2,758 research outputs found
Cutoff-independent regularization of four-fermion interactions for color superconductivity
We implement a cutoff-independent regularization of four-fermion interactions
to calculate the color-superconducting gap parameter in quark matter. The
traditional cutoff regularization has difficulties for chemical potentials \mu
of the order of the cutoff \Lambda, predicting in particular a vanishing gap at
\mu \sim \Lambda. The proposed cutoff-independent regularization predicts a
finite gap at high densities and indicates a smooth matching with the weak
coupling QCD prediction for the gap at asymptotically high densities.Comment: 5 pages, 1 eps figure - Revised manuscript to match the published
pape
Hadronic current correlation functions at finite temperature in the NJL model
Recently there have been suggestions that for a proper description of
hadronic matter and hadronic correlation functions within the NJL model at
finite density/temperature the parameters of the model should be taken
density/temperature dependent. Here we show that qualitatively similar results
can be obtained using a cutoff-independent regularization of the NJL model. In
this regularization scheme one can express the divergent parts at finite
density/temperature of the amplitudes in terms of their counterparts in vacuum.Comment: Presented at 9th Hadron Physics and 8th Relativistic Aspects of
Nuclear Physics (HADRON-RANP 2004): A Joint Meeting on QCD and QGP, Angra dos
Reis, Rio de Janeiro, Brazil, 28 Mar - 3 Apr 200
Extension of the Nambu--Jona-Lasinio model at high densities and temperatures by using an implicit regularization scheme
Traditional cutoff regularization schemes of the Nambu--Jona-Lasinio model
limit the applicability of the model to energy-momentum scales much below the
value of the regularizing cutoff. In particular, the model cannot be used to
study quark matter with Fermi momenta larger than the cutoff. In the present
work an extension of the model to high temperatures and densities recently
proposed by Casalbuoni, Gatto, Nardulli, and Ruggieri is used in connection
with an implicit regularization scheme. This is done by making use of scaling
relations of the divergent one-loop integrals that relate these integrals at
different energy-momentum scales. Fixing the pion decay constant at the chiral
symmetry breaking scale in the vacuum, the scaling relations predict a running
coupling constant that decreases as the regularization scale increases,
implementing in a schematic way the property of asymptotic freedom of quantum
chromodynamics. If the regularization scale is allowed to increase with density
and temperature, the coupling will decrease with density and temperature,
extending in this way the applicability of the model to high densities and
temperatures. These results are obtained without specifying an explicit
regularization. As an illustration of the formalism, numerical results are
obtained for the finite density and finite temperature quark condensate, and to
the problem of color superconductivity at high quark densities and finite
temperature.Comment: 7 pages, 5 eps figures - in version 3, substantial changes in text,
results and conclusions unchanged. To be published in Phys. Rev.
Dielectric mismatch and shallow donor impurities in GaN/HfO2 quantum wells
In this work we investigate electron-impurity binding energy in GaN/HfO
quantum wells. The calculation considers simultaneously all energy
contributions caused by the dielectric mismatch: (i) image self-energy (i.e.,
interaction between electron and its image charge), (ii) the direct Coulomb
interaction between the electron-impurity and (iii) the interactions among
electron and impurity image charges. The theoretical model account for the
solution of the time-dependent Schr\"odinger equation and the results shows how
the magnitude of the electron-impurity binding energy depends on the position
of impurity in the well-barrier system. The role of the large dielectric
constant in the barrier region is exposed with the comparison of the results
for GaN/HfO with those of a more typical GaN/AlN system, for two different
confinement regimes: narrow and wide quantum wells.Comment: 6 Pages, 7 figure
All-strain based valley filter in graphene nanoribbons using snake states
A pseudo-magnetic field kink can be realized along a graphene nanoribbon
using strain engineering. Electron transport along this kink is governed by
snake states that are characterized by a single propagation direction. Those
pseudo-magnetic fields point towards opposite directions in the K and K'
valleys, leading to valley polarized snake states. In a graphene nanoribbon
with armchair edges this effect results in a valley filter that is based only
on strain engineering. We discuss how to maximize this valley filtering by
adjusting the parameters that define the stress distribution along the graphene
ribbon.Comment: 8 pages, 6 figure
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