86,754 research outputs found
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 Gal (Gal~=~~m/s). We also show that this effect is
not compensated when averaging over the two directions of the Raman wavevector
. This thus constitutes a limit to the rejection efficiency of the
-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 the -
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 ( 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 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
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