986 research outputs found
OZI violating eight-quark interactions as a thermometer for chiral transitions
This work is a follow-up of our recent observation that in the SU(3) flavor
limit with vanishing current quark masses the temperature for the chiral
transition is substantially reduced by adding eight-quark interactions to the
Nambu - Jona-Lasinio Lagrangian with U_A(1) breaking. Here we generalize the
case to realistic light and strange quark masses and confirm our prior result.
Additionally, we demonstrate that depending on the strength of OZI violating
eight-quark interactions, the system undergoes either a rapid crossover or a
first order phase transition. The meson mass spectra of the low lying
pseudoscalars and scalars at T=0 are not sensitive to the difference in the
parameter settings that correspond to these two alternatives, except for the
singlet-octet mixing scalar channels, mainly the sigma meson.Comment: LaTeX, 5 pages, 3 figure
Eight-quark interactions as a chiral thermometer
A NJL Lagrangian extended to six and eight quark interactions is applied to
study temperature effects (SU(3) flavor limit, massless case), and (realistic
massive case). The transition temperature can be considerably reduced as
compared to the standard approach, in accordance with recent lattice
calculations. The mesonic spectra built on the spontaneously broken vacuum
induced by the 't Hooft interaction strength, as opposed to the commonly
considered case driven by the four-quark coupling, undergoes a rapid crossover
to the unbroken phase, with a slope and at a temperature which is regulated by
the strength of the OZI violating eight-quark interactions. This strength can
be adjusted in consonance with the four-quark coupling and leaves the spectra
unchanged, except for the sigma meson mass, which decreases. A first order
transition behavior is also a possible solution within the present approach.Comment: 4 pages, 4 figures, prepared for the proceedings of Quark Matter 2008
- 20th International Conference on Ultra-Relativistic Nucleus Nucleus
Collisions, February 4-10, Jaipur (India
Path integral bosonization of the 't Hooft determinant: fluctuations and multiple vacua
The 't Hooft six quark flavor mixing interaction (N_f=3) is bosonized by the
path integral method. The considered complete Lagrangian is constructed on the
basis of the combined 't Hooft and U(3)X U(3) extended chiral four fermion
Nambu-Jona-Lasinio interactions. The method of the steepest descents is used to
derive the effective mesonic Lagrangian. Additionally to the known lowest order
stationary phase (SP) result of Reinhardt and Alkofer we obtain the
contribution from the small quantum fluctuations of bosonic configurations
around their stationary phase trajectories. It affects the vacuum state of
hadrons at low energies: whereas without the inclusion of quantum fluctuations
the vacuum is uniquely defined for a fixed set of the model parameters,
fluctuations give rise to multivalued solutions of the gap equations, marked at
instances by drastic changes in the quark condensates. We derive the new gap
equations and analyse them in comparison with known results. We classify the
solutions according to the number of extrema they may accomodate. We find up to
four solutions in the 0<m_(u,s)<3$ GeV region.Comment: RevTex, 9 pages, 8 figures, slightly modified introduction, one added
reference and added acknowledgements, version accepted in Phys. Lett.
Long distance expansion for the NJL model with SU(3) and U_A(1) breaking
This work is a follow up of recent investigations, where we study the
implications of a generalized heat kernel expansion, constructed to incorporate
non-perturbatively the effects of a non-commutative quark mass matrix in a
fully covariant way at each order of the expansion. As underlying Lagrangian we
use the Nambu -- Jona-Lasinio model of QCD, with and
breaking, the latter generated by the 't Hooft flavour determinant interaction.
The associated bosonized Lagrangian is derived in leading stationary phase
approximation (SPA) and up to second order in the generalized heat kernel
expansion. Its symmetry breaking pattern is shown to have a complex structure,
involving all powers of the mesonic fields allowed by symmetry. The considered
Lagrangian yields a reliable playground for the study of the implications of
symmetry and vacuum structure on the mesonic spectra, which we evaluate for the
scalar and pseudoscalar meson nonets and compare with other approaches and
experiment.Comment: LaTeX, 30 pages, added discussions and references, title change,
version to appear in Nucl. Phys.
Lowering the critical temperature with eight-quark interactions
It is shown that eight-quark interactions, which are needed to stabilize the
ground state of the combined three flavor Nambu -- Jona-Lasinio and 't Hooft
Lagrangians, play also an important role in determining the critical
temperature at which transitions occur from the dynamically broken chiral phase
to the symmetric phase.Comment: 4 pages, 2 figure
Implications of a New Effective Chiral Meson Lagrangian
Based on a recently derived effective chiral meson Lagrangian from the
extended SU(2)\otimes SU(2) Nambu -- Jona-Lasinio (ENJL) model, in the linear
realization of chiral symmetry, we extract to leading order in the 1/N_c
expansion all associated relevant three-point functions \rho \to \pi\pi, \sigma
\to \pi\pi, a_1 \to \rho\pi, a_1 \to \sigma\pi, as well as the amplitude for
\pi\pi scattering. We discuss the formal differences of these amplitudes as
compared with those derived in the literature and calculate the associated
decay widths and scattering parameters. The differences have two origins: i)
new terms, which are proportional to the current quark mass and arise from
taking the correct NJL vacuum from the first steps in a proper-time expansion,
are present in the Lagrangian; ii) an implemented chiral covariant treatment of
the diagonalization in the pseudoscalar - axialvector sector induces new
couplings between three or more mesonic fields. Both effects have been derived
from the chiral Ward Takahashi identities, which are fully taken into account
at each order of the proper-time expansion.Comment: Plain LaTex, 15 page
Charge transfer and weak bonding between molecular oxygen and graphene zigzag edges at low temperatures
Electron paramagnetic resonance (EPR) study of air-physisorbed defective
carbon nano-onions evidences in favor of microwave assisted formation of
weakly-bound paramagnetic complexes comprising negatively-charged O2- ions and
edge carbon atoms carrying pi-electronic spins. These complexes being located
on the graphene edges are stable at low temperatures but irreversibly
dissociate at temperatures above 50-60 K. These EPR findings are justified by
density functional theory (DFT) calculations demonstrating transfer of an
electron from the zigzag edge of graphene-like material to oxygen molecule
physisorbed on the graphene sheet edge. This charge transfer causes changing
the spin state of the adsorbed oxygen molecule from S = 1 to S = 1/2 one. DFT
calculations show significant changes of adsorption energy of oxygen molecule
and robustness of the charge transfer to variations of the graphene-like
substrate morphology (flat and corrugated mono- and bi-layered graphene) as
well as edges passivation. The presence of H- and COOH- terminated edge carbon
sites with such corrugated substrate morphology allows formation of ZE-O2-
paramagnetic complexes characterized by small (<50 meV) binding energies and
also explains their irreversible dissociation as revealed by EPR.Comment: 28 pages, 8 figures, 2 tables, accepted in Carbon journa
Aspects of U_A(1) breaking in the Nambu and Jona-Lasinio model
The six-quark instanton induced 't Hooft interaction, which breaks the
unwanted U_A (1) symmetry of QCD, is a source of perturbative corrections to
the leading order result formed by the four-quark forces with the U_L(3)X
U_R(3) chiral symmetry. A detailed quantitative calculation is carried out to
bosonize the model by the functional integral method. We concentrate our
efforts on finding ways to integrate out the auxiliary bosonic variables. The
functional integral over these variables cannot be evaluated exactly. We show
that the modified stationary phase approach leads to a resummation within the
perturbative series and calculate the integral in the ``two-loop''
approximation. The result is a correction to the effective mesonic Lagrangian
which may be important for the low-energy spectrum and dynamics of the scalar
and pseudoscalar nonets.Comment: 42 pages, 3 figures; concluding section and references adde
Dynamical chiral symmetry breaking by a magnetic field and multi-quark interactions
Catalysis of dynamical symmetry breaking by a constant magnetic field in
(3+1) dimensions is considered. We use the three flavour Nambu -- Jona-Lasinio
type model with 't Hooft and eight-quark interaction terms. It is shown that
the multi-quark interactions introduce new additional features to this
phenomenon: (a) the local minimum of the effective potential catalyzed by the
constant magnetic field is smoothed out with increasing strength of the field
at the characteristic scale H~10^{19} G, (b) the multi-quark forces generate
independently another local minimum associated with a larger dynamical fermion
mass. This state may exist even for multi-quark interactions with a subcritical
set of couplings, and is globally stable with respect to a further increase of
the magnetic field.Comment: 6 pages, 3 figures, added discussion and references, version to
appear in Phys.Lett.
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