198 research outputs found
Born-Again Braneworld
We propose a cosmological braneworld scenario in which two branes collide and
emerge as reborn branes with signs of tensions opposite to the original
tensions of respective branes. In this scenario, the branes are assumed to be
inflating. However, the whole dynamics is different from the usual inflation
due to the non-trivial dynamics of the radion field. Transforming the conformal
frame to the Einstein frame, this born-again scenario resembles the
pre-big-bang scenario. Thus our scenario has features of both inflation and
pre-big-bang scenarios. In particular, the gravitational waves produced from
vacuum fluctuations will have a very blue spectrum, while the inflaton field
will give rise to a standard scale-invariant spectrum.Comment: 5 pages, talk presented at The 12th Workshop on General Relativity
and Gravitation, Tokyo, Japan, November, 200
Destabilizing Tachyonic Vacua at or above the BF Bound
It is well known that tachyonic vacua in an asymptotically Anti-de Sitter
(AdS) space-time are classically stable if the mass squared is at or above the
Breitenlohner and Freedman (BF) bound. We study the quantum stability of these
tachyonic vacua in terms of instantons. We find a series of exact instanton
solutions destabilizing tachyonic state at or above the BF bound in
asymptotically AdS space. We also give an analytic formula for the decay rate
and show that it is finite. Comparing our result with the well-known algebraic
condition for the stability, we discuss stability conditions of tachyonic vacua
at or above the BF bound.Comment: 11 pages, 6 figure
Kaluza-Klein braneworld cosmology with static internal dimensions
We investigate the Kaluza-Klein braneworld cosmology from the point of view
of observers on the brane. We first generalize the Shiromizu-Maeda-Sasaki (SMS)
equations to higher dimensions. As an application, we study a (4+n)-dimensional
brane with n dimensions compactified on the brane, in a (5+n)-dimensional bulk.
By assuming that the size of the internal space is static, that the bulk
energy-momentum tensor can be neglected, we determine the effect of the bulk
geometry on the Kaluza-Klein braneworld. Then we derive the effective Friedmann
equation on the brane. It turns out that the Friedmann equation explicitly
depends on the equation of state, in contrast to the braneworld in a
5-dimensional bulk spacetime. In particular, in a radiation-dominated era, the
effective Newton constant depends on the scale factor logarithmically. If we
include a pressureless matter on the brane, this dependence disappears after
the radiation-matter equality. This may be interpreted as stabilization of the
Newton constant by the matter on the brane. Our findings imply that the
Kaluza-Klein braneworld cosmology is quite different from the conventional
Kaluza-Klein cosmology even at low energy.Comment: 9 pages. References adde
More on the Burkhardt-Cottingham Sum Rule in QCD
The QCD higher order effects to the polarized structure function are reanalyzed for massive quarks in the context of the operator product
expansion. We confirm that the lowest moment of which
corresponds to the Burkhardt-Cottingham sum rule does {\sl not} suffer from
radiative corrections in perturbative QCD.Comment: LaTeX, 9 pages, 1 figure appended after \end{document} as an
uu-encoded and compressed .ps file, KUCP-70;HUPD-9410;YNU-HEPTh-94-10
Pylorus preserving pancreatoduodenectomy in a 6-year-old girl with recurrent pancreatitis due to an annular pancreas
AbstractThe pancreatitis caused by an annular pancreas rarely needs a surgical management in children. Here, we report a case of a 6-year old girl in whom pylorus-preserving pancreatoduodenectomy (PPPD) was performed for the pancreatitis caused by an annular pancreas. As she had previous operations for duodenal atresia and pancreaticobiliary maljunction, PPPD was chosen as a definitive surgical treatment of annular pancreas. She has been free from symptoms for 2 years after the operation
Black String Perturbations in RS1 Model
We present a general formalism for black string perturbations in
Randall-Sundrum 1 model (RS1). First, we derive the master equation for the
electric part of the Weyl tensor . Solving the master equation
using the gradient expansion method, we give the effective Teukolsky equation
on the brane at low energy. It is useful to estimate gravitational waves
emitted by perturbed rotating black strings. We also argue the effect of the
Gregory-Laflamme instability on the brane using our formalism.Comment: 14 pages, Based on a talk presented at ACRGR4, the 4th Australasian
Conference on General Relativity and Gravitation, Monash University,
Melbourne, January 2004. To appear in the proceedings, in General Relativity
and Gravitatio
Spin Structure Function and Twist-3 Operators in QCD
We investigate the spin structure function in the framework
of the operator product expansion and the renormalization group. The twist-3
operators appearing in QCD are examined and their relations are studied. It is
noted that operators proportional to equation of motion appear in the operator
mixing through renormalization, which can be studied from the relevant Green's
functions. We also note that the coefficient functions can be properly fixed
after the choice of independent operators.Comment: LaTeX, 11 pages, KUCP-71; HUPD-941
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