11,223 research outputs found
Primordial black holes from cosmic necklaces
Cosmic necklaces are hybrid topological defects consisting of monopoles and
strings. We argue that primordial black holes(PBHs) may have formed from loops
of the necklaces, if there exist stable winding states, such as coils and
cycloops. Unlike the standard scenario of PBH formation from string loops, in
which the kinetic energy plays important role when strings collapse into black
holes, the PBH formation may occur in our scenario after necklaces have
dissipated their kinetic energy. Then, the significant difference appears in
the production ratio. In the standard scenario, the production ratio
becomes a tiny fraction , however it becomes in our
case. On the other hand, the typical mass of the PBHs is much smaller than the
standard scenario, if they are produced in the same epoch. As the two
mechanisms may work at the same time, the necklaces may have more than one
channel of the gravitational collapse. Although the result obtained in this
paper depends on the evolution of the dimensionless parameter , the
existence of the winding state could be a serious problem in some cases. Since
the existence of the winding state in brane models is due to the existence of a
non-tivial circle in the compactified space, the PBH formation can be used to
probe the structure of the compactified space. Black holes produced by this
mechanism may have peculiar properties.Comment: 22pages, 3 figures, added many comments, +1 figure, accepted for
publication in JHE
Generating the curvature perturbation with instant preheating
A new mechanism for generating the curvature perturbation at the end of
inflaton has been investigated. The dominant contribution to the primordial
curvature perturbation may be generated during the period of instant
preheating. The mechanism converts isocurvature perturbation related to a light
field into curvature perturbation, where the ``light field'' is not the
inflaton field. This mechanism is important in inflationary models where
kinetic energy is significant at the end of inflaton. We show how one can apply
this mechanism to various brane inflationary models.Comment: 17 pages, 1 figure, To appear in JCA
Formation of monopoles and domain walls after brane inflation
We study cosmological defect formation after brane inflation. The
cosmological defects are corresponding to the branes that have less than three
spacial dimensions in the uncompactified spacetime. Contrary to the previous
arguments, production of monopoles and domain walls are not always negligible.
Monopoles and domain walls are formed by the branes extended between mother
branes.Comment: 27pages, 7 figures, many comments, footnotes and reviews are added,
to appear in JHE
Dark matter production from cosmic necklaces
Cosmic strings have gained a great interest, since they are formed in a large
class of brane inflationary models. The most interesting story is that cosmic
strings in brane models are distinguished in future cosmological observations.
If the strings in brane models are branes or superstrings that can move along
compactified space, and also if there are degenerated vacua along the
compactified space, kinks interpolate between degenerated vacua become
``beads'' on the strings. In this case, strings turn into necklaces. In the
case that the compact manifold in not simply connected, a string loop that
winds around a nontrivial circle is stable due to the topological reason. Since
the existence of the (quasi-)degenerated vacua and the nontrivial circle is a
common feature of the brane models, it is important to study cosmological
constraints on the cosmic necklaces and the stable winding states. In this
paper, we consider dark matter production from loops of the cosmic necklaces.
Our result suggests that necklaces can put stringent bound on certain kinds of
brane models.Comment: 27 pages, 5 figures, added many comments and 3 figures, accepted for
publication in JCA
Elliptic Inflation: Generating the curvature perturbation without slow-roll
There are many inflationary models in which inflaton field does not satisfy
the slow-roll condition. However, in such models, it is always difficult to
generate the curvature perturbation during inflation. Thus, to generate the
curvature perturbation, one must introduce another component to the theory. To
cite a case, curvatons may generate dominant part of the curvature perturbation
after inflation. However, we have a question whether it is unrealistic to
consider the generation of the curvature perturbation during inflation without
slow-roll. Assuming multi-field inflation, we encounter the generation of the
curvature perturbation during inflation without slow-roll. The potential along
equipotential surface is flat by definition and thus we do not have to worry
about symmetry. We also discuss about KKLT models, in which corrections lifting
the inflationary direction may not become a serious problem if there is a
symmetry enhancement at the tip (not at the moving brane) of the inflationary
throat.Comment: 27pages, 8figures, to appear in JCA
Combining Syntactic and Semantic Bidirectionalization
Matsuda et al. [2007, ICFP] and Voigtlander [2009, POPL] introduced two techniques that given a source-to-view function provide an update propagation function mapping an original source and an updated view back to an updated source, subject to standard consistency conditions. Being fundamentally different in approach, both
techniques have their respective strengths and weaknesses. Here we develop a synthesis of the two techniques to good effect. On the intersection of their applicability domains we achieve more than what a simple union of applying the techniques side by side deliver
Neutrino Masses and Mixings in a Minimal SO(10) Model
We consider a minimal formulation of SO(10) Grand Unified Theory wherein all
the fermion masses arise from Yukawa couplings involving one 126 and one 10 of
Higgs multiplets. It has recently been recognized that such theories can
explain, via the type-II seesaw mechanism, the large \nu_\mu - \nu_\tau mixing
as a consequence of b-tau unification at the GUT scale. In this picture,
however, the CKM phase \delta lies preferentially in the second quadrant, in
contradiction with experimental measurements. We revisit this minimal model and
show that the conventional type-I seesaw mechanism generates phenomenologically
viable neutrino masses and mixings, while being consistent with CKM CP
violation. We also present improved fits in the type-II seesaw scenario and
suggest fully consistent fits in a mixed scenario.Comment: 27 pages, 13 eps figures, revtex4; references added, some minor
correction
How Can We Obtain a Large Majorana-Mass in Calabi-Yau Models ?
In a certain type of Calabi-Yau superstring models it is clarified that the
symmetry breaking occurs by stages at two large intermediate energy scales and
that two large intermediate scales induce large Majorana-masses of right-handed
neutrinos. Peculiar structure of the effective nonrenormalizable interactions
is crucial in the models. In this scheme Majorana-masses possibly amount to
O(10^{9 \sim 10}\gev) and see-saw mechanism is at work for neutrinos. Based
on this scheme we propose a viable model which explains the smallness of masses
for three kind of neutrinos .
Special forms of the nonrenormalizable interactions can be understood as a
consequence of an appropriate discrete symmetry of the compactified manifold.Comment: 30-pages + 6-figures, LaTeX, Preprint DPNU-94-02, AUE-01-9
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