11,955 research outputs found
The effect of different opacity data and chemical element mixture on the Petersen diagram
The Petersen diagram is a frequently used tool to constrain model parameters
such as metallicity of radial double-mode pulsators. In this diagram the period
ratio of the radial first overtone to the fundamental mode, P_1/P_0, is plotted
against the period of the fundamental mode. The period ratio is sensitive to
the chemical composition as well as to the rotational velocity of a star. In
the present study we compute stellar pulsation models to demonstrate the
sensitivity of the radial period ratio to the opacity data (OPAL and OP tables)
and we also examine the effect of different relative abundances of heavy
elements. We conclude that the comparison with observed period ratios could be
used successfully to test the opacity data.Comment: 5 pages, 5 figures, 1 table; to be published in the Proceedings of
the Conference 'Unsolved Problems in Stellar Physics', Cambridge, 2-6 July
200
Quantum Mechanics of the Vacuum State in Two-Dimensional QCD with Adjoint Fermions
A study of two-dimensional QCD on a spatial circle with Majorana fermions in
the adjoint representation of the gauge groups SU(2) and SU(3) has been
performed. The main emphasis is put on the symmetry properties related to the
homotopically non-trivial gauge transformations and the discrete axial symmetry
of this model. Within a gauge fixed canonical framework, the delicate interplay
of topology on the one hand and Jacobians and boundary conditions arising in
the course of resolving Gauss's law on the other hand is exhibited. As a
result, a consistent description of the residual gauge symmetry (for
SU(N)) and the ``axial anomaly" emerges. For illustrative purposes, the vacuum
of the model is determined analytically in the limit of a small circle. There,
the Born-Oppenheimer approximation is justified and reduces the vacuum problem
to simple quantum mechanics. The issue of fermion condensates is addressed and
residual discrepancies with other approaches are pointed out.Comment: 44 pages; for hardcopies of figures, contact
[email protected]
Improved Quantum Hard-Sphere Ground-State Equations of State
The London ground-state energy formula as a function of number density for a
system of identical boson hard spheres, corrected for the reduced mass of a
pair of particles in a sphere-of-influence picture, and generalized to fermion
hard-sphere systems with two and four intrinsic degrees of freedom, has a
double-pole at the ultimate \textit{regular} (or periodic, e.g.,
face-centered-cubic) close-packing density usually associated with a
crystalline branch. Improved fluid branches are contructed based upon exact,
field-theoretic perturbation-theory low-density expansions for many-boson and
many-fermion systems, appropriately extrapolated to intermediate densities, but
whose ultimate density is irregular or \textit{random} closest close-packing as
suggested in studies of a classical system of hard spheres. Results show
substantially improved agreement with the best available Green-function Monte
Carlo and diffusion Monte Carlo simulations for bosons, as well as with ladder,
variational Fermi hypernetted chain, and so-called L-expansion data for
two-component fermions.Comment: 15 pages and 7 figure
Templeting of Thin Films Induced by Dewetting on Patterned Surfaces
The instability, dynamics and morphological transitions of patterns in thin
liquid films on periodic striped surfaces (consisting of alternating less and
more wettable stripes) are investigated based on 3-D nonlinear simulations that
account for the inter-site hydrodynamic and surface-energetic interactions. The
film breakup is suppressed on some potentially destabilizing nonwettable sites
when their spacing is below a characteristic lengthscale of the instability,
the upper bound for which is close to the spinodal lengthscale. The thin film
pattern replicates the substrate surface energy pattern closely only when, (a)
the periodicity of substrate pattern matches closely with the characteristic
lengthscale, and (b) the stripe-width is within a range bounded by a lower
critical length, below which no heterogeneous rupture occurs, and an upper
transition length above which complex morphological features bearing little
resemblance to the substrate pattern are formed.Comment: 5 pages TeX (REVTeX 4), other comments: submitted to Phys. Rev.Let
Stopping Light All-Optically
We show that light pulses can be stopped and stored all-optically, with a
process that involves an adiabatic and reversible pulse bandwidth compression
occurring entirely in the optical domain. Such a process overcomes the
fundamental bandwidth-delay constraint in optics, and can generate arbitrarily
small group velocities for light pulses with a given bandwidth, without the use
of any coherent or resonant light-matter interactions. We exhibit this process
in optical resonator systems, where the pulse bandwidth compression is
accomplished only by small refractive index modulations performed at moderate
speeds. (Accepted for publication in Phys. Rev. Lett. Submitted on Sept. 10th
2003)Comment: 18 pages including 3 figures. Accepted for publication in Phys. Rev.
Let
Hamiltonian approach to the bound state problem in QCD_2
Bosonization of the two-dimensional QCD in the large N_C limit is performed
in the framework of Hamiltonian approach in the Coulomb gauge. The generalized
Bogoliubov transformation is applied to diagonalize the Hamiltonian in the
bosonic sector of the theory, and the composite operators creating/annihilating
bosons are obtained in terms of dressed quark operators. The bound state
equation is reconstructed as a result of the generalized Bogoliubov
transformation, and the form of its massless solution, chiral pion, is found
explicitly. Chiral properties of the theory are discussed.Comment: 9 pages, LaTeX2
Theoretical status of Bs-mixing and lifetimes of heavy hadrons
We review the theoretical status of the lifetime ratios τB+/τBd, τBs/τBd, τΛb/τBd and τBc and of the mixing quantities ΔMs, ΔΓs and ϕs. ΔMs and ΔΓs suffer from large uncertainties due to the badly known decay constants, while the ratio ΔΓs/ΔMs can be determined with almost no non-perturbative uncertainties, therefore it can be used perfectly to find possible new physics contributions in the mixing parameters. We suggest a very clear method of visualizing the bounds on new physics and demonstrate this by combining the latest experimental numbers on the mixing quantities quantities with theory – one already gets some hints for new physics contributions, but more precise experimental numbers are needed to draw some definite conclusions. We conclude with a ranking list of all the discussed quantities according to their current theoretical uncertainties and point out possible improvements
Deformed Gaussian Orthogonal Ensemble Analysis of the Interacting Boson Model
A Deformed Gaussian Orthogonal Ensemble (DGOE) which interpolates between the
Gaussian Orthogonal Ensemble and a Poissonian Ensemble is constructed. This new
ensemble is then applied to the analysis of the chaotic properties of the low
lying collective states of nuclei described by the Interacting Boson Model
(IBM). This model undergoes a transition order-chaos-order from the
limit to the limit. Our analysis shows that the quantum fluctuations of
the IBM Hamiltonian, both of the spectrum and the eigenvectors, follow the
expected behaviour predicted by the DGOE when one goes from one limit to the
other.Comment: 10 pages, 4 figures (avaiable upon request), IFUSP/P-1086 Replaced
version: in the previous version the name of one of the authors was omitte
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