52 research outputs found
Fermion Production in Strong Magnetic Field and its Astrophysical Implications
We calculate the effective potential of a strong magnetic field induced by
fermions with anomalous magnetic moments which couple to the electromagnetic
field in the form of the Pauli interaction. For a uniform magnetic field, we
find the explicit form of the effective potential. It is found that the
non-vanishing imaginary part develops for a magnetic field stronger than a
critical field and has a quartic form which is quite different from the
exponential form of the Schwinger process. We also consider a linear magnetic
field configuration as an example of inhomogeneous magnetic fields. We find
that the imaginary part of the effective potential is nonzero even below the
critical field and shows an exponentially decreasing behavior with respect to
the inverse of the magnetic field gradient, which is the non-perturbative
characteristics analogous to the Schwinger process. These results imply the
instability of the strong magnetic field to produce fermion pairs as a purely
magnetic effect. The possible applications to the astrophysical phenomena with
strong magnetic field are also discussed.Comment: 13 pages, 3 figure
Production of Neutral Fermion in Linear Magnetic Field through Pauli Interaction
We calculate the production rate of neutral fermions in linear magnetic
fields through the Pauli interaction. It is found that the production rate is
exponentially decreasing function with respect to the inverse of the magnetic
field gradient, which shows the non-perturbative characteristics analogous to
the Schwinger process. It turns out that the production rate density depends on
both the gradient and the strength of magnetic fields in 3+1 dimension. It is
quite different from the result in 2+1 dimension, where the production rate
depends only on the gradient of the magnetic fields, not on the strength of the
magnetic fields. It is also found that the production of neutral fermions
through the Pauli interaction is a magnetic effect whereas the production of
charged particles through minimal coupling is an electric effect.Comment: 11 pages, 2 figure
Effective Potential for Uniform Magnetic Fields through Pauli Interaction
We have calculated the explicit form of the real and imaginary parts of the
effective potential for uniform magnetic fields which interact with spin-1/2
fermions through the Pauli interaction. It is found that the non-vanishing
imaginary part develops for a magnetic field stronger than a critical field,
whose strength is the ratio of the fermion mass to its magnetic moment. This
implies the instability of the uniform magnetic field beyond the critical field
strength to produce fermion pairs with the production rate density
in the
presence of Pauli interaction.Comment: 9 pages with 1 figur
The Constraint of a General Effective Potential in Vector Torsion Coupled Conformally Induced Gravity
It is found that the deviation of an effective potential from the quartic
form is related to the metric and vector torsion dependencies of the effective
potential in the vector torsion coupled conformally induced gravity.Comment: 3pages Revtex 3.0, no figur
Phase Transition in Conformally Induced Gravity with Torsion
We have considered the quantum behavior of a conformally induced gravity in
the minimal Riemann-Cartan space. The regularized one-loop effective potential
considering the quantum fluctuations of the dilaton and the torsion fields in
the Coleman-Weinberg sector gives a sensible phase transition for an
inflationary phase in De Sitter space. For this effective potential, we have
analyzed the semi-classical equation of motion of the dilaton field in the
slow-rolling regime.Comment: 7pages, no figur
Conformal Couplings in Induced Gravity
It is found that the induced gravity with conformal couplings requires the
conformal invariance in both classical and quantum levels for consistency. This
is also true for the induced gravity with an extended conformal coupling
interacting with torsion.Comment: 10 pages, Revtex3.0, to appear in General Relativity and Gravitatio
Yang-Mills Instantons Sitting on a Ricci-flat Worldspace of Double D4-brane
Thus far, there seem to be no complete criteria that can settle the issue as
to what the correct generalization of the Dirac-Born-Infeld (DBI) action,
describing the low-energy dynamics of the D-branes, to the non-abelian case
would be. According to recent suggestions, one might pass the issue of
worldvolume solitons from abelian to non-abelian setting by considering the
stack of multiple, coincident D-branes and use it as a guideline to construct
or censor the relevant non-abelian version of the DBI action. In this spirit,
here we are interested in the explicit construction of SU(2) Yang-Mills (YM)
instanton solutions in the background geometry of two coincident probe D4-brane
worldspaces particularly when the metric of target spacetime in which the probe
branes are embedded is given by the Ricci-flat, magnetic extremal 4-brane
solution in type IIA supergravity theory with its worldspace metric being given
by that of Taub-NUT and Eguchi-Hanson solutions, the two best-known
gravitational instantons. And then we demonstrate that with this YM instanton-
gravitational instanton configuration on the probe D4-brane worldvolume, the
energy of the probe branes attains its minimum value and hence enjoys stable
state provided one employs the Tseytlin's non-abelian DBI action for the
description of multiple probe D-branes. In this way, we support the arguments
in the literature in favor of Tseytlin's proposal for the non-abelian DBI
action.Comment: 39 pages, Revtex, some more comments adde
Instanton-Meron Hybrid in the Background of Gravitational Instantons
When it comes to the topological aspects, gravity may have profound effects
even at the level of particle physics despite its negligibly small relative
strength well below the Planck scale. In spite of this intriguing possibility,
relatively little attempt has been made toward the exhibition of this
phenomenon in relevant physical systems. In the present work, perhaps the
simplest and the most straightforward new algorithm for generating solutions to
(anti) self-dual Yang-Mills (YM) equation in the typical gravitational
instanton backgrounds is proposed and then applied to find the solutions
practically in all the gravitational instantons known. Solutions thus obtained
turn out to be some kind of instanton-meron hybrids possessing mixed features
of both. Namely, they are rather exotic type of configurations obeying first
order (anti) self-dual YM equation which are everywhere non-singular and have
finite Euclidean YM actions on one hand while exhibiting meron-like large
distance behavior and carrying generally fractional topological charge values
on the other. Close inspection, however, reveals that the solutions are more
like instantons rather than merons in their generic natures.Comment: 33pages, Revtex, typos correcte
Differential responses to lithium in hyperexcitable neurons from patients with bipolar disorder.
Bipolar disorder is a complex neuropsychiatric disorder that is characterized by intermittent episodes of mania and depression; without treatment, 15% of patients commit suicide. Hence, it has been ranked by the World Health Organization as a top disorder of morbidity and lost productivity. Previous neuropathological studies have revealed a series of alterations in the brains of patients with bipolar disorder or animal models, such as reduced glial cell number in the prefrontal cortex of patients, upregulated activities of the protein kinase A and C pathways and changes in neurotransmission. However, the roles and causation of these changes in bipolar disorder have been too complex to exactly determine the pathology of the disease. Furthermore, although some patients show remarkable improvement with lithium treatment for yet unknown reasons, others are refractory to lithium treatment. Therefore, developing an accurate and powerful biological model for bipolar disorder has been a challenge. The introduction of induced pluripotent stem-cell (iPSC) technology has provided a new approach. Here we have developed an iPSC model for human bipolar disorder and investigated the cellular phenotypes of hippocampal dentate gyrus-like neurons derived from iPSCs of patients with bipolar disorder. Guided by RNA sequencing expression profiling, we have detected mitochondrial abnormalities in young neurons from patients with bipolar disorder by using mitochondrial assays; in addition, using both patch-clamp recording and somatic Ca2+ imaging, we have observed hyperactive action-potential firing. This hyperexcitability phenotype of young neurons in bipolar disorder was selectively reversed by lithium treatment only in neurons derived from patients who also responded to lithium treatment. Therefore, hyperexcitability is one early endophenotype of bipolar disorder, and our model of iPSCs in this disease might be useful in developing new therapies and drugs aimed at its clinical treatment
Visible Wavelength Color Filters using Dielectric Subwavelength Gratings for Backside-illuminated CMOS Image Sensor Technologies
We report transmissive color filters based on subwavelength dielectric gratings that can replace conventional dye-based color filters used in backside-illuminated CMOS image sensor (BSI CIS) technologies. The filters are patterned in an 80-nm-thick poly-silicon film on a 115-nm-thick SiO_2 spacer layer. They are optimized for operating at the primary RGB colors, exhibit peak transmittance of 60-80%, and an almost insensitive response over a ±20° angular range. This technology enables shrinking of the pixel sizes down to near a micrometer
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