Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userConstraining Warm Dark Matter candidates including sterile neutrinos and light gravitinos with WMAP and the Lyman-alpha forest
62
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The matter power spectrum at comoving scales of (1-40) h^{-1} Mpc is very sensitive to the presence of Warm Dark Matter (WDM) particles with large free streaming lengths. We present constraints on the mass of WDM particles from a combined analysis of the matter power spectrum inferred from the large samples of high resolution high signal-to-noise Lyman-alpha forest data of Kim et al. (2004) and Croft et al. (2002) and the cosmic microwave background data of WMAP. We obtain a lower limit of m_wdm > 550 eV (2 sigma for early decoupled thermal relics and m_wdm > 2.0 keV (2 sigma) for sterile neutrinos. We also investigate the case where in addition to cold dark matter a light thermal gravitino with fixed effective temperature contributes significantly to the matter density. In that case the gravitino density is proportional to its mass, and we find an upper limit m_{3/2} < 16 eV (2 sigma). This translates into a bound on the scale of supersymmetry breaking, Lambda_{susy} < 260 TeV, for models of supersymmetric gauge mediation in which the gravitino is the lightest supersymmetric particle.
rate research
Read More
In light of recent findings which seem to disfavor a scenario with (warm) dark matter entirely constituted of sterile neutrinos produced via the Dodelson-Widrow (DW) mechanism, we investigate the constraints attainable for this mechanism by relaxing the usual hypothesis that the relic neutrino abundance must necessarily account for all of the dark matter. We first study how to reinterpret the limits attainable from X-ray non-detection and Lyman-alpha forest measurements in the case that sterile neutrinos constitute only a fraction fs of the total amount of dark matter. Then, assuming that sterile neutrinos are generated in the early universe solely through the DW mechanism, we show how the X-ray and Lyman-alpha results jointly constrain the mass-mixing parameters governing their production. Furthermore, we show how the same data allow us to set a robust upper limit fs < 0.7 at the 2 sigma level, rejecting the case of dominant dark matter (fs = 1) at the ~ 3 sigma level.
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.
In these brief lecture notes, we introduce sterile neutrinos as dark matter candidates. We discuss in particular their production via oscillations, their radiative decay, as well as possible observational signatures and constraints.
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.
In this paper, we calculate the relic abundance of the dark matter particles when they can annihilate into sterile neutrinos with the mass $lesssim 100 text{ GeV}$ in a simple model. Unlike the usual standard calculations, the sterile neutrino may fall out of the thermal equilibrium with the thermal bath before the dark matter freezes out. In such a case, if the Yukawa coupling $y_N$ between the Higgs and the sterile neutrino is small, this process gives rise to a larger $Omega_{text{DM}} h^2$ so we need a larger coupling between the dark matter and the sterile neutrino for a correct relic abundance.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
