417 research outputs found
Gravitational Collapse in One Dimension
We simulate the evolution of one-dimensional gravitating collisionless
systems from non- equilibrium initial conditions, similar to the conditions
that lead to the formation of dark- matter halos in three dimensions. As in the
case of 3D halo formation we find that initially cold, nearly homogeneous
particle distributions collapse to approach a final equilibrium state with a
universal density profile. At small radii, this attractor exhibits a power-law
behavior in density, {\rho}(x) \propto |x|^(-{\gamma}_crit), {\gamma}_crit
\simeq 0.47, slightly but significantly shallower than the value {\gamma} = 1/2
suggested previously. This state develops from the initial conditions through a
process of phase mixing and violent relaxation. This process preserves the
energy ranks of particles. By warming the initial conditions, we illustrate a
cross-over from this power-law final state to a final state containing a
homogeneous core. We further show that inhomogeneous but cold power-law initial
conditions, with initial exponent {\gamma}_i > {\gamma}_crit, do not evolve
toward the attractor but reach a final state that retains their original
power-law behavior in the interior of the profile, indicating a bifurcation in
the final state as a function of the initial exponent. Our results rely on a
high-fidelity event-driven simulation technique.Comment: 14 Pages, 13 Figures. Submitted to MNRA
Nonexistence theorems for traversable wormholes
Gauss-Bonnet formula is used to derive a new and simple theorem of
nonexistence of vacuum static nonsingular lorentzian wormholes. We also derive
simple proofs for the nonexistence of lorentzian wormhole solutions for some
classes of static matter such as, for instance, real scalar fields with a
generic potential obeying and massless fermions fields
Decomposition of Sodium Aluminate Solutions. V. Coarse Grained Hydrargillite Seed and Induced Nucleation
Decompositions of sodium aluminate solutions of different
molar ratio (Na20 :Al20s) were carried out by seeding with coarse
grained hydrargillite. The induced nucleation is greater the more
supersaturated the decomposing solution. An outline of the actual
mechanism of induced nucleation is given. The importance of the
initial formation of new solid phase on the seed surface is stressed.
Its kinetics are highly dependent on supersaturation
Kinetic decoupling of neutralino dark matter
After neutralinos cease annihilating in the early Universe, they may still
scatter elastically from other particles in the primordial plasma. At some
point in time, however, they will eventually stop scattering. We calculate the
cross sections for neutralino elastic scattering from standard-model particles
to determine the time at which this kinetic decoupling occurs. We show that
kinetic decoupling occurs above a temperature MeV. Thereafter,
neutralinos act as collisionless cold dark matter.Comment: Replaced with revised version, new references adde
The Cosmological Gene Project: cluster analysis of the atmospheric fluctuations on arcmin-scale imaging of the Cosmic Microwave Background
We discuss some aspects of the Cosmological Gene Project started at the
Special Astrophysical Observatory (Russia) in 1999. The goal of the project is
to measure the anisotropy and polarization of the Cosmic Microwave Background
(CMB) and investigation of atmospheric fluctuations and foreground on
arcmin-scales using the radio-telescope RATAN-600. We develop the cluster
analysis of one-dimensional random fields for the application to the RATAN-600
scans. We analyze the specific properties of peak clusterisation in the
RATAN-600 scans which to separate the primordial CMB signal from noise.Comment: Submitted to Astronomy & Astrophysic
Phenomenology of non-universal gaugino masses and implications for the Higgs boson decay
Grand unified theories (GUTs) can lead to non-universal gaugino masses at the
unification scale. We study the implications of such non-universal gaugino
masses for the composition of the lightest neutralino in supersymmetric (SUSY)
theories based on SU(5) gauge group. We also consider the phenomenological
implications of non-universal gaugino masses for the phenomenology of Higgs
bosons in the context of Large Hadron Collider.Comment: 4 pages, 8 eps figures, style files included, Talk at LCWS06,
Bangalore, India; typos correcte
The isolation of gravitational instantons: Flat tori V flat R^4
The role of topology in the perturbative solution of the Euclidean Einstein
equations about flat instantons is examined.Comment: 15 pages, ICN-UNAM 94-1
Model-Independent Comparison of Direct vs. Indirect Detection of Supersymmetric Dark Matter
We compare the rate for elastic scattering of neutralinos from various nuclei
with the flux of upward muons induced by energetic neutrinos from neutralino
annihilation in the Sun and Earth. We consider both scalar and axial-vector
interactions of neutralinos with nuclei. We find that the event rate in a kg of
germanium is roughly equivalent to that in a - to -m muon
detector for a neutralino with primarily scalar coupling to nuclei. For an
axially coupled neutralino, the event rate in a 50-gram hydrogen detector is
roughly the same as that in a 10- to 500-m muon detector. Expected
experimental backgrounds favor forthcoming elastic-scattering detectors for
scalar couplings while the neutrino detectors have the advantage for
axial-vector couplings.Comment: 10 pages, self-unpacking uuencoded PostScript fil
The Suppression of Neutralino Annihilation into Zh
The Indirect Detection of neutralino Dark Matter is most promising through
annihilation channels producing a hard energy spectrum for the detected
particles, such as the neutralino annihilation into . A cancellation
however makes this particular annihilation channel generically subdominant in
the huge parameter space of supersymmetric models. This cancellation requires
non-trivial relations between neutralino mixings and masses, which we derive
from gauge independence and unitarity of the MSSM. To show how the cancellation
overshoots leaving only a subdominant result, we use a perturbative expansion
in powers of the electroweak/supersymmetry breaking ratio .Comment: 10 pages, 5 figures 10 pages, 5 figure
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