World-sheet instantons and the Peccei-Quinn symmetry

It is shown that world-sheets violate the Peccie-Quinn symmetries associated with some of the axions that arise in superstring compactification. In the case of unbroken low-energy supersymmetry, the Peccie-Quinn violating operators that arise are D terms of dimension six. One remaining axion is unaffected.     

A note on the Peccei-Quinn symmetry

A modified Peccei-Quinn symmetry proposed by Georgi, which is more suitable for studying the axions, is worked out and the relevant strong CP problem is briefly discussed.     

Grand unified models with an automatic Peccei-Quinn symmetry

We construct a grand unified model with an automatic Peccei-Quinn symmetry.The resulting axion is invisible because the symmetry is broken at the unification scale.     

Enlarged symmetry groups of finite-size clusters with periodic noundary conditions

Any system that approximates an infinite lattice by a family of finite clusters (with periodic boundary conditions) passes through an intermediate region with enlarged (hidden) symmetry as the system size is increased. The hidden symmetry allows for extra degeneracies and level crossings and has application to exact-diagonalization studies, Monte Carlo simulations, lattice gauge theories, and renormalization group calculations.     

Neutrinos from supernova 1987A

The neutrino detection associated with the recent supernova SN1987A is reexamined in terms of a newtonian cooling model, and the results confronted with the so far fragmentary theoretical simulations of post-explosion cooling. We find a binding energy for the compact remnant of (2.0 ± 0.50) × 10⁵³ erg, a mass 1.1–1.7 M_⊙, and an initial cooling temperature of 5.0 ± 0.6 MeV. T extraction of a neutrino mass limit is considered in this framework and found, in agreement with some previous work, to give a slightly superior limit to present terrestrial experiments.     

Neutrino mass and mixing constrained from the LMC supernova burst

Observation of the prompt neutronization burst by Kamiokande II is shown to constrain the mixing parameter sin²ϑ of a 10–100 eV mass range neutrino less than 10⁻⁷, implying that the neutrino is unlikely to provide the critical mass of the universe except in a special case of a neutrino decoupled from other lighter neutrinos. Model dependent bounds on neutrino masses are also given for a class of neutrino mixing models.     

Reconstructing the cosmic equation of state from supernova distances

Observations of high-redshift supernovae indicate that the Universe is accelerating. Here we present a model-independent method for estimating the form of the potential V(phi) of the scalar field driving this acceleration, and the associated equation of state w(phi). Our method is based on a versatile analytical form for the luminosity distance D(L), optimized to fit observed distances to distant supernovae and differentiated to yield V(straight phi) and w(straight phi). Our results favor w(phi) approximately -1 at the present epoch, steadily increasing with redshift. A cosmological constant is consistent with our results.     

Constraints on the mass of unstable neutrinos from the supernova

The cosmological constraint together with the information obtained from the supernova could be used to give a lower bound on the mass of unstable neutrinos. It is shown that if the only viable channel for the unstable neutrino decay is through three lighter neutrinos, the mass of this particle should be heavier than about 500 eV.     

Nonparametric dark energy reconstruction from supernova data

Understanding the origin of the accelerated expansion of the Universe poses one of the greatest challenges in physics today. Lacking a compelling fundamental theory to test, observational efforts are targeted at a better characterization of the underlying cause. If a new form of mass-energy, dark energy, is driving the acceleration, the redshift evolution of the equation of state parameter w(z) will hold essential clues as to its origin. To best exploit data from observations it is necessary to develop a robust and accurate reconstruction approach, with controlled errors, for w(z). We introduce a new, nonparametric method for solving the associated statistical inverse problem based on Gaussian process modeling and Markov chain Monte Carlo sampling. Applying this method to recent supernova measurements, we reconstruct the continuous history of w out to redshift z=1.5.     

Chiral effect caused by shock waves from the supernova explosion

The chiral effect of the switch-on shock wave from the supernova (SN) on interstellar cloud organics was estimated. It was found that this effect is weak and cannot violate the chiral universality of the influence caused by left-polarized electrons and neutrino from the SN.