbations, with the dependence k3. We explore the possibility that they could be observably large in CMB, LSS, and Lyman-α data. We find that a k3 component with a cutoff at some maximum k can modestly improve the fits (Δχ2 = 2.0, 5.4) of the low multipoles (ℓ ~ 10–50) or the second peak (ℓ ~ 540) of the CMB angular spectrum when the three-year WMAP data are used. Moreover, the results from WMAP are consistent with the CBI, ACBAR, 2dFGRS, and SDSS data when they are included in the analysis. Including the SDSS galaxy clustering power spectrum, we find weak positive evidence for the k3 component at the level of Δχ2′ = 2.4, with the caveat that the nonlinear evolution of the power spectrum may not be properly treated in the presence of the k3 distortion. To investigate the high-k regime, we use the Lyman-α forest data (LUQAS, Croft et al., and SDSS Lyman-α); here we find evidence at the level Δχ2′ = 3.8. Considering that there are two additional free parameters in the model, the above results do not give a strong evidence for features; however, they show that surprisingly large bumps are not ruled out. We give constraints on the ratio between the k3 component and the nearly scale-invariant component, r3 &lt; 1.5, over the range of wave numbers 2.3 × 10-3 Mpc -1 &lt; k &lt; 8.2 Mpc -1. We also discuss theoretical models which could lead to the k3 effect, including ordinary hybrid inflation and double D-term inflation models. We show that the well-motivated k3 component is also a good representative of the generic spikelike feature in the primordial perturbation power spectrum.

Lyman-α constraints on warm and on warm-plus-cold dark matter models

We revisit Lyman-α bounds on the dark matter mass in Λ Warm Dark Matter (ΛWDM) models, and derive new bounds in the case of mixed Cold plus Warm models (ΛCWDM), using a set up which is a good approximation for several theoretically well-motivated dark matter models. We combine WMAP5 results with two different Lyman-α data sets, including observations from the Sloan Digital Sky Survey. We pay a special attention to systematics, test various possible sources of error, and compare the results of different statistical approaches. Expressed in terms of the mass of a non-resonantly produced sterile neutrino, our bounds read mNRP ⩾ 8 keV (frequentist 99.7% confidence limit) or mNRP ⩾ 12.1 keV (Bayesian 95% credible interval) in the pure ΛWDM limit. For the mixed model, we obtain limits on the mass as a function of the warm dark matter fraction FWDM. Within the mass range studied here (5 keV < mNRP < ∞), we find that any mass value is allowed when FWDM < 0.6 (frequentist 99.7% confidence limit); similarly, the Bayesian joint probability on (FWDM, 1/mNRP) allows any value of the mass at the 95% confidence level, provided that FWDM < 0.35.

Observational bounds on the cosmic radiation density

We consider the inference of the cosmic radiation density,traditionally parametrized as the effective number of neutrino speciesNeff, from precision cosmological data. Paying particular attention to systematic effects, notablyscale-dependent biasing in the galaxy power spectrum, we find no evidence for a significant deviation ofNeff from thestandard value of Neff0 = 3.046 in any combination of cosmological data sets, in contrast to some recent conclusions of otherauthors. The combination of all available data in the linear regime favours, in the context of a‘vanilla+Neff’ cosmological model, 1.1<Neff<4.8 (95% CL) with a best-fit value of 2.6. Adding data at smaller scales, notably theLyman-α forest, we find 2.2<Neff<5.8 (95% CL) with 3.8 as the best fit. Inclusion of theLyman-α data shiftsthe preferred Neff upwards because the σ8 value derived from the SDSS (Sloan Digital Sky Survey)Lyman-α data is inconsistent with that inferred from the cosmic microwave background.In an extended cosmological model that includes a non-zero mass forNeff neutrino flavours, a running scalar spectral index and aw parameter for thedark energy, we find 0.8<Neff<6.1 (95% CL) with 3.0 as the best fit.

The neutrino mass bound from WMAP 3 year data, the baryon acoustic peak, the SNLS supernovae and theLyman-α forest

We have studied bounds on the neutrino mass using new data from theWMAP 3 year data, the Sloan Digital Sky Survey measurement of thebaryon acoustic (BAO) peak, the Type Ia supernovae from SNLS, and theLyman-α forest. We find that even in the most general models with a running spectral index wherethe number of neutrinos and the dark energy equation of state are allowed to vary, the 95%confidence limit (C.L.) bound on the sum of neutrino masses is eV (95% C.L.), a bound which we believe to be robust. In the more often used constrained analysiswith Nν = 3, w = −1,and αs = 0, we find a bound of 0.48 eV without using theLyman-α data.If the Lyman-α data are used, the bound shrinks to eV (95% C.L.), depending strongly on theLyman-α analysis used. Finally, we have also calculated how the effectiveA-parameter used in the SDSS BAO analyses changes under the influence of a non-zero neutrino mass. Wefind that A = 0.469(n/0.98)−0.35(1+0.94Ων/Ωm) ± 0.017.

Pioneer 10 and Voyagers 1 and 2 backscattered UV data and the nature of the interstellar medium

It has not yet been unambiguously established whether the bulk velocity of the very local interstellar medium (VLISM) relative to the Sun is subsonic or supersonic. Till now there has been no way to decide between the two possibilities although the backscattered UV data base obtained from the Pioneer 10 and Voyagers 1 and 2 missions in principle contain the required information. The principal difficulty in interpreting the UV data has been the lack of self-consistent heliospheric models. In recent years, however, several self-consistent models have become available. We have used two two-dimensional axisymmetric hydrodynamic models of the heliosphere developed by one of the authors for both supersonic and subsonic VLISM flow and compared their predictions with the observed backscattered Lyman-α data. We found that neither model can satisfactorily reproduce the observed Pioneer 10 and Voyager 2 UV data except for the large distance Pioneer 10 downstream UV data.