1,189 research outputs found
Coexistence of color superconductivity and chiral symmetry breaking within the NJL model
The phase diagram for quark matter is investigated within a simple
Nambu-Jona-Lasinio model without vector correlations. It is found that the
phase structure in the temperature-density plane depends sensitively on the
parametrization of the model. We present two schemes of parametrization of the
model where within the first one a first order phase transition from a phase
with broken chiral symmetry to a color superconducting phase for temperatures
below the triple point at T_t= 55 MeV occurs whereas for the second one a
second order phase transition for temperatures below T_t = 7 MeV is found. In
the latter case, there is also a coexistence phase of broken chiral symmetry
with color superconductivity, which is a new finding within this class of
models. Possible consequences for the phenomenology of the QCD phase transition
at high baryon densities are discussed.Comment: LaTeX, 23 pages, 7 figures, new references and discussion added,
typos correcte
A New Approach to Non-Commutative U(N) Gauge Fields
Based on the recently introduced model of arXiv:0912.2634 for non-commutative
U(1) gauge fields, a generalized version of that action for U(N) gauge fields
is put forward. In this approach to non-commutative gauge field theories, UV/IR
mixing effects are circumvented by introducing additional 'soft breaking' terms
in the action which implement an IR damping mechanism. The techniques used are
similar to those of the well-known Gribov-Zwanziger approach to QCD.Comment: 11 pages; v2 minor correction
Consequences of a strong phase transition in the dense matter equation of state for the rotational evolution of neutron stars
We explore the implications of a strong first-order phase transition region
in the dense matter equation of state in the interiors of rotating neutron
stars, and the resulting creation of two disjoint families of neutron-star
configurations (the so-called high-mass twins). We numerically obtained
rotating, axisymmetric, and stationary stellar configurations in the framework
of general relativity, and studied their global parameters and stability. The
instability induced by the equation of state divides stable neutron star
configurations into two disjoint families: neutron stars (second family) and
hybrid stars (third family), with an overlapping region in mass, the high-mass
twin-star region. These two regions are divided by an instability strip. Its
existence has interesting astrophysical consequences for rotating neutron
stars. We note that it provides a natural explanation for the rotational
frequency cutoff in the observed distribution of neutron star spins, and for
the apparent lack of back-bending in pulsar timing. It also straightforwardly
enables a substantial energy release in a mini-collapse to another neutron-star
configuration (core quake), or to a black hole.Comment: 9 pages, 7 figures, Astronomy and Astrophysics accepte
Chiral quark model with infrared cut-off for the description of meson properties in hot matter
A simple chiral quark model of the Nambu--Jona-Lasinio (NJL) type with a
quark confinement mechanism is constructed for the description of the light
meson sector of QCD at finite temperature. Unphysical quark production
thresholds in the NJL model are excluded by an infrared cut-off in the momentum
integration within quark loop diagrams. This chiral quark model satisfies the
low energy theorems. Using the vacuum masses and decay widths of \pi- and
\rho-mesons for fixing the model parameters, the properties of the \sigma-
meson are derived. Within the Matsubara formalism, the model is systematically
extended to finite temperatures where chiral symmetry restoration due to a
dropping constituent quark mass entails a vanishing of the infrared cut-off
(deconfinement) at the pion Mott temperature T_c=186 MeV. Besides of the pion
mass and weak decay constant, the masses, coupling constants and decay widths
of \sigma- and \rho-mesons in hot matter are investigated. The quark-antiquark
decay channel of the light mesons is opened for T>T_c only and becomes
particularly strong for the \rho- meson. The two-pion decay channel below T_c
has almost constant width for the \rho- meson up to T_c, but for the
\sigma-meson it closes below T_c such that a scalar meson state with vanishing
width is obtained as a precursor of the chiral/deconfinement transition.Comment: Latex file, 23 pages, 7 figure
On Non-Commutative U*(1) Gauge Models and Renormalizability
Based on our recent findings regarding (non-)renormalizability of
non-commutative U*(1) gauge theories [arxiv:0908.0467, arxiv:0908.1743] we
present the construction of a new type of model. By introducing a soft breaking
term in such a way that only the bilinear part of the action is modified, no
interaction between the gauge sector and auxiliary fields occurs. Demanding in
addition that the latter form BRST doublet structures, this leads to a
minimally altered non-commutative U*(1) gauge model featuring an IR damping
behavior. Moreover, the new breaking term is shown to provide the necessary
structure in order to absorb the inevitable quadratic IR divergences appearing
at one-loop level in theories of this kind. In the present paper we compute
Feynman rules, symmetries and results for the vacuum polarization together with
the one-loop renormalization of the gauge boson propagator and the three-point
functions.Comment: 20 pages, 4 figures; v2-v4: clarified several points, and minor
correction
Yukawa terms in noncommutative SO(10) and E6 GUTs
We propose a method for constructing Yukawa terms for noncommutative SO(10)
and E6 GUTs, when these GUTs are formulated within the enveloping-algebra
formalism. The most general noncommutative Yukawa term that we propose
contains, at first order in thetamunu, the most general BRS invariant Yukawa
contribution whose only dimensionful parameter is the noncommutativity
parameter. This noncommutative Yukawa interaction is thus renormalisable at
first order in thetamunu.Comment: 14 pages, no figure
Probing the QCD vacuum with an abelian chromomagnetic field: A study within an effective model
We study the response of the QCD vacuum to an external abelian chromomagnetic
field in the framework of a non local Nambu-Jona Lasinio model with the
Polyakov loop. We use the Lattice results on the deconfinement temperature of
the pure gauge theory to compute the same quantity in the presence of dynamical
quarks. We find a linear relationship between the deconfinement temperature
with quarks and the squared root of the applied field strength, , in
qualitative (and to some extent also quantitative) agreement with existing
Lattice calculations. On the other hand, we find a discrepancy on the
approximate chiral symmetry restoration: while Lattice results suggest the
deconfinement and the chiral restoration remain linked even at non-zero value
of , our results are consistent with a scenario in which the two
transitions are separated as is increased.Comment: 14 pages, 7 figures, RevTeX4. Published version, with enlarged
abstract and minor changes in the main tex
Fluctuations of the Color-superconducting Order Parameter in Heated and Dense Quark Matter
Fluctuations of the color superconducting order parameter in dense quark
matter at finite temperatures are investigated in terms of the phenomenological
Ginzburg - Landau approach. Our estimates show that fluctuations of the
di-quark gap may strongly affect some of thermodynamic quantities even far
below and above the critical temperature. If the critical temperature of the
di-quark phase transition were rather high one could expect a manifestation of
fluctuations of the di-quark gap in the course of heavy ion collisions.Comment: 12
Nonlinear sigma model approach for phase disorder transitions and the pseudogap phase in chiral Gross-Neveu, Nambu-Jona-Lasinio models and strong-coupling superconductors
We briefly review the nonlinear sigma model approach for the subject of
increasing interest: "two-step" phase transitions in the Gross-Neveu and the
modified Nambu-Jona-Lasinio models at low and condensation from pseudogap
phase in strong-coupling superconductors. Recent success in describing
"Bose-type" superconductors that possess two characterstic temperatures and a
pseudogap above is the development approximately comparable with the BCS
theory. One can expect that it should have influence on high-energy physics,
similar to impact of the BCS theory on this subject. Although first
generalizations of this concept to particle physics were made recently, these
results were not systematized. In this review we summarize this development and
discuss similarities and differences of the appearence of the pseudogap phase
in superconductors and the Gross-Neveu and Nambu-Jona-Lasinio - like models. We
discuss its possible relevance for chiral phase transition in QCD and color
superconductors. This paper is organized in three parts: in the first section
we briefly review the separation of temperatures of pair formation and pair
condensation in strong - coupling and low carrier density superconductors (i.e.
the formation of the {\it pseudogap phase}).
Second part is a review of nonlinear sigma model approach to an analogous
phenomenon in the Chiral Gross-Neveu model at small N. In the third section we
discuss the modified Nambu-Jona-Lasinio model where the chiral phase transition
is accompanied by a formation of a phase analogous to the pseudogap phase.Comment: A brief review. Replaced with journal version (some grammatical
corrections). The latest updates of this and related papers are also
available at the author home page http://www.teorfys.uu.se/PEOPLE/egor
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