5,870 research outputs found
Feshbach Resonances and Limiting Thermodynamics of Strongly Correlated Nucleons
A finite temperature model of strongly correlated nucleons with underlying
isospin symmetries is developed. The model can be used to study the role of
bound states and Feshbach resonances on the thermal properties of a spin 1/2,
isospin 1/2 system of protons and neutrons by varying the proton fraction. An
analysis of features associated with a universal thermodynamic limit or unitary
limit is given. In the limit of very large scattering length, the effective
range to quantum thermal wavelength appears as a limiting scale in an
interaction energy and equation of state.Comment: 8 pages, 4 figure
Gauge Invariant Treatment of the Electroweak Phase Transition
We evaluate the gauge invariant effective potential for the composite field
in the SU(2)-Higgs model at finite temperature.
Symmetric and broken phases correspond to the domains and
, respectively. The effective potential increases very steeply
at small values of . Predictions for several observables, derived from
the ordinary and the gauge invariant effective potential, are compared. Good
agreement is found for the critical temperature and the jump in the order
parameter. The results for the latent heat differ significantly for large Higgs
masses.Comment: 8 pages latex, DESY-94-043, 4 figures can be obtained via e-mail from
[email protected]
Reconstructing the potentials for the quintessence and tachyon dark energy, from the holographic principle
We propose an holographic quintessence and tachyon models of dark energy. The
correspondence between the quintessence and tachyon energy densities with the
holographic density, allows the reconstruction of the potentials and the
dynamics for the quintessence and tachyon fields, in flat FRW background. The
proposed infrared cut-off for the holographic energy density works for two
cases of the constant : for we reconstructed the holographic
quintessence model in the region before the crossing for the EoS
parameter. The cosmological dynamics for was also reconstructed for
the holographic quintessence and tachyon models.Comment: 21 pages, 18 figures, 2 table
A study of Feshbach resonances and the unitary limit in a model of strongly correlated nucleons
A model of strongly interacting and correlated hadrons is developed. The
interaction used contains a long range attraction and short range repulsive
hard core. Using this interaction and various limiting situations of it, a
study of the effect of bound states and Feshbach resonances is given. The
limiting situations are a pure square well interaction, a delta-shell potential
and a pure hard core potential. The limit of a pure hard core potential are
compared with results for a spinless Bose and Fermi gas. The limit of many
partial waves for a pure hard core interaction is also considered and result in
expressions involving the hard core volume. This feature arises from a scaling
relation similar to that for hard sphere scattering with diffractive
corrections. The role of underlying isospin symmetries associated with the
strong interaction of protons and neutrons in this two component model is
investigated. Properties are studied with varying proton fraction. An analytic
expression for the Beth Uhlenbeck continuum integral is developed which closely
approximates exact results based on the potential model considered. An analysis
of features associated with a unitary limit is given. In the unitary limit of
very large scattering length, the ratio of effective range to thermal
wavelength appears as a limiting scale. Thermodynamic quantities such as the
entropy and compressibility are also developed. The effective range corrections
to the entropy vary as the cube of this ratio for low temperatures and are
therefore considerably reduced compared to the corrections to the interaction
energy which varies linearly with this ratio. Effective range corrections to
the compressibility are also linear in the ratio.Comment: 39 pages, 15 figures, 2 table
Signature of short distance physics on inflation power spectrum and CMB anisotropy
The inflaton field responsible for inflation may not be a canonical
fundamental scalar. It is possible that the inflaton is a composite of fermions
or it may have a decay width. In these cases the standard procedure for
calculating the power spectrum is not applicable and a new formalism needs to
be developed to determine the effect of short range interactions of the
inflaton on the power spectrum and the CMB anisotropy. We develop a general
formalism for computing the power spectrum of curvature perturbations for such
non-canonical cases by using the flat space K\"all\'en-Lehmann spectral
function in curved quasi-de Sitter space assuming implicitly that the
Bunch-Davis boundary conditions enforces the inflaton mode functions to be
plane wave in the short wavelength limit and a complete set of mode functions
exists in quasi-de Sitter space. It is observed that the inflaton with a decay
width suppresses the power at large scale while a composite inflaton's power
spectrum oscillates at large scales. These observations may be vindicated in
the WMAP data and confirmed by future observations with PLANCK.Comment: 17 pages, 4 figures, Extended journal version, Accepted for
publication in JCA
R2R - software to speed the depiction of aesthetic consensus RNA secondary structures
<p>Abstract</p> <p>Background</p> <p>With continuing identification of novel structured noncoding RNAs, there is an increasing need to create schematic diagrams showing the consensus features of these molecules. RNA structural diagrams are typically made either with general-purpose drawing programs like Adobe Illustrator, or with automated or interactive programs specific to RNA. Unfortunately, the use of applications like Illustrator is extremely time consuming, while existing RNA-specific programs produce figures that are useful, but usually not of the same aesthetic quality as those produced at great cost in Illustrator. Additionally, most existing RNA-specific applications are designed for drawing single RNA molecules, not consensus diagrams.</p> <p>Results</p> <p>We created R2R, a computer program that facilitates the generation of aesthetic and readable drawings of RNA consensus diagrams in a fraction of the time required with general-purpose drawing programs. Since the inference of a consensus RNA structure typically requires a multiple-sequence alignment, the R2R user annotates the alignment with commands directing the layout and annotation of the RNA. R2R creates SVG or PDF output that can be imported into Adobe Illustrator, Inkscape or CorelDRAW. R2R can be used to create consensus sequence and secondary structure models for novel RNA structures or to revise models when new representatives for known RNA classes become available. Although R2R does not currently have a graphical user interface, it has proven useful in our efforts to create 100 schematic models of distinct noncoding RNA classes.</p> <p>Conclusions</p> <p>R2R makes it possible to obtain high-quality drawings of the consensus sequence and structural models of many diverse RNA structures with a more practical amount of effort. R2R software is available at <url>http://breaker.research.yale.edu/R2R</url> and as an Additional file.</p
Gravity of a static massless scalar field and a limiting Schwarzschild-like geometry
We study a set of static solutions of the Einstein equations in presence of a
massless scalar field and establish their connection to the Kantowski-Sachs
cosmological solutions based on some kind of duality transformations. The
physical properties of the limiting case of an empty hyperbolic spacetime
(pseudo-Schwarzschild geometry) are analyzed in some detail.Comment: 13 pages, 4 figure
Fluid Dynamics of Relativistic Quantum Dust
The microscopic transport equations for free fields are solved using the
Schwinger function. Thus, for general initial conditions, the evolution of the
energy-momentum tensor is obtained, incorporating the quantum effects exactly.
The result for relativistic fermions differs from classical hydrodynamics,
which is illustrated for Landau and Bjorken type initial conditions in this
model of exploding primordial matter. Free fermions behave like classical dust
concerning hydrodynamic observables. However, quantum effects which are present
in the initial state are preserved.Comment: 5 pages; LaTe
Normal frames and the validity of the equivalence principle. I. Cases in a neighborhood and at a point
A treatment in a neighborhood and at a point of the equivalence principle on
the basis of derivations of the tensor algebra over a manifold is given.
Necessary and sufficient conditions are given for the existence of local bases,
called normal frames, in which the components of derivations vanish in a
neighborhood or at a point. These frames (bases), if any, are explicitly
described and the problem of their holonomicity is considered. In particular,
the obtained results concern symmetric as well as nonsymmetric linear
connections.Comment: LaTeX2e, 9 pages, to be published in Journal of Physics A:
Mathematical and Genera
The Topology of Large Scale Structure in the 1.2 Jy IRAS Redshift Survey
We measure the topology (genus) of isodensity contour surfaces in volume
limited subsets of the 1.2 Jy IRAS redshift survey, for smoothing scales
\lambda=4\hmpc, 7\hmpc, and 12\hmpc. At 12\hmpc, the observed genus
curve has a symmetric form similar to that predicted for a Gaussian random
field. At the shorter smoothing lengths, the observed genus curve shows a
modest shift in the direction of an isolated cluster or ``meatball'' topology.
We use mock catalogs drawn from cosmological N-body simulations to investigate
the systematic biases that affect topology measurements in samples of this size
and to determine the full covariance matrix of the expected random errors. We
incorporate the error correlations into our evaluations of theoretical models,
obtaining both frequentist assessments of absolute goodness-of-fit and Bayesian
assessments of models' relative likelihoods. We compare the observed topology
of the 1.2 Jy survey to the predictions of dynamically evolved, unbiased,
gravitational instability models that have Gaussian initial conditions. The
model with an , power-law initial power spectrum achieves the best
overall agreement with the data, though models with a low-density cold dark
matter power spectrum and an power-law spectrum are also consistent. The
observed topology is inconsistent with an initially Gaussian model that has
, and it is strongly inconsistent with a Voronoi foam model, which has a
non-Gaussian, bubble topology.Comment: ApJ submitted, 39 pages, LaTeX(aasms4), 12 figures, 1 Tabl
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