6 research outputs found
Mesons and diquarks in neutral color superconducting quark matter with -equilibrium
The spectrum of meson and diquark excitations in cold color-superconducting
(2SC) quark matter is investigated under local color and electric neutrality
constraints with -equilibrium. A 2-flavored Nambu--Jona-Lasinio type
model including a baryon , color , and electric chemical
potentials is used. Two relations between coupling constants and in the
diquark- and quark-antiquark channels, correspondingly, are treated,
and . At the gapless- and at the gapped neutral color
superconductivity is realized. It is shown that color and electrical neutrality
together with -equilibrium lead to a strong mass splitting within the
pion isotriplet in the 2SC phase (both gapped and gapless), in contrast with
non--neutral matter. It is also shown that the properties of the physical
-singlet diquark excitation in the 2SC ground state varies for
different parameterization schemes. Thus, for one finds a heavy
resonance with mass 1100 MeV in the non--neutral (gapped) case, whereas,
if neutrality is imposed, a stable diquark with mass 200 MeV
appears in the gapless 2SC phase. For , there is again a resonance (with
the mass 300 MeV) in the neutral gapped 2SC phase. Hence, the existence
of the stable massive SU(2)-singlet diquark excitation is a new peculiarity
of the gapless 2SC.Comment: 18 pages, 9 figures; version accepted for publication in PR
Mesons and diquarks in the color neutral 2SC phase of dense cold quark matter
The spectrum of meson and diquark excitations of dense color neutral cold
quark matter is investigated in the framework of a 2-flavored
Nambu--Jona-Lasinio type model, including a quark - and color
chemical potential. It was found out that in the color superconducting (2SC)
phase, i.e. at MeV, aquires rather small values
10 MeV in order to ensure the color neutrality. In this phase the - and
meson masses are evaluated around 330 MeV. The spectrum of
scalar diquarks in the color neutral 2SC phase consists of a heavy (-singlet) resonance with mass 1100 MeV, four light diquarks with
mass , and one Nambu --Goldstone boson which is in accordance with
the Goldstone theorem. Moreover, in the 2SC phase there are five light stable
particles as well as a heavy resonance in the spectrum of pseudo-scalar
diquarks. In the color symmetric phase, i.e. for , a mass splitting
of scalar diquarks and antidiquarks is shown to arise if , contrary
to the case of , where the masses of scalar antidiquarks and diquarks
are degenerate at the value ~700 MeV. If the coupling strength in the
pseudo-scalar diquark channel is the same as in the scalar diquark one (as for
QCD-inspired NJL models), then in the color symmetric phase pseudo-scalar
diquarks are not allowed to exist as stable particles.Comment: 18 pages, 4 figures; version accepted for the publication in PR
Pion, sigma-meson and diquarks in the 2SC phase of dense cold quark matter
The spectrum of meson and diquark excitations of dense cold quark matter is
investigated in the framework of a Nambu--Jona-Lasinio type model for light
quarks of two flavors. It was found out that a first order phase transition
occurs when the chemical potential exceeds the critical value
MeV. Above , the diquark condensate \vev{qq} forms, breaking the color
symmetry of strong interaction. The masses of - and -mesons are
shown to grow with the chemical potential in the color-superconducting
phase, but the mesons themselves become almost stable particles due to the Mott
effect. Moreover, we have found in this phase an abnormal number of three,
instead of five, Nambu--Goldstone bosons, together with a color doublet of
light stable diquark modes and a color-singlet heavy diquark resonance with the
mass 1100 MeV. In the color symmetric phase, \textit{i.e.} for , the splitting between the masses of diquarks and antidiquarks is shown
to arise if , contrary to the case of vanishing chemical potential,
, where the mass spectrum of antidiquarks and diquarks is degenerate
at the value 700 MeV.Comment: 16 pages, 4 figure
Abnormal number of Nambu-Goldstone bosons in the color-asymmetric 2SC phase of an NJL-type model
We consider an extended Nambu--Jona-Lasinio model including both (q \bar q)-
and (qq)-interactions with two light-quark flavors in the presence of a single
(quark density) chemical potential. In the color superconducting phase of the
quark matter the color SU(3) symmetry is spontaneously broken down to SU(2). If
the usual counting of Goldstone bosons would apply, five Nambu-Goldstone (NG)
bosons corresponding to the five broken color generators should appear in the
mass spectrum. Unlike that expectation, we find only three gapless diquark
excitations of quark matter. One of them is an SU(2)-singlet, the remaining two
form an SU(2)-(anti)doublet and have a quadratic dispersion law in the small
momentum limit. These results are in agreement with the Nielsen-Chadha theorem,
according to which NG-bosons in Lorentz-noninvariant systems, having a
quadratic dispersion law, must be counted differently. The origin of the
abnormal number of NG-bosons is shown to be related to a nonvanishing
expectation value of the color charge operator Q_8 reflecting the lack of color
neutrality of the ground state. Finally, by requiring color neutrality, two
massive diquarks are argued to become massless, resulting in a normal number of
five NG-bosons with usual linear dispersion laws.Comment: 13 pages, 4 figures, revtex
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.