23,734 research outputs found
Toy Model for Pion Production II: The role of three-particle singularities
The influence of three-particle breakup singularities on s-wave meson
production in nucleon-nucleon collisions is studied within the distorted wave
Born approximation. This study is based on a simple scalar model for the
two-nucleon interaction and the production mechanism. An algorithm for the
exact numerical treatment of the inherent three-body cuts, together with its
straightforward implementation is presented. It is also shown that two
often-used approximations to avoid the calculation of the three-body breakup
are not justified. The possible impact on pion production observables is
discussed.Comment: 14 pages, 6 figure
The Emergent Universe: inflationary cosmology with no singularity
Observations indicate that the universe is effectively flat, but they do not
rule out a closed universe. The role of positive curvature is negligible at
late times, but can be crucial in the early universe. In particular, positive
curvature allows for cosmologies that originate as Einstein static universes,
and then inflate and later reheat to a hot big bang era. These cosmologies have
no singularity, no "beginning of time", and no horizon problem. If the initial
radius is chosen to be above the Planck scale, then they also have no quantum
gravity era, and are described by classical general relativity throughout their
history.Comment: minor changes; version to appear in Class Q Gra
Ethics of Artificial Intelligence
Artificial intelligence (AI) is a digital technology that will be of major importance for the development of humanity in the near future. AI has raised fundamental questions about what we should do with such systems, what the systems themselves should do, what risks they involve and how we can control these. -
After the background to the field (1), this article introduces the main debates (2), first on ethical issues that arise with AI systems as objects, i.e. tools made and used by humans; here, the main sections are privacy (2.1), manipulation (2.2), opacity (2.3), bias (2.4), autonomy & responsibility (2.6) and the singularity (2.7). Then we look at AI systems as subjects, i.e. when ethics is for the AI systems themselves in machine ethics (2.8.) and artificial moral agency (2.9). Finally we look at future developments and the concept of AI (3). For each section within these themes, we provide a general explanation of the ethical issues, we outline existing positions and arguments, then we analyse how this plays out with current technologies and finally what policy conse-quences may be drawn
Could a Weak Coupling Massless SU(5) Theory Underly the Standard Model S-Matrix?
The unitary Critical Pomeron connects to a unique massless left-handed SU(5)
theory that, remarkably, might provide an unconventional underlying unification
for the Standard Model. Multi-regge theory suggests the existence of a {\it
bound-state high-energy S-Matrix} that replicates Standard Model states and
interactions via massless fermion anomaly dynamics. Configurations of anomalous
wee gauge boson reggeons play a vacuum-like role. All particles, including
neutrinos, are bound-states with dynamical masses (there is no Higgs field)
that are formed (in part) by anomaly poles. The contributing zero-momentum
chirality transitions break the SU(5) symmetry to vector SU(3)xU(1) in the
S-Matrix. The high-energy interactions are vector reggeon exchanges accompanied
by wee boson sums (odd-signature for the strong interaction and even-signature
for the electroweak interaction) that strongly enhance couplings. The very
small SU(5) coupling, ~ 1/120, should be reflected in small (Majorana) neutrino
masses. A color sextet quark sector, still to be discovered, produces both Dark
Matter and Electroweak Symmetry Breaking. Anomaly color factors imply this
sector could be produced at the LHC with large cross-sections, and would be
definitively identified in double pomeron processes.Comment: Contributed to the Proceedings of the Gribov-80 Memorial Workshop
(without the Appendix
On hypercharge flux and exotics in F-theory GUTs
We study SU(5) Grand Unified Theories within a local framework in F-theory
with multiple extra U(1) symmetries arising from a small monodromy group. The
use of hypercharge flux for doublet-triplet splitting implies massless exotics
in the spectrum that are protected from obtaining a mass by the U(1)
symmetries. We find that lifting the exotics by giving vacuum expectation
values to some GUT singlets spontaneously breaks all the U(1) symmetries which
implies that proton decay operators are induced. If we impose an additional
R-parity symmetry by hand we find all the exotics can be lifted while proton
decay operators are still forbidden. These models can retain the gauge coupling
unification accuracy of the MSSM at 1-loop. For models where the generations
are distributed across multiple curves we also present a motivation for the
quark-lepton mass splittings at the GUT scale based on a Froggatt-Nielsen
approach to flavour.Comment: 38 pages; v2: emphasised possibility of avoiding exotics in models
without a global E8 structure, added ref, journal versio
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