1,201 research outputs found
Graviton Propagators in Supergravity and Noncommutative Gauge Theory
We investigate the graviton propagator in the type IIB supergravity
background which is dual to 4 dimensional noncommutative gauge theory. We
assume that the boundary is located not at the infinity but at the
noncommutative scale where the string frame metric exhibits the maximum. We
argue that the Neumann boundary condition is the appropriate boundary condition
to be adopted at the boundary. We find that the graviton propagator behaves
just as that of the 4 dimensional massless graviton. On the other hand, the
non-analytic behaviors of the other Kaluza-Klein modes are not significantly
affected by the Neumann boundary condition.Comment: 19 page
R-mediation of Dynamical Supersymmetry Breaking
We propose a simple scenario of the dynamical supersymmetry breaking in four
dimensional supergravity theories. The supersymmetry breaking sector is assumed
to be completely separated as a sequestered sector from the visible sector,
except for the communication by the gravity and U(1)_R gauge interactions, and
the supersymmetry breaking is mediated by the superconformal anomaly and U(1)_R
gauge interaction. Supersymmetry is dynamically broken by the interplay between
the non-perturbative effect of the gauge interaction and Fayet-Iliopoulos
D-term of U(1)_R which necessarily exists in supergravity theories with gauged
U(1)_R symmetry. We construct an explicit model which gives phenomenologically
acceptable mass spectrum of superpartners with vanishing (or very small)
cosmological constant.Comment: 12 pages, to be published in Phys. Rev.
Fermion Propagators in Type II Fivebrane Backgrounds
The fermion propagators in the fivebrane background of type II superstring
theories are calculated. The propagator can be obtained by explicitly
evaluating the transition amplitude between two specific NS-R boundary states
by the propagator operator in the non-trivial world-sheet conformal field
theory for the fivebrane background. The propagator in the field theory limit
can be obtained by using point boundary states. We can explicitly investigate
the lowest lying fermion states propagating in the non-trivial ten-dimensional
space-time of the fivebrane background: M^6 x W_k^(4), where W_k^(4) is the
group manifold of SU(2)_k x U(1). The half of the original supersymmetry is
spontaneously broken, and the space-time Lorentz symmetry SO(9,1) reduces to
SO(5,1) in SO(5,1) x SO(4) \subset SO(9,1) by the fivebrane background. We find
that there are no propagations of SO(4) (local Lorentz) spinor fields, which is
consistent with the arguments on the fermion zero-modes in the fivebrane
background of low-energy type II supergravity theories.Comment: 15 page
Magnetization-plateau state of the S=3/2 spin chain with single ion anisotropy
We reexamine the numerical study of the magnetized state of the S=3/2 spin
chain with single ion anisotropy D(> 0) for the magnetization M=M_{S}/3, where
M_{S} is the saturation magnetization. We find at this magnetization that for
D<D_{c1}=0.387 the system is critical and the magnetization plateau does not
appear. For D > D_{c1}, the parameter region is divided into two parts D_{c1} <
D < D_{c2}=0.943 and D_{c2} < D. In each region, the system is gapful and the
M=M_{S}/3 magnetization plateau appears in the magnetization process. From our
numerical calculation, the intermediate region D_{c1} < D < D_{c2} should be
characterized by a magnetized valence-bond-solid state.Comment: 6 pages, 8 figure
Nucleon decay in gauge unified models with intersecting D6-branes
Baryon number violation is discussed in gauge unified orbifold models of type
II string theory with intersecting Dirichlet branes. We consider setups of
D6-branes which extend along the flat Minkowski space-time directions and wrap
around 3-cycles of the internal 6-d manifold. The discussion is motivated by
the enhancement effect of low energy amplitudes anticipated for M-theory and
type II string theory models with matter modes localized at points of the
internal manifold. The conformal field theory formalism is used to evaluate the
open string amplitudes at tree level. We study the single baryon number
violating processes of dimension 6 and 5, involving four quarks and leptons and
in supersymmetry models, two pairs of matter fermions and superpartner
sfermions. The higher order processes associated with the baryon number
violating operators of dimension 7 and 9 are also examined, but in a
qualitative way. We discuss the low energy representation of string theory
amplitudes in terms of infinite series of poles associated to exchange of
string Regge resonance and compactification modes. The comparison of string
amplitudes with the equivalent field theory amplitudes is first studied in the
large compactification radius limit. Proceeding next to the finite
compactification radius case, we present a numerical study of the ratio of
string to field theory amplitudes based on semi-realistic gauge unified
non-supersymmetric and supersymmetric models employing the Z3 and Z2xZ2
orbifolds. We find a moderate enhancement of string amplitudes which becomes
manifest in the regime where the gauge symmetry breaking mass parameter exceeds
the compactification mass parameter, corresponding to a gauge unification in a
seven dimensional space-time.Comment: 63 pages revtex4. 8 postscript figures. 4 tables. Subsection II.B
revised. Several new references added. To appear in Physical Review
On Climbing Scalars in String Theory
In string models with "brane supersymmetry breaking" exponential potentials
emerge at (closed-string) tree level but are not accompanied by tachyons.
Potentials of this type have long been a source of embarrassment in flat space,
but can have interesting implications for Cosmology. For instance, in ten
dimensions the logarithmic slope |V'/V| lies precisely at a "critical" value
where the Lucchin--Matarrese attractor disappears while the scalar field is
\emph{forced} to climb up the potential when it emerges from the Big Bang. This
type of behavior is in principle perturbative in the string coupling, persists
after compactification, could have trapped scalar fields inside potential wells
as a result of the cosmological evolution and could have also injected the
inflationary phase of our Universe.Comment: 14 pages, LateX, 3 eps figure
Gravitino condensation in fivebrane backgrounds
We calculate the tension of the D3-brane in the fivebrane background which is
described by the exactly solvable SU(2)_k x U(1) world-sheet conformal field
theory with large Kac-Moody level k. The D3-brane tension is extracted from the
amplitude of one closed string exchange between two parallel D3-branes, and the
amplitude is calculated by utilizing the open-closed string duality. The
tension of the D3-brane in the background does not coincide with the one in the
flat space-time even in the flat space-time limit: k -> infinity. The finite
curvature effect should vanish in the flat space-time limit and only the
topological effect can remain. Therefore, the deviation indicates the
condensation of gravitino and/or dilatino which has been expected in the
fivebrane background as a gravitational instanton.Comment: 16 pages, 1 figur
Magnetic properties of the distorted diamond chain at T=0
We explore, at T=0, the magnetic properties of the antiferromagnetic
distorted diamond chain described by the Hamiltonian {\cal H}
= \sum_{j=1}^{N/3}{J_1 ({\bi S}_{3j-1} \cdot {\bi S}_{3j}
+ {\bi S}_{3j} \cdot {\bi S}_{3j+1})
+ J_2 {\bi S}_{3j+1} \cdot {\bi S}_{3j+2}
+ J_3 ({\bi S}_{3j-2} \cdot {\bi S}_{3j}
+ {\bi S}_{3j} \cdot {\bi S}_{3j+2})}
\allowbreak - H \sum_{l=1}^{N} S_l^z with , which well
models with , and azurite . We employ the physical
consideration, the degenerate perturbation theory, the level spectroscopy
analysis of the numerical diagonalization data obtained by the Lanczos method
and also the density matrix renormalization group (DMRG) method. We investigate
the mechanisms of the magnetization plateaux at and , and
also show the precise phase diagrams on the plane
concerning with these magnetization plateaux, where
and is the saturation magnetization. We also calculate the magnetization
curves and the magnetization phase diagrams by means of the DMRG method.Comment: 21 pages, 29 figure
Recursion Relations in Liouville Gravity coupled to Ising Model satisfying Fusion Rules
The recursion relations of 2D quantum gravity coupled to the Ising model
discussed by the author previously are reexamined. We study the case in which
the matter sector satisfies the fusion rules and only the primary operators
inside the Kac table contribute. The theory involves unregularized divergences
in some of correlators. We obtain the recursion relations which form a closed
set among well-defined correlators on sphere, but they do not have a beautiful
structure that the bosonized theory has and also give an inconsistent result
when they include an ill-defined correlator with the divergence. We solve them
and compute the several normalization independent ratios of the well-defined
correlators, which agree with the matrix model results.Comment: Latex, 22 page
Size-correlated polymorphisms in phyllotaxis-like periodic and symmetric tentacle arrangements in hydrozoan Coryne uchidai
Introduction: Periodic organ arrangements occur during growth and development and are widespread in animals and plants. In bilaterian animals, repetitive organs can be interpreted as being periodically arranged along the two-dimensional space and defined by two body axes; on the other hand, in radially symmetrical animals and plants, organs are arranged in the three-dimensional space around the body axis and around plant stems, respectively. The principles of periodic organ arrangement have primarily been investigated in bilaterians; however, studies on this phenomenon in radially symmetrical animals are scarce.Methods: In the present study, we combined live imaging, quantitative analysis, and mathematical modeling to elucidate periodic organ arrangement in a radially symmetrical animal, Coryne uchidai (Cnidaria, Hydrozoa).Results: The polyps of C. uchidai simultaneously formed multiple tentacles to establish a regularly angled, ring-like arrangement with radial symmetry. Multiple rings periodically appeared throughout the body and mostly maintained symmetry. Furthermore, we observed polymorphisms in symmetry type, including tri-, tetra-, and pentaradial symmetries, as individual variations. Notably, the types of radial symmetry were positively correlated with polyp diameter, with a larger diameter in pentaradial polyps than in tetra- and triradial ones. Our mathematical model suggested the selection of size-correlated radial symmetry based on the activation-inhibition and positional information from the mouth of tentacle initiation.Discussion: Our established quantification methods and mathematical model for tentacle arrangements are applicable to other radially symmetrical animals, and will reveal the widespread association between size-correlated symmetry and periodic arrangement principles
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