11,817 research outputs found
Supersymmetry of Noncompact MQCD-like Membrane Instantons and Heat Kernel Asymptotics
We perform a heat kernel asymptotics analysis of the nonperturbative
superpotential obtained from wrapping of an M2-brane around a supersymmetric
noncompact three-fold embedded in a (noncompact) G_2-manifold as obtained in
[1], the three-fold being the one relevant to domain walls in Witten's MQCD
[2], in the limit of small "zeta", a complex constant that appears in the
Riemann surfaces relevant to defining the boundary conditions for the domain
wall in MQCD. The MQCD-like configuration is interpretable, for small but
non-zero zeta as a noncompact/"large" open membrane instanton, and for
vanishing zeta, as the type IIA D0-brane (for vanishing M-theory cicle radius).
We find that the eta-function Seeley de-Witt coefficients vanish, and we get a
perfect match between the zeta-function Seeley de-Witt coefficients (up to
terms quadratic in zeta) between the Dirac-type operator and one of the two
Laplace-type operators figuring in the superpotential. This is an extremely
strong signature of residual supersymmetry for the nonperturbative
configurations in M-theory considered in this work.Comment: 21 pages, LaTeX; v3: several clarifying remarks added, to appear in
JHE
Formation of the 0.511.-MeV line in solar flares
The gamma-ray line produced at 0.51-MeV was studied and is shown to be the result of either of free annihilation of positrons with electrons or of the decay of positronium by 2-photon emission. Positron annihilation from the bound state of positronium may also proceed by 3-photon emission, resulting in a continuum with energies up to 0.51-MeV. Accurate calculations of the rates of free annihilation and positronium formation in a solar-flare plasma are presented. Estimates of the positronium-formulation rates by charge exchange and the rates of dissociation and quenching are also considered. The temperature and density dependence of the ratio of 3-photon to 2-photon emission was obtained. It is shown that when the ratio of free electrons to neutral atoms in the plasma is approximately unity or greater, the Doppler width of the 0.51-MeV line is a function of the temperature of the annihilation region. For the small ion densities characteristics of the photosphere, the width is predominantly a function of the density
Analysis of wind tunnel test results for a 9.39-per cent scale model of a VSTOL fighter/attack aircraft. Volume 1: Study overview
The ability of current methodologies to accurately predict the aerodynamic characteristics identified as uncertainties was evaluated for two aircraft configurations. The two wind tunnel models studied horizontal altitude takeoff and landing V/STOL fighter aircraft derivatives
A New Source for Electroweak Baryogenesis in the MSSM
One of the most experimentally testable explanations for the origin of the
baryon asymmetry of the universe is that it was created during the electroweak
phase transition, in the minimal supersymmetric standard model. Previous
efforts have focused on the current for the difference of the two Higgsino
fields, , as the source of biasing sphalerons to create the baryon
asymmetry. We point out that the current for the orthogonal linear combination,
, is larger by several orders of magnitude. Although this increases
the efficiency of electroweak baryogenesis, we nevertheless find that large
CP-violating angles are required to get a large enough baryon
asymmetry.Comment: 4 pages, 2 figures; numerical error corrected, which implies that
large CP violation is needed to get observed baryon asymmetry. We improved
solution of diffusion equations, and computed more accurate values for
diffusion coefficient and damping rate
Spanning tree generating functions and Mahler measures
We define the notion of a spanning tree generating function (STGF) , which gives the spanning tree constant when evaluated at and gives
the lattice Green function (LGF) when differentiated. By making use of known
results for logarithmic Mahler measures of certain Laurent polynomials, and
proving new results, we express the STGFs as hypergeometric functions for all
regular two and three dimensional lattices (and one higher-dimensional
lattice). This gives closed form expressions for the spanning tree constants
for all such lattices, which were previously largely unknown in all but one
three-dimensional case. We show for all lattices that these can also be
represented as Dirichlet -series. Making the connection between spanning
tree generating functions and lattice Green functions produces integral
identities and hypergeometric connections, some of which appear to be new.Comment: 26 pages. Dedicated to F Y Wu on the occasion of his 80th birthday.
This version has additional references, additional calculations, and minor
correction
Analysis of wind tunnel test results for a 9.39-per cent scale model of a VSTOL fighter/attack aircraft. Volume 3: Effects of configuration variations from baseline
The aerodynamic characteristics of the components of the baseline E205 configuration is presented. Geometric variations from the baseline E205 configuration are also given including a matrix of conrad longitudinal locations and strake shapes
Impact of Conditional Cash Transfers and Remittances on Credit Market Outcomes in Rural Nicaragua
The impact of public and private transfers on credit markets has not been sufficiently studied and understanding any spill over effects caused by these transfers may be useful for policy makers. This paper estimates the impact of Conditional Cash Transfers (CCTs) and remittances received by poor households in rural Nicaragua on their decision to request a loan. We find that, on average, CCTs did not affect the request of credit while remittances increased it, controlling for potential endogeneity. We argue the reduction in income risk provided by remittances changes borrowers’ expected marginal returns to a loan and/or their creditworthiness, as perceived by lenders. The successful enforcement of the use of CCTs on long-term investments seems to have avoided externalities on the use of short-term credit these households have access to and their creditworthiness.International Development, D14, F22, O15,
The asymptotic quasi-stationary states of the two-dimensional magnetically confined plasma and of the planetary atmosphere
We derive the differential equation governing the asymptotic quasi-stationary
states of the two dimensional plasma immersed in a strong confining magnetic
field and of the planetary atmosphere. These two systems are related by the
property that there is an intrinsic constant length: the Larmor radius and
respectively the Rossby radius and a condensate of the vorticity field in the
unperturbed state related to the cyclotronic gyration and respectively to the
Coriolis frequency. Although the closest physical model is the
Charney-Hasegawa-Mima (CHM) equation, our model is more general and is related
to the system consisting of a discrete set of point-like vortices interacting
in plane by a short range potential. A field-theoretical formalism is developed
for describing the continuous version of this system. The action functional can
be written in the Bogomolnyi form (emphasizing the role of Self-Duality of the
asymptotic states) but the minimum energy is no more topological and the
asymptotic structures appear to be non-stationary, which is a major difference
with respect to traditional topological vortex solutions. Versions of this
field theory are discussed and we find arguments in favor of a particular form
of the equation. We comment upon the significant difference between the CHM
fluid/plasma and the Euler fluid and respectively the Abelian-Higgs vortex
models.Comment: Latex 126 pages, 7 eps figures included. Discussion on various forms
of the equatio
A statistical mechanical description of metastable states and hysteresis in the 3D soft-spin random-field model at T=0
We present a formalism for computing the complexity of metastable states and
the zero-temperature magnetic hysteresis loop in the soft-spin random-field
model in finite dimensions. The complexity is obtained as the Legendre
transform of the free-energy associated to a certain action in replica space
and the hysteresis loop above the critical disorder is defined as the curve in
the field-magnetization plane where the complexity vanishes; the nonequilibrium
magnetization is therefore obtained without having to follow the dynamical
evolution. We use approximations borrowed from condensed-matter theory and
based on assumptions on the structure of the direct correlation functions (or
proper vertices), such as a local approximation for the self-energies, to
calculate the hysteresis loop in three dimensions, the correlation functions
along the loop, and the second moment of the avalanche-size distribution.Comment: 28 pages, 12 figure
Statistics of nested spiral self-avoiding loops: exact results on the square and triangular lattices
The statistics of nested spiral self-avoiding loops, which is closely related
to the partition of integers into decreasing parts, is studied on the square
and triangular lattices.Comment: Old paper, for archiving. 7 pages, 2 figures, epsf, IOP macr
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