Light pseudo-Goldstone bosons without explicit symmetry breaking

A mechanism is discussed to obtain light scalar fields from a spontaneously broken continuous symmetry without explicitly breaking it. If there is a continuous manifold of classical vacua in orbit space, its tangent directions describe classically massless fields that may acquire mass from perturbations of the potential that do not break the symmetry. We consider the simplest possible example, involving a scalar field in the adjoint representation of SU(N). We study the scalar mass spectrum and its RG running at one-loop level including scalar and pseudoscalar Yukawa couplings to a massive Dirac fermion.Comment: minor typographical changes, 12 pages, 4 figure

Nucleation of quark matter in neutron stars cores

We consider the general conditions of quark droplets formation in high density neutron matter. The growth of the quark bubble (assumed to contain a sufficiently large number of particles) can be described by means of a Fokker-Planck equation. The dynamics of the nucleation essentially depends on the physical properties of the medium it takes place. The conditions for quark bubble formation are analyzed within the frameworks of both dissipative and non-dissipative (with zero bulk and shear viscosity coefficients) approaches. The conversion time of the neutron star to a quark star is obtained as a function of the equation of state of the neutron matter and of the microscopic parameters of the quark nuclei. As an application of the obtained formalism we analyze the first order phase transition from neutron matter to quark matter in rapidly rotating neutron stars cores, triggered by the gravitational energy released during the spinning down of the neutron star. The endothermic conversion process, via gravitational energy absorption, could take place, in a very short time interval, of the order of few tens seconds, in a class of dense compact objects, with very high magnetic fields, called magnetars.Comment: 31 pages, 2 figures, to appear in Ap

Influence of chirping the Raman lasers in an atom gravimeter: phase shifts due to the Raman light shift and to the finite speed of light

We present here an analysis of the influence of the frequency dependence of the Raman laser light shifts on the phase of a Raman-type atom gravimeter. Frequency chirps are applied to the Raman lasers in order to compensate gravity and ensure the resonance of the Raman pulses during the interferometer. We show that the change in the Raman light shift when this chirp is applied only to one of the two Raman lasers is enough to bias the gravity measurement by a fraction of $\mu$Gal ($1~\mu$Gal~=~$10^{-8}$~m/s$^2$). We also show that this effect is not compensated when averaging over the two directions of the Raman wavevector $k$. This thus constitutes a limit to the rejection efficiency of the $k$-reversal technique. Our analysis allows us to separate this effect from the effect of the finite speed of light, which we find in perfect agreement with expected values. This study highlights the benefit of chirping symmetrically the two Raman lasers

Flavor and Spin Contents of the Nucleon in the Quark Model with Chiral Symmetry

A simple calculation in the framework of the chiral quark theory of Manohar and Georgi yields results that can account for many of the ''failures'' of the naive quark model: significant strange quark content in the nucleon as indicated by the value of $\sigma _{\pi N},$ the $\overline{u}$-$\overline{d}$ asymmetry in the nucleon as measured by the deviation from Gottfried sum rule and by the Drell-Yan process, as well as the various quark contributions to the nucleon spin as measured by the deep inelastic polarized lepton-nucleon scatterings.Comment: figure has been separated from tex file. No other changes. Preprint CMU-HEP94-3

Structure of the electrospheres of bare strange stars

We consider a thin ($\sim 10^2-10^3$ fm) layer of electrons (the electrosphere) at the quark surface of a bare strange star, taking into account the surface effects at the boundary with the vacuum. The quark surface holds the electron layer by an extremely strong electric field, generated in the electrosphere to prevent the electrons from escaping to infinity by counterbalancing the degeneracy and thermal pressure. Because of the surface tension and depletion of $s$ quarks a very thin (a few fm) charged layer of quarks forms at the surface of the star. The formation of this layer modifies the structure of the electrosphere, by significantly changing the electric field and the density of the electrons, in comparison with the case when the surface effects are ignored. Some consequences of the modification of the electrosphere structure on the properties of strange stars are briefly discussed.Comment: 23 pages, 6 figures, to appear in Ap