13,088 research outputs found
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
Determination of and Extraction of from Semileptonic Decays
By globally analyzing all existing measured branching fractions and partial
rates in different four momentum transfer-squared bins of decays, we obtain the product of the form factor and magnitude of
CKM matrix element to be . With this
product, we determine the semileptonic form factor
in conjunction with the value of
determined from the SM global fit. Alternately, with the product together with
the input of the form factor calculated in lattice QCD recently, we
extract , where the error is
still dominated by the uncertainty of the form factor calculated in lattice
QCD. Combining the
extracted from all existing measurements of decays and
together, we find the most
precisely determined to be , which improves
the accuracy of the PDG'2014 value by
Thermoelectric Properties of Silicon Carbide Nanowires with Nitrogen Dopants and Vacancies
The thermoelectric properties of cubic zincblend silicon carbide nanowires
(SiCNWs) with nitrogen impurities and vacancies along [111] direction are
theoretically studied by means of atomistic simulations. It is found that the
thermoelectric figure of merit ZT of SiCNWs can be significantly enhanced by
doping N impurities together with making Si vacancies. Aiming at obtaining a
large ZT, we study possible energetically stable configurations, and disclose
that, when N dopants locate at the center, a small number of Si vacancies at
corners are most favored for n-type nanowires, while a large number of Si
vacancies spreading into the flat edge sites are most favored for p-type
nanowires. For the SiCNW with a diameter of 1.1 nm and a length of 4.6 nm, the
ZT value for the n-type is shown capable of reaching 1.78 at 900K. The
conditions to get higher ZT values for longer SiCNWs are also addressed.Comment: 9 pages, 10 figure
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