39,546 research outputs found
Real-time thermal Schwinger-Dyson equation for quark self-energy in Landau gauge
By means of a formal expression of the Cornwall-Jackiw-Tomboulis effective
potential for quark propagator at finite temperature and finite quark chemical
potential, we derive the real-time thermal Schwinger-Dyson equation for quark
propagator in Landau gauge. Denote the inverse quark propagator by
, we argue that, when temperature is less than the
given infrared momentum cutoff , is a feasible approximation
and can be assumed in discussions of chiral symmetry phase transition problem
in QCD.Comment: 8 pages, Latex, no figur
Quark-Antiquark and Diquark Condensates in Vacuum in a 3D Two-Flavor Gross-Neveu Model
The effective potential analysis indicates that, in a 3D two-flavor
Gross-Neveu model in vacuum, depending on less or bigger than the critical
value 2/3 of , where and are respectively the coupling
constants of scalar quark-antiquark channel and pseudoscalar diquark channel,
the system will have the ground state with pure diquark condensates or with
pure quark-antiquark condensates, but no the one with coexistence of the two
forms of condensates. The similarities and differences in the interplay between
the quark-antiquark and the diquark condensates in vacuum in the 2D, 3D and 4D
two-flavor four-fermion interaction models are summarized.Comment: 5 pages, revtex4, no figure, minor typos correcte
Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model
We derive the effective potentials for composite operators in a
Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in
each case they are equivalent to the corresponding effective potentials based
on an auxiliary scalar field. The both effective potentials could lead to the
same possible spontaneous breaking and restoration of symmetries including
chiral symmetry if the momentum cutoff in the loop integrals is large enough,
and can be transformed to each other when the Schwinger-Dyson (SD) equation of
the dynamical fermion mass from the fermion-antifermion vacuum (or thermal)
condensates is used. The results also generally indicate that two effective
potentials with the same single order parameter but rather different
mathematical expressions can still be considered physically equivalent if the
SD equation corresponding to the extreme value conditions of the two potentials
have the same form.Comment: 7 pages, no figur
Pairing Mechanism of the Heavily Electron Doped FeSe Systems: Dynamical Tuning of the Pairing Cutoff Energy
We studied pairing mechanism of the heavily electron doped FeSe (HEDIS)
systems, which commonly have one incipient hole band -- a band top below the
Fermi level by a finite energy distance -- at point and
ordinary electron bands at points in Brillouin zone (BZ). We found that the
system allows two degenerate superconducting solutions with the exactly same
in clean limit: the incipient -gap (,
) and -gap (, ) solutions with different pairing cutoffs, (spin fluctuation
energy) and , respectively. The -gap solution, in
which the system dynamically renormalizes the original pairing cutoff
to (), therefore
actively eliminates the incipient hole band from forming Cooper pairs, but
without loss of , becomes immune to the impurity pair-breaking. As a
result, the HEDIS systems, by dynamically tuning the pairing cutoff and
selecting the -pairing state, can always achieve the maximum
-- the of the degenerate solution in the ideal clean limit
-- latent in the original pairing interactions, even in dirty limit.Comment: 12 pages, 11 figures; Appendix A is adde
Random Guess and Wishful Thinking are the Best Blinding Scenarios.
Blinding is a methodologic safeguard of treatment evaluation, yet severely understudied empirically. Mathieu et al.'s theoretical analysis (2014) provided an important message that blinding cannot eliminate potential for bias associated with belief about allocation in randomized controlled trial; just like the intent-to-treat principle does not guarantee unbiased estimation under noncompliance, the blinded randomized trial as a golden standard may produce bias. They showed possible biases but did not assess how large the bias could be in different scenarios. In this paper, we examined their findings, and numerically assessed and compared the bias in treatment effect parameters by simulation under frequently encountered blinding scenarios, aiming to identify the most ideal blinding scenarios in practice. We conclude that Random Guess and Wishful Thinking (e.g., participants tend to believe they received treatment) are the most ideal blinding scenarios, incurring minimal bias. We also find some evidence that imperfect or partial blinding can be better than no blinding
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