9,959 research outputs found
Formula for Fixed Point Resolution Matrix of Permutation Orbifolds
We find a formula for the resolution of fixed points in extensions of
permutation orbifold conformal field theories by its (half-)integer spin simple
currents. We show that the formula gives a unitary and modular invariant S
matrix.Comment: 42 page
Simple current extensions and permutation orbifolds in string theory
We review extensions by integer spin simple currents in two-dimensional
conformal field theories and their applications in string theory. In
particular, we study the problem of resolving the fixed points of a simple
current and apply the formalism to the permutation orbifold. In terms of string
compactifications, we construct permutations of N=2 minimal models and use them
as building blocks in heterotic Gepner models.Comment: 5 pages, 4 figures, extended version of the Proceedings of the
Cargese Summer School 2010 "Formal Developments and Applications
Radiative feedback and cosmic molecular gas: the role of different radiative sources
We present results from multifrequency radiative hydrodynamical chemistry
simulations addressing primordial star formation and related stellar feedback
from various populations of stars, stellar energy distributions (SEDs) and
initial mass functions. Spectra for massive stars, intermediate-mass stars and
regular solar-like stars are adopted over a grid of 150 frequency bins and
consistently coupled with hydrodynamics, heavy-element pollution and
non-equilibrium species calculations. Powerful massive population III stars are
found to be able to largely ionize H and, subsequently, He and He, causing
an inversion of the equation of state and a boost of the Jeans masses in the
early intergalactic medium. Radiative effects on star formation rates are
between a factor of a few and 1 dex, depending on the SED. Radiative processes
are responsible for gas heating and photoevaporation, although emission from
soft SEDs has minor impacts. These findings have implications for cosmic gas
preheating, primordial direct-collapse black holes, the build-up of "cosmic
fossils" such as low-mass dwarf galaxies, the role of AGNi during reionization,
the early formation of extended disks and angular-momentum catastrophe.Comment: 19 pages on MNRA
A cellular automaton for the factor of safety field in landslides modeling
Landslide inventories show that the statistical distribution of the area of
recorded events is well described by a power law over a range of decades. To
understand these distributions, we consider a cellular automaton to model a
time and position dependent factor of safety. The model is able to reproduce
the complex structure of landslide distribution, as experimentally reported. In
particular, we investigate the role of the rate of change of the system
dynamical variables, induced by an external drive, on landslide modeling and
its implications on hazard assessment. As the rate is increased, the model has
a crossover from a critical regime with power-laws to non power-law behaviors.
We suggest that the detection of patterns of correlated domains in monitored
regions can be crucial to identify the response of the system to perturbations,
i.e., for hazard assessment.Comment: 4 pages, 3 figure
Population III stars and the Long Gamma Ray Burst rate
Because massive, low-metallicity population III (PopIII) stars may produce
very powerful long gamma-ray bursts (LGRBs), high-redshift GRB observations
could probe the properties of the first stars. We analyze the correlation
between early PopIII stars and LGRBs by using cosmological
N-body/hydrodynamical simulations, which include detailed chemical evolution,
cooling, star formation, feedback effects and the transition between PopIII and
more standard population I/II (PopII/I) stars. From the Swift observed rate of
LGRBs, we estimate the fraction of black holes that will produce a GRB from
PopII/I stars to be in the range 0.028<f_{GRB}<0.140, depending on the assumed
upper metallicity of the progenitor. Assuming that as of today no GRB event has
been associated to a PopIII star, we estimate the upper limit for the fraction
of LGRBs produced by PopIII stars to be in the range 0.006<f_{GRB}<0.022. When
we apply a detection threshold compatible with the BAT instrument, we find that
the expected fraction of PopIII GRBs (GRB3) is ~10% of the full LGRB population
at z>6, becoming as high has 40% at z>10. Finally, we study the properties of
the galaxies hosting our sample of GRB3. We find that the average metallicity
of the galaxies hosting a GRB3 is typically higher than the critical
metallicity used to select the PopIII stars, due to the efficiency in polluting
the gas above such low values. We also find that the highest probability of
finding a GRB3 is within galaxies with a stellar mass <10^7 Msun, independently
from the redshift.Comment: 8 pages,3 figures. Submitted to MNRAS, revised version after
referee's comment
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