553 research outputs found
Goldstone boson counting in linear sigma models with chemical potential
We analyze the effects of finite chemical potential on spontaneous breaking
of internal symmetries within the class of relativistic field theories
described by the linear sigma model. Special attention is paid to the emergence
of ``abnormal'' Goldstone bosons with quadratic dispersion relation. We show
that their presence is tightly connected to nonzero density of the Noether
charges, and formulate a general counting rule. The general results are
demonstrated on an SU(3)xU(1) invariant model with an SU(3)-sextet scalar
field, which describes one of the color-superconducting phases of QCD.Comment: 10 pages, REVTeX4, 4 eps figures, v2: general discussion in Sec. IV
expanded and improved, references added, other minor corrections throughout
the tex
Spontaneous symmetry breaking in the linear sigma model at finite chemical potential: One-loop corrections
We investigate spontaneous symmetry breaking within the linear sigma model
with the SU(2)xU(1) internal symmetry at finite chemical potential, which was
suggested as a model for kaon condensation in the CFL phase of dense quark
matter. One-loop corrections to the scalar field effective potential as well as
its propagator are calculated. Particular attention is paid to the type-II
Goldstone boson that appears in the Bose--Einstein condensed phase.
Furthermore, we show that the type-I Goldstone boson -- the superfluid phonon
-- is allowed to decay due to the nonlinearity of its dispersion relation at
high momentum, and determine its decay width.Comment: 13 pages, REVTeX4, 37 eps figures; v2: substantial error in Sec. IV
corrected, references added, other minor corrections; version to appear in
Phys. Rev.
TEMPERATURE-DEPENDENCE OF DOMAIN-WALL COERCIVE FIELD IN MAGNETIC GARNET-FILMS
The coercive properties of magnetically uniaxial liquid-phase epitaxy garnet films were investigated between 10 K and the Neel temperature (T(N) less-than-or-equal-to 500 K). Two independent methods, the results of which are nearly identical (magnetical response of oscillating domain walls and the method of coercive loops measured in a vibrating sample magnetometer), were used. Besides the usual domain-wall coercive field, H(dw), the critical coercive pressure, p(dw), was also introduced as it describes in a direct way the interactions of the domain walls with the wall-pinning traps. Both H(dw) and p(dw) were found to increase exponentially with decreasing temperature. Three different types of wall-pinning traps were identified in the sample and their strength, their rate of change with temperature, and their temperature range of activity were determined
Supercurrent-phase relationship of a Nb/InAs(2DES)/Nb Josephson junction in overlapping geometry
Superconductor/normal conductor/superconductor (SNS) Josephson junctions with
highly transparent interfaces are predicted to show significant deviations from
sinusoidal supercurrent-phase relationships (CPR) at low temperatures. We
investigate experimentally the CPR of a ballistic Nb/InAs(2DES)/Nb junction in
the temperature range from 1.3 K to 9 K using a modified Rifkin-Deaver method.
The CPR is obtained from the inductance of the phase-biased junction. Transport
measurements complement the investigation. At low temperatures, substantial
deviations of the CPR from conventional tunnel-junction behavior have been
observed. A theoretical model yielding good agreement to the data is presented.Comment: RevTex4, 4 pages including 3 figure
Spontaneous breaking of continuous translational invariance
Unbroken continuous translational invariance is often taken as a basic
assumption in discussions of spontaneous symmetry breaking (SSB), which singles
out SSB of translational invariance itself as an exceptional case. We present a
framework which allows us to treat translational invariance on the same footing
as other symmetries. It is shown that existing theorems on SSB can be
straightforwardly extended to this general case. As a concrete application, we
analyze the Nambu-Goldstone modes in a (ferromagnetic) supersolid. We prove on
the ground of the general theorems that the Bogoliubov mode stemming from a
spontaneously broken internal U(1) symmetry and the longitudinal phonon due to
a crystalline order are distinct physical modes.Comment: 14 pages, 4 pdf/jpg figures, REVTeX 4.1; v2: section IV expanded, new
appendix and references added, numerous other minor modifications throughout
the tex
k-Dirac operator and parabolic geometries
The principal group of a Klein geometry has canonical left action on the
homogeneous space of the geometry and this action induces action on the spaces
of sections of vector bundles over the homogeneous space. This paper is about
construction of differential operators invariant with respect to the induced
action of the principal group of a particular type of parabolic geometry. These
operators form sequences which are related to the minimal resolutions of the
k-Dirac operators studied in Clifford analysis
Josephson current through a molecular transistor in a dissipative environment
We study the Josephson coupling between two superconductors through a single
correlated molecular level, including Coulomb interaction on the level and
coupling to a bosonic environment. All calculations are done to the lowest,
i.e., the fourth, order in the tunneling coupling and we find a suppression of
the supercurrent due to the combined effect of the Coulomb interaction and the
coupling to environmental degrees of freedom. Both analytic and numerical
results are presented.Comment: 11 pages, 6 figures, to appear in Phys. Rev. B; v3: several misprints
corrected - in particular, sign inconsistencies throughout the paper should
be fixe
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