4,645 research outputs found
Ginzburg-Landau approach to the three flavor LOFF phase of QCD
We explore, using a Ginzburg-Landau expansion of the free energy, the
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors, using
the NJL four-fermion coupling to mimic gluon interactions. We find that, below
the point where the QCD homogeneous superconductive phases should give way to
the normal phase, Cooper condensation of the pairs u-s and d-u is possible, but
in the form of the inhomogeneous LOFF pairing.Comment: 8 pages, 4 figures. Eq. (20) corrected. As a consequence figures have
been modified to show only the solution with parallel total momenta of the
us, ud pairs, as the other configurations are suppressed. Main conclusions of
the paper are unchange
Aspects of the Color Flavor Locking phase of QCD in the Nambu-Jona Lasinio approximation
We study two aspects of the CFL phase of QCD in the NJL approximation. The
first one is the issue of the dependence on \mu of the ultraviolet cutoff in
the gap equation, which is solved allowing a running coupling constant. The
second one is the dependence of the gap on the strange quark mass; using the
high density effective theory we perform an expansion in the parameter
(m_s/\mu)^2 after checking that its numerical validity is very good already at
first order.Comment: LaTeX file, 6 figure
Effective gluon interactions in the Colour Superconductive Phase of two flavor QCD
The gluon self-energies and dispersion laws in the color superconducting
phase of QCD with two massless flavors are calculated using the effective
theory near the Fermi surface. These quantities are calculated at zero
temperature for all the eight gluons, those of the remaining SU(2) color group
and those corresponding to the broken generators. The construction of the
effective interaction is completed with the one loop calculation of the three-
and four-point gluon interactions.Comment: LaTeX, p 17, 4 figures. Final version to be published in Phys. Lett.
B. Several corrections have been done and some point clarifie
Effective Field Theory for the Crystalline Colour Superconductive Phase of QCD
We present an effective field theory for high density, low temperature QCD in
the crystalline colour superconductive phase (LOFF phase). This interesting
phase of QCD is characterized by a gap parameter with a crystalline pattern,
breaking traslational and rotational invariance, and could have astrophysical
applications. In the effective theory the fermions have a Majorana mass, which,
besides colour, breaks translation and rotation symmetries. Fermions couple to
the three phonons arising from the breaking of rotation and translation
invariance. Integrating out the fermions leads eventually to an effective
lagrangian in terms of the phonon fields only, which satisfies an anisotropic
dispersion relation.Comment: Latex, 17 pages, Modifications in the effective goldstone boson
descriptio
Heating (Gapless) Color-Flavor Locked Quark Matter
We explore the phase diagram of neutral quark matter at high baryon density
as a function of the temperature T and the strange quark mass Ms. At T=0, there
is a sharp distinction between the insulating color-flavor locked (CFL) phase,
which occurs where Ms^2/mu < 2 Delta, and the metallic gapless CFL phase, which
occurs at larger Ms^2/mu. Here, mu is the chemical potential for quark number
and Delta is the gap in the CFL phase. We find this distinction blurred at
nonzero T, as the CFL phase undergoes an insulator-to-metal crossover when it
is heated. We present an analytic treatment of this crossover. At higher
temperatures, we map out the phase transition lines at which the gap parameters
Delta_1, Delta_2 and Delta_3 describing ds-pairing, us-pairing and ud-pairing
respectively, go to zero in an NJL model. For small values of Ms^2/mu, we find
that Delta_2 vanishes first, then Delta_1, then Delta_3. We find agreement with
a previous Ginzburg-Landau analysis of the form of these transitions and find
quantitative agreement with results obtained in full QCD at asymptotic density
for ratios of coefficients in the Ginzburg-Landau potential. At larger Ms^2/mu,
we find that Delta_1 vanishes first, then Delta_2, then Delta_3. Hence, we find
a "doubly critical'' point in the (Ms^2/mu,T)-plane at which two lines of
second order phase transitions (Delta_1->0 and Delta_2->0) cross. Because we do
not make any small-Ms approximation, if we choose a relatively strong coupling
leading to large gap parameters, we are able to pursue the analysis of the
phase diagram all the way up to such large values of Ms that there are no
strange quarks present.Comment: 24 pages; 22 figures; typos in labelling of Figs. 7, 20 correcte
Self-consistent parametrization of the two-flavor isotropic color-superconducting ground state
Lack of Lorentz invariance of QCD at finite quark chemical potential in
general implies the need of Lorentz non-invariant condensates for the
self-consistent description of the color-superconducting ground state.
Moreover, the spontaneous breakdown of color SU(3) in this state naturally
leads to the existence of SU(3) non-invariant non-superconducting expectation
values. We illustrate these observations by analyzing the properties of an
effective 2-flavor Nambu-Jona-Lasinio type Lagrangian and discuss the
possibility of color-superconducting states with effectively gapless fermionic
excitations. It turns out that the effect of condensates so far neglected can
yield new interesting phenomena.Comment: 16 pages, 3 figure
Influence of finite quark chemical potentials on the three flavor LOFF phase of QCD
We study in the Ginzburg-Landau approximation, the
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) phase of QCD with three flavors and one
plane wave, including terms of order O(1/mu). We show that the LOFF window is
slightly enlarged, and actually splits into two different regions, one
characterized by u-s and d-u pairings and the other with d-u pairs only.Comment: 8 pages, 3 figure
A quark action for very coarse lattices
We investigate a tree-level O(a^3)-accurate action, D234c, on coarse
lattices. For the improvement terms we use tadpole-improved coefficients, with
the tadpole contribution measured by the mean link in Landau gauge.
We measure the hadron spectrum for quark masses near that of the strange
quark. We find that D234c shows much better rotational invariance than the
Sheikholeslami-Wohlert action, and that mean-link tadpole improvement leads to
smaller finite-lattice-spacing errors than plaquette tadpole improvement. We
obtain accurate ratios of lattice spacings using a convenient ``Galilean
quarkonium'' method.
We explore the effects of possible O(alpha_s) changes to the improvement
coefficients, and find that the two leading coefficients can be independently
tuned: hadron masses are most sensitive to the clover coefficient, while hadron
dispersion relations are most sensitive to the third derivative coefficient
C_3. Preliminary non-perturbative tuning of these coefficients yields values
that are consistent with the expected size of perturbative corrections.Comment: 22 pages, LaTe
Mass-Induced Crystalline Color Superconductivity
We demonstrate that crystalline color superconductivity may arise as a result
of pairing between massless quarks and quarks with nonzero mass m_s. Previous
analyses of this phase of cold dense quark matter have all utilized a chemical
potential difference \delta\mu to favor crystalline color superconductivity
over ordinary BCS pairing. In any context in which crystalline color
superconductivity occurs in nature, however, it will be m_s-induced. The effect
of m_s is qualitatively different from that of \delta\mu in one crucial
respect: m_s depresses the value of the BCS gap \Delta_0 whereas \delta\mu
leaves \Delta_0 unchanged. This effect in the BCS phase must be taken into
account before m_s-induced and \delta\mu-induced crystalline color
superconductivity can sensibly be compared.Comment: 12 pages, 4 figures. v2: very small change onl
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