1,017 research outputs found
Ultra high energy neutrinos from hidden-sector topological defects
We study Topological Defects (TD) in hidden (mirror) matter as possible
sources of ultra-high energy neutrinos. The hidden/mirror and ordinary matter
are assumed to interact very weakly through gravity or superheavy particles. An
inflationary scenario is outlined in which superheavy defects are formed in
hidden/mirror matter (and not in ordinary matter), and at the same time the
density of mirror matter produced at the end of inflation is much smaller than
that of ordinary matter. Superheavy particles produced by hidden-sector TD and
the products of their decays are all sterile in our world. Only mirror
neutrinos oscillate into ordinary neutrinos. We show that oscillations with
maximal mixing of neutrinos from both worlds are possible and that values of
, needed for for solution of solar-neutrino and
atmospheric-neutrino problems, allow the oscillation of ultra-high energy
neutrinos on a timescale of the age of the Universe. A model of mass-degenerate
visible and mirror neutrinos with maximal mixing is constructed. Constraints on
UHE neutrino fluxes are obtained. The estimated fluxes can be 3 orders of
magnitude higher than those from ordinary matter. Detection of these fluxes is
briefly discussed.Comment: Revtex, 31 page
Spinning cosmic strings: a general class of solutions
In this work, we give a general class of solutions of the spinning cosmic
string in Einstein's theory of gravity. After treating same problem in Einstein
Cartan (EC) theory of gravity, the exact solution satisfying both exterior and
interior space-times representing a spin fluid moving along the symmetry axis
is presented in the EC theory. The existence of closed timelike curves in this
spacetime are also examined
Tunneling in quantum cosmology: numerical study of particle creation
We consider a minisuperspace model for a closed universe with small and
positive cosmological constant, filled with a massive scalar field conformally
coupled to gravity. In the quantum version of this model, the universe may
undergo a tunneling transition through an effective barrier between regions of
small and large scale factor. We solve numerically the minisuperspace
Wheeler--De Witt equation with tunneling boundary conditions for the wave
function of the universe, and find that tunneling in quantum cosmology is quite
different from that in quantum mechanics. Namely, the matter degree of freedom
gets excited under the barrier, provided its interaction with the scale factor
is not too weak, and makes a strong back reaction onto tunneling. In the
semiclassical limit of small values of cosmological constant, the matter energy
behind the barrier is close to the height of the barrier: the system ``climbs
up'' the barrier, and then evolves classically from its top. These features are
even more pronounced for inhomogeneous modes of matter field. Extrapolating to
field theory we thus argue that high momentum particles are copiously created
in the tunneling process. Nevertheless, we find empirical evidence for the
semiclassical-type scaling with the cosmological constant of the wave function
under and behind the barrier.Comment: 29 pages, 17 figure
Cosmic Rays from Cosmic Strings with Condensates
We re-visit the production of cosmic rays by cusps on cosmic strings. If a
scalar field (``Higgs'') has a linear interaction with the string world-sheet,
such as would occur if there is a bosonic condensate on the string, cusps on
string loops emit narrow beams of very high energy Higgses which then decay to
give a flux of ultra high energy cosmic rays. The ultra-high energy flux and
the gamma to proton ratio agree with observations if the string scale is GeV. The diffuse gamma ray and proton fluxes are well below current
bounds. Strings that are {\it lighter} and have linear interactions with
scalars produce an excess of direct and diffuse cosmic rays and are ruled out
by observations, while heavier strings ( GeV) are constrained by
their gravitational signatures. This leaves a narrow window of parameter space
for the existence of cosmic strings with bosonic condensates.Comment: 9 pages, 5 figures; revised reference
Weak-Field Gravity of Revolving Circular Cosmic Strings
A weak-field solution of Einstein's equations is constructed. It is generated
by a circular cosmic string revolving in its plane about the centre of the
circle. (The revolution is introduced to prevent the string from collapsing.)
This solution exhibits a conical singularity, and the corresponding deficit
angle is the same as for a straight string of the same linear energy density,
irrespective of the angular velocity of the string.Comment: 13 pages, LaTe
A prescription for probabilities in eternal inflation
Some of the parameters we call ``constants of Nature'' may in fact be
variables related to the local values of some dynamical fields. During
inflation, these variables are randomized by quantum fluctuations. In cases
when the variable in question (call it ) takes values in a continuous
range, all thermalized regions in the universe are statistically equivalent,
and a gauge invariant procedure for calculating the probability distribution
for is known. This is the so-called ``spherical cutoff method''. In
order to find the probability distribution for it suffices to consider a
large spherical patch in a single thermalized region. Here, we generalize this
method to the case when the range of is discontinuous and there are
several different types of thermalized region. We first formulate a set of
requirements that any such generalization should satisfy, and then introduce a
prescription that meets all the requirements. We finally apply this
prescription to calculate the relative probability for different bubble
universes in the open inflation scenario.Comment: 15 pages, 5 figure
Electrostatic in Reissner-Nordstrom space-time with a conical defect
We calculate the electrostatic potential generated by a point charge in the
space-time of Reissner-Nordstrom with a conical defect. An expression for the
self-energy is also presented.Comment: 7 pages, LATEX fil
Unambiguous probabilities in an eternally inflating universe
``Constants of Nature'' and cosmological parameters may in fact be variables
related to some slowly-varying fields. In models of eternal inflation, such
fields will take different values in different parts of the universe. Here I
show how one can assign probabilities to values of the ``constants'' measured
by a typical observer. This method does not suffer from ambiguities previously
discussed in the literature.Comment: 7 pages, Final version (minor changes), to appear in Phys. Rev. Let
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