4,932 research outputs found
Non-Supersymmetric F-Theory Compactifications on Spin(7) Manifolds
We propose a novel approach to obtain non-supersymmetric four-dimensional
effective actions by considering F-theory on manifolds with special holonomy
Spin(7). To perform such studies we suggest that a duality relating M-theory on
a certain class of Spin(7) manifolds with F-theory on the same manifolds times
an interval exists. The Spin(7) geometries under consideration are constructed
as quotients of elliptically fibered Calabi-Yau fourfolds by an
anti-holomorphic and isometric involution. The three-dimensional minimally
supersymmetric effective action of M-theory on a general Spin(7) manifold with
fluxes is determined and specialized to the aforementioned geometries. This
effective theory is compared with an interval Kaluza-Klein reduction of a
non-supersymmetric four-dimensional theory with definite boundary conditions
for all fields. Using this strategy a minimal set of couplings of the
four-dimensional low-energy effective actions is obtained in terms of the
Spin(7) geometric data. We also discuss briefly the string interpretation in
the Type IIB weak coupling limit.Comment: 39 pages, 4 figures, v2: improvements and clarifications on the 4d
interpretation and weak coupling limit; typos correcte
The effective action of warped M-theory reductions with higher-derivative terms - Part II
We study the three-dimensional effective action obtained by reducing
eleven-dimensional supergravity with higher-derivative terms on a background
solution including a warp-factor, an eight-dimensional compact manifold, and
fluxes. The dynamical fields are K\"ahler deformations and vectors from the
M-theory three-form. We show that the potential is only induced by fluxes and
the naive contributions obtained from higher-curvature terms on a Calabi-Yau
background vanish once the back-reaction to the full solution is taken into
account. For the resulting three-dimensional action we analyse the K\"ahler
potential and complex coordinates and show compatibility with N=2
supersymmetry. We argue that the higher-order result is also compatible with a
no-scale condition. We find that the complex coordinates should be formulated
as divisor integrals for which a non-trivial interplay between the warp-factor
terms and the higher-curvature terms allow a derivation of the moduli space
metric. This leads us to discuss higher-derivative corrections to the M5-brane
action.Comment: 26 page
On M-theory fourfold vacua with higher curvature terms
We study solutions to the eleven-dimensional supergravity action, including
terms quartic and cubic in the Riemann curvature, that admit an
eight-dimensional compact space. The internal background is found to be a
conformally Kahler manifold with vanishing first Chern class. The metric
solution, however, is non-Ricci-flat even when allowing for a conformal
rescaling including the warp factor. This deviation is due to the possible
non-harmonicity of the third Chern-form in the leading order Ricci-flat metric.
We present a systematic derivation of the background solution by solving the
Killing spinor conditions including higher curvature terms. These are
translated into first-order differential equations for a globally defined real
two-form and complex four-form on the fourfold. We comment on the supersymmetry
properties of the described solutions.Comment: 14 page
Correlations Between Metallurgical Characterization Studies, Exploratory Mechanical Tests, and Continuum Mechanics Approaches to Constitutive Equations
Austenitic stainless steels, such as types 316 and 304, are widely used as pressure vessel materials in the temperature range of 425 to 650 C. Stainless steel specimens were tested to rupture at two different stress levels sigma and sigma 2 sigma 1 sigma 2) to establish the normal stain-time behavior. A subsequent test was performed in which the specimen was crept at the higher stress (sigma 1) to the beginning of the secondary stage of creep, presumed to be the strain/time conditions at which a steady state microstructure is developed, and then the stress was reduced to the lower level (sigma 2). The associated microstructure, and significance of this microstructure on the creep strain-hardening model for variable uniaxial loads were assesed and found to be consistent with the use of creep-recovery models at high stresses and temperatures and strain-hardening models at low stresses and tempertures
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