2,156 research outputs found
Quark mass effects on the stability of hybrid stars
We perform a study of the possible existence of hybrid stars with color
superconducting quark cores using a specific hadronic model in a combination
with an NJL-type quark model. It is shown that the constituent mass of the
non-strange quarks in vacuum is a very important parameter that controls the
beginning of the hadron-quark phase transition. At relatively small values of
the mass, the first quark phase that appears is the two-flavor color
superconducting (2SC) phase which, at larger densities, is replaced by the
color-flavor locked (CFL) phase. At large values of the mass, on the other
hand, the phase transition goes from the hadronic phase directly into the CFL
phase avoiding the 2SC phase. It appears, however, that the only stable hybrid
stars obtained are those with the 2SC quark cores.Comment: 12 pages, 7 eps figures; v2: figures and table modified after
correction of a minor numerical mistake, discussion clarified, references
added, conclusions unchanged; version to appear in PL
Gapless formation in the condensed color-flavor locked quark matter : a model-independent treatment
The electric/color neutral solution and the critical conditions for gapless
formation are investigated in the condensed color-flavor locked matter.
We point out that there exist no longer gapless modes for down-strange quark
pairing while the gapless phenomenon for up-strange one is dominated in the
condensed environment. In a model-independent way, the phase transition
to the resulting gapless phase is found to be of first-order. The novel phase
structure implies that the chromomagnetic instability happens in the
previous-predicted gapless phase might be removed at least partly.Comment: 2 figure
Numerical solution of the color superconductivity gap in a weak coupling constant
We present the numerical solution of the full gap equation in a weak coupling
constant . It is found that the standard approximations to derive the gap
equation to the leading order of coupling constant are essential for a secure
numerical evaluation of the logarithmic singularity with a small coupling
constant. The approximate integral gap equation with a very small should be
inverted to a soft integral equation to smooth the logarithmic singularity near
the Fermi surface. The full gap equation is solved for a rather large coupling
constant . The approximate and soft integral gap equations are solved
for small values. When their solutions are extrapolated to larger
values, they coincide the full gap equation solution near the Fermi surface.
Furthermore, the analytical solution matches the numerical one up to the order
one O(1). Our results confirm the previous estimates that the gap energy is of
the order tens to 100 MeV for the chemical potential MeV. They
also support the validity of leading approximations applied to the full gap
equation to derive the soft integral gap equation and its analytical solution
near the Fermi surface.Comment: 7 pages+ 6 figs, Stanford, Frankfurt and Bethlehe
Dense quark matter in compact stars
The densest predicted state of matter is colour-superconducting quark matter,
in which quarks near the Fermi surface form a condensate of Cooper pairs. This
form of matter may well exist in the core of compact stars, and the search for
signatures of its presence is an ongoing enterprise. Using a bag model of quark
matter, I discuss the effects of colour superconductivity on the mass-radius
relationship of compact stars, showing that colour superconducting quark matter
can occur in compact stars at values of the bag constant where ordinary quark
matter would not be allowed. The resultant ``hybrid'' stars with colour
superconducting quark matter interior and nuclear matter surface have masses in
the range 1.3-1.6 Msolar and radii 8-11 km. Once perturbative corrections are
included, quark matter can show a mass-radius relationship very similar to that
of nuclear matter, and the mass of a hybrid star can reach 1.8 \Msolar.Comment: 11 pages, for proceedings of SQM 2003 conference; references added,
abstract reworde
Asymmetric superconductivity in metallic systems
Different types of superfluid ground states have been investigated in systems
of two species of fermions with Fermi surfaces that do not match. This study is
relevant for cold atomic systems, condensed matter physics and quark matter. In
this paper we consider this problem in the case the fermionic quasi-particles
can transmute into one another and only their total number is conserved. We use
a BCS approximation to study superconductivity in two-band metallic systems
with inter and intra-band interactions. Tuning the hybridization between the
bands varies the mismatch of the Fermi surfaces and produces different
instabilities. For inter-band attractive interactions we find a first order
normal-superconductor and a homogeneous metastable phase with gapless
excitations. In the case of intra-band interactions, the transition from the
superconductor to the normal state as hybridization increases is continuous and
associated with a quantum critical point. The case when both interactions are
present is also considered.Comment: new enlarged version, new title, 7 pages, 7 figure
Prelude to Compressed Baryonic Matter
This is intended to appear as the introduction to "The CBM Physics Book:
compressed baryonic matter in laboratory experiments" (ed. B. Friman, C.
H\"ohne, S. Leupold, J. Knoll, J. Randrup, R. Rapp, P. Senger), to be published
by Springer. At the end there is a new proposal for numerically tractable
models of interacting many-body systems.Comment: 12 pages, to appear in "The CBM Book: compressed baryonic matter in
laboratory experiments
LOFF Pairing vs. Breached Pairing in Asymmetric Fermion Superfluids
A general analysis for the competition between breached pairing (BP) and LOFF
pairing mechanisms in asymmetric fermion superfluids is presented in the frame
of a four fermion interaction model. Two physical conditions which can induce
mismatched Fermi surfaces are considered: (1) fixed chemical potential
asymmetry and (2) fixed fermion number asymmetry . In case
(1), the BP state is ruled out because of Sarma instability and LOFF state is
thermodynamically stable in a narrow window of . In case (2), while
the Sarma instability can be avoided and both the BP and LOFF states can
survive provided is less than the corresponding critical value, the BP
state suffers magnetic instability and the LOFF state is always
thermodynamically stable. While the LOFF window in case (2) is much larger than
the one in the conventional case (1), for small the longitudinal
superfluid density of the LOFF state is negative and it suffers also magnetic
instability.Comment: 12 pages, 13 figures, published in Physical Review B. Notice: an
algebra error in Equation (39) correcte
Analytical and numerical evaluation of the Debye and Meissner masses in dense neutral three-flavor quark matter
We calculate the Debye and Meissner masses and investigate chromomagnetic
instability associated with the gapless color superconducting phase changing
the strange quark mass and the temperature . Based on the analytical
study, we develop a computational procedure to derive the screening masses
numerically from curvatures of the thermodynamic potential. When the
temperature is zero, from our numerical results for the Meissner masses, we
find that instability occurs for and gluons entirely in the gapless
color-flavor locked (gCFL) phase, while the Meissner masses are real for ,
, , and until exceeds a certain value that is larger than
the gCFL onset. We then handle mixing between color-diagonal gluons ,
, and photon , and clarify that, among three eigenvalues of the
mass squared matrix, one remains positive, one is always zero because of an
unbroken U(1)_\tilde{Q} symmetry, and one exhibits chromomagnetic instability
in the gCFL region. We also examine the temperature effects that bring
modifications into the Meissner masses. The instability found at large
for , , , and persists at finite into the -quark
color superconducting (uSC) phase which has - and - but no -
quark pairing and also into the two-flavor color superconducting (2SC) phase
characterized by - quark pairing only. The and instability
also goes into the uSC phase, but the 2SC phase has no instability for ,
, and . We map the unstable region for each gluon onto the phase
diagram as a function of and .Comment: 17 pages, 18 figure
Imaginary chemical potential and finite fermion density on the lattice
Standard lattice fermion algorithms run into the well-known sign problem at
real chemical potential. In this paper we investigate the possibility of using
imaginary chemical potential, and argue that it has advantages over other
methods, particularly for probing the physics at finite temperature as well as
density. As a feasibility study, we present numerical results for the partition
function of the two-dimensional Hubbard model with imaginary chemical
potential.
We also note that systems with a net imbalance of isospin may be simulated
using a real chemical potential that couples to I_3 without suffering from the
sign problem.Comment: 9 pages, LaTe
Pulsar kicks by anisotropic neutrino emission from quark matter in strong magnetic fields
We discuss a pulsar acceleration mechanism based on asymmetric neutrino
emission from the direct quark Urca process in the interior of proto neutron
stars. The anisotropy is caused by a strong magnetic field which polarises the
spin of the electrons opposite to the field direction. Due to parity violation
the neutrinos and anti-neutrinos leave the star in one direction accelerating
the pulsar. We calculate for varying quark chemical potentials the kick
velocity in dependence of the quark phase temperature and its radius. Ignoring
neutrino quark scattering we find that within a quark phase radius of 10 km and
temperatures larger than 5 MeV kick velocities of 1000km s can be
reached very easily. On the other hand taking into account the small neutrino
mean free paths it seems impossible to reach velocities higher than 100km
s even when including effects from colour superconductivity where the
neutrino quark interactions are suppressed.Comment: 14 pages, 10 figure
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