10 research outputs found
Hybrid stars that masquerade as neutron stars
We show that a hybrid (nuclear + quark matter) star can have a mass-radius
relationship very similar to that predicted for a star made of purely nucleonic
matter. We show this for a generic parameterization of the quark matter
equation of state, and also for an MIT bag model, each including a
phenomenological correction based on gluonic corrections to the equation of
state. We obtain hybrid stars as heavy as 2 M_solar for reasonable values of
the bag model parameters. For nuclear matter, we use the equation of state
calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques.
Both mixed and homogeneous phases of nuclear and quark matter are considered.Comment: 22 pages, LaTeX. Extra figure and explanation adde
Viscosity spectral functions of the dilute Fermi gas in kinetic theory
We compute the viscosity spectral function of the dilute Fermi gas for different values of the s-wave scattering length , including the unitarity limit . We perform the calculation in kinetic theory by studying the response to a non-trivial background metric. We find the expected structure consisting of a diffusive peak in the transverse shear channel and a sound peak in the longitudinal channel. At zero momentum the width of the diffusive peak is where is the energy density and is the shear viscosity. At finite momentum the spectral function approaches the collisionless limit and the width is of order
Critical temperature for kaon condensation in color-flavor locked quark matter
We study the behavior of Goldstone bosons in color-flavor-locked (CFL) quark
matter at nonzero temperature. Chiral symmetry breaking in this phase of cold
and dense matter gives rise to pseudo-Goldstone bosons, the lightest of these
being the charged and neutral kaons K^+ and K^0. At zero temperature,
Bose-Einstein condensation of the kaons occurs. Since all fermions are gapped,
this kaon condensed CFL phase can, for energies below the fermionic energy gap,
be described by an effective theory for the bosonic modes. We use this
effective theory to investigate the melting of the condensate: we determine the
temperature-dependent kaon masses self-consistently using the two-particle
irreducible effective action, and we compute the transition temperature for
Bose-Einstein condensation. Our results are important for studies of transport
properties of the kaon condensed CFL phase, such as bulk viscosity.Comment: 24 pages, 8 figures, v2: new section about effect of electric
neutrality on critical temperature added; references added; version to appear
in J.Phys.
Bulk viscosity in kaon-condensed color-flavor locked quark matter
Color-flavor locked (CFL) quark matter at high densities is a color
superconductor, which spontaneously breaks baryon number and chiral symmetry.
Its low-energy thermodynamic and transport properties are therefore dominated
by the H (superfluid) boson, and the octet of pseudoscalar pseudo-Goldstone
bosons of which the neutral kaon is the lightest. We study the CFL-K^0 phase,
in which the stress induced by the strange quark mass causes the kaons to
condense, and there is an additional ultra-light "K^0" Goldstone boson arising
from the spontaneous breaking of isospin. We compute the bulk viscosity of
matter in the CFL-K^0 phase, which arises from the beta-equilibration processes
K^0H+H and K^0+HH. We find that the bulk viscosity varies as T^7, unlike
the CFL phase where it is exponentially Boltzmann-suppressed by the kaon's
energy gap. However, in the temperature range of relevance for r-mode damping
in compact stars, the bulk viscosity in the CFL-K^0 phase turns out to be even
smaller than in the uncondensed CFL phase, which already has a bulk viscosity
much smaller than all other known color-superconducting quark phases.Comment: 23 pages, 8 figures, v2: references added; minor rephrasings in the
conclusions; version to appear in J. Phys.
Viscosity spectral functions of the dilute Fermi gas in kinetic theory
We compute the viscosity spectral function of the dilute Fermi gas for
different values of the s-wave scattering length , including the unitarity
limit . We perform the calculation in kinetic theory by studying
the response to a non-trivial background metric. We find the expected structure
consisting of a diffusive peak in the transverse shear channel and a sound peak
in the longitudinal channel. At zero momentum the width of the diffusive peak
is where is the energy density
and is the shear viscosity. At finite momentum the spectral function
approaches the collisionless limit and the width is of order .Comment: 15 pages, 6 figure