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The Lyman-$alpha$ forest is a valuable probe of dark matter models featuring a scale-dependent suppression of the power spectrum as compared to $Lambda$CDM. In this work, we present a new estimator of the Lyman-$alpha$ 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 $Lambda$CDM, we derive conservative constraints on interacting dark matter models from BOSS Lyman-$alpha$ 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-to-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 $H_0$ and $sigma_8$ tensions, are compatible with BOSS Lyman-$alpha$ data.
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The renewed interest in the possibility that primordial black holes (PBHs) may constitute a significant part of the dark matter has motivated revisiting old observational constraints, as well as developing new ones. We present new limits on the PBH abundance, from a comprehensive analysis of high-resolution, high-redshift Lyman-$alpha$ forest data. Poisson fluctuations in the PBH number density induce a small-scale power enhancement which departs from the standard cold dark matter prediction. Using a grid of hydrodynamic simulations exploring different values of astrophysical parameters, {we obtain a marginalized upper limit on the PBH mass of $f_{rm PBH}M_{rm PBH} sim 60~M_{odot}$ at $2sigma$, when a Gaussian prior on the reionization redshift is imposed, preventing its posterior distribution to peak on very high values, which are disfavoured by the most recent estimates obtained both through Cosmic Microwave Background and Inter-Galactic Medium observations. Such bound weakens to $f_{rm PBH}M_{rm PBH} sim 170~M_{odot}$, when a conservative flat prior is instead assumed. Both limits significantly improves previous constraints from the same physical observable.} We also extend our predictions to non-monochromatic PBH mass distributions, ruling out large regions of the parameter space for some of the most viable PBH extended mass functions.
We present constraints on the masses of extremely light bosons dubbed fuzzy dark matter from Lyman-$alpha$ forest data. Extremely light bosons with a De Broglie wavelength of $sim 1$ kpc have been suggested as dark matter candidates that may resolve some of the current small scale problems of the cold dark matter model. For the first time we use hydrodynamical simulations to model the Lyman-$alpha$ flux power spectrum in these models and compare with the observed flux power spectrum from two different data sets: the XQ-100 and HIRES/MIKE quasar spectra samples. After marginalization over nuisance and physical parameters and with conservative assumptions for the thermal history of the IGM that allow for jumps in the temperature of up to $5000rm,K$, XQ-100 provides a lower limit of 7.1$times 10^{-22}$ eV, HIRES/MIKE returns a stronger limit of 14.3$times 10^{-22}$ eV, while the combination of both data sets results in a limit of 20 $times 10^{-22}$ eV (2$sigma$ C.L.). The limits for the analysis of the combined data sets increases to 37.5$times 10^{-22}$ eV (2$sigma$ C.L.) when a smoother thermal history is assumed where the temperature of the IGM evolves as a power-law in redshift. Light boson masses in the range $1-10 times10^{-22}$ eV are ruled out at high significance by our analysis, casting strong doubts that FDM helps solve the small scale crisis of the cold dark matter models.
We derive new constraints on models of decaying and annihilating dark matter (DM) by requiring that the energy injected into the intergalactic medium (IGM) not overheat it at late times, when measurements of the Lyman-$alpha$ forest constrain the IGM temperature. We improve upon previous analyses by using the recently developed $texttt{DarkHistory}$ code package, which self-consistently takes into account additional photoionization and photoheating processes due to reionization and DM sources. Our constraints are robust to the uncertainties of reionization and competitive with leading limits on sub-GeV DM that decays preferentially to electrons.
The Lyman-$alpha$ forest is a powerful tool to constrain warm dark matter models (WDM). Its main observable -- flux power spectrum -- should exhibit a suppression at small scales in WDM models. This suppression, however, can be mimicked by a number of thermal effects related to the instantaneous temperature of the intergalactic medium (IGM), and to the history of reionization and of the IGM heating (pressure effects). Therefore, to put robust bounds on WDM one needs to disentangle the effect of free-streaming of dark matter particles from the influence of all astrophysical effects. This task cannot be brute-forced due to the complexity of the IGM modelling. In this work, we model the sample of high-resolution and high-redshift quasar spectra (Boera et al 2018) assuming a thermal history that leads to the smallest pressure effects while still being broadly compatible with observations. We explicitly marginalize over observationally allowed values of IGM temperature and find that (thermal) WDM models with masses above 1.9 keV (at 95% CL) are consistent with the spatial shape of the observed flux power spectrum at $z=4-5$. Even warmer models would produce a suppression at scales that are larger than observed, independently of assumptions about thermal effects. This bound is significantly lower than previously claimed bounds, demonstrating the importance of the knowledge about the reionization history and of the proper marginalization over unknowns.
We present new measurements of the free-streaming of warm dark matter (WDM) from Lyman-$alpha$ flux-power spectra. We use data from the medium resolution, intermediate redshift XQ-100 sample observed with the X-shooter spectrograph ($z=3 - 4.2$) and the high-resolution, high-redshift sample used in Viel et al. (2013) obtained with the HIRES/MIKE spectrographs ($z=4.2 - 5.4$). Based on further improved modelling of the dependence of the Lyman-$alpha$ flux-power spectrum on the free-streaming of dark matter, cosmological parameters, as well as the thermal history of the intergalactic medium (IGM) with hydrodynamical simulations, we obtain the following limits, expressed as the equivalent mass of thermal relic WDM particles. The XQ-100 flux power spectrum alone gives a lower limit of 1.4 keV, the re-analysis of the HIRES/MIKE sample gives 4.1 keV while the combined analysis gives our best and significantly strengthened lower limit of 5.3 keV (all 2$sigma$ C.L.). The further improvement in the joint analysis is partly due to the fact that the two data sets have different degeneracies between astrophysical and cosmological parameters that are broken when the data sets are combined, and more importantly on chosen priors on the thermal evolution. These results all assume that the temperature evolution of the IGM can be modelled as a power law in redshift. Allowing for a non-smooth evolution of the temperature of the IGM with sudden temperature changes of up to 5000K reduces the lower limit for the combined analysis to 3.5 keV. A WDM with smaller thermal relic masses would require, however, a sudden temperature jump of $5000,K$ or more in the narrow redshift interval $z=4.6-4.8$, in disagreement with observations of the thermal history based on high-resolution resolution Lyman-$alpha$ forest data and expectations for photo-heating and cooling in the low density IGM at these redshifts.
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