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1.
We consider sterile neutrinos as a component of dark matter in the Milky Way and clusters, and compare their rest mass, decay
rate and the mixing angle. A radiative decaying rate of order Γ∼10−19 s−1 for sterile neutrino rest mass m
s
=18–19 keV can satisfactorily account for the cooling flow problem and heating source in Milky Way center simultaneously.
Also, these ranges of decay rate and rest mass match the prediction of the mixing angle sin 22θ∼10−3 with a low reheating temperature in the inflation model, which enables the sterile-active neutrino oscillation to be visible
in future experiments. However, decaying sterile neutrinos have to be ruled out as a major component of dark matter because
of the high decay rate. 相似文献
2.
B. V. Sreekantan 《Journal of Astrophysics and Astronomy》1984,5(3):251-271
Conclusion In conclusion, as of 1984 January, it may be stated that the existence of super-heavy monopoles and the phenomenon of nucleon
decay, both of which are extremely important from the point of view of grand unification theories, are still very open questions.
While there has been just one magnetic monopole candidate so far, there have been several as far as nucleon decay is concerned.
The first candidates for nucleon decay came from the fine-grain calorimeters of KGF, and NUSEX; recently there have been candidates
from the water Cerenkov experiments as well. The experimental situation regarding the other important phenomena of relevance
to grand unification which we have not discussed in this article — like the finite mass of neutrinos, neutrino oscillations,
and neutron oscillations — continues to be indefinite though many dedicated experiments are in progress.
With the continued operation of the nucleon decay experiments already collecting data and the commissioning of the new generation
of experiments over the next few years, the stage is set for a resolution of this problem in a time scale of 5–10 years. The
present indication that the dominant decay mode for the proton (even if it decays) is notp → e+π0 and that the lower limit to the lifetime of the nucleon is 1031 yr, does not favour the simple SU(5) type models.
The remarkable discoveries of W± and Z0 with mass values exactly as predicted, have given a boost to the unification based on the gauge theoretical approaches. Whether
grand unification can be extended to super-unification, experiment alone can tell. This will be the challenge for the remaining
years of this century. 相似文献
3.
In the framework of ‘microscopic’ theory of black holes (J. Phys. Soc. Jpn. Suppl. B 70, 84, 2001; Astrophys. USSR 4, 659, 1996; 35, 335, 1991, 33, 143, 1990, 31, 345, 1989a; Astrophys. Space Sci. 1, 1992; Dokl. Akad. Nauk USSR 309, 97, 1989b), and references therein, we address the ‘pre-radiation time’ (PRT) of neutrinos from black holes, which implies the lapse
of time from black hole’s birth till radiation of an extremely high energy neutrinos. For post-PRT lifetime, the black hole
no longer holds as a region of spacetime that cannot communicate with the external universe. We study main features of spherical
accretion onto central BH and infer a mass accretion rate onto it, and, further, calculate the resulting PRT versus bolometric
luminosity due to accretion onto black hole. We estimate the PRTs of AGN black holes, with the well-determined masses and
bolometric luminosities, collected from the literature by Woo Jong-Hak and Urry (Astrophys. J. 579, 530, 2002) on which this paper is partially based. The simulations for the black holes of masses M
BH
≃(1.1⋅106
÷4.2⋅109) M
⊙ give the values of PRTs varying in the range of about T
BH
≃(4.3⋅105
÷5.6⋅1011) yr. The derived PRTs for the 60 AGN black holes are longer than the age of the universe (∼13.7 Gyr) favored today. At present,
some of remaining 174 BHs may radiate neutrinos. However, these results would be underestimated if the reservoir of gas for
accretion in the galaxy center is quite modest, and no obvious way to feed the BHs with substantial accretion. 相似文献
4.
B. I. Goryachev 《Astronomy Letters》2011,37(4):281-285
The tritium chain of the hydrogen cycle on the Sun including the reactions 3He(e−, ν
e) 3H(p, γ)4He is considered. The flux of tritium neutrinos at a distance of 1 AU is 8.1 × 104 cm−2 s−1. It exceeds the neutrino flux from the (hep)-reaction by one order of magnitude. The radial distribution of the yield of
3H neutrinos inside the Sun and their energy spectrum, which has the form of a line at an energy of 2.5–3.0 keV, have also
been calculated. The flux of thermal tritium neutrinos is accompanied by a very weak flux of antineutrinos (∼103 cm−2 yr−1) with an energy below 18.6 keV. These antineutrinos are produced in the URCA processes 3He ⇆ 3H. 相似文献
5.
Pijushpani Bhattacharjee 《Journal of Astrophysics and Astronomy》1997,18(4):263-269
The detection of the Cosmic Thermal Neutrino Background (CTNB) would provide the “cleanest” evidence for the hot big bang
model of the early Universe. I discuss some recent thoughts on the possibility of detecting the CTNB (especially if neutrinos
have a small mass of ~ few eV) by looking for certain CTNB-induced features in the extremely high energy (E ≳ 1020 eV) cosmic neutrino spectrum that may become measurable in the future by some of the large-area extensive air-shower detectors
being built for detecting extremely high energy cosmic rays.
NAS/NRC Senior Research Associate on sabbatical leave from Indian Institute of Astrophysics, Bangalore 560 034, India. 相似文献
6.
Simon F. Portegies Zwart Jasinta Dewi Tom Maccarone 《Astrophysics and Space Science》2005,300(1-3):247-253
The evolution of young (≲ 10 Myr) star clusters with a density exceeding about 105 star pc−3 are strongly affected by physical stellar collisions during their early lifetime. In such environments the same star may
participate in several tens to hundreds of collisions ultimately leading to the collapse of the star to a black hole of intermediate
mass. At later time, the black hole may acquire a companion star by tidal capture or by dynamical – three-body – capture.
When the captured star evolves it starts to fill its Roche-lobe and transfers mass to its accompanying black hole. This then
leads to a bright phase of X-ray emission, which lasts for the remaining main-sequence lifetime of the donor. If the star
captured by the intermediate mass black hole is relatively low mass ≲ 2 M⊙) the binary will also be visible as a bright source in gravitational waves. Based on empirical models we argue that, for
as long as the donor remains on the main sequence, the source will be ultraluminous Lx >rsim 1040 ergs-1 for about a week every few month. When the donor star is more massive >15 M⊙, or evolved off the main sequence the bright time is longer, but the total accretion phase lasts much shorter. 相似文献
7.
If massive sterile neutrinos exist, their decays into photons and/or electron-positron pairs may give rise to observable consequences.
We consider the possibility that MeV sterile neutrino decays lead to the diffuse positron annihilation line in the Milky Way
center, and we thus obtain bounds on the sterile neutrino decay rate Γ
e
≥10−28 s−1 from relevant astrophysical/cosmological data. Also, we expect a soft gamma flux of 1.2×10−4–9.7×10−4 ph cm−2 s−1 from the Milky Way center which shows up as a small MeV bump in the background photon spectrum. Furthermore, we estimate
the flux of active neutrinos produced by sterile neutrino decays to be 0.02–0.1 cm−2 s−1 passing through the earth. 相似文献
8.
Markus Ackermann 《Astrophysics and Space Science》2007,309(1-4):421-427
The AMANDA-II telescope, operated by the IceCube collaboration, is currently the world’s most sensitive telescope to fluxes
of neutrinos from individual sources. A data sample of 4282 neutrino induced events collected in 1001 days of detector livetime
during the years 2000–2004 have now been analyzed looking for a neutrino signal from point-like sources. A sensitivity to
fluxes of
of d
Φ/dE=1.0×10−10(E/TeV)−2 TeV−1 cm−2s−1 was reached in the energy range between 1.7 TeV and 2.4 PeV. So far no statistically significant localized excess of events
over the background of atmospheric neutrinos has been found, which would be ascribed to a neutrino source. However, the flux
upper limits derived from the non-observation of a signal are comparable to observed fluxes of high energy gamma rays from
blazars and within the range of current models for neutrino emission from selected sources. Possible constraints on these
models are discussed.
相似文献
9.
We argue that observations on Milky Way and dwarf spheroidals imply existence of individual haloes around dwarf spheroidals.
If neutrinos (or any other ‘hot’ particle) provide the dark matter then we show that: (i) Embedding of visible matter inside
large (∼ few Mpc) dark matter islands is observationally untenable. (ii) Dwarf spheroidals possess dark matter haloes of about
10 kpc radius around them, and have an (M/L) ratio of about 104. (iii) The haloes of spiral galaxies (e.g. Milky Way) extend to about 100 kpc in radius. If ‘cold’ dark matter makes up the haloes, then no significant constraints
are obtained. We discuss briefly the effect of these constraints on larger scales. 相似文献
10.
A. D. Kaminker D. G. Yakovlev A. Y. Potekhin N. Shibazaki P. S. Shternin O. Y. Gnedin 《Astrophysics and Space Science》2007,308(1-4):423-430
We model thermal evolution of magnetars with a phenomenological heat source in a spherical internal layer and compare the
results with observations of persistent thermal radiation from magnetars. We show that the heat source should be located in
the outer magnetar’s crust, at densities ρ≲5×1011 g cm−3, and the heating rate should be ∼1020 erg cm−3 s−1. Heating deeper layers is extremely inefficient because the thermal energy is mainly radiated away by neutrinos and does
not warm up the surface to the magnetar’s level. This deep heating requires too much energy; it is inconsistent with the energy
budget of neutron stars.
相似文献
11.
Based on Hinode SOT/NFI observations with greatly improved spatial and temporal resolution and polarization sensitivity, the lifestory of
the intranetwork (IN) magnetic elements are explored in a solar quiet region. A total of 2282 IN elements are followed from
their appearance to disappearance and their fluxes measured. By tracing individual IN elements their lifetimes are obtained,
which fall in the range from 1 to 20 min. The average lifetime is 2.9±2.0 min. The observed lifetime distribution is well
represented by an exponential function. Therefore, the e-fold characteristic lifetime is determined by a least-square fitting
to the observations, which is 2.1±0.3 min. The lifetime of IN elements is correlated closely with their flux. The evolution
of IN elements is described according to the forms of their birth and disappearance. Based on the lifetime and flux obtained
from the new observations, it is estimated that the IN elements have the capacity of heating the corona with a power of 2.1×1028 erg s−1 for the whole Sun. 相似文献
12.
The dynamical masses of dwarf-spheroidals, spiral and elliptical galaxies, dwarf irregular binaries, groups of galaxies and
clusters are shown to lie in a band about the M ∼ ρR3
line. The value of ρ is approximately the same as that estimated for unseen matter in the solar neighbourhood. The clusters themselves
lie about theM ∼ R
-3
line derived for a self-gravitating neutrino gas; their masses are distributed around the maximum Jeans-mass, MJmax. corresponding to mv - 10 eV in an expanding universe. The present day length scales of clusters and the dispersion in the velocities observed
within them are understood in terms of a 100-fold expansion subsequent to the initial growth of the fluctuations at MJmax. These systematics on theR-M plane imply that the initial condensations in the expanding universe are on the scale of the rich clusters of galaxies, these
condensations were triggered dominantly by the gravitation of the neutrinos and the constant density of al systems arises
naturally due to the embedding of these systems in the large scale neutrino condensations. If the neutrino density falls off
asr
-2 beyond the cluster edge till the distributions from different clusters overlap, then the mean density of the neutrinos approximately
equals the closure density of the universe. 相似文献
13.
In the problem of 2+2 bodies in the Robe’s setup, one of the primaries of mass m*1m^{*}_{1} is a rigid spherical shell filled with a homogeneous incompressible fluid of density ρ
1. The second primary is a mass point m
2 outside the shell. The third and the fourth bodies (of mass m
3 and m
4 respectively) are small solid spheres of density ρ
3 and ρ
4 respectively inside the shell, with the assumption that the mass and the radius of third and fourth body are infinitesimal.
We assume m
2 is describing a circle around m*1m^{*}_{1}. The masses m
3 and m
4 mutually attract each other, do not influence the motion of m*1m^{*}_{1} and m
2 but are influenced by them. We also assume masses m
3 and m
4 are moving in the plane of motion of mass m
2. In the paper, the equations of motion, equilibrium solutions, linear stability of m
3 and m
4 are analyzed. There are four collinear equilibrium solutions for the given system. The collinear equilibrium solutions are
unstable for all values of the mass parameters μ,μ
3,μ
4. There exist an infinite number of non collinear equilibrium solutions each for m
3 and m
4, lying on circles of radii λ,λ′ respectively (if the densities of m
3 and m
4 are different) and the centre at the second primary. These solutions are also unstable for all values of the parameters μ,μ
3,μ
4, φ, φ′. Such a model may be useful to study the motion of submarines due to the attraction of earth and moon. 相似文献
14.
Using one-minute cadence time-series full disk magnetograms taken by the SOHO/MDI, we have studied the magnetic field elements
at high latitude (poleward of 65° in latitude). It is found that an average lifetime of the magnetic field elements is 16.5
h during solar minimum, much longer than that during solar maximum (7.3 h). During solar minimum, number of the magnetic field
elements with the dominant polarity is about 3 times as that of the opposite polarity elements. Their lifetime is 21.0 h on
average, longer than that of the opposite polarity elements (2.3 h). It is also found that the lifetime of the magnetic field
elements is related with their size, consistent with the magnetic field elements in the quiet sun at low latitude found by
Hagenaar et al. (Astrophys. J. 511:932, 1999). During solar maximum, the polar regions are equally occupied by magnetic field elements with both polarities, and their
lifetimes are roughly the same on average. No evidence shows there is a correlation between the lifetime and size of the magnetic
field elements. Using an image cross-correlation method, we also measure the solar rotation rate at high latitude, up to 85°
in latitude. The rate is ω=2.914−0.342sin 2
φ−0.482sin 4
φ μrad s−1 sidereal. It agrees with previous studies using the spectroscopic and image cross-correlation methods, and also agrees with
the results using the element tracking method when the sample of the tracked magnetic field elements is large. The consistency
of those results strongly suggests that this rate at high latitude is reliable. 相似文献
15.
A numerical model of the transient behavior of a radiation-dominated shock was calculated in order to demonstrate the relatively
large initial escape of internal energy that takes place when the opacity law is a positive power of temperature, as for neutrinos,K∼T
2. Attention was given to the consequences of diffusive transport of radiation versus local production of internal energy by
duplicating the calculation with and without artificial viscosity. It is concluded that a shock formed on the neutron star
core of an imploding supernova may radiate its internal energy in electron neutrinos more effectively than had hithertofore
been considered. 相似文献
16.
The gravitational instability of expanding shells evolving in a homogeneous and static medium is discussed. In the low density
environment (n = 1 cm-3), the fragmentation starts in shells with diameters of a few 100 pc and fragment masses are in the range of 5 × 103 - 106
M
⊙. In the high density environment (n = 105 - 107 cm-3), shells fragment at diameters of
pc producing clumps of stellar masses. The mass spectrum in both environments is approximated by a power law dN/dm ∼ m
-2.3. This is close to the slope of the stellar IMF. To reproduce the observed mass spectrum of clouds (the spectral index close
to ∼ -2.0) we have to assume, that the cloud formation time is independent of the cloud size, similarly to the Jeans unstable
medium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
In neutron star matter over the density range 4.3×1011<-ϱ≤4×1014 g cm−3 there are both free neutrons and neutron-rich nuclei. If there is a weak neutral current interaction between neutrinos and
neutrons, as suggested by recent experiments, then when neutrons scatter off nuclei they may emit
pairs as bremsstrahlung radiation. We calculate the associated emissivity for degenerate (but not superfluid) neutrons and
uncorrelated (not crystallized) nuclei. We find that, under these conditions. this emissivity can under some conditions compare
with that calculated by Festa and Ruderman for
bremsstrahlung in electron-nucleus collisions. 相似文献
18.
Neutrino energy spectra have been calculated based on the recently measured energy spectra of Galactic very high energy γ-ray
sources. Based on these neutrino spectra the expected event rates in the ANTARES neutrino telescope and KM3NeT, a future neutrino
telescope in the Mediterranean Sea with an instrumented volume of one km3, have been calculated. For the brightest γ-ray sources we find event rates of the order of one neutrino per year. Although
the neutrino event rates are comparable to the background from atmospheric neutrinos the detection of individual sources seems
possible. 相似文献
19.
Indications on clustering features in the two-point correlation function of Ly α line separations in published high-resolution spectra of quasars are presented. They are in contradiction to the self-similar hierarchical clustering model, but they could be explained by a first generation of small-scale pancakes in a model with unstable dark matter. A characteristic scale of velocity dispersion Δv ≈ 150 km/s of absorption clouds within pancakes is described by corresponding coherent regions of positive correlation, while the structure adjacent on the lines of sight are separated by a comoving distance of (18 ± 6) Mpc (H0 = 50 km/s Mpc). The appropriate coherence length of the fluctuation spectrum may result from the free streaming length of (unstable) neutrinos of (100 … 200) eV rest mass. 相似文献
20.
Iu. Babyk A. Elyiv O. Melnyk V. N. Krivodubskij 《Kinematics and Physics of Celestial Bodies》2012,28(2):69-76
The mass distribution for the galaxy cluster Abell 2744 (z = 0.308) is investigated on the base of the archival X-ray data of the Chandra observatory. The temperature of the hot gas
in the cluster (kT = 9.82−0.41+0.43 keV) and the cluster total mass (M
200 = 2.22−0.12+0.13 × 1015
M
⊙) for the radius R
200 = 2.38−0.31+0.36 Mpc are estimated. The density and mass profiles for the intergalactic gas and dark matter are obtained. The fractions of
the intergalactic gas and dark matter in the total mass of the cluster are 15.4−1.3+1.3% and 84.6−1.3+1.4%, respectively. 相似文献