1,123 research outputs found
Cosmological attractors in massive gravity
We study Lorentz-violating models of massive gravity which preserve rotations
and are invariant under time-dependent shifts of the spatial coordinates. In
the linear approximation the Newtonian potential in these models has an extra
``confining'' term proportional to the distance from the source. We argue that
during cosmological expansion the Universe may be driven to an attractor point
with larger symmetry which includes particular simultaneous dilatations of time
and space coordinates. The confining term in the potential vanishes as one
approaches the attractor. In the vicinity of the attractor the extra
contribution is present in the Friedmann equation which, in a certain range of
parameters, gives rise to the cosmic acceleration.Comment: 26 pages, 1 figur
Estimate of the correlation signal between cosmic rays and BL Lacs in future data
The existing correlation between BL Lacertae objects (BL Lacs) and cosmic-ray
events observed by HiRes experiment provide sufficient information to formulate
quantitatively the hypothesis about the flux of neutral cosmic-ray particles
originated from BL Lacs. We determine the potential of future cosmic ray
experiments to test this hypothesis by predicting the number of coincidences
between arrival directions of cosmic rays and positions of BL Lacs on the
celestial sphere, which should be observed in the future datasets. We find that
the early Pierre Auger data will not have enough events to address this
question. On the contrary, the final Pierre Auger data and the early Telescope
Array data will be sufficient to fully test this hypothesis. If confirmed, it
would imply the existence of highest-energy neutral particles coming from
cosmological distances.Comment: 5 page
Violation of Lorentz Invariance and neutral component of UHECR
The observed clustering of ultra-high energy cosmic rays suggests the
existence of a neutral component. The models with violation of Lorentz
invariance may explain this component by neutrons becoming stable above some
threshold energy E_0. The protons, in turn, may become unstable above some
energy E_1>E_0. We calculate the dependence of the threshold energies E_0 and
E_1 on the parameters of the model and find E_1/E_0\gsim 1.5. We argue that the
characteristic threshold behavior of charged and neutral components may be used
as the specific signature of models with violation of Lorentz invariance. The
existence of the neutron stability threshold E_0 can be investigated with
already existing data.Comment: 14 pages, 2 figure
Quantum Dew
We consider phase separation in nonequilibrium Bose gas with an attractive
interaction between the particles. Using numerical integrations on a lattice,
we show that the system evolves into a state that contains drops of
Bose-Einstein condensate suspended in uncondensed gas. When the initial gas is
sufficiently rarefied, the rate of formation of this quantum dew scales with
the initial density as expected for a process governed by two-particle
collisions.Comment: 4 pages, revtex, 5 figure
Evidence for a connection between the gamma-ray and the highest energy cosmic-ray emissions by BL Lacertae objects
A set of potentially gamma-ray--loud BL Lac objects is selected by
intersecting the EGRET and BL Lac catalogs. Of the resulting 14 objects, eight
are found to correlate with arrival directions of ultra--high-energy cosmic
rays (UHECRs), with significance of the order of 5 sigma. This suggests that
gamma-ray emission can be used as a distinctive feature of those BL Lac objects
that are capable of producing UHECR.Comment: 11 pages, 1 figure, version published in APJ Letter
First-order nonthermal phase transition after preheating
During preheating after inflation, parametric resonance rapidly generates
very large fluctuations of scalar fields. In models where the inflaton field
oscillates in a double-well potential and interacts with another scalar
field , fluctuations of X can keep the \phi to -\phi symmetry temporarily
restored. If the coupling of \phi to X is much stronger than the inflaton
self-coupling, the subsequent symmetry breaking is a first-order phase
transition. We demonstrate the existence of this nonthermal phase transition
with lattice simulations of the full nonlinear dynamics of the interacting
fields. In particular, we observe nucleation of an expanding bubble.Comment: RevTeX, 4 page
Testing the correlations between ultra-high-energy cosmic rays and BL Lac type objects with HiRes stereoscopic data
Previously suggested correlations of BL Lac type objects with the arrival
directions of the ultra-high-energy cosmic ray primaries are tested by making
use of the HiRes stereoscopic data. The results of the study support the
conclusion that BL Lacs may be the cosmic ray sources and suggest the presence
of a small (a few percent) fraction of neutral primaries at E>10^{19} eV.Comment: 4 pages, 3 figure
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