1,721,010 research outputs found
GLOBAL CONTINUOUS SYMMETRY AND THE 17 KEV NEUTRINO
No full textThe effects of a very small explicit breaking of a continuous global symmetry advocated in elegant and phenomenologically successful models for the 17 keV neutrino are discussed. It is shown that these effects are substantial, even if the explicit breaking terms are suppressed by powers of a scale as large as the Planck mass
Relevance of axionlike particles for very-high-energy astrophysics (vol 84, 105030, 2011)
No full text
X-ray emission from dark clusters of MACHOs
No full textMACHOs (Massive Astrophysical Compact Halo
Objects) - as discovered by microlensing experiments towards the LMC - provide a natural explanation for the galactic halo dark matter. A realistic possibility is that MACHOs are brown dwarfs of mass 0.1M. Various arguments suggest that brown dwarfs should have a coronal X-ray emission of 10^27 erg s^−1. As MACHOs are presumably clumped into dark clusters
(DCs), each DC is expected to have a total X-ray luminosity of 10^29 − 10^32 erg s^−1. We discuss the possibility that dark clusters contribute to the diffuse X-ray background (XRB) or show up as discrete sources in very deep field X-ray satellite observations.
Moreover, from the observed diffuse XRB we infer
that the amount of virialized diffuse gas present in the galactic halo can at most make up 5% of the halo dark matter
Observing molecular clouds in halo dark clusters through absorption lines
No full textIn addition to Massive Astrophysical Compact Halo Objects (MACHOs), as detected by microlensing, cold molecular clouds (mainly ofH 2) may well contribute substantially to the galactic halo dark matter. Here, we argue that the existence of such halo clouds can be inferred from the observation of absorption lines (due to heavy molecules located in the clouds themselves) towards stars of the Large Magellanic Cloud, which lie very close, within ̃1', to a previously microlensed one
A scenario for a baryonic dark halo
No full textThe recent observations of microlensing events in the LMC by the MACHO and EROS collaborations suggest that an important fraction of the galactic halo is in the form of Massive Halo Objects (MHO) of about 0.1Msun_. Here, we argue that the galactic halo is mainly baryonic and that besides MHO also H_2_ molecular clouds may significantly contribute to it. We propose a scenario in which dark clusters of MHO and/or H_2_ molecular clouds form in the halo at galactocentric distances larger than ~10-20kpc, since there we expect less collisions among proto globular cluster clouds and a smaller UV radiation flux. Cosmic ray protons may induce a significant γ-ray flux in H_2_ molecular clouds. Our calculation gives an upper bound to this flux which is below present detectability
Gamma Ray Emission From A Baryonic Dark Halo
No full textA re-analysis of EGRET data by Dixon et al has led to the discovery of a statistically significant diffuse γ-ray emission from the galactic halo. We show that this emission can naturally be accounted for within a previously proposed
model for baryonic dark matter, according to which dark clusters of brown dwarfs and cold self-gravitating H2 clouds populate the outer galactic halo and can show up in microlensing observations. Basically, cosmic-ray protons in the galactic halo scatter on the clouds clumped into dark clusters, giving rise to the observed γ-ray flux. We derive maps for the corresponding intensity distribution, which turn out to be in remarkably good agreement with those obtained by Dixon et al. We also address future prospects to test our predictions
Gamma-Ray Astronomy and Baryonic Dark Matter
No full textRecently, Dixon et al. have reanalyzed the EGRET data, finding a statistically significant diffuse g-ray emission
from the Galactic halo. We show that this emission can naturally be explained within a previously proposed
model for baryonic dark matter, in which g-rays are produced through the interaction of high-energy cosmic-ray
protons with cold H2 clouds clumped into dark clusters; these dark clusters supposedly populate the outer Galactic
halo and can show up in microlensing observations. Our estimate for the halo g-ray flux turns out to be in
remarkably good agreement with the discovery by Dixon et al. in 1998. We also address future prospects to test
our predictions
Is the Galactic halo baryonic?
No full textRecent observations of microlensing events in the Large Magellanic Cloud suggest that a sizeable fraction of the Galactic halo is in the form of massive astrophysical compact halo objects (MACHOs) with mass less than about 0.1 Msun. Here, the authors argue that molecular clouds (mainly of H2) located in the Galactic halo can contribute substantially to its total mass. They outline a scenario in which dark clusters of MACHOs and molecular clouds naturally form in the halo at large galactocentric distances. Possible ways of detecting MACHOs via infrared emission and molecular clouds via the induced γ-ray flux are discussed. Molecular clouds located in the dark halo of M31 could be discovered through cosmic background radiation anisotropies or emission lines in the microwave band
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