1,899 research outputs found
Hierarchy of QM SUSYs on a Bounded Domain
We systematically formulate a hierarchy of isospectral Hamiltonians in
one-dimensional supersymmetric quantum mechanics on an interval and on a
circle, in which two successive Hamiltonians form N=2 supersymmetry. We find
that boundary conditions compatible with supersymmetry are severely restricted.
In the case of an interval, a hierarchy of, at most, three isospectral
Hamiltonians is possible with unique boundary conditions, while in the case of
a circle an infinite tower of isospectral Hamiltonians can be constructed with
two-parameter family of boundary conditions.Comment: 15 pages, 3 figure
Willmore minimizers with prescribed isoperimetric ratio
Motivated by a simple model for elastic cell membranes, we minimize the
Willmore functional among two-dimensional spheres embedded in R^3 with
prescribed isoperimetric ratio
Evolution of Topological Defects During Inflation
Topological defects can be formed during inflation by phase transitions as
well as by quantum nucleation. We study the effect of the expansion of the
Universe on the internal structure of the defects. We look for stationary
solutions to the field equations, i.e. solutions that depend only on the proper
distance from the defect core. In the case of very thin defects, whose core
dimensions are much smaller than the de Sitter horizon, we find that the
solutions are well approximated by the flat space solutions. However, as the
flat space thickness parameter increases we notice a deviation from
this, an effect that becomes dramatic as approaches . Beyond this critical value we find no stationary solutions to the field
equations. We conclude that only defects that have flat space thicknesses less
than the critical value survive, while thicker defects are smeared out by the
expansion.Comment: 14 page
Entropy: From Black Holes to Ordinary Systems
Several results of black holes thermodynamics can be considered as firmly
founded and formulated in a very general manner. From this starting point we
analyse in which way these results may give us the opportunity to gain a better
understanding in the thermodynamics of ordinary systems for which a
pre-relativistic description is sufficient. First, we investigated the
possibility to introduce an alternative definition of the entropy basically
related to a local definition of the order in a spacetime model rather than a
counting of microstates. We show that such an alternative approach exists and
leads to the traditional results provided an equilibrium condition is assumed.
This condition introduces a relation between a time interval and the reverse of
the temperature. We show that such a relation extensively used in the black
hole theory, mainly as a mathematical trick, has a very general and physical
meaning here; in particular its derivation is not related to the existence of a
canonical density matrix. Our dynamical approach of thermodynamic equilibrium
allows us to establish a relation between action and entropy and we show that
an identical relation exists in the case of black holes. The derivation of such
a relation seems impossible in the Gibbs ensemble approach of statistical
thermodynamics. From these results we suggest that the definition of entropy in
terms of order in spacetime should be more general that the Boltzmann one based
on a counting of microstates. Finally we point out that these results are
obtained by reversing the traditional route going from the Schr\"{o}dinger
equation to statistical thermodynamics
Curvature-induced phase transitions in the inflationary universe - Supersymmetric Nambu-Jona-Lasinio Model in de Sitter spacetime -
The phase structure associated with the chiral symmetry is thoroughly
investigated in de Sitter spacetime in the supersymmetric Nambu-Jona-Lasinio
model with supersymmetry breaking terms. The argument is given in the three and
four space-time dimensions in the leading order of the 1/N expansion and it is
shown that the phase characteristics of the chiral symmetry is determined by
the curvature of de Sitter spacetime. It is found that the symmetry breaking
takes place as the first order as well as second order phase transition
depending on the choice of the coupling constant and the parameter associated
with the supersymmetry breaking term. The critical curves expressing the phase
boundary are obtained. We also discuss the model in the context of the chaotic
inflation scenario where topological defects (cosmic strings) develop during
the inflation.Comment: 29 pages, 6 figures, REVTe
Effect of pre-existing baryon inhomogeneities on the dynamics of quark-hadron transition
Baryon number inhomogeneities may be generated during the epoch when the
baryon asymmetry of the universe is produced, e.g. at the electroweak phase
transition. The regions with excess baryon number will have a lower temperature
than the background temperature of the universe. Also the value of the quark
hadron transition temperature will be different in these regions as
compared to the background region. Since a first-order quark hadron transition
is very susceptible to small changes in temperature, we investigate the effect
of the presence of such baryonic lumps on the dynamics of quark-hadron
transition. We find that the phase transition is delayed in these lumps for
significant overdensities. Consequently, we argue that baryon concentration in
these regions grows by the end of the transition. We briefly discuss some
models which may give rise to such high overdensities at the onset of the
quark-hadron transition.Comment: 16 pages, no figures, minor changes, version to appear in Phys. Rev.
Zirconia Translucency and Cement Systems as Factors Influencing the Zirconia-Titanium and Zirconia-Zirconia Shear Bond Strength
Purpose: To evaluate the bonding ability of self-adhesive and dual-cure resin cement systems applied to zirconia materials of different translucency in combination with each other and with titanium. Materials and Methods: Computer-aided design/computer-assisted manufacture (CAD/CAM) disks of three different zirconia materials (Zenostar MO 0 [medium opacity], MT 0 [medium translucency], and T 1 [translucent], Wieland Dental) were milled and hard sintered in order to obtain cylindrical samples of either 12 mm high × 12 mm diameter (used as a substrate) or 12 mm high × 8 mm diameter (to be bonded to the substrate). CAD/CAM disks of titanium (Starbond Ti4 Disc, S&S Scheftner) were milled in order to obtain a cylinder shape (12 mm high × 8 mm diameter to be bonded to the zirconia substrate). The bonding surfaces were sandblasted with alumina particles (70 μm/2 ATM). Two resin cement systems were tested in this study: a self-adhesive resin cement (SpeedCEM Plus, Ivoclar Vivadent) and a dual-cure resin cement (Variolink Esthetic DC, Ivoclar Vivadent) in combination with a primer (Monobond Plus, Ivoclar Vivadent). The smaller cylinders were bonded to the substrate following the manufacturer’s instructions. After 24 hours at 37°C storage, each specimen was subjected to shear bond strength testing in a universal testing machine. The substrate was fixed to the machine, and shear force was applied to the small cylinder close to the bonding interface. Shear bond strength data were statistically analyzed by a three-way analysis of variance (ANOVA) followed by the Tukey test for post hoc comparison (P < .05). Results: No significant differences were found between substrates in the shear bond strength test (P = .078). Variolink Esthetic DC showed a statistically significantly higher bond strength compared with the SpeedCEM Plus (P = .001) with the exception of Zenostar MT substrate (P = .014). Conclusion: The resin cement systems showed high shear bond strength values when zirconia was resin bonded to either titanium or the corresponding zirconia substrate. Different zirconia translucencies did not affect the bond strength. The use of MDP primer and a dual-cure cement showed statistically significantly higher strength compared with the self-adhesive resin cement system with the only exception being the bonding of the translucent zirconia Zenostar MT
L\'evy-Schr\"odinger wave packets
We analyze the time--dependent solutions of the pseudo--differential
L\'evy--Schr\"odinger wave equation in the free case, and we compare them with
the associated L\'evy processes. We list the principal laws used to describe
the time evolutions of both the L\'evy process densities, and the
L\'evy--Schr\"odinger wave packets. To have self--adjoint generators and
unitary evolutions we will consider only absolutely continuous, infinitely
divisible L\'evy noises with laws symmetric under change of sign of the
independent variable. We then show several examples of the characteristic
behavior of the L\'evy--Schr\"odinger wave packets, and in particular of the
bi-modality arising in their evolutions: a feature at variance with the typical
diffusive uni--modality of both the L\'evy process densities, and the usual
Schr\"odinger wave functions.Comment: 41 pages, 13 figures; paper substantially shortened, while keeping
intact examples and results; changed format from "report" to "article";
eliminated Appendices B, C, F (old names); shifted Chapters 4 and 5 (old
numbers) from text to Appendices C, D (new names); introduced connection
between Relativistic q.m. laws and Generalized Hyperbolic law
Are nontopological strings produced at the electroweak phase transition?
We formulate a local condition for a nontopological defect to be present. We
apply it for electroweak strings and estimate the probability of their
existence at the Ginzburg temperature. As a result we find strings long enough
to serve for baryon-number generation are unlikely to be produced.Comment: 12 pages (REVTeX), no figure, Physical Review Letters in pres
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