10,026 research outputs found
Heterotic Anomaly Cancellation in Five Dimensions
We study the constraints on five-dimensional N=1 heterotic M-theory imposed
by a consistent anomaly-free coupling of bulk and boundary theory. This
requires analyzing the cancellation of triangle gauge anomalies on the
four-dimensional orbifold planes due to anomaly inflow from the bulk. We find
that the semi-simple part of the orbifold gauge groups and certain U(1)
symmetries have to be free of quantum anomalies. In addition there can be
several anomalous U(1) symmetries on each orbifold plane whose anomalies are
cancelled by a non-trivial variation of the bulk vector fields. The mixed U(1)
non-abelian anomaly is universal and there is at most one U(1) symmetry with
such an anomaly on each plane. In an alternative approach, we also analyze the
coupling of five-dimensional gauged supergravity to orbifold gauge theories. We
find a somewhat generalized structure of anomaly cancellation in this case
which allows, for example, non-universal mixed U(1) gauge anomalies. Anomaly
cancellation from the perspective of four-dimensional N=1 effective actions
obtained from E_8xE_8 heterotic string- or M-theory by reduction on a
Calabi-Yau three-fold is studied as well. The results are consistent with the
ones found for five-dimensional heterotic M-theory. Finally, we consider some
related issues of phenomenological interest such as model building with
anomalous U(1) symmetries, Fayet-Illiopoulos terms and threshold corrections to
gauge kinetic functions.Comment: 46 pages, Late
Kink-boundary collisions in a two dimensional scalar field theory
In a two-dimensional toy model, motivated from five-dimensional heterotic
M-theory, we study the collision of scalar field kinks with boundaries. By
numerical simulation of the full two-dimensional theory, we find that the kink
is always inelastically reflected with a model-independent fraction of its
kinetic energy converted into radiation. We show that the reflection can be
analytically understood as a fluctuation around the scalar field vacuum. This
picture suggests the possibility of spontaneous emission of kinks from the
boundary due to small perturbations in the bulk. We verify this picture
numerically by showing that the radiation emitted from the collision of an
initial single kink eventually leads to a bulk populated by many kinks.
Consequently, processes changing the boundary charges are practically
unavoidable in this system. We speculate that the system has a universal final
state consisting of a stack of kinks, their number being determined by the
initial energy
Nonordinary edge criticaliy of two-dimensional quantum critical magnets
Based on large-scale quantum Monte Carlo simulations, we examine the
correlations along the edges of two-dimensional semi-infinite quantum critical
Heisenberg spin- systems. In particular, we consider coupled quantum
spin-dimer systems at their bulk quantum critical points, including the
columnar-dimer model and the plaquette-square lattice. The alignment of the
edge spins strongly affects these correlations and the corresponding scaling
exponents, with remarkably similar values obtained for various quantum
spin-dimer systems. We furthermore observe subtle effects on the scaling
behavior from perturbing the edge spins that exhibit the genuine quantum nature
of these edge states. Our observations furthermore challenge recent attempts
that relate the edge spin criticality to the presence of symmetry-protected
topological phases in such quantum spin systems.Comment: 9 pages, 11 figures, v2: as publishe
Topological Invariants and Fibration Structure of Complete Intersection Calabi-Yau Four-Folds
We investigate the mathematical properties of the class of Calabi-Yau
four-folds recently found in [arXiv:1303.1832]. This class consists of 921,497
configuration matrices which correspond to manifolds that are described as
complete intersections in products of projective spaces. For each manifold in
the list, we compute the full Hodge diamond as well as additional topological
invariants such as Chern classes and intersection numbers. Using this data, we
conclude that there are at least 36,779 topologically distinct manifolds in our
list. We also study the fibration structure of these manifolds and find that
99.95 percent can be described as elliptic fibrations. In total, we find
50,114,908 elliptic fibrations, demonstrating the multitude of ways in which
many manifolds are fibered. A sub-class of 26,088,498 fibrations satisfy
necessary conditions for admitting sections. The complete data set can be
downloaded at
http://www-thphys.physics.ox.ac.uk/projects/CalabiYau/Cicy4folds/index.html .Comment: 25 pages, 7 figures, 1 table. v2: references added and minor changes.
Final version accepted for publicatio
Awakening effects of simulated sonic booms and subsonic aircraft noise on six subjects, 7 to 72 years of age
Awakening response of humans to sonic booms and subsonic aircraft nois
Statistical properties of supersonic turbulence in the Lagrangian and Eulerian frameworks
We present a systematic study of the influence of different forcing types on
the statistical properties of supersonic, isothermal turbulence in both the
Lagrangian and Eulerian frameworks. We analyse a series of high-resolution,
hydrodynamical grid simulations with Lagrangian tracer particles and examine
the effects of solenoidal (divergence-free) and compressive (curl-free) forcing
on structure functions, their scaling exponents, and the probability density
functions of the gas density and velocity increments. Compressively driven
simulations show a significantly larger density contrast, a more intermittent
behaviour, and larger fractal dimension of the most dissipative structures at
the same root mean square Mach number. We show that the absolute values of
Lagrangian and Eulerian structure functions of all orders in the integral range
are only a function of the root mean square Mach number, but independent of the
forcing. With the assumption of a Gaussian distribution for the probability
density function of the velocity increments on large scales, we derive a model
that describes this behaviour.Comment: 24 pages, 13 figures, Journal of Fluid Mechanics in pres
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