Leptogenesis at the Electroweak Scale
In this note we propose a model of leptogenesis in which the scale for the mass of the necessary heavy neutral lepton is similar to the scale of electroweak symmetry breaking.
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arXiv subjects
Gino Segre
Publications and source records attributed to Gino Segre.
A Scalar Doublet at the Tevatron?
We propose a particularly simple explanation of the W+dijet excess reported by the CDF collaboration. No symmetries beyond those of the standard model are necessary, and the only new particles involved are a spin-zero weak SU(2) doublet with no vacuum expectation value. Possible tests of the model and comparisons to other proposals are discussed.
hep-ph↗
Implications of Gauge Unification for Time Variation of the Fine Structure Constant
Unification of the gauge couplings would imply that time variations of the fine structure constant are accompanied by calculable and very significant time variations in the QCD scale parameter $Λ_{QCD}$. Since $Λ_{QCD}$ is the dominant factor in setting the hadron masses, estimates made by simple variations of the fine structure constant may not provide meaningful limits. There may also be related variations in Yukawa couplings and the electroweak scale. Implications for the 21 cm hyperfine transition, big bang nucleosynthesis, and the triple alpha process are discussed. We find that the first of these already provides strong constraints on the underlying theory. It is emphasized more generally that time (and space) variations of fundamental couplings and their correlations may be a significant probe of ultra-high-energy physics.
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Pulsar kicks from neutrino oscillations
Neutrino oscillations can explain the observed motion of pulsars. We show that two different models of neutrino emission from a cooling neutron star are in good quantitative agreement and predict the same order of magnitude for the pulsar kick velocity, consistent with the data.
astro-ph↗
Neutrino transport: no asymmetry in equilibrium
A small asymmetry in the flux of neutrinos emitted by a hot newly-born neutron star could explain the observed motions of pulsars. However, even in the presence of parity-violating processes with anisotropic scattering amplitudes, no asymmetry is generated in thermal equilibrium. We explain why this no-go theorem stymies some of the proposed explanations for the pulsar ``kick'' velocities.
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Cyclotron Emissivity in the Early Universe
Primordial magnetic fields present between the eras of neutrino decoupling and of positron-electron annihilation can lead to the emission of neutrino-anti neutrino pairs or axions by electrons in excited Landau levels, thereby changing the electron energy spectrum. The rate is calculated and shown to not affect significantly the standard Big Bang picture.
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Reply to Comment on "Pulsar velocities and neutrino oscillations"
We have recently proposed an explanation for the birth velocities of pulsars based on neutrino oscillations (hep-ph/9606428). One of the quantities, dN/dT, was evaluated in the approximation of constant chemical potential for the electrons. An alternative approximation based on the assumption Ye=const, used by Qian (astro-ph/9705055), yields a somewhat higher prediction for the magnetic field inside a neutron star. If the same input parameters are used, the two approximations are in reasonable agreement, given the uncertainty in the geometry of the magnetic field and the simplified picture of neutrino emission that comes with the notion of a neutrinosphere.
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Neutral current induced neutrino oscillations in a supernova
Neutral currents induced matter oscillations of electroweak-active (anti-)neutrinos to sterile neutrinos can explain the observed motion of pulsars. In contrast to a recently proposed explanation of the pulsar birth velocities based on the electron to tau (muon) neutrino oscillations [hep-ph/9606428], the heaviest neutrino (either active or sterile) would have to have mass of order several keV.
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Velocities of pulsars and neutrino oscillations
Neutrino oscillations, biased by the magnetic field, alter the shape of the neutrinosphere in a cooling protoneutron star emerging from the supernova collapse. The resulting anisotropy in the momentum of outgoing neutrinos can be the origin of the observed proper motions of pulsars. The connection between the pulsars velocities and neutrino oscillations results in a prediction for the tau neutrino mass of order 100 eV.
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The origin of pulsar velocities
We have recently proposed an explanation for the birth velocities of pulsars as resulting from asymmetries due to neutrino oscillations in the cooling protoneutron star. A specific prediction of this mechanism is that the correlation of velocities and magnetic fields should be stronger for slowly rotating neutron stars and weaker for those whose periods are less than 1 s. A remarkable agreement of this prediction with the data favors the oscillation mechanism over the alternative explanations for the proper motion of pulsars.
astro-ph↗
Phase Transitions and Vacuum Tunneling Into Charge and Color Breaking Minima in the MSSM
The scalar potential of the MSSM may have local and global minima characterized by non-zero expectation values of charged and colored bosons. Even if the true vacuum is not color and charge conserving, the early Universe is likely to occupy the minimum of the potential in which only the neutral Higgs fields have non-zero vev's. The stability of this false vacuum with respect to quantum tunneling imposes important constraints on the values of the MSSM parameters. We analyze these constraints using some novel methods for calculating the false vacuum decay rate. Some regions of the MSSM parameter space are ruled out because the lifetime of the corresponding physically acceptable false vacuum is small in comparison to the present age of the Universe. However, there is a significant fraction of the parameter space that is consistent with the hypothesis that the Universe rests in the false vacuum that is stable on a cosmological time scale.
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Re-Examination of Generation of Baryon and Lepton Number Asymmetries by Heavy Particle Decay
It is shown that wave function renormalization can introduce an important contribution to the generation of baryon and lepton number asymmetries by heavy particle decay. These terms, omitted in previous analyses, are of the same order of magnitude as the standard terms. A complete cancellation of leading terms can result in some interesting cases.
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