192 research outputs found
Modeling the strangeness content of hadronic matter
The strangeness content of hadronic matter is studied in a string-flip model
that reproduces various aspects of the QCD-inspired phenomenology, such as
quark clustering at low density and color deconfinement at high density, while
avoiding long range van der Waals forces. Hadronic matter is modeled in terms
of its quark constituents by taking into account its internal flavor (u,d,s)
and color (red, blue, green) degrees of freedom. Variational Monte-Carlo
simulations in three spatial dimensions are performed for the ground-state
energy of the system. The onset of the transition to strange matter is found to
be influenced by weak, yet not negligible, clustering correlations. The phase
diagram of the system displays an interesting structure containing both
continuous and discontinuous phase transitions. Strange matter is found to be
absolutely stable in the model.Comment: 14 pages, 1 table, 8 eps figures, revtex. Submitted to Phys. Rev. C,
Presented at INPC2001 Berkeley, Ca. july 29-Aug
Wavy Strings: Black or Bright?
Recent developments in string theory have brought forth a considerable
interest in time-dependent hair on extended objects. This novel new hair is
typically characterized by a wave profile along the horizon and angular
momentum quantum numbers in the transverse space. In this work, we
present an extensive treatment of such oscillating black objects, focusing on
their geometric properties. We first give a theorem of purely geometric nature,
stating that such wavy hair cannot be detected by any scalar invariant built
out of the curvature and/or matter fields. However, we show that the tidal
forces detected by an infalling observer diverge at the `horizon' of a black
string superposed with a vibration in any mode with . The same
argument applied to longitudinal () waves detects only finite tidal
forces. We also provide an example with a manifestly smooth metric, proving
that at least a certain class of these longitudinal waves have regular
horizons.Comment: 45 pages, latex, no figure
Small Black Holes on Cylinders
We find the metric of small black holes on cylinders, i.e. neutral and static
black holes with a small mass in d-dimensional Minkowski-space times a circle.
The metric is found using an ansatz for black holes on cylinders proposed in
hep-th/0204047. We use the new metric to compute corrections to the
thermodynamics which is seen to deviate from that of the (d+1)-dimensional
Schwarzschild black hole. Moreover, we compute the leading correction to the
relative binding energy which is found to be non-zero. We discuss the
consequences of these results for the general understanding of black holes and
we connect the results to the phase structure of black holes and strings on
cylinders.Comment: 23 pages, 1 figure. v2: typos corrected, introduction expanded, v3:
presentation of sections 2 and 3 reordered and improved, explanatory remarks
added, refs adde
Black Holes on Cylinders
We take steps toward constructing explicit solutions that describe
non-extremal charged dilatonic branes of string/M-theory with a transverse
circle. Using a new coordinate system we find an ansatz for the solutions with
only one unknown function. We show that this function is independent of the
charge and our ansatz can therefore also be used to construct neutral black
holes on cylinders and near-extremal charged dilatonic branes with a transverse
circle. For sufficiently large mass these solutions have a horizon
that connects across the cylinder but they are not translationally invariant
along the circle direction. We argue that the neutral solution has larger
entropy than the neutral black string for any given mass. This means that for
the neutral black string can gain entropy by redistributing its mass
to a solution that breaks translational invariance along the circle, despite
the fact that it is classically stable. We furthermore explain how our
construction can be used to study the thermodynamics of Little String Theory.Comment: latex, 68 pages, 4 figures. v2: Typos fixed, argument about \chi
corrected in sec. 7.4, discussion of space of physical solutions corrected
and clarified in sec. 9; v3: v=\pi clarified, typos fixed, figure 1 change
Flux-branes and the Dielectric Effect in String Theory
We consider the generalization to String and M-theory of the Melvin solution.
These are flux p-branes which have (p+1)-dimensional Poincare invariance and
are associated to an electric (p+1)-form field strength along their
worldvolume. When a stack of Dp-branes is placed along the worldvolume of a
flux (p+3)-brane it will expand to a spherical D(p+2)-brane due to the
dielectric effect. This provides a new setup to consider the gauge
theory/gravity duality. Compactifying M-theory on a circle we find the exact
gravity solution of the type IIA theory describing the dielectric expansion of
N D4-branes into a spherical bound state of D4-D6-branes, due to the presence
of a flux 7-brane. In the decoupling limit, the deformation of the dual field
theory associated with the presence of the flux brane is irrelevant in the UV.
We calculate the gravitational radius and energy of the dielectric brane which
give, respectively, a prediction for the VEV of scalars and vacuum energy of
the dual field theory. Consideration of a spherical D6-brane probe with n units
of D4-brane charge in the dielectric brane geometry suggests that the dual
theory arises as the Scherk-Schwarz reduction of the M5-branes (2,0) conformal
field theory. The probe potential has one minimum placed at the locus of the
bulk dielectric brane and another associated to an inner dielectric brane
shell.Comment: v2 Major Additions: dielectric radius in gravity solution matches
exactly stable and unstable points of Myers probe potential, as well as the
upper bound on D-brane charge. New section probing dielectric brane that
clarifies dual field theory discussion and is consistent with Scherk-Schwarz
reduction of (2,0) M5-brane theory. References added. 43 pages, 4 figure
Hagedorn transition and chronology protection in string theory
We conjecture chronology is protected in string theory due to the
condensation of light winding strings near closed null curves. This
condensation triggers a Hagedorn phase transition, whose end-point target space
geometry should be chronological. Contrary to conventional arguments,
chronology is protected by an infrared effect. We support this conjecture by
studying strings in the O-plane orbifold, where we show that some winding
string states are unstable and condense in the non-causal region of spacetime.
The one-loop string partition function has infrared divergences associated to
the condensation of these states.Comment: 40 pages, 11 figures. Expanded discussion on evolution of on-shell
modes and added appendi
Organic film thickness influence on the bias stress instability in Sexithiophene Field Effect Transistors
In this paper, the dynamics of bias stress phenomenon in Sexithiophene (T6)
Field Effect Transistors (FETs) has been investigated. T6 FETs have been
fabricated by vacuum depositing films with thickness from 10 nm to 130 nm on
Si/SiO2 substrates. After the T6 film structural analysis by X-Ray diffraction
and the FET electrical investigation focused on carrier mobility evaluation,
bias stress instability parameters have been estimated and discussed in the
context of existing models. By increasing the film thickness, a clear
correlation between the stress parameters and the structural properties of the
organic layer has been highlighted. Conversely, the mobility values result
almost thickness independent
Interior Structure of a Charged Spinning Black Hole in -Dimensions
The phenomenon of mass inflation is shown to occur for a rotating black hole.
We demonstrate this feature in dimensions by extending the charged
spinning BTZ black hole to Vaidya form. We find that the mass function diverges
in a manner quantitatively similar to its static counterparts in ,
and dimensions.Comment: 5 pages, 2 figures (appended as postscript files), WATPHYS-TH94/0
Relativistic Mean Field Model with Generalized Derivative Nucleon-Meson Couplings
The quantum hadrodynamics (QHD) model with minimal nucleon-meson couplings is
generalized by introducing couplings of mesons to derivatives of the nucleon
field in the Lagrangian density. This approach allows an effective description
of a state-dependent in-medium interaction in the mean-field approximation.
Various parametrizations for the generalized couplings are developed and
applied to infinite nuclear matter. In this approach, scalar and vector
self-energies depend on both density and momentum similarly as in the
Dirac-Brueckner theory. The Schr\"{o}diger-equivalent optical potential is much
less repulsive at high nucleon energies as compared to standard relativistic
mean field models and thus agrees better with experimental findings. The
derivative couplings in the extended model have significant effects on
properties of symmetric nuclear matter and neutron matter.Comment: 35 pages, 1 table, 10 figure
On Some New Black String Solutions in Three Dimensions
We derive several new solutions in three-dimensional stringy gravity. The
solutions are obtained with the help of string duality transformations. They
represent stationary configurations with horizons, and are surrounded by
(quasi) topologically massive Abelian gauge hair, in addition to the dilaton
and the Kalb-Ramond axion. Our analysis suggests that there exists a more
general family, where our solutions are special limits. Finally, we use the
generating technique recently proposed by Garfinkle to construct a traveling
wave on the extremal variant of one of our solutions.Comment: revtex, 38 pages including 3 figure
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