22,666 research outputs found
Spontaneous Z2 Symmetry Breaking in the Orbifold Daughter of N=1 Super Yang-Mills Theory, Fractional Domain Walls and Vacuum Structure
We discuss the fate of the Z2 symmetry and the vacuum structure in an
SU(N)xSU(N) gauge theory with one bifundamental Dirac fermion. This theory can
be obtained from SU(2N) supersymmetric Yang--Mills (SYM) theory by virtue of Z2
orbifolding. We analyze dynamics of domain walls and argue that the Z2 symmetry
is spontaneously broken. Since unbroken Z2 is a necessary condition for
nonperturbative planar equivalence we conclude that the orbifold daughter is
nonperturbatively nonequivalent to its supersymmetric parent. En route, our
investigation reveals the existence of fractional domain walls, similar to
fractional D-branes of string theory on orbifolds. We conjecture on the fate of
these domain walls in the true solution of the Z2-broken orbifold theory. We
also comment on relation with nonsupersymmetric string theories and
closed-string tachyon condensation.Comment: 37 pages, 7 figures. v2: various significant changes; revisions
explained in the introduction. Final version to appear in Phys.Rev.
Electron Capture In Pseudo-two-electron Systems: Ar8++He
Molecular-structure calculations using the pseudopotential method have been performed on the (ArHe)8+ system. The cross section for single-electron capture in Ar8++He collisions was calculated for energies from 20 eV to 10 keV/amu. The perturbed-stationary-state method [M. Kimura, H. Sato, and R. E. Olson, Phys. Rev. A 28, 2085 (1983)], modified to include electron translation factors appropriate to two-electron systems, was used. The total cross section is relatively energy independent with a value of approximately 2.5x10-15 cm2. The n=4 level of Ar7+ is found to be preferentially populated, with the 4f level being dominant. © 1985 The American Physical Society
Angular Scattering In Slow Multiple-charged Ion, Atom Collisions
The C6++H system is used to illustrate the importance of large-angle scattering in collisions between slow multiply charged ions and atoms. A quantum mechanical description based on a diabatic formalism of the collision system is used to obtain differential cross sections for electron capture in the relative velocity range nu =1*107 to 3*107 cm s-1 (Ecm approximately=48 to 430 eV). The threshold for angular scattering is at E theta approximately=0.2 keV deg which correlates with the curve crossing between initial and final molecular states located at Rx approximately=8a0. The centre-of-mass acceptance angles required to observe fixed fractions of the total electron capture cross sections are presented. Representative examples for the detection of 90% of the total electron capture cross section requires angular acceptances of 78 degrees at 1*107 cm s-1 and 8.5 degrees at 3*107 cm s-1
Petrology of Chondrule Rims in Yamato-791498 and Asuka-881828, the Least-Altered CR Chondrites in the Japanese NIPR Collection
CR chondrites are a group of car-bonaceous chondrites with well-preserved records of formation of their components in the solar nebula. The CR chondrites have undergone a wide range of aqueous alteration from nearly anhydrous (CR2.8 or CR3.0) to extensive recrystallization of primary minerals, including replacement of coarse-grained silicates in chondrules (CR2.0). At the same time, CRs have experienced only minor thermal metamorphism except for rare CR6 samples. Identifying minimally altered CR chondrites is a priority because they preserve (1) relatively pristine records of the solar nebula and (2) minerals and textures at the beginning stages of aqueous alteration. Here we report the petrologic characteristics of Y-791498 and A-881828 as the least aqueously altered CR chondrites in the Japanese NIPR meteorite collection. Previous studies have shown that fine-grained rims on chondrules are indicators of incipient alteration of primitive CR chondrites, there-fore we focus on rims around chondrules in the two meteorites
Scale-free networks are not robust under neutral evolution
Recently it has been shown that a large variety of different networks have
power-law (scale-free) distributions of connectivities. We investigate the
robustness of such a distribution in discrete threshold networks under neutral
evolution. The guiding principle for this is robustness in the resulting
phenotype. The numerical results show that a power-law distribution is not
stable under such an evolution, and the network approaches a homogeneous form
where the overall distribution of connectivities is given by a Poisson
distribution.Comment: Submitted for publicatio
Unoccupied topological surface state in BiTeSe
Bias voltage dependent scattering of the topological surface state is studied
by scanning tunneling microscopy/spectroscopy for a clean surface of the
topological insulator BiTeSe. A strong warping of constant energy
contours in the unoccupied part of the spectrum is found to lead to a
spin-selective scattering. The topological surface state persists to higher
energies in the unoccupied range far beyond the Dirac point, where it coexists
with the bulk conduction band. This finding sheds light on the spin and charge
dynamics over the wide energy range and opens a way to designing
opto-spintronic devices.Comment: 5 pages, 4 figure
Virus Propagation in Multiple Profile Networks
Suppose we have a virus or one competing idea/product that propagates over a
multiple profile (e.g., social) network. Can we predict what proportion of the
network will actually get "infected" (e.g., spread the idea or buy the
competing product), when the nodes of the network appear to have different
sensitivity based on their profile? For example, if there are two profiles
and in a network and the nodes of profile
and profile are susceptible to a highly spreading
virus with probabilities and
respectively, what percentage of both profiles will actually get infected from
the virus at the end? To reverse the question, what are the necessary
conditions so that a predefined percentage of the network is infected? We
assume that nodes of different profiles can infect one another and we prove
that under realistic conditions, apart from the weak profile (great
sensitivity), the stronger profile (low sensitivity) will get infected as well.
First, we focus on cliques with the goal to provide exact theoretical results
as well as to get some intuition as to how a virus affects such a multiple
profile network. Then, we move to the theoretical analysis of arbitrary
networks. We provide bounds on certain properties of the network based on the
probabilities of infection of each node in it when it reaches the steady state.
Finally, we provide extensive experimental results that verify our theoretical
results and at the same time provide more insight on the problem
Maximum principle and mutation thresholds for four-letter sequence evolution
A four-state mutation-selection model for the evolution of populations of
DNA-sequences is investigated with particular interest in the phenomenon of
error thresholds. The mutation model considered is the Kimura 3ST mutation
scheme, fitness functions, which determine the selection process, come from the
permutation-invariant class. Error thresholds can be found for various fitness
functions, the phase diagrams are more interesting than for equivalent
two-state models. Results for (small) finite sequence lengths are compared with
those for infinite sequence length, obtained via a maximum principle that is
equivalent to the principle of minimal free energy in physics.Comment: 25 pages, 16 figure
Surface Scattering via Bulk Continuum States in the 3D Topological Insulator BiSe
We have performed scanning tunneling microscopy and differential tunneling
conductance () mapping for the surface of the three dimensional
topological insulator BiSe. The fast Fourier transformation applied
to the image shows an electron interference pattern near Dirac node
despite the general belief that the backscattering is well suppressed in the
bulk energy gap region. The comparison of the present experimental result with
theoretical surface and bulk band structures shows that the electron
interference occurs through the scattering between the surface states near the
Dirac node and the bulk continuum states.Comment: 5 pages, 4 figure
Molecular Treatment Of Charge Transfer In Li+ +Ca Collisions
The perturbed-stationary-state method, appended with electron translation factors, has been applied to charge transfer in Li+ +Ca collisions for energies from 0.1 to 20 keV/amu. The Born-Oppenheimer wave functions and eigenvalues were generated using the pseudopotential technique, which reduced the many-electron system to a simpler two-electron problem. The molecular ground-state X +1 is calculated to be bound and has the potential-well parameters Re=6.20a0, De=1.11 eV, e=235 cm-1, and Be=0.263 cm-1. From the scattering computations, a representative value for the charge-transfer cross section is 4x10-15 cm2 at 5 keV/amu. The cross section decreases rapidly as the energy is reduced below 1 keV/amu. At all energies studied, the dominant electron-capture reaction product is the ground-state Li atom. © 1983 The American Physical Society
- …