arXiv subjects

Alexander Kusenko

Publications and source records attributed to Alexander Kusenko.

At least 145 records · Page 8Linked to original sources

arXiv2006

Sterile neutrinos, dark matter, and the pulsar velocities in models with a Higgs singlet

We identify the range of parameters for which the sterile neutrinos can simultaneously explain the cosmological dark matter and the observed velocities of pulsars. To satisfy all cosmological bounds, the relic sterile neutrinos must be produced sufficiently cold. This is possible in a class of models with a gauge-singlet Higgs boson coupled to the neutrinos. Sterile dark matter can be detected by the x-ray telescopes. The presence of the singlet in the Higgs sector can be tested at the Large Hadron Collider.

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arXiv2006

Sterile neutrino states

Neutrino masses are likely to be a manifestation of the right-handed, or sterile neutrinos. The number of sterile neutrinos and the scales of their Majorana masses are unknown. We explore theoretical arguments in favor of the high and low scale seesaw mechanisms, review the existing experimental results, and discuss the astrophysical hints regarding sterile neutrinos.

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arXiv2006

Thermal evolution of the primordial clouds in warm dark matter models with keV sterile neutrinos

We analyze the processes relevant for star formation in a model with dark matter in the form of sterile neutrinos. Sterile neutrino decays produce an X-ray background radiation that has a two-fold effect on the collapsing clouds of hydrogen. First, the X-rays ionize the gas and cause an increase in the fraction of molecular hydrogen, which makes it easier for the gas to cool and to form stars. Second, the same X-rays deposit a certain amount of heat, which could, in principle, thwart the cooling of gas. We find that, in all the cases we have examined, the overall effect of sterile dark matter is to facilitate the cooling of gas. Hence, we conclude that dark matter in the form of sterile neutrinos can help the early collapse of gas clouds and the subsequent star formation.

astro-ph↗

arXiv2006

Sterile dark matter and reionization

Sterile neutrinos with masses in the keV range can be the dark matter, and their emission from a supernova can explain the observed velocities of pulsars. The sterile neutrino decays could produce the x-ray radiation in the early universe, which could have an important effect on the formation of the first stars. X-rays could ionize gas and could catalyze the production of molecular hydrogen during the ``dark ages''. The increased fraction of molecular hydrogen could facilitate the cooling and collapse of the primordial gas clouds in which the first stars were formed.

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arXiv2006

Detecting sterile dark matter in space

Space-based instruments provide new and, in some cases, unique opportunities to search for dark matter. In particular, if dark matter comprises sterile neutrinos, the x ray detection of their decay line is the most promising strategy for discovery. Sterile neutrinos with masses in the keV range could solve several long-standing astrophysical puzzles, from supernova asymmetries and the pulsar kicks to star formation, reionization, and baryogenesis. The best current limits on sterile neutrinos come from Chandra and XMM-Newton. Future advances can be achieved with a high-resolution x-ray spectrometry in space.

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arXiv2006

Opening a new window for warm dark matter

We explore the range of parameters for dark-matter sterile neutrinos in an extention of the Minimal Standard Model by three singlet fermions with masses below the electroweak scale (the $ν$MSM). This simple model can explain a wide range of phenomena, including neutrino oscillations, baryogenesis, the pulsar velocities, and the early reionization. The presence of two heavier sterile neutrinos and the possibility of entropy production in their decays broadens the allowed range of parameters for the dark-matter sterile neutrinos (or other types of dark matter, for example, the gravitino). In addition, the primordial production of dark matter sterile neutrinos allows to escape most of the constraints.

hep-ph↗

arXiv2006

Gamma ray bursts and the origin of galactic positrons

A recent observation of the 511 keV electron-positron annihilation line from the Galactic bulge has prompted a debate on the origin of the galactic positrons responsible for this emission. Assuming equilibrium between annihilation and injection of positrons in the Galaxy, we investigate the possibility that positrons were produced by past gamma ray bursts (GRBs). We compare the positron annihilation rate inferred from the observed 511 keV line with the predicted injection rate due to electron-positron pairs leaking out of individual GRBs and those pairs produced by GRB photons in the dense molecular clouds at the Galactic center. We conclude that the proposed scenario is marginally consistent with observations, and can reproduce the observed normalization of the annihilation line only for higher-than-average values of the GRB rate in the Galaxy and/or the molecular clouds optical depth for pair production.

astro-ph↗

arXiv2006

Relic keV sterile neutrinos and reionization

A sterile neutrino with mass of several keV can account for cosmological dark matter, as well as explain the observed velocities of pulsars. We show that X-rays produced by the decays of these relic sterile neutrinos can boost the production of molecular hydrogen, which can speed up the cooling of gas and the early star formation, which can, in turn, lead to a reionization of the universe at a high enough redshift to be consistent with the WMAP results.

astro-ph↗

arXiv2005

Effects of neutrino-driven kicks on the supernova explosion mechanism

We show that neutrino-driven pulsar kicks can increase the energy of the supernova shock. The observed large velocities of pulsars are believed to originate in the supernova explosion, either from asymmetries in the ejecta or from an anisotropic emission of neutrinos (or other light particles) from the cooling neutron star. In this paper we assume the velocities are caused by anisotropic neutrino emission and study the effects of these neutrino-driven kicks on the supernova explosion. We find that if the collapsed star is marginally unable to produce an explosion, the neutrino-driven mechanisms can drive the convection to make a successful explosion. The resultant explosion is asymmetric, with the strongest ejecta motion roughly in the direction of the neutron star kick. This is in sharp contrast with the ejecta-driven mechanisms, which predict the motion of the ejecta in the opposite direction. This difference can be used to distinguish between the two mechanisms based on the observations of the supernova remnants.

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arXiv2005

Bounds on heavy sterile neutrinos revisited

We revise the bounds on heavy sterile neutrinos, especially in the case of their mixing with muon neutrinos in the charged current. We summarize the present experimental limits, and we reanalyze the existing data from the accelerator neutrino experiments and from Super-Kamiokande to set new bounds on a heavy sterile neutrino in the range of masses from 8 MeV to 390 MeV. We also discuss how the future accelerator neutrino experiments can improve the present limits.

hep-ph↗

arXiv2005

Comment on "Pulsar kicks via spin-1 color superconductivity"

In a recent paper, Phys. Rev. Lett. 94, 211101 (2005) [hep-ph/0502166], Schmitt et al. have proposed a new mechanism to explain the observed velocities of pulsars. The proposed explanation is based on anisotropic emission of neutrinos from a cooling neutron star at temperatures below 0.1 MeV, thousands of years after the supernova. However, while neutrinos are copiously produced during the first minute of the supernova explosion, at later times the neutrino emission is negligible. Therefore, the proposed mechanism is not viable.

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arXiv2005

Interactions of ultrahigh-energy cosmic rays with photons in the galactic center

Ultrahigh-energy cosmic rays passing through the central region of the Galaxy interact with starlight and the infrared photons. Both nuclei and protons generate secondary fluxes of photons and neutrinos on their passage through the central region. We compute the fluxes of these secondary particles, the observations of which can be used to improve one's understanding of origin and composition of ultrahigh-energy comic rays, especially if the violation of the Greisen--Zatespin--Kuzmin cutoff is confirmed by the future data.

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arXiv2005

Astrophysical bounds on supersymmetric dark-matter Q-balls

Stable baryonic Q-balls, which appear in supersymmetric extensions of the Standard Model, could form at the end of cosmological inflation from fragmentation of the Affleck -- Dine condensate. We reconsider astrophysical constraints on such Q-balls as dark matter candidates. Baryonic Q-balls interact with matter by absorbing the baryon number and, effectively, leading to a rapid baryon number non-conservation. We have recently shown that this process can occur at a much faster rate than that used in previous calculations. As a consequence, stability of neutron stars imposes a stringent constraint on the types of Q-balls that can be dark matter. Only the Q-balls that correspond to baryonic flat directions lifted by baryon-number violating operators are allowed as dark-matter candidates.

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arXiv2005

Supersymmetric dark-matter Q-balls and their interactions in matter

Supersymmetric extensions of the Standard Model contain non-topological solitons, Q-balls, which can be stable and can be a form of cosmological dark matter. Understanding the interaction of SUSY Q-balls with matter fermions is important for both astrophysical limits and laboratory searches for these dark matter candidates. We show that a baryon scattering off a baryonic SUSY Q-ball can convert into its antiparticle with a high probability, while the baryon number of the Q-ball is increased by two units. For a SUSY Q-ball interacting with matter, this process dominates over those previously discussed in the literature.

hep-ph↗

arXiv2004

Effects of atmospheric electric fields on detection of ultrahigh-energy cosmic rays

We show that atmospheric electric fields may affect the cosmic ray observations in several ways and may lead to an overestimation of the cosmic ray energies. The electric field in thunderclouds can be as high as a few kV/cm. This field can accelerate the shower electrons and can feed some additional energy into the shower. Therefore, ground array observations in certain weather conditions may overestimate the energy of ultrahigh-energy cosmic rays if they don't take this effect into account. In addition, the electric field can bend the muon trajectories and affect the direction and energy reconstruction of inclined showers. Finally, there is a possibility of an avalanche multiplication of the shower electrons due to a runaway breakdown, which may lead to a significant miscalculation of the cosmic ray energy.

hep-ph↗

arXiv2004

Pulsar kicks from neutrino oscillations

Neutrino oscillations in a core-collapse supernova may be responsible for the observed rapid motions of pulsars. Given the present bounds on the neutrino masses, the pulsar kicks require a sterile neutrino with mass 2-20 keV and a small mixing with active neutrinos. The same particle can be the cosmological dark matter. Its existence can be confirmed the by the X-ray telescopes if they detect a 1-10 keV photon line from the decays of the relic sterile neutrinos. In addition, one may be able to detect gravity waves from a pulsar being accelerated by neutrinos in the event of a nearby supernova.

astro-ph↗

arXiv2004

Neutrino oscillations, and the origin of pulsar velocities and dark matter

Neutrino oscillations in a core-collapse supernova may be responsible for the observed rapid motions of pulsars. Three-dimensional numerical calculations show that, in the absence of neutrino oscillations, the recoil velocities of neutron stars should not exceed 200 km/s, while there exists a substantial population of pulsars that move faster than 1000 km/s. A small asymmetry in the neutrino emission may be the solution of this long-standing puzzle. Such an asymmetry could arise from neutrino oscillations, but, given the present bounds on the neutrino masses, the pulsar kicks require a sterile neutrino with a 1-20 keV mass and a small mixing with active neutrinos. The same particle can be the cosmological dark matter. Its existence can be confirmed by X-ray telescopes if they detect X-ray photons from the decays of the relic sterile neutrinos. One can also verify the neutrino kick mechanism by observing gravity waves from a nearby supernova.

astro-ph↗

arXiv2004

Possible astrophysical clues of dark matter

The physics of the supernova may provide a clue of the cosmological dark matter. In the absence of new physics, the supernova calculations do not explain the observed velocities of pulsars. However, if there exists a singlet fermion with mass in the 1-20 keV range and a small mixing with neutrinos, this particle could be emitted asymmetrically from a cooling neutron star in the event of a supernova explosion. The asymmetry could explain the long-standing puzzle of pulsar velocities. The same particle could be the dark matter. Observations of X-ray telescopes, as well as a future detection of gravitational waves from a nearby supernova can confirm or rule out this possibility.

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