Degenerate Fermi gas perturbations at standard background cosmology

The hypothesis of a tiny fraction of the cosmic inventory evolving cosmologically as a degenerate Fermi gas test fluid at some dominant cosmological background is investigated. Our analytical results allow for performing preliminary computations to the evolution of perturbations for relativistic and non-relativistic test fluids. The density fluctuation, $\delta$, the fluid velocity divergence, $\theta$, and an explicit expression for the dynamics of the shear stress, $\sigma$, are obtained for a degenerate Fermi gas in the background regime of radiation. Extensions to the dominance of matter and to the $\Lambda$CDM cosmological background are also investigated and lessons concerning the formation of large structures of degenerate Fermi gas are depicted.Comment: 20 pages, 4 figure

Dark Matter at the Center and in the Halo of the Galaxy

All presently known stellar-dynamical constraints on the size and mass of the supermassive compact dark object at the Galactic center are consistent with a ball of self-gravitating, nearly non-interacting, degenerate fermions with mass between 76 and 491 keV, for degeneracy factor g=2. Sterile neutrinos of 76 keV mass, which are mixed with at least one of the active neutrinos with a mixing angele ~10^{-7}, are produced in about the right amount in the early Universe by incoherent resonant and non-resonant scattering of active neutrinos having asymmetry of ~0.01. The former process yields sterile neutrinos with a quasi-degenerate spectrum while the latter leads to a thermal spectrum. As the production mechanism of the sterile neutrino is consistent with the constraints from large scale structure formation, core collapse supernovae, and diffuse X-ray background, it could be the dark matter particle of the Universe.Comment: 6 pages, to appear in the Beyond 2003 conference proceeding

Degenerate sterile neutrino dark matter in the cores of galaxies

We study the distribution of fermionic dark matter at the center of galaxies using NFW, Moore and isothermal density profiles and show that dark matter becomes degenerate for particle masses of a few {\rm keV} and for distances less than a few parsec from the center of our galaxy. A compact degenerate core forms after galaxy merging and boosts the growth of supermassive black holes at the center of galaxies. To explain the galactic center black hole of mass of $\sim 3.5 \times 10^{6}M_{\odot}$ and a supermassive black hole of $\sim 3 \times 10^{9}M_{\odot}$ at a redshift of 6.41 in SDSS quasars, we require a degenerate core of mass between $3 \times 10^{3} M_{\odot}$ and $3.5 \times 10^{6}M_{\odot}$. This constrains the mass of the dark matter particle between $0.6 {\rm keV}$ and $82 {\rm keV}$. The lower limit on the dark matter mass is improved to {\rm 7 keV} if exact solutions of Poisson's equation are used in the isothermal power law case. We argue that the constrained particle could be the long sought dark matter of the Universe that is interpreted here as a sterile neutrino.Comment: 4 pages, 1 figure, Accepted for publication in Astronomy & Astrophysics Letter

Sgr A^*: A supermassive black hole or a spatially extended object?

We report here on a calculation of possible orbits of the fast moving infrared source S1 which has been recently observed by Eckart and Genzel (1997) near the Galactic center. It is shown that tracking of the orbit of S1 or any other fast moving star near Sgr A^* offers a possibility of distinguishing between the supermassive black hole and extended object scenarios of Sgr A^*. In our calculations we assumed that the extended object at the Galactic center is a non-baryonic ball made of degenerate, self-gravitating heavy neutrino matter, as it has been recently proposed by Tsiklauri & Viollier (1998a,b).Comment: AASTEX, 5 postscript figs., submitted to ApJ Let

Fast Growth of Supermassive Black Holes in Galaxies

We report on a calculation of the growth of the mass of supermassive black holes at galactic centers from dark matter and Eddington - limited baryonic accretion. Assuming that dark matter halos are made of fermions and harbor compact degenerate Fermi balls of masses from $10^{3}M_{\odot}$ to $10^{6}M_{\odot}$, we find that dark matter accretion can boost the mass of seed black holes from about $\sim 5M_{\odot}$ to $10^{3-4}M_{\odot}$ black holes, which then grow by Eddington - limited baryonic accretion to supermassive black holes of $10^{6 - 9}M_{\odot}$. We then show that the formation of the recently detected supermassive black hole of $3\times 10^{9}M_{\odot}$ at a redshift of $z = 6.41$ in the quasar SDSS J114816.64+525150.3 could be understood if the black hole completely consumes the degenerate Fermi ball and then grows by Eddington - limited baryonic accretion. In the context of this model we constrain the dark matter particle masses to be within the range from 12 ${\rm keV/c}^{2}$ to about 450 ${\rm keV/c}^{2}$. Finally we investigate the black hole growth dependence on the formation time of the seed BH and on the mass of the seed BH. We find that in order to fit the observed data point of $M_{BH} \sim 3 \times 10^{9}M_{\odot}$ and $z \sim 6.41$, dark matter accretion cannot start later than about $2 \times 10^{8}$ years and the seed BH cannot be greater than about $10^{4}M_{\odot}$. Our results are in full agreement with the WMAP observations that indicate that the first onset of star formation might have occurred at a redshift of $z \sim 15 - 20$. For other models of dark matter particle masses, corresponding constraints may be derived from the growth of black holes in the center of galaxies.Comment: New black hole growth mechnism, references added, 13 pages, accepted for publication in Astronomy & Astrophysics Journa

Lightest sterile neutrino abundance within the nuMSM

We determine the abundance of the lightest (dark matter) sterile neutrinos created in the Early Universe due to active-sterile neutrino transitions from the thermal plasma. Our starting point is the field-theoretic formula for the sterile neutrino production rate, derived in our previous work [JHEP 06(2006)053], which allows to systematically incorporate all relevant effects, and also to analyse various hadronic uncertainties. Our numerical results differ moderately from previous computations in the literature, and lead to an absolute upper bound on the mixing angles of the dark matter sterile neutrino. Comparing this bound with existing astrophysical X-ray constraints, we find that the Dodelson-Widrow scenario, which proposes sterile neutrinos generated by active-sterile neutrino transitions to be the sole source of dark matter, is only possible for sterile neutrino masses lighter than 3.5 keV (6 keV if all hadronic uncertainties are pushed in one direction and the most stringent X-ray bounds are relaxed by a factor of two). This upper bound may conflict with a lower bound from structure formation, but a definitive conclusion necessitates numerical simulations with the non-equilibrium momentum distribution function that we derive. If other production mechanisms are also operative, no upper bound on the sterile neutrino mass can be established.Comment: 34 pages. v2: clarifications and a reference added; published version. v3: erratum appende

Evaluation of Beet Leafhopper Transmitted Virescence Agent Damage in the Columbia Basin

Potato purple top disease is caused by a phytoplasma known as Beet Leafhopper Transmitted Virescence Agent (BLTVA), which is vectored by the beet leafhopper (BLH, Circulifer tenellus Baker). Previous studies determined that BLTVA can cause significant reductions in yield and tuber quality; however, quantifying the damage caused by BLTVA and the insect vector has been challenging. In 2009–2011, potato plants at different growth stages were exposed to varying densities of BLH in a screen house located at the Hermiston Agricultural Research and Extension Center in Hermiston, OR. The densities of potentially infective BLH were one BLH per plant (low), two BLH per plant (medium), and five BLH per plant (high). Releases occurred at the following growth stages: vegetative, tuber initiation, tuber bulking, and maturation. The treatments were arranged in a randomized complete block design with three replications per treatment. Disease incidence was monitored weekly and yield was assessed. When all 3 years were combined, we found that increasing rates of disease incidence correlated with decreasing yields. We also found that greater yield losses were observed with later BLH release times. With both correlations, differences between years were a strong contributing factor. There was a mean decrease in yield of 0–12% at a density of one BLH per plant, 6–19% at two BLH per plant, and 6–20% for five BLH per plant. These general trends in yield loss suggest that economically relevant damage may occur at levels as low as one or two potentially infective BLH per plant in the Columbia Basin.Keywords: Phytoplasma, Purple top disease, Circulifer, Integrated pest management, Economic threshold

Sterile neutrino production via active-sterile oscillations: the quantum Zeno effect

We study several aspects of the kinetic approach to sterile neutrino production via active-sterile mixing. We obtain the neutrino propagator in the medium including self-energy corrections up to $\mathcal{O}(G^2_F)$, from which we extract the dispersion relations and damping rates of the propagating modes. The dispersion relations are the usual ones in terms of the index of refraction in the medium, and the damping rates are $\Gamma_1(k) = \Gamma_{aa}(k) \cos^2\theta_m(k); \Gamma_2(k) = \Gamma_{aa}(k) \sin^2\theta_m(k)$ where $\Gamma_{aa}(k)\propto G^2_F k T^4$ is the active neutrino scattering rate and $\theta_m(k)$ is the mixing angle in the medium. We provide a generalization of the transition probability in the \emph{medium from expectation values in the density matrix}: $P_{a\to s}(t) = \frac{\sin^22\theta_m}{4}[e^{-\Gamma_1t} + e^{-\Gamma_2 t}-2e^{-{1/2}(\Gamma_1+\Gamma_2)t} \cos\big(\Delta E t\big)]$ and study the conditions for its quantum Zeno suppression directly in real time. We find the general conditions for quantum Zeno suppression, which for $m_s\sim \textrm{keV}$ sterile neutrinos with $\sin2\theta \lesssim 10^{-3}$ \emph{may only be} fulfilled near an MSW resonance. We discuss the implications for sterile neutrino production and argue that in the early Universe the wide separation of relaxation scales far away from MSW resonances suggests the breakdown of the current kinetic approach.Comment: version to appear in JHE

Astrophysical implications of gravitational microlensing of gravitational waves

Astrophysical implications of gravitational microlensing of gravitational waves emitted by rotating neutron stars (NSs) are investigated. In particular, attention is focused on the following situations: i) NSs in the galactic bulge lensed by a central black hole of $2.6\times 10^6 M_{\odot}$ or by stars and MACHOs distributed in the galactic bulge, disk and halo between Earth and the sources; ii) NSs in globular clusters lensed by a central black hole of $\sim 10^3 M_{\odot}$ or by stars and MACHOs distributed throughout the Galaxy. The detection of such kind of microlensing events will give a unique opportunity for the unambiguous mapping of the central region of the Galaxy and of globular clusters. In addition, the detection of such events will provide a new test of the General Theory of Relativity. Gravitational microlensing will, moreover, increase the challenge of detecting gravitational waves from NSs.Comment: 5 pages, laa.sty required. Accepted for pubblication on Astronomy and Astrophysics on November, 7 200