10,832 research outputs found
Creation of the universe with a stealth scalar field
The stealth scalar field is a non-trivial configuration without any
back-reaction to geometry, which is characteristic for non-minimally coupled
scalar fields. Studying the creation probability of the de Sitter universe with
a stealth scalar field by the Hartle and Hawking's semi-classical method, we
show that the effect of the stealth field can be significant. For the class of
scalar fields we consider, creation with a stealth field is possible for a
discrete value of the coupling constant and its creation probability is always
less than that with a trivial scalar field. However, those creation rates can
be almost the same depending on the parameters of the theory.Comment: 7 pages; v2, references added; v3, creation of the open universe
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Subaru and Keck Observations of the Peculiar Type Ia Supernova 2006gz at Late Phases
Recently, a few peculiar Type Ia supernovae (SNe) that show exceptionally
large peak luminosity have been discovered. Their luminosity requires more than
1 Msun of 56Ni ejected during the explosion, suggesting that they might have
originated from super-Chandrasekhar mass white dwarfs. However, the nature of
these objects is not yet well understood. In particular, no data have been
taken at late phases, about one year after the explosion. We report on Subaru
and Keck optical spectroscopic and photometric observations of the SN Ia
2006gz, which had been classified as being one of these "overluminous" SNe Ia.
The late-time behavior is distinctly different from that of normal SNe Ia,
reinforcing the argument that SN 2006gz belongs to a different subclass than
normal SNe Ia. However, the peculiar features found at late times are not
readily connected to a large amount of 56Ni; the SN is faint, and it lacks [Fe
II] and [Fe III] emission. If the bulk of the radioactive energy escapes the SN
ejecta as visual light, as is the case in normal SNe Ia, the mass of 56Ni does
not exceed ~ 0.3 Msun. We discuss several possibilities to remedy the problem.
With the limited observations, however, we are unable to conclusively identify
which process is responsible. An interesting possibility is that the bulk of
the emission might be shifted to longer wavelengths, unlike the case in other
SNe Ia, which might be related to dense C-rich regions as indicated by the
early-phase data. Alternatively, it might be the case that SN 2006gz, though
peculiar, was actually not substantially overluminous at early times.Comment: 8 pages, 6 figures, 4 tables. Accepted for publication in The
Astrophysical Journa
Universal temperature dependence of the magnetization of gapped spin chains
Temperature dependence of the magnetization of the Haldane spin chain at
finite magnetic field is analyzed systematically. Quantum Monte Carlo data
indicates a clear minimum of magnetization as a function of temperature in the
gapless regime. On the basis of the Tomonaga-Luttinger liquid theory, we argue
that this minimum is rather universal and can be observed for general axially
symmetric quasi-one-dimensional spin systems. Our argument is confirmed by the
magnetic-field dependence of the spin-wave velocity obtained numerically. One
can estimate a magnitude of the gap of any such systems by fitting the
experimental data with the magnetization minimum.Comment: 9 pages, 7 figure
Mirror effect induced by the dilaton field on the Hawking radiation
We discuss the string creation in the near-extremal NS1 black string
solution. The string creation is described by an effective field equation
derived from a fundamental string action coupled to the dilaton field in a
conformally invariant manner. In the non-critical string model the dilaton
field causes a timelike mirror surface outside the horizon when the size of the
black string is comparable to the Planck scale. Since the fundamental strings
are reflected by the mirror surface, the negative energy flux does not
propagate across the surface. This means that the evaporation stops just before
the naked singularity of the extremal black string appears even though the
surface gravity is non-zero in the extremal limit.Comment: 15 page
Collision of Domain Walls and Reheating of the Brane Universe
We study a particle production at the collision of two domain walls in
5-dimensional Minkowski spacetime. This may provide the reheating mechanism of
an ekpyrotic (or cyclic) brane universe, in which two BPS branes collide and
evolve into a hot big bang universe. We evaluate a production rate of particles
confined to the domain wall. The energy density of created particles is given
as where is a coupling
constant of particles to a domain-wall scalar field, is the number of
bounces at the collision and is a fundamental mass scale of the domain
wall. It does not depend on the width of the domain wall, although the
typical energy scale of created particles is given by . The
reheating temperature is evaluated as . In order to have the baryogenesis at the electro-weak energy scale,
the fundamental mass scale is constrained as m_\eta \gsim 1.1\times 10^7 GeV
for .Comment: 10 pages, 12 figure
Absence of non-linear Meissner effect in YBa2Cu3O6.95
We present measurements the field and temperature dependence of the
penetration depth (lambda) in high purity, untwinned single crystals of
YBa2Cu3O6.95 in all three crystallographic directions. The temperature
dependence of lambda is linear down to low temperatures, showing that our
crystals are extremely clean. Both the magnitude and temperature dependence of
the field dependent correction to lambda however, are considerably different
from that predicted from the theory of the non-linear Meissner effect for a
d-wave superconductor (Yip-Sauls theory). Our results suggest that the
Yip-Sauls effect is either absent or is unobservably small in the Meissner
state of YBa2Cu3O6.95.Comment: 4 pages, 4 figures (Latex file + Postscipt figures
Discrete derivatives and symmetries of difference equations
We show on the example of the discrete heat equation that for any given
discrete derivative we can construct a nontrivial Leibniz rule suitable to find
the symmetries of discrete equations. In this way we obtain a symmetry Lie
algebra, defined in terms of shift operators, isomorphic to that of the
continuous heat equation.Comment: submitted to J.Phys. A 10 Latex page
Cosmic Colored Black Holes
We present spherically symmetric static solutions (a particle-like solution
and a black hole solution) in the Einstein-Yang-Mills system with a
cosmological constant.Although their gravitational structures are locally
similar to those of the Bartnik-McKinnon particles or the colored black holes,
the asymptotic behavior becomes quite different because of the existence of a
cosmological horizon. We also discuss their stability by means of a catastrophe
theory as well as a linear perturbation analysis and find the number of
unstable modes.Comment: 12 pages, latex, 4 figures (available upon request
The fate of Reissner-Nortstr\"{o}m black hole in the Einstein-Yang-Mills-Higgs system
We study about an evaporating process of black holes in SO(3)
Einstein-Yang-Mills-Higgs system. We consider a massless scalar field which
couple neither with the Yang-Mills field nor with the Higgs field surrounding
the black hole. We discuss differences in evaporating rate between a monopole
black hole and a Reissner-Nortstr\"{o}m (RN) black hole.Comment: 9 pages, 8 figure
Causality violation and singularities
We show that singularities necessarily occur when a boundary of causality
violating set exists in a space-time under the physically suitable assumptions
except the global causality condition in the Hawking-Penrose singularity
theorems. Instead of the global causality condition, we impose some
restrictions on the causality violating sets to show the occurrence of
singularities.Comment: 11 pages, latex, 2 eps figure
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