16,682 research outputs found
Supersymmetric Electroweak Baryogenesis in the WKB approximation
We calculate the baryon asymmetry generated at the electroweak phase
transition in the minimal supersymmetric standard model, treating the particles
in a WKB approximation in the bubble wall background. A set of diffusion
equations for the particle species relevant to baryon generation, including
source terms arising from the CP violation associated with the complex phase
of the parameter, are derived from Boltzmann equations, and
solved. The conclusion is that must be \gsim 0.1 to generate a
baryon asymmetry consistent with nucleosynthesis. We compare our results to
several other recent computations of the effect, arguing that some are
overestimates.Comment: 12 pages, 1 figure, corrected some criticisms of hep-ph/9702409; to
appear in Phys. Lett.
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
Micro-simulating child poverty in 2010 and 2020
The 2008 Pre-Budget Report (PBR) said that 'the Government will take stock of progress towards its 2010 and 2020 child poverty target in the [2009] Budget'. As background to that exercise, this paper updates our previous analysis of the prospects for child poverty in the UK in 2010-11 and 2020-21
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
SOME TESTS OF THE ECONOMIC THEORY OF COOPERATIVES: METHODOLOGY AND APPLICATION TO COTTON GINNING
Little progress has been made in testing the often conflicting hypotheses generated from theoretical research on cooperatives. This paper addresses the deficiency by describing and applying (to California cotton ginning cooperatives) a methodology to test key hypotheses concerning (a) cooperativesÂ’ price-output equilibrium, (b) allocative efficiency, and (c) utilization of capital inputs. The empirical results (a) are consistent with predictions from the game theory model of cooperative behavior, (b) reject the null hypothesis of absolute allocative efficiency, and (c) indicate absolute overutilization of capital inputs among the sample cooperatives.Agribusiness, Crop Production/Industries,
Quantum-Mechanical Dualities on the Torus
On classical phase spaces admitting just one complex-differentiable
structure, there is no indeterminacy in the choice of the creation operators
that create quanta out of a given vacuum. In these cases the notion of a
quantum is universal, i.e., independent of the observer on classical phase
space. Such is the case in all standard applications of quantum mechanics.
However, recent developments suggest that the notion of a quantum may not be
universal. Transformations between observers that do not agree on the notion of
an elementary quantum are called dualities. Classical phase spaces admitting
more than one complex-differentiable structure thus provide a natural framework
to study dualities in quantum mechanics. As an example we quantise a classical
mechanics whose phase space is a torus and prove explicitly that it exhibits
dualities.Comment: New examples added, some precisions mad
Hydrographic data from R/V endeavor cruise #90
The final cruise of the NSF sponsored Warm Core Rings Program studied a Warm Core Ring (WCR) in the Fall of 1982 as it formed from a large northward meander of the Gulf Stream. This ring, known as 82-H or the eighth ring identified in 1982, formed over the New England Seamounts near 39.5 deg N, 65 deg W. Surveys using Expendable Bathythermographs, Conductivity-Temperature-Depth-Oxygen stations and Doppler Current Profiling provide a look at the genesis of a WCR. These measurements reveal that WCR 82-H separated from the Gulf Stream sometime between October 2-5. This ring was a typical WCR with a diameter of about 200 km and speeds in the high velocity core of the 175 cm/sec. Satellite imagery of 82-H following the cruise showed that it drifted WSW in the Slope Water region at almost 9 km/day, had at least one interaction with the Gulf Stream and was last observed on February 8, 1983 at 39 deg N, 72 deg W
Generalized mirror symmetry and trace anomalies
We consider compactification of M-theory on X7 with betti numbers (b_0, b_1,
b_2, b_3, b_3, b_2, b_1, b_0) and define a generalized mirror symmetry (b_0,
b_1, b_2, b_3) goes to (b_0, b_1, b_2 -rho/2, b_3+rho/2)$ under which rho =
7b_0-5b_1+3b_2 -b_3 changes sign. Generalized self-mirror theories with rho=0
have massless sectors with vanishing trace anomaly (before dualization).
Examples include pure supergravity with N \geq 4 and supergravity plus matter
with N \leq 4.Comment: 19 pages late
Spectral Properties of delta-Plutonium: Sensitivity to 5f Occupancy
By combining the local density approximation (LDA) with dynamical mean field
theory (DMFT), we report a systematic analysis of the spectral properties of
-plutonium with varying occupancy. The LDA Hamiltonian is
extracted from a tight-binding (TB) fit to full-potential linearized augmented
plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact
quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We have shown
for the first time the strong sensitivity of the spectral properties to the
occupancy, which suggests using this occupancy as a fitting parameter in
addition to the Hubbard . By comparing with PES data, we conclude that the
``open shell'' configuration gives the best agreement, resolving the
controversy over ``open shell'' versus ``close shell'' atomic
configurations in -Pu.Comment: 6 pages, 2 embedded color figures, to appear in Physical Review
Quasi-stationary states and the range of pair interactions
"Quasi-stationary" states are approximately time-independent out of
equilibrium states which have been observed in a variety of systems of
particles interacting by long-range interactions. We investigate here the
conditions of their occurrence for a generic pair interaction V(r \rightarrow
\infty) \sim 1/r^a with a > 0, in d>1 dimensions. We generalize analytic
calculations known for gravity in d=3 to determine the scaling parametric
dependences of their relaxation rates due to two body collisions, and report
extensive numerical simulations testing their validity. Our results lead to the
conclusion that, for a < d-1, the existence of quasi-stationary states is
ensured by the large distance behavior of the interaction alone, while for a >
d-1 it is conditioned on the short distance properties of the interaction,
requiring the presence of a sufficiently large soft-core in the interaction
potential.Comment: 5 pages, 3 figures; final version to appear in Phys. Rev. Let
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