2,459 research outputs found
Nutrition and physical fitness of white, coloured, and bantu high-school children
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Bounds on the cosmological abundance of primordial black holes from diffuse sky brightness: single mass spectra
We constrain the mass abundance of unclustered primordial black holes (PBHs),
formed with a simple mass distribution and subject to the Hawking evaporation
and particle absorption from the environment. Since the radiative flux is
proportional to the numerical density, an upper bound is obtained by comparing
the calculated and observed diffuse background values, (similarly to the Olbers
paradox in which point sources are considered) for finite bandwidths. For a
significative range of formation redshifts the bounds are better than several
values obtained by other arguments ; and they apply
to PBHs which are evaporating today.Comment: 20 pages, 5 figures, to appear in PR
Computing periodic orbits using the anti-integrable limit
Chaotic dynamics can be effectively studied by continuation from an
anti-integrable limit. Using the Henon map as an example, we obtain a simple
analytical bound on the domain of existence of the horseshoe that is equivalent
to the well-known bound of Devaney and Nitecki. We also reformulate the popular
method for finding periodic orbits introduced by Biham and Wenzel. Near an
anti-integrable limit, we show that this method is guaranteed to converge. This
formulation puts the choice of symbolic dynamics, required for the algorithm,
on a firm foundation.Comment: 11 Pages Latex2e + 1 Figure (eps). Accepted for publication in
Physics Lettes
Temperature and Polarization Patterns in Anisotropic Cosmologies
We study the coherent temperature and polarization patterns produced in
homogeneous but anisotropic cosmological models. We show results for all
Bianchi types with a Friedman-Robertson-Walker limit (i.e. Types I, V,
VII, VII and IX) to illustrate the range of possible behaviour. We
discuss the role of spatial curvature, shear and rotation in the geodesic
equations for each model and establish some basic results concerning the
symmetries of the patterns produced. We also give examples of the
time-evolution of these patterns in terms of the Stokes parameters , and
.Comment: 24 pages, 7 Figures, submitted to JCAP. Revised version: numerous
references added, text rewritten, and errors corrected
Can Solar Neutrinos be a Serious Background in Direct Dark Matter Searches?
The coherent contribution of all neutrons in neutrino nucleus scattering due
to the neutral current is examined considering the boron solar neutrinos. These
neutrinos could potentially become a source of background in the future dark
matter searches aiming at nucleon cross sections in the region well below the
few events per ton per year.Comment: 15 pages, 17 eps figure
Cosmological constant, violation of cosmological isotropy and CMB
We suggest that the solution to the cosmological vacuum energy puzzle does
not require any new field beyond the standard model, but rather can be
explained as a result of the interaction of the infrared sector of the
effective theory of gravity with standard model fields. The cosmological
constant in this framework can be presented in terms of QCD parameters and the
Hubble constant as follows, \epsilon_{vac} \sim H \cdot m_q\la\bar{q}q\ra
/m_{\eta'} \sim (4.3\cdot 10^{-3} \text{eV})^4, which is amazingly close to
the observed value today. In this work we explain how this proposal can be
tested by analyzing CMB data. In particular, knowing the value of the observed
cosmological constant fixes univocally the smallest size of the spatially flat,
constant time 3d hypersurface which, for instance in the case of an effective
1-torus, is predicted to be around 74 Gpc. We also comment on another important
prediction of this framework which is a violation of cosmological isotropy.
Such anisotropy is indeed apparently observed by WMAP, and will be confirmed
(or ruled out) by future PLANCK data.Comment: uses revtex4 - v2 as publishe
Homoclinic Bifurcations for the Henon Map
Chaotic dynamics can be effectively studied by continuation from an
anti-integrable limit. We use this limit to assign global symbols to orbits and
use continuation from the limit to study their bifurcations. We find a bound on
the parameter range for which the Henon map exhibits a complete binary
horseshoe as well as a subshift of finite type. We classify homoclinic
bifurcations, and study those for the area preserving case in detail. Simple
forcing relations between homoclinic orbits are established. We show that a
symmetry of the map gives rise to constraints on certain sequences of
homoclinic bifurcations. Our numerical studies also identify the bifurcations
that bound intervals on which the topological entropy is apparently constant.Comment: To appear in PhysicaD: 43 Pages, 14 figure
Optimized random phase approximations for arbitrary reference systems: extremum conditions and thermodynamic consistence
The optimized random phase approximation (ORPA) for classical liquids is
re-examined in the framework of the generating functional approach to the
integral equations. We show that the two main variants of the approximation
correspond to the addition of the same correction to two different first order
approximations of the homogeneous liquid free energy. Furthermore, we show that
it is possible to consistently use the ORPA with arbitrary reference systems
described by continuous potentials and that the same approximation is
equivalent to a particular extremum condition for the corresponding generating
functional. Finally, it is possible to enforce the thermodynamic consistence
between the thermal and the virial route to the equation of state by requiring
the global extremum condition on the generating functional.Comment: 8 pages, RevTe
Consistent Anisotropic Repulsions for Simple Molecules
We extract atom-atom potentials from the effective spherical potentials that
suc cessfully model Hugoniot experiments on molecular fluids, e.g., and
. In the case of the resulting potentials compare very well with the
atom-atom potentials used in studies of solid-state propertie s, while for
they are considerably softer at short distances. Ground state (T=0K) and
room temperatu re calculations performed with the new potential resolve
the previous discrepancy between experimental and theoretical results.Comment: RevTeX, 5 figure
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