199 research outputs found
Chiral Symmetry Breaking with the Curtis-Pennington Vertex
We study chiral symmetry breaking in quenched QED, using a vertex Ansatz
recently proposed by Curtis and Pennington. Bifurcation analysis is employed to
establish the existence of a critical coupling and to estimate its value. The
main results are in qualitative agreement with the ladder approximation, the
numerical changes being minor.Comment: 19 pages, LaTe
Infrared cutoff dependence of the critical flavor number in three-dimensional QED
We solve, analytically and numerically, a gap equation in parity invariant
QED_3 in the presence of an infrared cutoff \mu and derive an expression for
the critical fermion number N_c as a function of \mu. We argue that this
dependence of N_c on the infrared scale might solve the discrepancy between
continuum Schwinger-Dyson equations studies and lattice simulations of QED_3.Comment: 5 pages, 1 figure (revtex4), final versio
On the theory of superconductivity in ferromagnetic superconductors with triplet pairing
We point out that ferromagnetic superconductors with triplet pairing and
strong spin-orbit coupling are even in the simplest case at least two-band
superconductors. The Gor'kov type formalism for such superconductors is
developed and the Ginzburg-Landau equations are derived. The dependence of the
critical temperature on the concentration of ordinary point-like impurities is
found. Its nonuniversality could serve as a qualitative measure of the two-band
character of ferromagnetic superconductors. The problem of the upper critical
field determination is also discussed.Comment: 8 pages, no figure; important changes with respect to the previous
versions due to the correction of a mistake: in this new version, a more
general form is considered for the order parameter (the two-components of the
order parameter were considered before as equal, which is in general not
true) ; submitted to Physical Review
Gap generation for Dirac fermions on Lobachevsky plane in a magnetic field
We study symmetry breaking and gap generation for fermions in the 2D space of
constant negative curvature (the Lobachevsky plane) in an external covariantly
constant magnetic field in a four-fermion model. It is shown that due to the
magnetic and negative curvature catalysis phenomena the critical coupling
constant is zero and there is a symmetry breaking condensate in the chiral
limit even in free theory. We analyze solutions of the gap equation in the
cases of zero, weak, and strong magnetic fields. As a byproduct we calculate
the density of states and the Hall conductivity for noninteracting fermions
that may be relevant for studies of graphene.Comment: 12 pages, no figure
Angular distributions of gamma-radiation of 1.2 GeV electrons in silicon monocrystals of great thickness
Possible symmetries of the superconducting order parameter in a hexagonal ferromagnet
We study the order parameter symmetry in a hexagonal crystal with co-existing
superconductivity and ferromagnetism. An experimental example is provided by
carbon-based materials, such as graphite-sulfur composites, in which an
evidence of such co-existence has been recently discovered. The presence of a
non-zero magnetization in the normal phase brings about considerable changes in
the symmetry classification of superconducting states, compared to the
non-magnetic case.Comment: 4 pages, REVTe
Raman scattering in LiNiPO₄ single crystal
The complete Raman spectra of a single crystal of LiNiPO₄ for a wide temperature range are reported. Among the 36 Raman-active modes predicted by group theory, 33 have been detected. The analysis of the spectra in terms of internal modes of the (PO₄)³⁻ group and of external modes is done with success. Besides, the multiphonon Raman scattering is discussed. Low-frequency lines, observed in the antiferromagnetic phase, are assigned to magnon scattering and are discussed briefly
Order parameter symmetry in ferromagnetic superconductors
We analyze the symmetry and the nodal structure of the superconducting order
parameter in a cubic ferromagnet, such as ZrZn. We demonstrate how the
order parameter symmetry evolves when the electromagnetic interaction of the
conduction electrons with the internal magnetic induction and the spin-orbit
coupling are taken into account. These interactions break the cubic symmetry
and lift the degeneracy of the order parameter. It is shown that the order
parameter which appears immediately below the critical temperature has two
components, and its symmetry is described by {\em co-representations} of the
magnetic point groups. This allows us to make predictions about the location of
the gap nodes.Comment: 12 pages, ReVTeX, submitted to PR
Dynamical chiral symmetry breaking in gauge theories with extra dimensions
We investigate dynamical chiral symmetry breaking in vector-like gauge
theories in dimensions with () compactified extra dimensions, based on
the gap equation (Schwinger-Dyson equation) and the effective potential for the
bulk gauge theories within the improved ladder approximation. The non-local
gauge fixing method is adopted so as to keep the ladder approximation
consistent with the Ward-Takahashi identities.
Using the one-loop gauge coupling of the truncated KK
effective theory which has a nontrivial ultraviolet fixed point (UV-FP)
for the (dimensionless) bulk gauge coupling , we find that there
exists a critical number of flavors, ( for
for SU(3) gauge theory): For , the dynamical
chiral symmetry breaking takes place not only in the ``strong-coupling phase''
() but also in the ``weak-coupling phase'' ()
when the cutoff is large enough. For , on the other hand,
only the strong-coupling phase is a broken phase and we can formally define a
continuum (infinite cutoff) limit, so that the physics is insensitive to the
cutoff in this case.
We also perform a similar analysis using the one-loop ``effective gauge
coupling''. We find the turns out to be a value similar to
that of the case, notwithstanding the enhancement of the
coupling compared with that of the .Comment: REVTEX4, 38 pages, 18 figures. The abstract is shortened; version to
be published in Phys. Rev.
Transverse spin dynamics in a spin-polarized Fermi liquid
The linear equations for transverse spin dynamics in weakly polarised
degenerate Fermi liquid with arbitrary relationship between temperature and
polarization are derived from Landau-Silin phenomenological kinetic equation
with general form of two-particle collision integral. The temperature and
polarization dependence of the spin current relaxation time is established. It
is found in particular that at finite polarization transverse spin wave damping
has a finite value at T=0. The analogy between temperature dependences of spin
waves attenuation and ultrasound absorption in degenerate Fermi liquid at
arbitrary temperature is presented. We also discuss spin-polarized Fermi liquid
in the general context of the Fermi-liquid theory and compare it with "Fermi
liquid" with spontaneous magnetization.Comment: 10 page
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