Are James Webb Space Telescope Observations Consistent with Warm Dark Matter?

We compare observed with predicted distributions of galaxy stellar masses M* and galaxy rest-frame ultra-violet luminosities per unit bandwidth LUV, in the redshift range z=2 to 13. The comparison is presented as a function of the comoving warm dark matter free-streaming cut-off wavenumber kfs. For this comparison the theory is a minimal extension of the Press-Schechter formalism with only two parameters: the star formation efficiency, and a proportionality factor between the star formation rate per galaxy and LUV. These two parameters are fixed to their values obtained prior to the James Webb Space Telescope (JWST) data. The purpose of this comparison is to identify if, and where, detailed astrophysical evolution is needed to account for the new JWST observations.

Exploring Inflation Options for Warm Dark Matter Coupled to the Higgs Boson

We extend the Standard Model with a scalar warm dark matter field S with an interaction with the Higgs boson ∅. This warm dark matter scenario is in agreement with cosmological observations if S and ∅ come into thermal and diffusive equilibrium before the temperature drops below the Higgs boson mass mH. We study inflation driven by the fields ∅ or S, and also study preheating and reheating, in order to constrain the parameters of this extension of the Standard Model. It is remarkable that, with the current data, these models pass a closure test with no free parameters.

Understanding the Formation of Galaxies with Warm Dark Matter

The formation of galaxies with warm dark matter is approximately adiabatic. The cold dark matter limit is singular and requires relaxation. In these lecture notes, we develop, step-by-step, the physics of galaxies with warm dark matter, and their formation. The theory is validated with observed spiral galaxy rotation curves. These observations constrain the properties of the dark matter particles.

A Study of Three Galaxy Types, Galaxy Formation, and Warm Dark Matter

We try to bridge the gap between the theory of linear density-velocity-gravitational perturbations in the early universe, and the relaxed galaxies we observe today. We succeed quantitatively for dark matter if dark matter is warm. The density runs of baryons and of dark matter of relaxed galaxies are well described by hydro-static equations. The evolution from initial linear perturbations to final relaxed galaxies is well described by hydro-dynamical equations. These equations necessarily include dark matter velocity dispersion. If the initial perturbation is large enough, the halo becomes self-gravitating. The adiabatic compression of the dark matter core determines the final core density, and provides a negative stabilizing feedback. The relaxed galaxy halo may form adiabatically if dark matter is warm. The galaxy halo radius continues to increase indefinitely, so has an ill-defined mass.

Cold or Warm Dark Matter?: A Study of Galaxy Stellar Mass Distributions

We compare the observed galaxy stellar mass distributions in the redshift range with expectations of the cold ΛCDM and warm ΛWDM dark matter models, and obtain the warm dark matter cut-off wavenumber: . This result is in agreement with the independent measurements with spiral galaxy rotation curves, confirms that kfs is due to warm dark matter free-streaming, and is consistent with the scenario of dark matter with no freeze-in and no freeze-out. Detailed properties of warm dark matter can be derived from kfs. The data disfavors the ΛCDM model.

Comments on Warm Dark Matter Measurements and Limits

Observed spiral galaxy rotation curves allow a measurement of the warm dark matter particle velocity dispersion and mass. The measured thermal relic mass mh ≈100 eV is in disagreement with limits, typically in the range 1 to 4 keV. We review the measurements, update the no freeze-in and no freeze-out scenario of warm dark matter, and try to identify the cause of the discrepancies between measurements and limits.

Warm Dark Matter and the Formation of First Galaxies

By numerical integration of hydro-dynamical equations, we study the formation of elliptical and spiral galaxies starting from primordial linear density-velocity-gravitational perturbations. Both dark matter and baryons are included. Warm dark matter perturbations acquire two low mass cut-offs: the free-streaming cut-off due to the power spectrum free-streaming cut-off factor τ2(k), and the velocity dispersion cut-off. The Press-Schechter mass distribution does not include velocity dispersion, and should not be used below the velocity dispersion cut-off mass. From the formation of first galaxies and reionization, we estimate limits on the non-relativistic warm dark matter velocity dispersion at expansion parameter , with .

Simulations and Measurements of Warm Dark Matter Free-Streaming and Mass

We compare simulated galaxy distributions in the cold ΛCDM and warm ΛWDM dark matter models. The ΛWDM model adds one parameter to the ΛCDM model, namely the cut-off wavenumber kfs of linear density perturbations. The challenge is to measure kfs. This study focuses on “smoothing lengths” π/kfs in the range from 12 Mpc to 1 Mpc. The simulations reveal two distinct galaxy populations at any given redshift z: hierarchical galaxies that form bottom up starting at the transition mas?Mfs, and stripped down galaxies that lose mass to neighboring galaxies during their formation, are near larger galaxies, often have filamentary distributions, and seldom fill voids. We compare simulations with observations, and present four independent measurements of kfs, and the mass mh of dark matter particles, based on the redshift of first galaxies, galaxy mass distributions, and rotation curves of spiral galaxies.

Measurement of the Dark Matter Velocity Dispersion with Galaxy Stellar Masses, UV Luminosities, and Reionization

The root-mean-square of non-relativistic warm dark matter particle velocities scales as vhrms(a)=vhrms(1)/a , where a is the expansion parameter of the universe. This velocity dispersion results in a cut-off of the power spectrum of density fluctuations due to dark matter free-streaming. Let kfs (teq) be the free-streaming comoving cut-off wavenumber at the time of equal densities of radiation and matter. We obtain , and , at 68% confidence, from the observed distributions of galaxy stellar masses and rest frame ultra-violet luminosities. This result is consistent with reionization. From the velocity dispersion cut-off mass we obtain the limits vhrms(1)kfs (teq) >1.5 Mpc-1. These results are in agreement with previous measurements based on spiral galaxy rotation curves, and on the formation of first galaxies and reionization. These measured parameters determine the temperature-to-mass ratio of warm dark matter. This ratio happens to be in agreement with the no freeze-in and no freeze-out warm dark matter scenario of spin 0 dark matter particles decoupling early on from the standard model sector. Spin 1/2 and spin 1 dark matter are disfavored if nature has chosen the no freeze-in and no freeze-out scenario. An extension of the standard model of quarks and leptons, with scalar dark matter that couples to the Higgs boson that is in agreement with all current measurements, is briefly reviewed. Discrepancies with limits on dark matter particle mass that can be found in the literature are addressed.

Measurement of the Dark Matter Velocity Dispersion with Dwarf Galaxy Rotation Curves

Warm dark matter has, by definition, a velocity dispersion. Let vhms(a)=vhms(1)/a be the root-mean-square velocity of non-relativistic warm dark matter particles in the early universe at expansion parameter a. vhms(1) is an adiabatic invariant. We obtain vhms(1) in the core of 11 dwarf galaxies dominated by dark matter, from their observed rotation curves, up to a rotation and relaxation correction. We obtain a mean 0.490 km/s and standard deviation 0.160 km/s, with a distribution peaked at the lower end. We apply a mild, data driven, rotation and relaxation correction that obtains the adiabatic invariant in the core of the galaxies: vhms(1)=0.406 ±0.069 km/s. These two small relative standard deviations justify the prediction that the adiabatic invariant vhms(1) in the core of the galaxies is of cosmological origin if dark matter is warm. This result is in agreement with measurements of vhms(1) based on spiral galaxy rotation curves, galaxy ultra-violet luminosity distributions, galaxy stellar mass distributions, the formation of first galaxies, reionization, and the velocity dispersion cut-off mass.

早始新世气候适宜期形成机制探讨

早始新世气候适宜期发生在53—51 Ma,是新生代早期一段气候持续温暖时期。与中中新世气候适宜期和上新世气候适宜期相比,早始新世气候适宜期更加温暖。对于该时期驱动机制的理解有助于深入认识未来温暖气候状况的变化。本文总结了前人提出的构造尺度气候变化的假说,推断出早始新世气候适宜期可能是由于板块构造活动变化导致的温室气体变化所造成,而星际暗物质变化对早始新世气候适宜期的影响有待进一步评估。

NANOGrav results and dark first order phase transitions

The recent NANOGrav evidence of a common-source stochastic background provides a hint to gravitational waves(GW)radiation from the Early Universe.We show that this result can be interpreted as a GW spectrum produced from first order phase transitions(FOPTs)around a temperature in the keV-MeV window.Such a class of FOPTs at temperatures much below the electroweak scale can be naturally envisaged in several warm dark matter models such as Majoron dark matter.