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Lightlike Branes as Natural Candidates for Wormhole Throats
We first briefly present a consistent world-volume Lagrangian description of
lightlike p-branes (LL-branes) in two equivalent forms - a Polyakov-type and a
dual to it Nambu-Goto-type formulations. The most important characteristic
features of LL-brane dynamics are: (i) the brane tension appears as a
non-trivial additional dynamical degree of freedom; (ii) consistency of
LL-brane dynamics in a spherically or axially symmetric gravitational
background of codimension one requires the presence of an event horizon which
is automatically occupied by the LL-brane ("horizon straddling"). Next we
consider a bulk Einstein-Maxwell system interacting self-consistently with a
codimension one LL-brane. We find spherically symmetric traversable wormhole
solutions of Misner-Wheeler type produced by the LL-brane sitting at the
wormhole throat with wormhole parameters being functions of the dynamical
LL-brane tension.Comment: Contribution to 4th RTN "Forces-Universe" Workshop, Varna (Sept.
2008
Negative Electron-electron Drag Between Narrow Quantum Hall Channels
Momentum transfer due to Coulomb interaction between two parallel,
two-dimensional, narrow, and spatially separated layers, when a current
I_{drive} is driven through one layer, is studied in the presence of a
perpendicular magnetic field B. The current induced in the drag layer,
I_{drag}, is evaluated self-consistently with I_{drive} as a parameter.
I_{drag} can be positive or negative depending on the value of the filling
factor \nu of the highest occupied bulk Landau level (LL). For a fully occupied
LL, I_{drag} is negative, i.e., it flows opposite to I_{drive}, whereas it is
positive for a half-filled LL. When the circuit is opened in the drag layer, a
voltage \Delta V_{drag} develops in it; it is negative for a half-filled LL and
positive for a fully occupied LL. This positive \Delta V_{drag}, expressing a
negative Coulomb drag, results from energetically favored near-edge inter-LL
transitions that occur when the highest occupied bulk LL and the LL just above
it become degenerate.Comment: Text file in Latex/Revtex/preprint format, 7 separate PS figures,
Physical Review B, in pres
Lightlike Brane as a Gravitational Source of Misner-Wheeler-Type Wormhole
Consistent Lagrangian description of lightlike p-branes (LL-branes) is
presented in two equivalent forms - a Polyakov-type formulation and a dual to
it Nambu-Goto-type formulation. An important characteristic feature of the
LL-branes is that the brane tension appears as a non-trivial additional
dynamical degree of freedom. Next, properties of p=2 LL-brane dynamics (as a
test brane) in D=4 Kerr or Kerr-Newman gravitational backgrounds are discussed
in some detail. It is shown that the LL-brane automatically positions itself on
the horizon and rotates along with the same angular velocity. Finally, a
Misner-Wheeler-type of Reissner-Nordstroem wormhole is constructed in a
self-consistent electrically sourceless Einstein-Maxwell system in the D=4 bulk
interacting with a LL-brane. The pertinent wormhole throat is located precisely
at the LL-brane sitting on the outer Reissner-Nordstroem horizon with the
Reissner-Nordstroem mass and charge being functions of the dynamical LL-brane
tension.Comment: improved derivation in section 4; additional comment in conclusions;
results unchange
Spherically Symmetric and Rotating Wormholes Produced by Lightlike Branes
Lightlike p-branes (LL-branes) with dynamical (variable) tension allow simple
and elegant Polyakov-type and dual to it Nambu-Goto-like world-volume action
formulations. Here we first briefly describe the dynamics of LL-branes as test
objects in various physically interesting gravitational backgrounds of black
hole type, including rotating ones. Next we show that LL-branes are the
appropriate gravitational sources that provide proper matter energy momentum
tensors in the Einstein equations of motion needed to generate traversable
wormhole solutions, in particular, self-consistent cylindrical rotating
wormholes, with the LL-branes occupying their throats. Here a major role is
being played by the dynamical LL-brane tension which turns out to be negative
but may be of arbitrary small magnitude. As a particular solution we obtain
traversable wormhole with Schwarzschild geometry generated by a LL-brane
positioned at the wormhole throat, which represents the correct consistent
realization of the original Einstein-Rosen "bridge" manifold.Comment: 27 pages; important clarifications regarding the meaning of the
original Einstein-Rosen "bridge" construction; an important addition to the
Appendix; acknowledgments adde
On the specific heat of a fermionic atomic cloud in the unitary regime
In the unitary regime, when the scattering amplitude greatly exceeds in
magnitude the average inter-particle separation, and below the critical
temperature thermal properties of an atomic fermionic cloud are governed by the
collective modes, specifically the Bogoliubov-Anderson sound modes. The
specific heat of an atomic cloud in a elongated trap in particular has a rather
compex temperature dependence, which changes from an exponential behavior at
very low temperatures (), to for
and then continuosly to at temperatures just below the critical temperature, when the surface
modes play a dominant role. Only the low () and high () temperature
power laws are well defined. For the intermediate temperatures one can
introduce at most a gradually increasing with temperature exponent.Comment: 4 page
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