1,431 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
Semi-Leptonic b-decay at Intermediate Recoil
We compute the O(\alpha_s^2) corrections to the differential rate of the
semileptonic decay b -> clv at the "intermediate recoil" point, where the
c-quark mass and the invariant mass of the leptons are equal. The calculation
is based on an expansion around two opposite limits of the quark masses
m_{b,c}: m_c ~ m_b and m_c << m_b. The former case was previously studied; we
correct and extend that result. The latter case is new. The smooth matching of
both expansions provides a check of both. We clarify the discrepancy between
the recent determinations of the full NNLO QCD correction to the semileptonic b
-> c rate, and its earlier estimate.Comment: 9 pages, 6 figures, Replaced figures, small format and typo
corrections, added appendix and reference
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
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