1,708,062 research outputs found
Resilient Reducibility in Nuclear Multifragmentation
The resilience to averaging over an initial energy distribution of
reducibility and thermal scaling observed in nuclear multifragmentation is
studied. Poissonian reducibility and the associated thermal scaling of the mean
are shown to be robust. Binomial reducibility and thermal scaling of the
elementary probability are robust under a broad range of conditions. The
experimental data do not show any indication of deviation due to averaging.Comment: 5 pages, 6 figures, submitted to Physical Review
Do phase transitions survive binomial reducibility and thermal scaling?
First order phase transitions are described in terms of the microcanonical
and canonical ensemble, with special attention to finite size effects.
Difficulties in interpreting a "caloric curve" are discussed. A robust
parameter indicating phase coexistence (univariance) or single phase
(bivariance) is extracted for charge distributions.Comment: 10 pages, TeX type, psfig, also available at
http://csa5.lbl.gov/moretto/ps/lgm.ps, to appear in the Proceedings of the
1st Catania Relativistic Ion Studies: Critical Phenomena and Collective
Observables, Acicastello, May 27-31, 199
Graviton as a Goldstone boson: Nonlinear Sigma Model for Tensor Field Gravity
Spontaneous Lorentz invariance violation (SLIV) realized through a nonlinear
tensor field constraint H_{}^2=\pm M^2 (M is the proposed scale for Lorentz
violation) is considered in tensor field gravity theory, which mimics
linearized general relativity in Minkowski space-time. We show that such a SLIV
pattern, due to which the true vacuum in the theory is chosen, induces massless
tensor Goldstone modes some of which can naturally be associated with the
physical graviton. When expressed in terms of the pure Goldstone modes, this
theory looks essentially nonlinear and contains a variety of Lorentz and CPT
violating couplings. Nonetheless, all SLIV effects turn out to be strictly
cancelled in all the lowest order processes considered, provided that the
tensor field gravity theory is properly extended to general relativity (GR).
So, as we generally argue, the measurable effects of SLIV, induced by
elementary vector or tensor fields, are related to the accompanying gauge
symmetry breaking rather than to spontaneous Lorentz violation. The latter
appears by itself to be physically unobservable, only resulting in a
non-covariant gauge choice in an otherwise gauge invariant and Lorentz
invariant theory. However, while Goldstonic vector and tensor field theories
with exact local invariance are physically indistinguishable from conventional
gauge theories, there might appear some principal distinctions if this local
symmetry were slightly broken at very small distances controlled by quantum
gravity in an explicit, rather than spontaneous, way that could eventually
allow one to differentiate between them observationally.Comment: 15 pages, some minor additions mad
Z-dependent Barriers in Multifragmentation from Poissonian Reducibility and Thermal Scaling
We explore the natural limit of binomial reducibility in nuclear
multifragmentation by constructing excitation functions for intermediate mass
fragments (IMF) of a given element Z. The resulting multiplicity distributions
for each window of transverse energy are Poissonian. Thermal scaling is
observed in the linear Arrhenius plots made from the average multiplicity of
each element. ``Emission barriers'' are extracted from the slopes of the
Arrhenius plots and their possible origin is discussed.Comment: 15 pages including 4 .ps figures. Submitted to Phys. Rev. Letters.
Also available at http://csa5.lbl.gov/moretto
The observed spiral structure of the Milky Way
The spiral structure of the Milky Way is not yet well determined. The keys to
understanding this structure are to increase the number of reliable spiral
tracers and to determine their distances as accurately as possible. HII
regions, giant molecular clouds (GMCs), and 6.7-GHz methanol masers are closely
related to high mass star formation, and hence they are excellent spiral
tracers. We update the catalogs of Galactic HII regions, GMCs, and 6.7-GHz
methanol masers, and then outline the spiral structure of the Milky Way. We
collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7-GHz
methanol masers. If the photometric or trigonometric distance was not yet
available, we determined the kinematic distance using a Galaxy rotation curve
with the current IAU standard, = 8.5 kpc and = 220 km
s, and the most recent updated values of = 8.3 kpc and
= 239 km s, after we modified the velocities of tracers with the adopted
solar motions. With the weight factors based on the excitation parameters of
HII regions or the masses of GMCs, we get the distributions of these spiral
tracers. The distribution of tracers shows at least four segments of arms in
the first Galactic quadrant, and three segments in the fourth quadrant. The
Perseus Arm and the Local Arm are also delineated by many bright HII regions.
The arm segments traced by massive star forming regions and GMCs are able to
match the HI arms in the outer Galaxy. We found that the models of three-arm
and four-arm logarithmic spirals are able to connect most spiral tracers. A
model of polynomial-logarithmic spirals is also proposed, which not only
delineates the tracer distribution, but also matches the observed tangential
directions.Comment: 22 Pages, 16 Figures, 7 Tables, updated to match the published
versio
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