Galaxy phase-space density data exclude Bose-Einstein condensate Axion Dark Matter

Light scalars (as the axion) with mass m ~ 10^{-22} eV forming a Bose-Einstein condensate (BEC) exhibit a Jeans length in the kpc scale and were therefore proposed as dark matter (DM) candidates. Our treatment here is generic, independent of the particle physics model and applies to all DM BEC, in or out of equilibrium. Two observed quantities crucially constrain DM in an inescapable way: the average DM density rho_{DM} and the phase-space density Q. The observed values of rho_{DM} and Q in galaxies today constrain both the possibility to form a BEC and the DM mass m. These two constraints robustly exclude axion DM that decouples just after the QCD phase transition. Moreover, the value m ~ 10^{-22} eV can only be obtained with a number of ultrarelativistic degrees of freedom at decoupling in the trillions which is impossible for decoupling in the radiation dominated era. In addition, we find for the axion vacuum misalignment scenario that axions are produced strongly out of thermal equilibrium and that the axion mass in such scenario turns to be 17 orders of magnitude too large to reproduce the observed galactic structures. Moreover, we also consider inhomogenous gravitationally bounded BEC's supported by the bosonic quantum pressure independently of any particular particle physics scenario. For a typical size R ~ kpc and compact object masses M ~ 10^7 Msun they remarkably lead to the same particle mass m ~ 10^{-22} eV as the BEC free-streaming length. However, the phase-space density for the gravitationally bounded BEC's turns to be more than sixty orders of magnitude smaller than the galaxy observed values. We conclude that the BEC's and the axion cannot be the DM particle. However, an axion in the mili-eV scale may be a relevant source of dark energy through the zero point cosmological quantum fluctuations.Comment: 8 pages, no figures. Expanded versio

Equation of state, universal profiles, scaling and macroscopic quantum effects in Warm Dark Matter galaxies

The Thomas-Fermi approach to galaxy structure determines selfconsistently and nonlinearly the gravitational potential of the fermionic WDM particles given their quantum distribution function f(E). Galaxy magnitudes as the halo radius r_h, mass M_h, velocity dispersion and phase space density are obtained. We derive the general equation of state for galaxies (relation between the pressure and the density), and provide an analytic expression. This clearly exhibits two regimes: (i) Large diluted galaxies for M_h > 2.3 10^6 Msun corresponding to temperatures T_0 > 0.017 K, described by the classical self gravitating WDM Boltzman regime and (ii) Compact dwarf galaxies for 1.6 10^6 Msun > M_h>M_{h,min}=30000 (2keV/m)^{16/5} Msun, T_0<0.011 K described by the quantum fermionic WDM regime. The T_0=0 degenerate quantum limit predicts the most compact and smallest galaxy (minimal radius and mass M_{h,min}). All magnitudes in the diluted regime exhibit square root of M_h scaling laws and are universal functions of r/r_h when normalized to their values at the origin or at r_h. We find that universality in galaxies (for M_h > 10^6 Msun) reflects the WDM perfect gas behaviour. These theoretical results contrasted to robust and independent sets of galaxy data remarkably reproduce the observations. For the small galaxies, 10^6>M_h>M_{h,min} corresponding to effective temperatures T_0 < 0.017 K, the equation of state is galaxy dependent and the profiles are no more universal. These non-universal properties in small galaxies account to the quantum physics of the WDM fermions in the compact regime. Our results are independent of any WDM particle physics model, they only follow from the gravitational interaction of the WDM particles and their fermionic quantum nature.Comment: 21 pages, 9 figures. arXiv admin note: substantial text overlap with arXiv:1309.229

Statistical Mechanics of the Self-Gravitating Gas: Thermodynamic Limit, Unstabilities and Phase Diagrams

We show that the self-gravitating gas at thermal equilibrium has an infinite volume limit in the three ensembles (GCE, CE, MCE) when (N, V) -> infty, keeping N/V^{1/3} fixed, that is, with eta = G m^2 N/[ V^{1/3} T] fixed. We develop MonteCarlo simulations, analytic mean field methods (MF) and low density expansions. We compute the equation of state and find it to be locally p(r) = T rho_V(r), that is a local ideal gas equation of state. The system is in a gaseous phase for eta < eta_T = 1.51024...and collapses into a very dense object for eta > eta_T in the CE with the pressure becoming large and negative. The isothermal compressibility diverges at eta = eta_T. We compute the fluctuations around mean field for the three ensembles. We show that the particle distribution can be described by a Haussdorf dimension 1 < D < 3.Comment: 12 pages, Invited lecture at `Statistical Mechanics of Non-Extensive Systems', Observatoire de Paris, October 2005, to be published in a Special issue of `Les Comptes rendus de l'Acade'mie des sciences', Elsevie

Intrinsic Curie temperature bistability in ferromagnetic semiconductor resonant tunneling diodes

We predict bistability in the Curie temperature-voltage characteristic of double barrier resonant-tunneling structures with dilute ferromagnetic semiconductor quantum wells. Our conclusions are based on simulations of electrostatics and ballistic quantum transport combined with a mean-field theory description of ferromagnetism in dilute magnetic semiconductors.Comment: 10 pages, 3 figures, submitted to Phys. Rev. B; typo removed in revised version - spurious eq.12 immediately after eq.1