3,152 research outputs found
Shear Viscosity of Yang-Mills Theory in the Confinement Phase
In terms of a simple holographic model, we study the absorption cross section
and the shear viscosity of a pure Yang-Mills field at low temperature where the
system is in the confinement phase. Then we expect that the glueball states are
the dominant modes in this phase. In our holographic model an infrared cutoff
r_m is introduced as a parameter which fixes the lowest mass of the glueball.
As a result the critical temperature of gluon confinement T_c is estimated to
be about 127 MeV. For T < T_c, we find that both the absorption cross section
and the shear viscosity are independent of the temperature. Their values are
frozen at the values corresponding to the critical point, for 0 < T < T_c. We
discuss this behavior by considering the glueball mass and its temperature
dependence.Comment: 11 pages latex, 2 figures; minor changes in the discussion, reference
added. To appear in Int. J. Mod. Phys.
Geometric phases, gauge symmetries and ray representation
The conventional formulation of the non-adiabatic (Aharonov-Anandan) phase is
based on the equivalence class which is not
a symmetry of the Schr\"{o}dinger equation. This equivalence class when
understood as defining generalized rays in the Hilbert space is not generally
consistent with the superposition principle in interference and polarization
phenomena. The hidden local gauge symmetry, which arises from the arbitrariness
of the choice of coordinates in the functional space, is then proposed as a
basic gauge symmetry in the non-adiabatic phase. This re-formulation reproduces
all the successful aspects of the non-adiabatic phase in a manner manifestly
consistent with the conventional notion of rays and the superposition
principle. The hidden local symmetry is thus identified as the natural origin
of the gauge symmetry in both of the adiabatic and non-adiabatic phases in the
absence of gauge fields, and it allows a unified treatment of all the geometric
phases. The non-adiabatic phase may well be regarded as a special case of the
adiabatic phase in this re-formulation, contrary to the customary understanding
of the adiabatic phase as a special case of the non-adiabatic phase. Some
explicit examples of geometric phases are discussed to illustrate this
re-formulation.Comment: 30 pages. Some clarifying sentences have been added in abstract and
in the body of the paper. A new additional reference and some typos have been
corrected. To appear in Int. J. Mod. Phys.
D3/D7 holographic Gauge theory and Chemical potential
N=2 supersymmetric Yang-Mills theory with flavor hypermultiplets at finite
temperature and in the dS are studied for finite quark number density
() by a dual supergravity background with non-trivial dilaton and axion.
The quarks and its number density are introduced by embedding a probe D7
brane. We find a critical value of the chemical potential at the limit of
, and it coincides with the effective quark mass given in each theory
for . At this point, a transition of the D7 embedding configurations
occurs between their two typical ones. The phase diagrams of this transition
are shown in the plane of chemical potential versus temperature and
cosmological constant for YM theory at finite temperature and in dS
respectively. In this phase transition, the order parameter is considered as
. % and the critical value of the chemical potential This result seems to
be reasonable since both theories are in the quark deconfinement phase.Comment: 17 pages, 8 figure
Long-range ferromagnetic correlations between Anderson impurities in a semiconductor host
We study the two-impurity Anderson model for a semiconductor host using the
quantum Monte Carlo technique. We find that the impurity spins exhibit
ferromagnetic correlations with a range which can be much more enhanced than in
a half-filled metallic band. In particular, the range is longest when the Fermi
level is located above the top of the valence band and decreases as the
impurity bound state becomes occupied. Comparisons with the photoemission and
optical absorption experiments suggest that this model captures the basic
electronic structure of Ga_{1-x}Mn_xAs, the prototypical dilute magnetic
semiconductor (DMS). These numerical results might also be useful for
synthesizing DMS or dilute-oxide ferromagnets with higher Curie temperatures.Comment: 4 pages, 4 figure
Measured Quantum Fourier Transform of 1024 Qubits on Fiber Optics
Quantum Fourier transform (QFT) is a key function to realize quantum
computers. A QFT followed by measurement was demonstrated on a simple circuit
based on fiber-optics. The QFT was shown to be robust against imperfections in
the rotation gate. Error probability was estimated to be 0.01 per qubit, which
corresponded to error-free operation on 100 qubits. The error probability can
be further reduced by taking the majority of the accumulated results. The
reduction of error probability resulted in a successful QFT demonstration on
1024 qubits.Comment: 15 pages, 6 figures, submitted to EQIS 2003 Special issue, Int. J.
Quantum Informatio
Holographic Confining Gauge theory and Response to Electric Field
We study the response of confining gauge theory to the external electric
field by using holographic Yang-Mills theories in the large limit.
Although the theories are in the confinement phase, we find a transition from
the insulator to the conductor phase when the electric field exceeds its
critical value. Then, the baryon number current is generated in the conductor
phase. At the same time, in this phase, the meson melting is observed through
the quasi-normal modes of meson spectrum. Possible ideas are given for the
string state corresponding to the melted mesons, and they lead to the idea that
the source of this current may be identified with the quarks and anti-quarks
supplied by the melted mesons. We also discuss about other possible carriers.
Furthermore, from the analysis of the massless quark, chiral symmetry
restoration is observed at the insulator-conductor transition point by studying
a confining theory in which the chiral symmetry is broken.Comment: 27 pages, 14 figure
Model compilation: An approach to automated model derivation
An approach is introduced to automated model derivation for knowledge based systems. The approach, model compilation, involves procedurally generating the set of domain models used by a knowledge based system. With an implemented example, how this approach can be used to derive models of different precision and abstraction is illustrated, and models are tailored to different tasks, from a given set of base domain models. In particular, two implemented model compilers are described, each of which takes as input a base model that describes the structure and behavior of a simple electromechanical device, the Reaction Wheel Assembly of NASA's Hubble Space Telescope. The compilers transform this relatively general base model into simple task specific models for troubleshooting and redesign, respectively, by applying a sequence of model transformations. Each transformation in this sequence produces an increasingly more specialized model. The compilation approach lessens the burden of updating and maintaining consistency among models by enabling their automatic regeneration
Meson mass and confinement force driven by dilaton
Meson spectra given as fluctuations of a D7 brane are studied under the
background driven by the dilaton. This leads to a dual gauge theory with quark
confinement due to the gauge condensate. We find that the effect of the gauge
condensate on the meson spectrum is essential in order to make a realistic
hadron spectrum in the non-supersymmetric case. In the supersymmetric case,
however, only the spectra of the scalars are affected, but they are changed in
an opposite way compared to the non-supersymmetric case.Comment: 11 pages, 2 figure
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