Abstract
We revisit the properties of positron cloud in quark nugget (QN) model of dark matter (DM). In this model, dark matter particles are represented by compact composite objects composed of a large number of quarks or antiquarks with total baryon number $B\sim 10^{24}$. These particles have a very small number density in our galaxy which makes them "dark" to all DM detection experiments and cosmological observations. In this scenario, anti-quark nuggets play special role because they may manifest themselves in annihilation with visible matter. We study electron-positron annihilation in collisions of free electrons, hydrogen and helium gases with the positron cloud of anti-quark nuggets. We show that a strong electric field of anti-quark nuggets destroys positronium, hydrogen and helium atoms and prevents electrons from penetrating deeply in positron cloud, thus reducing the probability of the electron-positron annihilation by nearly five orders of magnitude. Therefore, electron annihilation in the positron cloud of QNs cannot explain the observed by SPI/INTEGRAL detector photons with energy 511 keV in the center of our galaxy. These photons may be explained by a different mechanism in which QN captures protons which annihilate with anti-quarks in the quark core or transform to neutrons thus reducing the QN core charge and increasing QN temperature. As a result QN loses positrons to space which annihilate with electrons there. Even more positrons are produced from charged pions resulting from the proton annihilation. Another manifestation may be emission of photons from $\pi^0$ decays.
Highlights
The conventional view that dark matter is weakly interacting has an important exception: if the ratio of the cross section to mass of DM particles is sufficiently small, σ=M ≪ 1 cm2=g, such dark matter is not excluded by any cosmological and astrophysical observations
We revisit the properties of positron cloud in quark nugget (QN) model of dark matter (DM)
We show that a strong electric field of antiquark nuggets destroys positronium, hydrogen and helium atoms and prevents electrons from penetrating deeply in positron cloud, reducing the probability of the electron-positron annihilation by nearly five orders of magnitude
Summary
The conventional view that dark matter is weakly interacting has an important exception: if the ratio of the cross section to mass of DM particles is sufficiently small, σ=M ≪ 1 cm2=g, such dark matter is not excluded by any cosmological and astrophysical observations. In this paper we revisit some of these results by taking into account the effects of electric field of the quark nuggets, screening of the electric charge and positronium formation We extend these results by considering the annihilation of atoms and molecules on anti-QNs and compare the emitted radiation with the one observed by SPI/INTEGRAL detector [20] which registered an excess of 511 keV photons from bulge of our galaxy. VI we consider the radiation produced by annihilation of interstellar gases on antiquark nuggets assuming that the latter saturate the dark matter density in our galaxy We compare this radiation with the one from the bulge of our galaxy observed by the SPI/INTEGRAL detector.
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