1,038 research outputs found
Q-ball formation in the gravity-mediated SUSY breaking scenario
We study the formation of Q-balls which are made of flat directions that
appear in the supersymmetric extension of the standard model in the context of
gravity-mediated supersymmetry breaking. The full non-linear calculations for
the dynamics of the complex scalar field are made. Since the scalar potential
in this model is flatter than \phi^2, we have found that fluctuations develop
and go non-linear to form non-topological solitons, Q-balls. The size of a
Q-ball is determined by the most amplified mode, which is completely determined
by the model parameters. On the other hand, the charge of Q-balls depends
linearly on the initial charge density of the Affleck-Dine (AD) field. Almost
all the charges are absorbed into Q-balls, and only a tiny fraction of the
charges is carried by a relic AD field. It may lead to some constraints on the
baryogenesis and/or parameters in the particle theory. The peculiarity of
gravity-mediation is the moving Q-balls. This results in collisions between
Q-balls. It may increase the charge of Q-balls, and change its fate.Comment: 9 pages, RevTex, 11 postscript figures included, to appear in Phys.
Rev.
Entropy production by Q-ball decay for diluting long-lived charged particles
The cosmic abundance of a long-lived charged particle such as a stau is
tightly constrained by the catalyzed big bang nucleosynthesis. One of the ways
to evade the constraints is to dilute those particles by a huge entropy
production. We evaluate the dilution factor in a case that non-relativistic
matter dominates the energy density of the universe and decays with large
entropy production. We find that large Q balls can do the job, which is
naturally produced in the gauge-mediated supersymmetry breaking scenario.Comment: 8 pages, 1 figur
Minimum of enzymes cocktail obtained from white rot fungi by solid state fermentation to cellulase total activity.
Polymorphism in the internal transcribed spacer (ITS) of the ribosomal DNA of 26 isolates of ectomycorrhizal fungi.
Inter- and intraspecific variation among 26 isolates of ectomycorrhizal fungi belonging to 8 genera and 19 species were evaluated by analysis of the internal transcribed sequence (ITS) of the rDNA region using restriction fragment length polymorphism (RFLP). The ITS region was first amplified by polymerase chain reaction (PCR) with specific primers and then cleaved with different restriction enzymes. Amplification products, which ranged between 560 and 750 base pairs (bp), were obtained for all the isolates analyzed. The degree of polymorphism observed did not allow proper identification of most of the isolates. Cleavage of amplified fragments with the restriction enzymes Alu I, Hae III, Hinf I, and Hpa II revealed extensive polymorphism. All eight genera and most species presented specific restriction patterns. Species not identifiable by a specific pattern belonged to two genera: Rhizopogon (R. nigrescens, R. reaii, R. roseolus, R. rubescens and Rhizopogon sp.), and Laccaria (L. bicolor and L. amethystea). Our data confirm the potential of ITS region PCR-RFLP for the molecular characterization of ectomycorrhizal fungi and their identification and monitoring in artificial inoculation programs
Tuning the Non-local Spin-Spin Interaction between Quantum Dots with a Magnetic Field
We describe a device where the non-local spin-spin interaction between two
quantum dots can be turned on and off and even changed sign with a very small
magnetic field. The setup consists of two quantum dots at the edge of two
two-dimensional electron gases (2DEGs). The quantum dots' spins are coupled
through a RKKY-like interaction mediated by the electrons in the 2DEGs. A small
magnetic field perpendicular to the plane of the 2DEG is used as a tuning
parameter. When the cyclotron radius is commensurate with the interdot
distance, the spin-spin interaction is amplified by a few orders of magnitude.
The sign of the interaction is controlled by finely tuning the magnetic field.
Our setup allows for several dots to be coupled in a linear arrangement and it
is not restricted to nearest-neighbors interaction.Comment: 4 pages, 5 figures. Published versio
Interpocket polarization model for magnetic structures in rare-earth hexaborides
The origin of peculiar magnetic structures in cubic rare-earth (R)
hexaborides RB_6 is traced back to their characteristic band structure. The
three sphere-like Fermi surfaces induce interpocket polarization of the
conduction band as a part of a RKKY-type interaction. It is shown for the
free-electron-like model that the interpocket polarization gives rise to a
broad maximum in the intersite interaction I(q) around q=(1/4,1/4,1/2) in the
Brillouin zone. This maximum is consistent with the superstructure observed in
R=Ce, Gd and Dy. The wave-number dependence of I(q) is independently extracted
from analysis of the spin-wave spectrum measured for NdB_6. It is found that
I(q) obtained from fitting the data has a similarly to that derived by the
interpocket polarization model, except that the absolute maximum now occurs at
(0,0,1/2) in consistency with the A-type structure. The overall shape of I(q)
gives a hint toward understanding an incommensurate structure in PrB_6 as well.Comment: 5 pages, 3 figures, submitted to J.Phys.Soc.Jp
Partial Disorder in the Periodic Anderson Model on a Triangular Lattice
We report our theoretical results on the emergence of a partially-disordered
state at zero temperature and its detailed nature in the periodic Anderson
model on a triangular lattice at half filling. The partially-disordered state
is characterized by coexistence of a collinear antiferromagnetic order on an
unfrustrated honeycomb subnetwork and nonmagnetic state at the remaining sites.
This state appears with opening a charge gap between a noncollinear
antiferromagnetic metal and Kondo insulator while changing the hybridization
and Coulomb repulsion. We also find a characteristic crossover in the
low-energy excitation spectrum as a result of coexistence of magnetic order and
nonmagnetic sites. The result demonstrates that the partially-disordered state
is observed distinctly even in the absence of spin anisotropy, in marked
contrast to the partial Kondo screening state found in the previous study for
the Kondo lattice model.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
Indirect RKKY interaction in any dimensionality
We present an analytical method which enables one to find the exact spatial
dependence of the indirect RKKY interaction between the localized moments via
the conduction electrons for the arbitrary dimensionality . The
corresponding momentum dependence of the Lindhard function is exactly found for
any as well. Demonstrating the capability of the method we find the RKKY
interaction in a system of metallic layers weakly hybridized to each other.
Along with usual in-plane oscillations the RKKY interaction has the
sign-reversal character in a direction perpendicular to layers, thus favoring
the antiferromagnetic type of layers' stacking.Comment: 3 pages, REVTEX, accepted to Phys.Rev.
Curvatons in Supersymmetric Models
We study the curvaton scenario in supersymmetric framework paying particular
attention to the fact that scalar fields are inevitably complex in
supersymmetric theories. If there are more than one scalar fields associated
with the curvaton mechanism, isocurvature (entropy) fluctuations between those
fields in general arise, which may significantly affect the properties of the
cosmic density fluctuations. We examine several candidates for the curvaton in
the supersymmetric framework, such as moduli fields, Affleck-Dine field, -
and -flat directions, and right-handed sneutrino. We estimate how the
isocurvature fluctuations generated in each case affect the cosmic microwave
background angular power spectrum. With the use of the recent observational
result of the WMAP, stringent constraints on the models are derived and, in
particular, it is seen that large fraction of the parameter space is excluded
if the Affleck-Dine field plays the role of the curvaton field. Natural and
well-motivated candidates of the curvaton are also listed.Comment: 34 pages, 5 figure
Microscopic Theory of Magnon-Drag Thermoelectric Transport in Ferromagnetic Metals
A theoretical study of the magnon-drag Peltier and Seebeck effects in
ferromagnetic metals is presented. A magnon heat current is described
perturbatively from the microscopic viewpoint with respect to electron--magnon
interactions and the electric field. Then, the magnon-drag Peltier coefficient
\Pi_\MAG is obtained as the ratio between the magnon heat current and the
electric charge current. We show that \Pi_\MAG=C_\MAG T^{5/2} at a low
temperature ; that the coefficient C_\MAG is proportional to the spin
polarization of the electric conductivity; and that for C_\MAG<0,
but . From experimental results for magnon-drag Peltier
effects, we estimate that the strength of the electron--magnon interaction is
about 0.3 eV for permalloy.Comment: 3 pages, 2 figures, accepted for publication in Journal of the
Physical Society of Japa
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