2,104 research outputs found
Can a gravitational wave and a magnetic monopole coexist?
We investigate the behavior of small perturbations around the Kaluza-Klein
monopole in the five dimensional space-time. We find that the even parity
gravitational wave does not propagate in the five dimensional space-time with
Kaluza-Klein monopole provided that the gravitational wave is constant in the
fifth direction. We conclude that a gravitational wave and a U(1) magnetic
monopole do not coexist in five dimensional Kaluza-Klein spacetime.Comment: 10 pages, LaTeX. To appear in Modern Physics Letters
Oscillating scalar-field dark matter in supergravity
We show that an oscillating scalar field in supergravity of mass of the order
of TeV with a nonzero vacuum expectation value ( GeV) can
be a candidate of cold dark matter (CDM). To avoid the gravitino problem, we
need a low reheating temperature after the primordial inflation. Then, the
energy density of the oscillating scalar field satisfies all the requirements
for CDM at present in the universe.Comment: LaTeX JHEP-format, to appear in JHE
Hiding cosmic strings in supergravity D-term inflation
The influence of higher-order terms in the K\"{a}hler potential of the
supergravity D-term inflation model on the density perturbation is studied. We
show that these terms can make the inflaton potential flatter, which lowers the
energy scale of inflation under the COBE/WMAP normalization. As a result, the
mass per unit length of cosmic strings, which are produced at the end of
inflation, can be reduced to a harmless but detectable level without
introducing a tiny Yukawa coupling. Our scenario can naturally be implemented
in models with a low cut-off as in Type I or Type IIB orientifold models.Comment: 15 pages, 4 figure
Nuclear effects in Neutrino Nuclear Cross-sections
Nuclear effects in the quasielastic and inelastic scattering of
neutrinos(antineutrinos) from nuclear targets have been studied. The
calculations are done in the local density approximation which take into
account the effect of nucleon motion as well as renormalisation of weak
transition strengths in the nuclear medium. The inelastic reaction leading to
production of pions is calculated in a dominance model taking into
account the renormalization of properties in the nuclear medium.Comment: 4 pages,3 figures, Ninth International Workshop on Neutrino
Factories, Superbeams and Betabeams (NuFact07), August 6-11, 2007, Okayama
University, Okayama, Japa
Non-Gaussianity and gravitational wave background in curvaton with a double well potential
We study the density perturbation by a curvaton with a double well potential
and estimate the nonlinear parameters for non-Gaussianity and the amplitude of
gravitational wave background generated during inflation. The predicted
nonlinear parameters strongly depend on the size of a curvaton self-coupling
constant as well as the reheating temperature after inflation for a given
initial amplitude of the curvaton. The difference from usual massive
self-interacting curvaton is also emphasized.Comment: 23 pages, 6 figure
Modulated reheating by curvaton
There might be a light scalar field during inflation which is not responsible
for the accelerating inflationary expansion. Then, its quantum fluctuation is
stretched during inflation. This scalar field could be a curvaton, if it decays
at a late time. In addition, if the inflaton decay rate depends on the light
scalar field expectation value by interactions between them, density
perturbations could be generated by the quantum fluctuation of the light field
when the inflaton decays. This is modulated reheating mechanism. We study
curvature perturbation in models where a light scalar field does not only play
a role of curvaton but also induce modulated reheating at the inflaton decay.
We calculate the non-linearity parameters as well as the scalar spectral index
and the tensor-to-scalar ratio. We find that there is a parameter region where
non-linearity parameters are also significantly enhanced by the cancellation
between the modulated effect and the curvaton contribution. For the simple
quadratic potential model of both inflaton and curvaton, both tensor-to-scalar
ratio and nonlinearity parameters could be simultaneously large.Comment: 26 pages, 22 figure
Quantum Hall States of Gluons in Quark Matter
We have recently shown that dense quark matter possesses a color
ferromagnetic phase in which a stable color magnetic field arises
spontaneously. This ferromagnetic state has been known to be Savvidy vacuum in
the vacuum sector. Although the Savvidy vacuum is unstable, the state is
stabilized in the quark matter. The stabilization is achieved by the formation
of quantum Hall states of gluons, that is, by the condensation of the gluon's
color charges transmitted from the quark matter. The phase is realized between
the hadronic phase and the color superconducting phase. After a review of
quantum Hall states of electrons in semiconductors, we discuss the properties
of quantum Hall states of gluons in quark matter in detail. Especially, we
evaluate the energy of the states as a function of the coupling constant. We
also analyze solutions of vortex excitations in the states and evaluate their
energies. We find that the states become unstable as the gauge coupling
constant becomes large, or the chemical potential of the quarks becomes small,
as expected. On the other hand, with the increase of the chemical potential,
the color superconducting state arises instead of the ferromagnetic state. We
also show that the quark matter produced by heavy ion collisions generates
observable strong magnetic field Gauss when it enters the
ferromagnetic phase.Comment: 11 pages, 2 figure
Criterion for Generation of Winds from Magnetized Accretion Disks
An analytic model is proposed for non-radiating accretion flows accompanied
by up or down winds in a global magnetic field. Physical quantities in this
model solution are written in variable-separated forms, and their radial parts
are simple power law functions including one parameter for wind strength.
Several, mathematically equivalent but physically different expressions of the
criterion for wind generation are obtained. It is suggested also that the
generation of wind is a consequence of the intervention of some mechanism that
redistributes the locally available gravitational energy, and that the
Bernoulli sum can be a good indicator of the existence of such mechanisms.Comment: 24 pages, 0 figures, ApJ accepte
Precursory localization and development of microfractures along the ultimate fracture plane in amphibolite under triaxial creep
In a triaxial creep experiment in amphibolite, we clearly found a precursorylo calizationa nd developmento f microfracturesa long the final fracture planeu singa n AE (acoustice missions) ourcelo cation technique.T he precursorylo calizationo f AE hypocenters first nucleatedn ear a pre-existingm acroscopidc efecta ndt hene xtendedg raduallya longt hef inalf racture plane prior to failure. On the other hand, no significant precursorylo calizationo f AE hypocenteros n the final fracture plane before failure has been reported in rock samplesf ree of pre-existingm acroscopidce fects. This differencein AE occurrencep atterns beforef ailure could be explainedb y the differencein the degreeo f damage in the portion of the rock surrounding the localization zone when it nucleates
VLBI Monitoring Observations of Water Masers Around the Semi-Regular Variable Star R Crateris
We monitored water-vapor masers around the semi-regular variable star R
Crateris with the Japanese VLBI Network (J-Net) at the 22 GHz band during four
epochs with intervals of one month. The relative proper motions and
Doppler-velocity drifts of twelve maser features were measured. Most of them
existed for longer than 80 days. The 3-D kinematics of the features indicates a
bipolar expanding flow. The major axis of the asymmetric flow was estimated to
be at P.A. = 136 degrees. The existence of a bipolar outflow suggests that a
Mira variable star had already formed a bipolar outflow. The water masers are
in a region of apparent minimum radii of 1.3 x 10^12 m and maximum radii of 2.6
x 10^12 m, between which the expansion velocity ranges from 4.3 to 7.4 km/s.
These values suggest that the water masers are radially accelerated, but still
gravitationally bound, in the water-maser region. The most positive and
negative velocity-drifting features were found relatively close to the systemic
velocity of the star. We found that the blue-shifted features are apparently
accelerated and the red-shifted apparently decelerated. The acceleration of
only the blue-shifted features seems to be consistent with that of the
expanding flow from the star.Comment: 15 pages, 5 figures, Accepted for publication in PASJ (2001),
preprint can be obtained via WWW on
http://www.nro.nao.ac.jp/library/report/list.htm
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