Gino Segrè

E6 symmetry breaking in the superstring theory

We derive two methods for determining the symmetry breaking of E6 in the low energy superstring theory, and classify all breaking patterns. A method for calculating the effective Higgs vacuum expectation values is presented. We show that there are theories with naturally light SU2w Higgs doublets, and classify all theories in which this occurs. The phenomenology of spontaneously broken E6 theories is discussed, emphasizing the issues of nucleon decay and neutrino masses.

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 nonzero 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 nonzero VEVs. 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.

Implications of Gauge Unification for Time Variation of the Fine Structure Constant

Abstract 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.

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 νµ,� ↔ νe oscillations, the heaviest neutrino (either active or sterile) would have to have mass of order several keV.

Pulsar Velocities and Neutrino Oscillations

We show that two long-standing astrophysical puzzles may have a simultaneous solution. 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. Since the birth velocities generated this way are proportional to the strength of the magnetic field, this may also explain the observed isotropy of the γ-ray bursts if they originate from old neutron stars. The connection between the motion of pulsars and neutrino oscillations results in a prediction for the τ neutrino mass of m(ν τ) ∼ 100 eV.

Reexamination of generation of baryon and lepton number asymmetries in the early Universe 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.

The one-loop effective lagrangian of the superstring

Abstract Using the low-energy effective lagrangian of the superstring, we discuss the breaking of supersymmetry and the internal gauge group. We calculate the quadratically divergent part of the one-loop potential and examine the stability of the vacuum. The problem of generating masses for matter fields and fixing m 3 2 is discussed in detail.

Neutrino transport: no asymmetry in equilibrium

Abstract 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.

Absolute proton stability in unified models of strong, weak and electromagnetic interactions

Abstract We show that the proton can be made absolutely stable, without introducing superheavy bosons, by imposing a global U(1) color symmetry on the Higgs couplings of the theory. Vector-like SU(5) and SU(6) models are discussed in detail.

Baryon asymmetry of the universe and large lepton asymmetries

Abstract It is shown how a large lepton asymmetry of the universe L = (n v −n v )/n γ ⩾ 1 can lead to a small baryon asymmetry B = (n b − n b )/n γ ∼ 10 −9 via sphaleron mediated transitions.