143,024 research outputs found
Z_{12-I} Orbifold Compactification toward SUSY Standard Model
We explain the orbifold compactification in string models and present a
Z_{12-I} orbifold compactification toward supersymmetric standard models. We
also point out an effective R-parity from this string construction. The VEVs of
gauge singlets are chosen such that phenomenological constraints are satisfied.Comment: 13 pages with 5 figure. Talk presented at "CTP Symposium on SUSY at
LHC", Cairo, 11-14 March 200
Approximate Coulomb distortion effects in (e,e'p) reactions
In this paper we apply a well-tested approximation of electron Coulomb
distortion effects to the exclusive reaction (e,e'p) in the quasielastic
region. We compare the approximate treatment of Coulomb distortion effects to
the exact distorted wave Born approximation evaluated by means of partial wave
analysis to gauge the quality of our approximate treatment. We show that the
approximate M\"oller potential has a plane-wave-like structure and hence
permits the separation of the cross section into five terms which depend on
bilinear products of transforms of the transition four current elements. These
transforms reduce to Fourier transforms when Coulomb distortion is not present,
but become modified with the inclusion of Coulomb distortion. We investigate
the application of the approximate formalism to a model of 208Pb(e,e'p) using
Dirac-Hartree single particle wave functions for the ground state and
relativistic optical model wave functions for the continuum proton. We show
that it is still possible to extract, albeit with some approximation, the
various structure functions from the experimentally measured data even for
heavy nuclei.Comment: 32 pages, 11 figures, 19 reference
Cosmological constant is probably adjustable in brane worlds
In the brane world scenario, possessing the self-tuning property of the
cosmological constant, we study the probability amplitude for an initial state
of the Universe to transform to final states with some curvatures. In the Kim,
Kyae and Lee model, there exists a finite range of parameters such that the
transition amplitude to a near flat universe is exponentially dominated by the
smallness of curvature, > e^{positive number}/{Lambda-bar}^2}, i.e. is
dominated by an almost flat universe of |Lambda-bar|<epsilon.Comment: 6 pages with 2 figure
Fate of global symmetries in the Universe: QCD axion, quintessential axion and trans-Planckian inflaton decay-constant
Pseudoscalars appearing in particle physics are reviewd systematically. From
the fundamental point of view at an ultra-violat completed theory, they can be
light if they are realized as pseudo-Goldstone bosons of some spontaneously
broken global symmetries. The spontaneous breaking scale is parametrized by the
decay constant . The global symmetry is defined by the lowest order terms
allowed in the effective theory consistent with the gauge symmetry in question.
Since any global symmetry is known to be broken at least by quantum
gravitational effects, all pseudoscalars should be massive. The mass scale is
determined by and the explicit breaking terms in the effective
potential and also anomaly terms for some non-Abelian gauge
groups . The well-known example by non-Abelian gauge group breaking is the
potential for the "invisible" QCD axion, via the Peccei-Quinn symmetry, which
constitutes a major part of this review. Even if there is no breaking terms
from gauge anomalies, there can be explicit breaking terms in the
potential in which case the leading term suppressed by determines the
pseudoscalar mass scale. If the breaking term is extremely small and the decay
constant is trans-Planckian, the corresponding pseudoscalar can be a candidate
for a `quintessential axion'. In general, is considered to
be smaller than , and hence the pseudo-Goldstone boson mass scales are
considered to be smaller than the decay constants. In such a case, the
potential of the pseudo-Goldstone boson at the grand unification scale is
sufficiently flat near the top of the potential that it can be a good candidate
for an inflationary model, which is known as `natural inflation'. We review all
these ideas in the bosonic collective motion framework.Comment: 41 pages with 27 figure
Means for growing ribbon crystals without subjecting the crystals to thermal shock-induced strains
A susceptor particularly suited for use in growing a ribbon crystal employing edge defined film fed growth techniques is described. The susceptor includes a die through which a melt is drawn for forming a crystal ribbon. This is combined with a coolant delivery system characterized by a pair of jets for directing a stream of fluid coolant along a path extended to impinge on the susceptor in close proximity with the die in nonincident relation with the crystal being grown
Betweenness centrality correlation in social networks
Scale-free (SF) networks exhibiting a power-law degree distribution can be
grouped into the assortative, dissortative and neutral networks according to
the behavior of the degree-degree correlation coefficient. Here we investigate
the betweenness centrality (BC) correlation for each type of SF networks. While
the BC-BC correlation coefficients behave similarly to the degree-degree
correlation coefficients for the dissortative and neutral networks, the BC
correlation is nontrivial for the assortative ones found mainly in social
networks. The mean BC of neighbors of a vertex with BC is almost
independent of , implying that each person is surrounded by almost the
same influential environments of people no matter how influential the person
is.Comment: 4 pages, 4 figures, 1 tabl
Supersymmetric three family chiral SU(6) grand unification model from F-theory
We obtain a supersymmetric three family chiral SU(6) grand unification model
with the global family symmetry SU(3)[family] from F-theory. This model has
nice features such as all the fermion masses are reasonably generated and there
results only one pair of Higgs doublets, realizing the doublet-triplet
splitting from the family symmetry SU(3)[family]. The proton hexality is
realized toward the proton stability problem. There is a room to fit the three
gauge couplings using the F-theory flux idea and we obtain the proton lifetime
in the 10^{36-37} yr region.Comment: 5 pages, to be published in Phys. Rev.
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