1,227 research outputs found
Hydro+Cascade, Flow, the Equation of State, Predictions and Data
A Hydro+Cascade model has been used to describe radial and elliptic flow at
the SPS and successfully predicted the radial and elliptic flow measured by the
both STAR and PHENIX collaborations . Furthermore, a combined description of
the radial and elliptic flow for different particle species, restricts the
Equation of State(EoS) and points towards an EoS with a phase transition to the
Quark Gluon Plasma(QGP) .Comment: Quark Matter 2001 Procedings. Corrected Fig. 3b for all charged. Some
typos fixe
Anisotropically Inflating Universes
We show that in theories of gravity that add quadratic curvature invariants
to the Einstein-Hilbert action there exist expanding vacuum cosmologies with
positive cosmological constant which do not approach the de Sitter universe.
Exact solutions are found which inflate anisotropically. This behaviour is
driven by the Ricci curvature invariant and has no counterpart in the general
relativistic limit. These examples show that the cosmic no-hair theorem does
not hold in these higher-order extensions of general relativity and raises new
questions about the ubiquity of inflation in the very early universe and the
thermodynamics of gravitational fields.Comment: 5 pages, further discussion and references adde
Quasi-K\"ahler Chern-flat manifolds and complex 2-step nilpotent Lie algebras
The study of quasi-K\"ahler Chern-flat almost Hermitian manifolds is strictly
related to the study of anti-bi-invariant almost complex Lie algebras. In the
present paper we show that quasi-K\"ahler Chern-flat almost Hermitian
structures on compact manifolds are in correspondence to complex parallelisable
Hermitian structures satisfying the second Gray identity. From an algebraic
point of view this correspondence reads as a natural correspondence between
anti-bi-invariant almost complex structures on Lie algebras to bi-invariant
complex structures. Some natural algebraic problems are approached and some
exotic examples are carefully described.Comment: 15 pages. Final version to appear in Ann. Sc. Norm. Super. Pisa Cl.
Sc
Strongly isospectral manifolds with nonisomorphic cohomology rings
For any , , we give pairs of compact flat -manifolds with holonomy groups , that are strongly isospectral, hence
isospectral on -forms for all values of , having nonisomorphic cohomology
rings. Moreover, if is even, is K\"ahler while is not.
Furthermore, with the help of a computer program we show the existence of large
Sunada isospectral families; for instance, for and there is a
family of eight compact flat manifolds (four of them K\"ahler) having very
different cohomology rings. In particular, the cardinalities of the sets of
primitive forms are different for all manifolds.Comment: 25 pages, to appear in Revista Matem\'atica Iberoamerican
Directional emission of stadium-shaped micro-lasers
The far-field emission of two dimensional (2D) stadium-shaped dielectric
cavities is investigated. Micro-lasers with such shape present a highly
directional emission. We provide experimental evidence of the dependance of the
emission directionality on the shape of the stadium, in good agreement with ray
numerical simulations. We develop a simple geometrical optics model which
permits to explain analytically main observed features. Wave numerical
calculations confirm the results.Comment: 4 pages, 8 figure
Spectra of lens spaces from 1-norm spectra of congruence lattices
To every -dimensional lens space , we associate a congruence lattice
in , with and we prove a formula relating
the multiplicities of Hodge-Laplace eigenvalues on with the number of
lattice elements of a given -length in . As a
consequence, we show that two lens spaces are isospectral on functions (resp.\
isospectral on -forms for every ) if and only if the associated
congruence lattices are -isospectral (resp.\
-isospectral plus a geometric condition). Using this fact, we
give, for every dimension , infinitely many examples of Riemannian
manifolds that are isospectral on every level and are not strongly
isospectral.Comment: Accepted for publication in IMR
Non-strongly isospectral spherical space forms
In this paper we describe recent results on explicit construction of lens
spaces that are not strongly isospectral, yet they are isospectral on -forms
for every . Such examples cannot be obtained by the Sunada method. We also
discuss related results, emphasizing on significant classical work of Ikeda on
isospectral lens spaces, via a thorough study of the associated generating
functions
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