28,528 research outputs found
Zero average values of cosmological perturbations as an indispensable condition for the theory and simulations
We point out a weak side of the commonly used determination of scalar
cosmological perturbations lying in the fact that their average values can be
nonzero for some matter distributions. It is shown that introduction of the
finite-range gravitational potential instead of the infinite-range one resolves
this problem. The concrete illustrative density profile is investigated in
detail in this connection.Comment: 5 pages, 2 figure
Decaying Dark Atom constituents and cosmic positron excess
We present a scenario where dark matter is in the form of dark atoms that can
accomodate the experimentally observed excess of positrons in PAMELA and AMS-02
while being compatible with the constraints imposed on the gamma-ray flux from
Fermi/LAT. This scenario assumes that the dominant component of dark matter is
in the form of a bound state between a helium nucleus and a particle and a
small component is in the form of a WIMP-like dark atom compatible with direct
searches in underground detectors. One of the constituents of this WIMP-like
state is a metastable particle with a mass of 1 TeV or slightly below that
by decaying to , and produces the
observed positron excess. These decays can naturally take place via GUT
interactions. If it exists, such a metastable particle can be found in the next
run of LHC. The model predicts also the ratio of leptons over baryons in the
Universe to be close to -3.Comment: 20 pages, 4 figures, submitted to Advances in High Energy Physic
Atomic Scattering in Presence of an External Confinement and a Gas of Impenetrable Bosons
We calculate, within the pseudopotential approximation, a one-dimensional
scattering amplitude and effective one-dimensional interaction potential for
atoms confined transversally by an atom waveguide or highly elongated
``cigar''-shaped atomic trap. We show that in the low-energy scattering regime,
the scattering process degenerates to a total reflection suggesting an
experimental realization of a famous model in theoretical physics - a
one-dimensional gas of impenetrable bosons (``Tonks'' gas). We give an estimate
for suitable experimental parameters for alkali atoms confined in waveguides.Comment: 5 pages, 2 figures; list of atoms - candidates for the Tonks gas
realisation is restricted to the positive scatt. length; Cs is excluded from
the list; some new references added; minor changes in the text; accepted in
PRL June 22, 199
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