1,234 research outputs found
Physical state representations and gauge fixing in string theory
We re-examine physical state representations in the covariant quantization of
bosonic string. We especially consider one parameter family of gauge fixing
conditions for the residual gauge symmetry due to null states (or BRST exact
states), and obtain explicit representations of observable Hilbert space which
include those of the DDF states. This analysis is aimed at giving a necessary
ingredient for the complete gauge fixing procedures of covariant string field
theory such as temporal or light-cone gauge.Comment: 16 page
New Covariant Gauges in String Field Theory
A single-parameter family of covariant gauge fixing conditions in bosonic
string field theory is proposed. It is a natural string field counterpart of
the covariant gauge in the conventional gauge theory, which includes the Landau
gauge as well as the Feynman (Siegel) gauge as special cases. The action in the
Landau gauge is largely simplified in such a way that numerous component fields
have no derivatives in their kinetic terms and appear in at most quadratic in
the vertex.Comment: 24 page
Supersymmetric extended string field theory in NS^n sector and NS^{n-1}-R sector
We construct a class of quadratic gauge invariant actions for extended string
fields defined on the tensor product of open superstring state space for
multiple open string Neveu-Schwarz (NS) sectors with or without one Ramond (R)
sector. The basic idea is the same as for the bosonic extended string field
theory developed by the authors [arXiv:1309.3850]. The theory for NS^n sector
and NS^{n-1}-R sector contains general n-th rank tensor fields and (n-1)-th
rank spinor-tensor fields in the massless spectrum respectively. In principle,
consistent gauge invariant actions for any generic type of 10-dimensional
massive or massless tensor or spinor-tensor fields can be extracted from the
theory. We discuss some simple examples of bosonic and fermionic massless
actions.Comment: 25 page
Theory of Macroscopic Quantum Tunneling and Dissipation in High-Tc Josephson Junctions
We have investigated macroscopic quantum tunneling (MQT) in in-plane high-Tc
superconductor Josephson junctions and the influence of the nodal-quasiparticle
and the zero energy bound states (ZES) on MQT. We have shown that the presence
of the ZES at the interface between the insulator and the superconductor leads
to strong Ohmic quasiparticle dissipation. Therefore, the MQT rate is
noticeably suppressed in comparison with the c-axis junctions in which ZES are
completely absent.Comment: 4 pages. 1 figur
Level Truncated Tachyon Potential in Various Gauges
New gauge fixing condition with single gauge parameter proposed by the
authors is applied to the level truncated analysis of tachyon condensation in
cubic open string field theory. It is found that the only one real non-trivial
extremum persists to appear in the well-defined region of the gauge parameter,
while the other solutions are turned out to be gauge-artifacts. Contrary to the
previously known pathology in the Feynman-Siegel gauge, tachyon potential is
remarkably smooth enough around Landau-type gauge.Comment: 13 pages, 5 figures. For associated movie files, see
http://hep1.c.u-tokyo.ac.jp/~kato/sft
Epitaxial growth and magnetic properties of Sr2CrReO6 thin films
The double perovskite Sr2CrReO6 is an interesting material for spintronics,
showing ferrimagnetism up to 635 K with a predicted high spin polarization of
about 86%. We fabricated Sr2CrReO6 epitaxial films by pulsed laser deposition
on (001)-oriented SrTiO3 substrates. Phase-pure films with optimum
crystallographic and magnetic properties were obtained by growing at a
substrate temperature of 700 degree C in pure O2 of 6.6x10-4 mbar. The films
are c-axis oriented, coherently strained, and show less than 20% anti-site
defects. The magnetization curves reveal high saturation magnetization of 0.8
muB per formula unit and high coercivity of 1.1 T, as well as a strong magnetic
anisotropy.Comment: accepted for publicatio
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