arXiv subjects

Michael Birkel

Publications and source records attributed to Michael Birkel.

5 recordsLinked to original sources

arXiv1998

Extremely high energy cosmic rays from relic particle decays

The expected proton and neutrino fluxes from decays of massive metastable relic particles is calculated using the HERWIG QCD event generator. The predicted proton spectrum can account for the observed flux of extremely high energy cosmic rays beyond the Greisen-Zatsepin-Kuzmin cutoff, for a decaying particle mass of O(10^{12}) GeV. The lifetime required is of O(10^{20}) yr if such particles constitute all of the dark matter (with a proportionally shorter lifetime for a smaller contribution). Such values are plausible if the metastable particles are hadron-like bound states from the hidden sector of supersymmetry breaking which decay through non-renormalizable interactions. The expected ratio of the proton to neutrino flux is given as a diagonistic of the decaying particle model for the forthcoming Pierre Auger project.

hep-ph↗

arXiv1997

On Pulsar Velocities from Neutrino Oscillations

It has been recently suggested that magnetically affected neutrino oscillations inside a cooling protoneutron star, created in a supernova explosion, could explain the large proper motion of pulsars. We investigate whether this hypothesis is in agreement with the observed properties of pulsars and find that present data disfavor the suggested mechanism. The relevance of our results for other models proposed to understand the origin of pulsar velocities is also discussed.

astro-ph↗

arXiv1997

Ruling out a critical density baryonic universe

It has been suggested by Bartlett and Hall that our universe may have the critical density in baryons by virtue of specific interactions with a `shadow' world. We show that this possibility is severely constrained by primordial nucleosynthesis, stellar evolution and the thermalization of the cosmic microwave background. In particular, recent observations of small angular-scale anisotropy in the cosmic microwave background conclusively rule out all such baryon-dominated cosmologies.

hep-ph↗

arXiv1997

Nucleosynthesis bounds on a time-varying cosmological 'constant'

We constrain proposed phenomenological models for a vacuum energy which decays with the expansion of the universe from considerations of standard big bang nucleosynthesis. Several such models which attempt to solve the cosmological age problem are disfavored or even ruled out.

astro-ph↗

arXiv1996

Nucleon Spin and the Mixing of Axial Vector Mesons

It is shown that the QCD anomaly may lead to an abnormal mixing behavior of the axial vector mesons similar to the pseudoscalar mesons. These mixing effects, involving a gluonic axial vector state, generate a non-vanishing strange quark component in the nucleon. They reduce the matrix element of the singlet axial vector in comparison to the value obtained in a naive quark model. The results are in agreement with the data obtained in the polarized lepton-nucleon scattering experiments.

hep-ph↗