6,826 research outputs found
Confinement Properties in the Multi-Instanton System
We investigate the confinement properties in the multi-instanton system,
where the size distribution is assumed to be for the large
instanton size . We find that the instanton vacuum gives the area law
behavior of the Wilson loop, which indicates existence of the linear confining
potential. In the multi-instanton system, the string tension increases
monotonously with the instanton density, and takes the standard value for the density . Thus, instantons
directly relate to color confinement properties.Comment: Talk presented by M. Fukushima at ``Lattice '97'', the International
Symposium on Lattice Field Theory, 22 - 26 July 1997, in Edinburgh, Scotland,
3 pages, Plain Late
Instanton and Monopole in External Chromomagnetic Fields
We study properties of instanton and monopole in an external chromomagnetic
field. Generally, the 't Hooft ansatz is no longer a solution of the Yang-Mills
field equation in the presence of external fields. Therefore, we investigate a
stabilized instanton solution with minimal total Yang-Mills action in a
nontrivial topological sector. With this aim, we consider numerical
minimization of the action with respect to the global color orientation, the
anisotropic scale transformation and the local gauge-like transformation
starting from a simple superposed gauge field of the 't Hooft ansatz and the
external color field. Here, the external color field is, for simplicity, chosen
to be a constant Abelian magnetic field along a certain direction. Then, the
4-dimensional rotational symmetry O(4) of the instanton solution is reduced to
two 2-dimensional rotational symmetries due to the effect of
a homogeneous external field. In the space \mib{R}^{3} at fixed , we find
a quadrupole deformation of this instanton solution. In the presence of a
magnetic field , a prolate deformation occurs along the direction of
. Contrastingly, in the presence of an electric field an
oblate deformation occurs along the direction of . We further discuss
the local correlation between the instanton and the monopole in the external
field in the maximally Abelian gauge. The external field affects the appearance
of the monopole trajectory around the instanton. In fact, a monopole and
anti-monopole pair appears around the instanton center, and this monopole loop
seems to partially screen the external field.Comment: 15 pages,8 figure
Comparative study of ordered and disordered Y1-xSrxCoO3-d
We have succeeded in preparing A-site ordered- and disordered-Y1/4Sr3/4CoO3-d
with various oxygen deficiencies delta, and have made comparative study of
their structural and physical properties. In the A-site ordered structure,
oxygen vacancies order, and d = 0.34 sample shows a weak ferromagnetic
transition beyond 300 K. On the other hand, in the A-site disordered structure,
no oxygen vacancy ordering is observed, and d = 0.16 sample shows a
ferromagnetic metallic transition around 150 K. A-site disordering destroys the
orderings of oxygen-vacancies and orbitals, leading to the strong modification
of the electronic phases.Comment: 3 pages, 3 figures, proceeding of 52nd Mangetism and Magnetic
Materials Conference (MMM 2007), published in Journal of Applied Physic
Hybrid stars in the light of the massive pulsar PSR J1614-2230
We perform a systematic study of hybrid star configurations using several
parametrizations of a relativistic mean-field hadronic EoS and the NJL model
for three-flavor quark matter. For the hadronic phase we use the stiff GM1 and
TM1 parametrizations, as well as the very stiff NL3 model. In the NJL
Lagrangian we include scalar, vector and 't Hooft interactions. The vector
coupling constant is treated as a free parameter. We also consider that
there is a split between the deconfinement and the chiral phase transitions
which is controlled by changing the conventional value of the vacuum pressure
in the NJL thermodynamic potential by , being a free parameter. We find that, as we
increase the value of , hybrid stars have a larger maximum
mass but are less stable, i.e. hybrid configurations are stable within a
smaller range of central densities. For large enough , stable
hybrid configurations are not possible at all. The effect of increasing the
coupling constant is very similar. We show that stable hybrid
configurations with a maximum mass larger than the observed mass of the pulsar
PSR J1614-2230 are possible for a large region of the parameter space of
and provided the hadronic equation of state contains nucleons
only. When the baryon octet is included in the hadronic phase, only a very
small region of the parameter space allows to explain the mass of PSR
J1614-2230. We compare our results with previous calculations of hybrid stars
within the NJL model. We show that it is possible to obtain stable hybrid
configurations also in the case that corresponds to the
conventional NJL model for which the pressure and density vanish at zero
temperature and chemical potential.Comment: 7 pages, 5 figures; typos in Table 1 have been correcte
Cr-doping effect on the orbital fluctuation of heavily doped Nd1-xSrxMnO3 (x ~ 0.625)
We have investigated the Cr-doping effect of Nd0.375Sr0.625MnO3 near the
phase boundary between the x2-y2 and 3z2-r2 orbital ordered states, where a
ferromagnetic correlation and concomitant large magnetoresistance are observed
owing to orbital fluctuation. Cr-doping steeply suppresses the ferromagnetic
correlation and magnetoresistance in Nd0.375Sr0.625Mn1-yCryO3 with 0 < y <
0.05, while they reappear in 0.05 < y < 0.10. Such a reentrant behavior implies
that a phase boundary is located at y = 0.05, or a phase crossover occurs
across y = 0.05.Comment: 3 pages, 3 figures, to be published in Journal of Applied Physic
Views of the Chiral Magnetic Effect
My personal views of the Chiral Magnetic Effect are presented, which starts
with a story about how we came up with the electric-current formula and
continues to unsettled subtleties in the formula. There are desirable features
in the formula of the Chiral Magnetic Effect but some considerations would lead
us to even more questions than elucidations. The interpretation of the produced
current is indeed very non-trivial and it involves a lot of confusions that
have not been resolved.Comment: 19 pages, no figure; typos corrected, references significantly
updated, to appear in Lect. Notes Phys. "Strongly interacting matter in
magnetic fields" (Springer), edited by D. Kharzeev, K. Landsteiner, A.
Schmitt, H.-U. Ye
Classical Phase Space Revealed by Coherent Light
We study the far field characteristics of oval-resonator laser diodes made of
an AlGaAs/GaAs quantum well. The resonator shapes are various oval geometries,
thereby probing chaotic and mixed classical dynamics. The far field pattern
shows a pronounced fine structure that strongly depends on the cavity shape.
Comparing the experimental data with ray-model simulations for a Fresnel
billiard yields convincing agreement for all geometries and reveals the
importance of the underlying classical phase space for the lasing
characteristics.Comment: 4 pages, 5 figures (reduced quality), accepted for publication in
Physical Review Letter
A perception based approach for acoustic events modeling in interactive sound field network
Presented at the 8th International Conference on Auditory Display (ICAD), Kyoto, Japan, July 2-5, 2002.This paper describes the relation between physical / acoustic parameters and psychological scale for the sound fields in order to create an artificial impulse response of the room based on the perception. First, 19 specific words were chosen that expressing subjective impressions of the sound field from a Japanese language dictionary with 42,000 vocabularies. To classify the 19 words, speech sounds are compared in the way of dichotic listening. The speech sounds are convolution of an anechoic speech and impulse responses of rooms measured by using a dummy head microphone. The words are clustered into 4 categories, 1) high tone timbre, 2) low tone timbre, 3) spaciousness and 4) naturalness or clearness. Then, the 'spatial impression' was selected among 19words and a scale of it was obtained by way of Thurstone's case V since it is one of the important factors in the sound field design. Second, to create an impulse response corresponding to the 'spatial impression', we investigate the relation between the 'spatial impression' and physical/acoustic parameters. As a result, we found that the initial part of impulse response is an important part for controlling 'spatial impression'. The result is confirmed by listening test using artificial impulse responses. Finally, we propose a psychological approach for AEML(Acoustic Modeling Language) for Interactive Sound Field Network
- …